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Plutonium and plutonium alloys as nuclear fuel materials
NUCLEARENGINEERING AND DESlGN15 (1971) 373-440. NOR’fH-HOLLAND PUBLISHING COkiPANY
PLIJTONIUM ANDPLUTONI'JMALLOYSAS NUCLEAR FUEL MATERIALS* 3.H.KITTEL, J. E. AYER, W. N. BECK, M. B. BRODSKY,D. R. O’BOYLE,and S. T. ZEGLER Argonne hlational Laboratory, Argonne, Illinois, USA
F. H. ELLINGER, W. N. MINER, and F. W. SCHONFELD Los Alamos Scientific Laboratu.;
Los.4 Iamos. New Mexico, USA
R. D. NELSON
FncificNorthwest Laboratorv.
Richland. Washington, USA
Received28 August1970
1. Introduction The second edition of the AEC Reactor Materials Handbook (RMH-2)presented in Chapter 11 an excellent summary of the early history of plutonium. The health hazards of handling and staring plutonium are also discussed in detail in Chapters 1 and 11 of RMH-2and will not be repeated here. Interest in plutonium, its alloys, and its compounds has increased at an accelerating rate in the intervening decade since preparation of RMH-2.Furthermore, it is clear that interest in plutonium fuels will continue unabated for at least the next decade. The widespread interest in plutonium fuels is due primarily to the
emergence of the fast breeder reactor as the principal long-range development objective of the civilian reactor programs of the United Statzs and of the other major nuclear powers. Aside from the technical importance of plutonium, the metal witi always intrigue metallurgists, and others interested in materials behavior, because of its many strange properties. Tc mention some of its more interesting properties, it is the only man-made element being used routinely in tonnage quantities, in the sense that “man-made” means that man must * Chapter2 of the projectedthirdeditionof the U.S.A.E.C. ReactorMaterials Handbook.
provide the proper conditions for nature to create plutonium from uranium; it undergoes an ugprece& dented number of phase transformations between room temperature and its relatively low melting point; it has a negative coefficient of expansion in two of its h&-temperature crystallographic forms. This article summarizes present knowledge on plutonium and its alloys. The material in this chapter is in many respects an updating of Chapter 11 in RMH-2. However, those parts of Chapter I 1 in RMH-2 that are still applicable without revision have not been repeated. The reader should, if possible, read that chapter as well as this article to be more completely informed on important aspects of plutonium and its alloys.
2. Phase relationships and crystal structures 2.1. rntroc!uction
Information is availablein the literature on the phase relationships and crystal structures of approximately 65 binary and 17 ternary systems of plutonium with other metals. Space limitations prevent even a limited presentation and discussion of all these alloy systems. The piutonium alloys discussed, therefore, have been restricted to those alloy systems judged to be of greatest present
374
S.H.Kittel et al., Plutonium and plutonium alloys
interest to those engaged in the development of reactor fuel elements. The alloy systems discussed here are also limited to those that are normally in the solid state at ordinary reactor operating temperatures. The phase relationships of plutonium with nonmetallic elements such as carbon and oxygen are not discussed herein. The information given is mainly in the form of constitutional diagrams and crystal structure tables. Only brief descriptions accompany the diagra~ns. In general, these descriptions are intended to document information sources, point out any significant differences that may exist between different versions of the diagrams, and clarify certain details of the phase relationships that are known but may not be readily apparent from the diagrams. Most of the diagrams are composites based on the results of more than one group of investigators. All binary systems in thiis chapter have been drawn with Pu as the base, i.e., at the left, and compositions are given in atomic percent (a/o). Standard nomenclature has been retained for the terminal phases; Greek letters are used to designate intermediate phases in order of increasing content of the nonplutonium alloying elements. 2.2. Bina~ systems
2.2.1. Plutonium-aluminum The phase diagram shown in fig. 1 is based on the thermal, microstructural, and X-ray data contained in refs. [ 1-5]. Most of the solid-state phase relationships were identified by Moeller and Schonfeld [ 1 ] and by Waldron et al. [2], but they did not obtain data adequate to locate the solidus and liquidus boundaries accurately. The results reported by Bochvar et al. [3] are in agreement with the diagram shown here, with five exceptions: (1) eutactoid decomposition of 5 at 175°C; (2) temperatures of 530 and "-'540°C, respectively, for the PuAl and Pu3Al peritectoid horizontals; (3) a eutectic temperature of 635 °C; (4) some indicated solubility of A1 in the 3' and/3 phases; and (5) absence of phase transformations in PuAl 3 and PuAl4. ltigh-pressure work [6] supports the conclusion that/i does not decompose eutectoidally, and other results [7] show that less than 0.25 a/o Al is soluble in 6'. Hall [8] has suggested that the solid solubility of Pu in Al is approximately 0.26 w/o (0.03 a/o) at 600°C, whereas Roy [9] has
1600
. . . . .
--7-
,:e'"xt
i400 1200 I000 800
I-
600 |'
~."~,A
*
I r~
V-_-'-I
', I
~°
I
!
_4
~',..
;
z ~AI
4OO
200 -4
0
0
i
~14b lI
I0
~J
O.
20
I i
!
! 4P0 I
!
30 40 50 60 70 80 ATOMIC PERCENT ALUMINUM
90
J
I00
Fig. 1. Plutonium-aluminum phase diagram. (Submitted by LASL July 1, 1967.)
reported a maximum solubility of 0.05 w/o (0.0056 a/o) at 650°C. Calais et al. [ 10] have confirmed the result of Roy. In phase equilibria studies, Runnalls [5J has observed a phase transformation in PuAI 4 and several polymorphic transformations in PuAI 3, and has provided crysta~ographic data. Runnalls [11 ], Ellinger [12], Singer [13] and Larson et al. [ 14] have also provided crygtallographic data on the iniermediate eonipounds (see table 1). 2.2.2. Plutonium-iron Phase diagrams for this system have been proposed by Konobeevsky [ 15 ], Mardon et al. [ 16] and Schonfeld [ 17]. In addition, the phase relationships in the 5'Pu region have been studied [7], liquidus points for alloys containing between 15 and 30 a/o Fe have been determined [18] and Avivi [19] has suggested minor modifications to the published diagrams in the Fe-rich region between Pu2Fe and Fe. In general, the results of the various investigators differ only in details. Konobeevsky did not report the inverse peritectie decomposition of the ePu solid solution, as observed by Mardon et al. and confirmed by Elliott and Larson [7]. Mardon et al. placed the Pu-Pu6Fe e'atectic temperature at 413°C, rather than at 410°C, the eutectic temperature tbund by Konobeevsky and Schonfeld. Also, Mardon et al. found somewhat higher solubilities of Fe iv : and ~1~ (~ 2.5 and 1.5 a/o) than did Elliott at,:, ~,rson
S.H. Kittel et al., Plutonium and plutonium alloys
375
Table 1 Crystal structure data for plutonium-aluminum alloys. Phase
Pu3AI
Strutture type
Symmetry
SrPbs
tetragonal
Space group a P4/mmm
cubic
Unit cell dimension, (A) b c 4.499 4.499 4.500
4.536 4.538 .
cubic
PuAI 77 PuA!2 0
PuAI3
PuMa K 0t-PuAl4 ~-PuAI4
Cu2Mg cubic
PuAI3
UA14
I... Fd3m
hexagonal
P63]mmc
cubic (3H) hexagonal (6H) rhombohedral (9HB) rhombohedral (9H~)
Pm3m P63/mmc R3M
orthorhomblc
Imma
orthorhombic orthothombic
R3M
lmma lmma
Formula units per unit cell
.
.
.
.
.
.
Ref.
13.45 13.45
[ 3l 1121 [41
1
.
.
.
.
.
.
.
.
.
10.76 10.769 7.831 7.840 (Pu-rich) 7.836 (Al-rich) 7.874 7.838 (Pu-rich) 7.848 (Al-tieh) 7.833
.
.
.
.
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.
.
29
10.25 10.253
[ 3] 14]
8
8.09
Ill] 131 131
.
.
.
.
.
14.40 14.427 14.47
6.08 6.084 6.10 4.262 6.083 7.879; = 45.94 ° 7.901 ; ot = 45.81 °
.
.
.
.
.
.
.
.
.
.
13.66 13.71a
4.41 4.396 4.396
6.29 6.266 6.266
13.79 ~.';0~ t3..~'~: .
.
.
141 1121
S.095
[12] 151
.
.
.
.
.
.
.
.
.
.
6.604 6.643 6.657
Illl 13} 1141 i5] [51 151
6.634
15]
6.8
14.410
6.26 6.262
8.06
.
6
4.42 4.387
(> 2 and 9.6 a/o). The temperature of the peritectic formation o f Pu6Fe has been reported variously, as 430°C by Konobeevsky, 428°C by Mardon et al., and 4250C by Miner [20]. Avivi has reported the existence of a hexagonal modification of PuFe 2 between 760 and 1020°C and has provided solubility data with respect to Pu ~ ~/Fe and Fe in PuFe 2. The diagram shown in fig. 2 is a composite based on the results of the various investigators. The crystal structure data shown in table 2 have been taken from references [11, 12, 15, 16, 19].
X-ray density (g/cma)
[lll 4
.
6.02 6.11
[31 [131 151 [51
5.680 5.680 .
.
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2.2.3. Plutonium-nickel Complete phase diagrams for tiffs system have been published [ 15, 21 ] and the effect of Ni additions on the phase equilibria associated with 5'Pu has been reported [7 ]. The diagram of Konobeevsky [ 15 ] is in general agreement with that of Wensda and Whytc [21 ], except that it did not include the intermediate phase Pu2Nil7. The diagram given in fig. 3 is based on refs. [7 and 21]. There are two eutectics: one at 12.5 a/o Ni and 465°C, the other at 92 a/o Ni and 1210°C. ePu dissolves a maximum of 4.3 a/o Ni at
$.H.Kittel et aL, Plutonium and plutonium alloys
376
Table 2 Crystal structure data for plutonium.iron alloys. Structure type
Symmetry
Pu6Fe
UeMn
tetsagonal
PuFe 2
Cu2Mg cubic
Phase
Space group
Unit cell dimensions, (,~) b c
a
14/mcm
10.404 10.403 10,405 7.150 (preparation '~'3 7.190 (preparation "b") 7.191 7.178 7.189 7,184 (Pu~ich) 7.189
Fd3M
n
(cubic)
hexagonal
PuF~
5,355 5.347 5.349
Formula units per unit cell
X-ray density (g/cm~)
ReL
4
17.07 17.10
[121 [15] [16]
12.74
[lll
12,53
[I11
12.53 12.59
[12] [15] [16] [16]
8
[19]
5.64
18.37
[19]
11
(hexagonal)
450°C. The solubility of Ni in the other Pu allotropes is very restricted. The maximum solubility of Pu in Ni is about 1.8 a/o Pu at 1210°C. Crystal structure data have been determined for all six of the intermediate phases and are given in table 3.
from the combined results of Bochvar et al. [3], Schonfeld [17] and Poole et al. [25]. The B-Th solid solution field described by Bochvar et al. has not been reported by Schonfeld or Poole etal., however, and thus is not shown. The composition of the single Pu-Th intermediate phase, ~', (see table 4) in the system has been bracketed between 30 and 33 a/o Th [25,26]. Under equilibrium conditions, ~"is fon~aed
2.2.4. Plutonium-thorium The phase diagram shown in fig. 4 was constructed
°6o0F - - T i ' ; ,~,--V--T --- F I 4BO,'-~'-~:Y_ - - ~
i
-~
1600:
•
i
!
!
-" 1400
,
oo-
o •
.,,o0o
1
,o7 "°
4ooV laoc ! 4.~ "~ i | - 2 // ] J . . . . O_w. I.ON - ~ - - - , - . . . . ~-i
/.
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=< coo ..... T 7 - ~ - - - t ~ - - - ~ - _ - . t
,.,
I
'4*
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k
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.
4oo ~;----~-r
u. i
f
I
I
L41-1~!
i
114~
I
IO~)O
F.._ . , , - F , ' ~ - - - ~
....
tu I000.
I~lm *e-Fe
I a-Fl"
I
;
I
I ~
I
~.
+ --
i
!
~
I£---~--i
l
i
I
1"4
I
I
I-~
rr ..j
n
--Jr---*----~
~
o_ -
P
"1
L~ ~ - - f - - ' n ; o - -
I
1200
o;-~e !,-F..J
Itl ,
nlU
ihi I--
i
a
3
I --L*il/ 6 0 0 ~'- /
I L
, /i
NICKEL~JI~---~TL'L~./-
.~/'i
] ~ / L, - ' / -
X ,/i/'" "1
4OO /
/ L*~ I
446 ~
,
Ii
.. ,i' "
,~i
I
t *I+ eoo ",'_._,I ~¢~! ]
q¢8 ,
k*NI
Ii
l 200
o°'~ i I~] 0
I0
20
30 40 ATOMIC
50 60 PERCENT
70 IRON
i
80
t /
90
I00
Fig. 2. Plutonium-ironphase diagram. (Submitted by LASL July 1, 1967.)
0
I0
20
30 40 60 60 TO 80 ATOMIC PERCENT NICKEL
90
I00
Fig. 3. Plutonium-nickelphase diagram.(Redrawn from tel [21].)
377
S.H.Kittel et al., Plutonium and plutonium alloys
Table 3 Cryst',d structure data for plutonium-nickel alloys. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Phase .
.
.
.
.
Structure type .
.
.
.
.
.
.
.
.
.
.
.
.
.
Symmetry
Space group
Unit cell dimensior, s, (fl~) b c
a .
.
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.
.
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.
.
.
.
.
10.21
.
.
.
.
.
.
.
Formula units per unit cell .
.
.
.
.
.
.
.
.
.
.
.
Ref.
4
,12.9
[ 22]
13.1
I 1i l l 121
.
.
.
.
.
.
.
PuNi
TII
orthorhombic
Cmem
3.59
PuNi2 r/
Cu2Mg
face-centered cubic
Fd3m
7.16 7.141 ~Pu-fich) 7.115 (Ni-rich) 7.14
8
3
! 1.8
[ 231
6
11.3
1241
t 151 [151
PuNi 3 0
PuNi 3
rhombohedrai
R3m
8.6 i 5; or: 33°44 '
PuNi4 t
PuNi 4
monoclinic
C 2/m
4.87
8.46
100 ° + 0,1
Pu2Nil7 h
CaZn s
P6/mmm
hexagonal
Th2Nil7 hexagonal
P63/mmc
10.27
1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PuNis
4.22
X-ray density (g/cm 3 )
4.875 4.872 (Pu-rich) 4.861 (Ni-rich)
3.970 3.980
8.30 8.29
8.00 8.01
by the peritectie reaction, L + a T h * ~" Under normal conditions, however, the peritectic reaction is suppressed on cooling, and ~"is formed by a nonequilibrium peritectoid reaction subsequent to eutectic solidification. 2.2.5. Plutonium-uranium C o m p l e t e phase diagrams for this system have been reported [3, 2 7 28]. All are in agreement as to the general f o r m o f the diagram b u t some o f the phase boundaries reported b y Bochvar et al. [3] are quite
1
10.8
3.982
[111 [ 12] t l2l
'
10.3
[ 11 ] 1121
different from the corresponding boundaries determined by Ellinger et al. [27] and b y Waldrou [28 ]. The diagram shown in fig. 5 is based on the thermal, dilatometric, X-ray and microstructural studies of Ellinger et al. and of Waldron. A major disagreement concerns the ~-Pu field, which Bochvar found to extend from about 4 a/o U in the vicinity of 120°C to roughly 17 a/o U at about 300°C. The data of Ellinger et al., on tile other hand, show the ~-Pu field extending from essentially 0 a/o U at 125°C t~ about 2 a/o U at 280°C. These latter result:; appear
Table 4 Crystal structure data for plutonium-thorium alioys. Phase
Structure type
Symmetry
Space group
.............................
orthorhombic (?)
a 9.820 7.90
Unit cell dimensions, ~A) b c
Formula u nits per unit ceil
X.ray density (g/'cma ,~
Ref.
' ...............................................................
8.164 8.43
6.681 9.79
6 8
[ 25 ] 13l
S.H.Kittel et al., Plutonium and plutonium alloys
378
eoc ..... 700
!
...... i-
~oo,-r. t
u
s
:,
..-<
o
o
~. . . . . . .
~
. I
i
!1
,
:I
........
I--
Y+g
200 ~_
i
. . . . . . .
'
!--,A ' ~ : /~' i / t - ~
.......~~--~--~ ....
=.,,v
s*I 300r
~--
-Y
L.;-T.
~--~o.-*~~--~
.~'l
t,.,-
:--~.r / !
L
~
-4 ....
,~- ..... ~ ....
I
i
i\~
:
i
~
',
~
!
l
~. . . . . .
~
i
1
'' ....... !! ......
; .......
;
. . ;f..* ;I
~ . =
~
~,
~. . . . . .
.... !!2 r~-~
......
,aoo
.....!....... i.....
,
. _~ ~,~"+"
I I
Oo t n n n _ ? . O O V , , 4 / - ? N ] UJ - - 0 I 2
....
==
i
:=+l:
.
~
~ ......
~
=E 6 0 0
-~ ......
x
~ ,
. ;
;
ATOMIC
PERCENt
fl+C, 4 §
I
I
I ._~ . . . . 6
~
1
~:,.
T-I )
! so
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~ .._. . ., 8 . i -,,,i
200r.,
-
L.'
',
o[o.....,o ~ .....=_.__~_.'~....._.' _._:-_._~___= ~o ~o ~o so 60 zo
1
3
.......
!
\ ~
i
i00 ~ ...... !
-aoo~__--.J~;~_J-----~-------- -
_ u I 0
~oo
THORIUM
i
='-, I; ! I0
~
\~
_-'~_
i ,~'5 "t
--
-
-
i_ ~.. . ..... c ........
I ~ I . - L . . . . . [~. _ . _ _ L _ _ 20 30 40 50 60 1'0 ATOMIC PERCENT URANIUM
I 80
90
I00
Fig. 4. Plu~:onium-thorium phase diagram. (Submitted by LASL July 1, 1967.)
Fig. 5. Plutonium-uranium phase diagram. (Submitted by LASL July 1, 1967.)
to be confirmed by the work of Waldron. Also, Bochvar et al. found the ~"field to extend to higher U contents from about 6 a/o U at 120°C, whereas Ellinger et al. found the corresponding point to be at about 25 a/o U and 278°C. There is better agreement among the three groups of investigators concerning the U-rid-, portion of the diagram. Work by Berndt [29] places the ~U/(aU + ~')boundary at about 85 a/o U at 400°C, which agrees reasonably well with the results of Ellinger et al. and Waldron as well as with revised work of Bochvar et al. as mentioned by Schonfeld [30]. Also, the solubility data of Calais et al. [10] between 410 and 546°C fall within "-1 a/o of the boundaries established by Ellinger et al. and
Waldron for the ~ + aU field. Crystal structure data are given in table 5. 2.2.6. Plutonium-zirconium Complete diagrams, which differ in several details, have been published by 8ochvar et al. [3] and Marples [31 ], additional work on Pu-lich alloys has been rei~orted by Ellinger [32] and Kutaitsev et al. [33 ], alloys containing between 30 and 60 a/o Pu have been studied by Robillard [34] and solubility data for Zr in liquid Pu between 700 and 950°C have been obtained by Bowersox and Leary [35 ]. The diagram given in fig. 6 is largely that of Marples but has been modified to show the ~ phase ("Pul9Zr) as
Table 5 Crystal structure data for plutonium-uranium alloys. Phase
Structure type
Symmetry
Space group a
Pu-U ~-
cubic (at room temp.)
Pu-U r~
tetragonal (?)
P...
Unit cell dimensions, (A) b c
10.692 (35 a/o U) 10.651 (70 a/o U) 10.57
10.76
10.73
10.44
Formula units per unit cell
X-ray density (g/cm 3)
Ref.
58 atoms
18.95
[27]
52 atoms 56 atoms
17.2
[27] [3l
S.H.Kittel et al,, Plutonium and phttonium alloys
2°°°I--~----:--- .......r....
o * "'
ix:
i
|
i
/
i
15OOl-"/-~ _ l
I,
!
i
i
~
1 I.
r ........
~
i
,
;J"
I
V"~'F/
~
4~
! , ....
i
i ~;..7/i
,
, ~-~ ~-~
,
.~-'L.a-z,/!
/ i I ,oooi.---4 ~-"
~
:.
i
' -I:I
~-
-~ ..... q ..... l
I-
-
.fi
! I ~ .... ~-.
a tetragonal unit cell [36]. Although K is believed to correspond stoiehiometrically to about PuZr3, its structure is based on the hexagonal A1B2 type. The maximum solubility of Pu in otZr was found to be at about 16 a/o Pu at 618°C and ! 1 a/o at 150°(" [3]. Crystal structure data are given in table 6.
-T---~ ,I
i./"
]
..., -" I ;..........
/
/
2.3. Ternary systems 2.3.1. Plutonium-iron-uranium Boucher et al. [37] have studied mainly two compositions, 74 U-25Pu-1 Fe and 73.5 U-25 Pu-l.5 Fe (in w/o). The cast alloys were composed predominantly of the Pu-U ~"phase togethe7 with U6 Fe and Pu6 Fe. The latter compounds tended to form (U, Pu)6 Fe on homogenization of the alloys. Dilatometric examination of these alloys revealed, respectively, transformations at 595 ° -+-3°C and 590 ° +--3°C, and fusion points at 705 ° +- 5°C and 680 ° +--5°C. Treating the alloys above the transformation temperatures resulted in the formation and retention of some Pu-U r/phase. Treating the alloys below the transformation temperatures resulted in the formation of some aU. Ellinger [ 12 ] reported that continuous solid solutions exist between Pu6Fe and U6F,z and between PuFe 2 and UFe 2. Also, he gives lattice parameter versus composition data.
i i ~ ..... 1
750
E--L-,,4, 250
--"
v
I0
;~0
30
ATOMIC
50 PERCENT
40
60 70 80 ZIRCONIUM
90
379
I00
Fig. 6. Plutonium-zirconium phase diagram. (Submitted by LASL Aug. 1, 1967.)
found by Ellinger and the solubility data ~ " Bowersox and Leafy. The solidus curve de mined by Boehvar et al. is consistently higher than th~. of Marples, being as much as 100°C higher at 50 a/o Zr. There is better agreement between their liquidus curves. ~', which has a complex crystal structure, was found to exist between "--3 and 5 a/o Zr and to decompose to ~ and O at ~220°C, although under conventional cooling it is stated that it is readily supercooled and may exist as a metastable phase at room tem~rature [33]. The O phase was reported to be formed at about 14 a/o Zr (Pu6Zr) and 350°C, and to have a homogeneity range from 12.1 to 20.6 a/o Zr [3]. The X-ray powder pattern for the O phase at 21 a[o Zr has been indexed on the basis of
2.3.2. Hutonium-fissium (or fizziurn)-uranium Phase studies in the Pu-Fs-U an~ l?u-.Fz-U quasiternary alloy systemsby means ot metallography and X-ray diffraction have been reported by Kruger I38, 39]. The source of interest in these alloys is given in sect. 7. Alloys investigated contained 20 w/o Pu and either 5, 10 or 15 w/o Fs or Fz*. The phases found in equilibrium after isothermal annealing are shown in the
Table 6 Crystal structura data for plutonium-zirconium alloys.
Phase
Structure
Symmetry
Space group
type
Pu4Zr
a
tetragonal
P4/ncc
hexagonal
P6/mmm
Unit cell dimensions, (.~) b
10.893
16.889
5.060 5.055
3.119 3.123
Formula units per unit cell
X-ray density (g/cm 3 )
Ref.
16
15.76
1361
0
P.z~
PuZr3 g
AIB2
131 1311
380
S.H.Kittel
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,
,
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ONormol flssium olloyg 200~- oFissium o l l o y , . . i l h odditionol Zr 0
5 no 15 WEIGHT PERCENT FnssIUM
20
Fig. 7. lsopleth showing equilibrium phases and transformations in the pseudo-ternary plutonium-fissium-uranium system at 20 w/o plutonium. (Reprinted from ref. 138] .) isopleth presented in fig. 7. The nomenclature used for the aU, ~U, 7U, ~'(U-Pu), and 17(U-Pu) phases is the same as that adopted by Ellinger et al. [27] for phases in the U-Pu system. Six other phases occur in the system: Alpha-prime (a'): A metastable modification of aU that is also referred to as "distorted alpha". Gamma-naught (`/0): A tetragonal modification of the `/phase having a c/a ratio of approximately 0.98. Gamma-prime (`/'): A tetragonal phase based on the binary U2Mo phase but which may take Pu in solution. Theta (O): A phase containing U, Pu and Pd that is present between room temperature and the solidus temperature in all alloys studied. Crystal structure type not identified.
* The term fissium (Fs) denotes the equilibrium concentration of second long period elements (Mo, To, Ru, Rh, Pd) that build up as fission products in the fuel during irradiation and which are not removed during the pyrometallurgical fuel reprocessing scheme presently in use at EBR-II. Fizzium (Fz) denotes the same group of solid fission products with the addition of Zr in approximately the same amount as Ru. The nominal composition of U-20 w/o Pu-5 w/o Fs is: 20 w/o Pu, i.90 w/o Mo, 2.02 w/o Ru, 0.72 w/o Pd, and 0.28 w/o Rh, balance U (stx components) and the nominal composition of U-20 w/o Pu-5 w/o Fz is: 20 w/o Pu, 1.31 w/o Mo, 1.38 w]o Ru, 1.45 w/o Zr, 0.53 w/o Pd, and 0.26 w/o Rh, balance U (seven components).
and plutonium
alloys
U2Ru: A monoclinic phase found in the Fs alloys. ZrRu: A CsCl-type phase found only in the Fz alloys. In addition to the phases shown in fig.7, allalloys contained the O phase at all temperatures below the solidus.U 2 R u was found in all Fs alloys and increased in stabilitywith an increasein Fs content. In all Fz alloys ZrRu was stablebetween room temperature and the solidus. 2.3.3. Plutonium-molybdenum-uranium Constitutional studies of this ternary alloy system, mainly by Mardon et al. [40] have been directed toward determining the boundaries of the `/-U solid solution region and the phase equilibria associated with its decomposition. Alloys containing 35 to 100 a/o U solidify either as the `/-U solid solution or as a mixture of 7-U and Mo. With decreasing temperatures the 7-13 region expands toward increasing Pu contents. A typical isothermal section (for 900°C) is shown in fig. 8. At about 630°C the 7-U solid solution splits into a U-rich region and a Pu-rich region, termed 3'] and "/2 U, respectively. Below about 700°C, where the Pu-U phases, 77 and ~', first appear, the ternary equilibria become comple, and have not been fully worked out. Six 4-phase invariant reactions occur between 610°C and 525°C. The `/1-U phase decomposes eutectoidally, `/1 -+ aU + `/' + ~, with the
u/
7
v
I0
v
20
v
30
/
/ v
4O
,,
50
\
,,\
60
ATOMIG PERGENT MOL.YBOENUM
Fig. 8. Plutonium-molybdenum-uranium 900°C partial isothermal section. (Redrawn from tel [40] .)
S.H.K~ttel et aL, Plutonium and plutonium alloys
381
eutectoid point lying in ~he neighborhood of 10 to 14 a/o Mo and 17 to 20 a/o Pu. This reaction has been observed to be very sluggish and to proceed in two stages [41]. Alloys quenched from the 3' phase show retained 3'1 and 72 phases plus the metastable phases designated 3'0 and oq. Anselin [41] has determined the lattice parameter-composition relationships of the 3' phase preserved to room temperature by quenching from 900°C. He also reported that the 3'0 phase has a tetragonally-deformed 3'-U structure, but the identity of the true unit cell is uncertain. The phase labelled (X1 has a distorted 0~-Utype of structure. Transformations in homogenized and as-cast alloys containing 20 w/o Pu and 8, 10, and 12 w/o Mo, and 30 w/o Pu and 10 w/o Mo were studied by Boucher [42].
peritectoid reaction/~U + ?U -~ r/at 710°C and the other two 3-phase regions remain in the ternary. The otTh + 7U + L three-pt'.ase region continues moving toward the Pu comer as the temperature decreases. The ~"phase is formed by a peritecto~d invariant reaction at 610°C. The phase relationships in the Pu corner of the system are complex and have not been experimentally def'med. The isopleth given as fig. 9 is a section through the Pu-Th-U system at 10 a/o Pu and shows the effect of U in decreasing the liquidus and solidus temperatures. As shown in the figure, an increase in U from 0 to 2 a/o reduces the solidus temperature from about 1300 to 905°C. Transformation temperatures indicated in the figure were determined by DTA and dilatometric analysis.
2.3.4. Plutonium-thorium-uranium Phase studies in the Pu-Th-U system have been reported by Blumenthal et al. [43 ]. Metallography, differential thermal analysis, and X-ray diffraction were used to establish solid-state phase transformations and to outline phase regions principally in the Th corner of the system. The L 1 + L 2 miscibility gap is believed to be restricted along the Th-U side of the ternary system below which/3Th is the first phase to crystallize. In the central region of the system o~This the first phase to crystallize from the melt. 7U(ePu) i.'~,the first phase to form from the liquid along the U-Pu side of the system, except for a small region near the Pu corner below 630°C where Pu2Th is the first phase to freeze. In constructing a liquidus projection, Blumenthal [43] assumed that otTh forms peritectically in the Th-Pu system ~ T h + L ~ o~That approximately 1400°C) and that the aTh +/~Th + L three-phase region crosses the Th corner of the system with decreasing temperature to exit along the Th-U side at 1265°C. Below 1086°C the offh + 3'U + L three-phase region enters the ternary system from the Th-U binary and moves toward the Th-Pu side with decreasing temperature. Below 760°C the aTh + flU + + 3'U three-phase region moves out from the Th-U binary and peritectoidally forms r/(U-Pu) at 714°C by the invariant reaction aTh + flU + 7U ~ rt(U-Pu). Of the three 3-phase regions formed at 714°C (aTh + ~U + rt, aTh + r / + 7U,/~U + 7U + rT), the flU + 3,U + rt region exits along the U-Pu side as the
2.3.5. Plutonium-titanium-uranium Alloys of interest as fast reactor fuels contain from 10 to 20 w/o Pu and from 7 to 14 w/o Ti, remainder U. Most phase studies in the ternary system have been restricted to alloys which contain more than
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Fig. 9. Plutonium-thorium-uranium isopleth at I0 atomic percent plutonium. (Reprinted from ref. 143).1
I
382
S.H.Kittel et ai.. Plutonium and plutonium alloys
40 a/o U. The bcc high-temperature aUotropes of both Ti (~Ti) and Pu (elhl) form a complete series of solid solutions with bcc 7U. Similarly, in the U corner of the ternary system the bcc T phase is the first phase to freeze from the melt over a wide composition range. In the binary U-Ti system the hexagonal intermediate phase U2Ti forms by a congruent solid state reaction at 898°C (3' "~ U2Ti) [44]. U2Ti is capable of dissolving at least 17 a/o Pu in solid solution and extends sufficiently far into the ternary system as (U, Pu)2Ti to exert a strong influence on the properties and transformations of U-rich alloys. Solidus temperatures for alloys containing more than 40 a/o U, as based on binary-solidus data and the metallographic and differential thermal analysis results of Blumenthal [45] for a limited number of ternary alloys, are given in fig. 10. An increase in Ti at a constant Pu:U ratio causes a moderate increase in the solidus temperature whereas the solidus temperature of binary U-Ti alloys is strongly reduced by the addition of Pu. Pu stabilizes the 7 phase of U-Ti alloys, based on the DTA and dilatometric results [45,46]. An increase in Pu from 0 to 30 a/o at 33.3 a/o Ti stabilizes the 3' phase flora 898 to 745°C. Over the composition range 0 to 30 a/o Pu, with 33.3 a/o Ti, the ? phase is not retained by quenching. Limited me:allographic and X-ray evidence [46A] suggests that in the ternary system the single-phase
region corresponds to the hyperstoichiometric compound (U, Pu)2 Til +x. Solid state transformations along the Pu-Ti side of the ternary system are complex and have not been established. In addition to the equilibrium phases that occur in the system, a commonly observed white extraneous phase has been identified as 0-stabilized aTi [47]. 2.3.6. Plutonium-uranium-zirconium Early work on Pu-U-Zr alloys of interest as fast reactor fuels, containing 10 to 20 w/o Pu and 10 to 15 w[o Zr, was done at both Fontenay [48] and Argonne [48A]. Zr increases the solidus temperatures of alloys in the U corner of the system as shown in fig. 11, based on the work at Argonne [49, 50]. Solidus and liquidus temperatures in the Pu corner of the system have been determined by Mound Laboratory [51 ] and are shown in fig. 12. Both the solidus and the liquidus temperatures of binary U-Pu alloys are increased with the addition of Zr. As shown in fig. 12, the liquidus temperature increases more rapidly with an increase in Zr than does the solidus. The effect of the minimum point in the solidus and liquidus of binary U-Pu alloys at about 15 a/o U is shown in fig. 12 by the curvature of the ternary isotherms in the ternary system. The three binary systems show complete solid miscibility of the bcc high-temperature allotropes (~,U, ePu,/3Zr). Similarly, in the ternary system the
O
U
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Fig. i0. Plutonium-titanium-uraniumsolidusprojection in the uranium comer of the system [45].
v
60
Fig. 11. Plutonium-uranium-zirconiumsolidusprojection in
the uranium corner of the system [49, 50].
S.H.Kittel et aL, Ph~tonium and plutonium allo),s
first phase to freeze over the entire range of compositions is the bcc 1' phase. In the U corner of the system both Pu and Zr are effective 1' stabilizers. As a result of the increase in solidus temperature in ternary alloys, the bee 3' phase is stable over a wide range of temperatures (300 to 400°C). As the temperature decreases, the 1' singlephase field moves toward the Zr-Pu binary and then pulls rapidly toward the Pu corner In the U corner of the system, invariant reactions at about 655 and 600°C have been observed [48, 49]. O'Boyle et al. [52] have suggested that these reactions are Class I1 type phase transformations: 655°C 600°C
3' +/3U ~ otU + ~'(U-Pu) aU + 3' -" cS(U-Zr) + ~'(U-eu).
In alloys annealed below the invariant reaction at 600°C, the aU + ~'(U-Pu) + 5(U-ZO phases have been identified by X-ray diffraction [48]. In addition to the ternary phases, a light-etching Zr-rich impurity phase has been identified as oxygen stabilized aZr [471.
3. Physical properties 3.1. Introduction
The second edition of the Reactor Handbook (RMH-2) presented an excellent discussion of the early history of plutonium metallurgy, and presented all of the information on the physical properties of plutonium and its alloys available up to early 1957. Most of that information had been presented at the First Geneva Conference 153], in a paper that covered many of the properties of the allotropes of pure plutonium, and presented a considerable amount of phase diagram information. Since that time, there have been four international conferences on plutonium, the proceedings of which have all been published [54-57 ]. Much additional material has appeared throughout the general literature as the properties of plutonium became interesting to chemists, metallurgists, physicists, etc., in each of the countries involved in plutonium work, i.e., the United States, United Kingdom, Soviet Union, and France. One development since that time has been the
....
383
COP4TOURS~~
SOLIDUS CONTOURS L/OUIDUS
\',,
,
\%..
\ Fig. 12. Plutonium-uranium-zirconiumsolidus and liquidus projections in the plutonium corner of lhe system. (Reprinted from ref. [511 .) routine production of high purity plutonium by electrorefining techniques [58, 59]. Surprisingly, use of the high purity metal (less than I O0 ppm tot~1 impurities) has had little effect on measurements of the properties of the metal. Lower residual electrical resistivities have been obtained (as low as 6.2/~ ~2cm), and varying transformation kinetics have been observed. But on the whole, the availability of this purer metal has not changed any of the "strange" properties of plutonium, e.g., electrical resistivity vs. temperature, allotropy, contraction of delta phase etc. (see below), The low melting temperature of pure plutonium, its large number of phase transformations, its anisotropy in the low temperature phases, and the large, 10% change in volume during the beta --, alpha transformation all work towards making pure plutonium an undesirable engineering material. It is not possible, however, to ignore the properties of unalloyed plutotuum since it is precisely those properties which ultimately limit the usefulness of particular alloy, cermet, and even ceramic fuel compositions. The alloys to be discussed are mainly of two types: those which retain the pure metal structure, and those based on U-Pu. Most of the former alloys are-in the face-centered-cubic delta phase, while the latter generally include one or more alloy additions to improve engineering properties.
S,H.Kittel et aL, Plutonium and plutonium alloys
384
Table 7 Properties of pure plutonium allotropes, Phase
Alpha
Beta
Gamma
Delta .
Delta-prime
Epsilon
Crystal structure
Monoclinic [60]
Body-centered monoclinic [60]
Face-centered orthorhombic 1621
Face-centered cubic [63]
Body-centered tetragonal
[631
Bodycentered cubic 163 ]
at 21°C
at 190°C
at 235°C
at 320°C
at 465°C
at 490°C
a = 6.183 b = 4.822 c = 10.963 = 101.79 °
a = 9.284 b = 10.463 c = 7.859 # = 92.13 °
a = 3.1587 b = 5.7682 c = 10.162
a = 46371
a = 3.327 c = 4.482
a = 3.6361
No. of atoms/unit cell
16
34
X-ray density t~'cm 3 )
19.86
17.70
17.14
15.92
16.00
16.51
Bulk expansion coefficient ( l ( l " cm/cmf~(} *
47 to 76
26 to 38
28 tO 35
- 8 t O - 33
- 50 t o - 1 0 0
20 tO 36
Magnetic susceptibility lemu/g/106) *
2.22 1671 2.38 1681
2.29 2.50
2.22 2.42
2.12 2.36
2.12 2.36
2.15 2.38
Specific heat, ('p (cal'mol°(") [ 691
8.66 at 47°(7
8.28 at 160°C
8.67 at 250°C
9.0 ~.t 377°("
24 at 473°C
8.4 at 500-600
Absolute thermoelectric power (mvl°C) 1701
+ 15.5 a t 27°61
Thermal conductivity (cal/cm-~ec ~C,~[711
0.005 at - 123°C to 0.032 at + 120~'C
Unit cell dimensions, (A)
8
4
2
2
oc
+ I0.0 at 127°(7
*9.2at227°C
+3.7at327°C
+2.3at452°C
+4.2at 527°c
0.037 at + 140~C
* Near rrAd-point of temperature range.
3.2. Unallo.w'd Plutonium Table 7 summarizes m u c h o f the data for the pure phases. A considerable a m o u n t o f detail exists for each o f the properties listed and the references shoul6! be consulted, where appropriate. In addS.lion t o the bulk thermal-expansion coefficients listed in the table, thermal expansion data are available for the unit cell dimensions for each o f the allotropes. N o a t t e m p t has been made t o choose a "best value" for the bulk expansion data because o f the large emisotropy in several o f tl~e phases, The negative
expansion o f the delta and delta-prone phases are very n o t e w o r t h y . Delta p l u t o n i u m is unique a m o n g face-centered-cubic metals in this respect, and considerable experimental and theoretical effort has been e x p e n d e d on the causes o f the p h e n o m e n o n . The various suggestions for this effect have been electronic p r o m o t i o n [72] ; special band-structure effects [73 ] ', and elimination o f traces o f covalent b o n d i n g [74]. The electrical resistivity data for all o f the phases are summarized in fig. 13 [67, 75, 7 6 ] . The negative slopes in the alpha, beta, g a m m a , and perhaps epsilon
S.H.Kittel etal., Plutonium and plutonbon alloys
,
osC(~
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K
DELTA-
ILON
DELTA-PRIME -]
l~
50 0
200
I
40(}
,
600
1
aoo
TEMPERATURE, =K
Fig, 13. Electrical resistivity o f plutonium allotropes.
phases are not understood, although a discussion has been presented based on band structure effects [77]. Much work has been directed towards the explanation of the resistivity maxima in alpha and supercooled beta plutonium. The proposed mechanisms have been atomic order-disorder, a combination of band structure effects, or antiferromagnetic ordering. The latter model is supported by thermal expansion, 700
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30
40
50
60
PRESSURE,
7O
k bars
Fig. 14. Pressure-temperature diagram for plutonium.
80
385
thermoelectric power, radiation damage, Hall effect, and magnetoresistivity measurements at low temperatures. Unfortunately no corroboration has been obtained in magnetic susceptibility, specific heat, or neutron diffraction studies [57]. The ttall coefficients near, or above room temperature, are + 3.5 and + 2.5 X 1 0 - 13 v-cm/amp-gauss for pure alpha and bets, respectively. These results led to a band picture with a nearly full 7s band and the remaining 6+ electrons in 5f or 6d bands. The pressure-temperature diagram is given in fig. 14 [78, 79]. Although the alpha-beta-liquid triple point indicated from the earlier work was not found by Liptai and Friddle, the latter workers have had some success in using high pressures and temperatures to grow usable single crystals of alpha plutonium. They find that best results are obtained near the zero-slope portion of the beta ~ alpha phase boundary, viz. at 55 kbars [80]. Preferred orientation may be introduced into alpha plutonium by rolling in the alpha phase [81 ] or by cooling through the beta -~ alpha transformation under compression [82]. In the latter approach. the (020) planes align perpendicularly to the pressing direction, which is consistent with a (201) rolling plane, [01 O] rolling direction texture found in the former [83]. In both cases, the resistivity-telnperature slopes are nearly zero, and the resistivity maximum is shifted t?om 100 K to about 130 K when measured in the [010] direction. The transformation behavior is summarized in table 8. Temperatures for the a , . 13and 13~ 1, transformations are very dependent on heating/cooling rates and on sample size. The parenthetic temperatures are for moderate heating rates, while the quoted results are from Hill's studies of transformation temperature as a function of rate of temperature change. The transformation mechanisms have been the subject of much study, and the results are summarized in table 9. Selle's measurements of internal friction have allowed a determination of the mechanisms for all of tile transformati~ms. His results which are based on a new hypothesis agree with the models most generally accepted. The retero ences should be checked to get a full bibliography for these studies. A new. interesting property of beta plutonium has been studied at Pacific No,.ttlwest Laboratories. They find that the mechanical
386
S.H.Kittel et aL, Plutonhtm and plutonnon alloys Table 8 Phase transformation data for pure plutonium.
"lran~ition
Or-+/3
~-+~
"y"+,8
6 -+6'
6' -+e
e -+liquid
Temperature of trans, on heating I°C) 164--66. It, 841
112 [85] (122-126)
184 [85] (202-213)
314-319
440-464
460-484
635-641
150
280
469
490
637
Temperature of trans, on • .o , cooling | ( ) [ 6 5 . 661 Volume change (9;-) [ 86 ! Ileat of transforma~.ion lcal/g-atom} [69. 841
91
2.4
8.9 880
146
properties of beta depend on whether it is formed from the alpha or gamma phases. Their explanation is based on stacking faults in the/3~ (beta formed from gamma) while Selle [87] suggests that the difference is due to the different mechanisms of beta formation in a ~/3 and 7 "+/3. this is discussed in greater detail in sect. 4. A property which has been extensively studied in the last few years, primarily for basic understanding but whizh has some application to engineering problems, is self-radiation damage [57, 9 4 - 9 8 ] . The effect has been studied by electrical resistivity, thermal conductivity, lattice parameter, thermoelectric power, and specific heat methods. A saturation is found at high damage levels in alpha plutonium and is thougllt to be related to the proposed magnetic transivion. Damage studies with highly enriched pu238show a decrease in resistivity after saturation for reasons not fully understood. Similar behavior has Table 9 Transformation mechanisms for plutonium. Transformation
Mechanism
o~--*~3 ~'~ 3' -" ~ ,5 -~-6 ~'~'e e -"6' 6' -+ 6 -*3" "r ~ ¢ -+~x
Shear [ 87.88] D~ffusional [89] Diffu~ional [87, 88, 90, 91 ] Diffusional [ 87, 91 ] Shear [ 871 Shear [871 Diffusional [87] Diffusional [ 87 ] Shear [87, 90, 911 Diffusionai [87, 88, 90, 91] Shear [87, 88,921 Mixed [931
6.8 152
-0.1 15
-3.0 434
-2.4 732
been observed in supercooled beta and alloy-stabilized delta. Table 10 summarizes the results. Data are available at ofl~er temperatures and also on compounds. It should be noted that some of the radiation damage is not annealed out at room temperature. Results of tracer and mechanical testing studies have been used to calculate the activation energies for self-diffusion in the ailotropes. The data, listed in table 11, are not in good agreement. However, Nelson [99] found that his results depend on the stress-.strain exponent, and Selle [87 ] surmised that his activation energies may be low. Seile has also separated the results into vacancy formation and migration contributions. Several systems have been studied for chemical diffusion coefficient determinations. Results are in table 12. 3.3. Alloys with plutonium structure Alpha: Alpha plutonium may dissolve 75 a/o neptunium and very small amounts of uranium, in general, the addition of 2 a/o uranium shrinks the lattice parameters by about 0.1 to 0.3% and has little effect on the angle,/L The thermal expansion coefficients are also changed with the expansion in the a direction increased, and in the b and c directions both decreased and made nearly equal. There is a monotonic decrease in each of the lattice parameters with neptunium additions and the density at 75 a/o Np is 20.1 g/cm 3, compared to 19.86 g/cm 3 for pure plutonium [ 103]. Additions of neptunium to alpha plutonium eliminated the maximum in the resistivity-temperature curves above 4 a/o Np and all compositions up to 50 a/o Np have a negative slope in these plots [ 104].
S.H.Kittel eta'.. Plutonium and plutonium alloys Table 10 Effect of self-radiation damage on the electrical resistivity of plutonium.
387
Table 11 Activation energies for self-diffusion of the plutonium allotropes*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Alpha Initial damage rate at 4K (u s2 em/hr) Temperature of annealing stages (K) Damage remaining at room temperature (%)
Beta
0.06 75; 150
5
0.10 ' ( 4.2; 30-180
**
Delta 0.01
Selfdiffusion
Ot
3
"f
~
aef.
20.9 23
19.4 27
21.0 31 16.7
21.2 30 23.8
1~71 l ~9 J [ 1(10. loll
50*; 150
Vacancy formatien
15.7
11.0
12.7
10.0
[87}
10
Vacancy migration
5.2
8.4
8.3
11.2
1871
* In kcal/mole * This stage is a function of cornposition of delta-stabilizer. ** Metastable beta transforms to alpha phase on heating above 180°K. Beta: This phase may be retained with zirconium or titanium additions. The phase can dissolve uranium, aluminum, and neptunium also. Neptunium additions decrease the beta lattice parameters with a larger decrease per atom percent than for the alpha phase [103]. The electrical resistivity of a 4 a/o Ti alloy was found to lie about 3 / a ~ c m above the curve for pure beta plutonium, and with a negative slope, also, No maximum was found in the resistivity-temperature curve down to ~5 K [75]. Time-temperature-transformation data have been obtained on titanium-stabilized alloys. The results are interpreted to suggest two transformation mechanisms; martensitic at low temperatures and massive at higher temperatures. The "nose" of the T-T-T curve is near 0°C, and 2.5 a/o Ti alloys begin their transformation at 20 sec near the nose [ 105 ]. A study of the effects o f pressure on the Pu-Ti phase boundaries shows no beta ~ alpha transformation above 1 a/o Ti at pressures up to 50 kbar [1061. Gamma: Very small amounts of uranium, neptunium, zinc, zirconium, and perhaps :aluminum are soluble. The phase has not been retained at room temperature and no physical property measurements exist. Delta: A large number of elements dissolve in this phase, retain the structure on cooling, and/or stabilize the phase to very low temperatures. Among these are: aluminum, americium, cerium, gallium, indium, scandium, zinc and a large number o f rare
earths. Aluminum. gallium, and zinc contract the del~: cell, while the other elements mentioned expand the unit cell. Gschneidner et al. have considered the factors which cause delta-retention and concluded that only trivalent and tetravalent metals (zinc is an exception) with a favorable size factor are delta retainers [107]. Other models such as the influence of alloying on stored elastic energy or electronegativity considerations have been proposed, and
Table 12 Chemical diffusion in plutonium [ 102]. System
Pu-Mg (Mg)
Pu-Zr (6-Pu)
Pu-U (0t-U)
Comp. (a/o Pu)
Do (cm2/sec)
Q tkcal/ mole~
0.045 0.562 1.124
1 X 104 2.45 X 10-2 1.05 X 10-- 2
35 28.32 28.30
1.686
3.6
_~..38
X 10 - 4
38.5 46.2 61.6 69.3
7,70 X 10 -e 3.56 X 10-" 8.86 X 10 -9 9.60X 10- 9
23.50 15.05 11.80 12.65
1.75 3.50 5.25 7.00 8.75 10.50 12.25 14.00 15.75
O.14X 1(I-7 O.15X 10-7 0.18X 10--7 0.28X I 0 7 C44 X 10 - 7 0.88X 10-7 1.18X !q--7 290X 1 0 - 7 2.57)'. I0- 7
13.4 13.7 14.1 15.2 16,3 17.9 If,.8 20.0 20.6
S.H.Kittel et eL, Plutonium and plutonium alloys
388
Table 13 Effects of deRa-stabilizer additions on physical properties* 1
Thermal expansion coeff. (X 106 cm/cm°C) [107,108] Residua| resistivity (u 1-1cm) [ 110] Temperature of resistivity maximum (°K) [ 110] Thermoelectric power at (uV/°K) [ 1111 Magnetic susceptibility (emu/g X 106) [ 1121 Hall coefficient at room temperature t V cm/amp gauss X 1013) [ 113]
a/o
AI
5 a/o AI
10 a/o AI
+
+ 13.4 131 100 "~ 5 2.22 2.0
7.7 122 145 "~ 5 2.40 2.8
-
6 103 190 > 5.5 2.41 3.6
* E xtrapolaled when necessary
Table 14 Summary of data on delta-stabilized Pu-dch binary alloys at high pressures [114]. System
Pu-AI
Composition
1.7
2.5 3.4 4.0 5.0 7.5 10.0 12.5
a]o AI a/o AI a{o AI a/o Ai a/o AI a/o AI a/o AI a/o AI
Max. press, (alto)
Transformation press, (atm)
8,880 8,920 8,920 10,060 8,670 8,470 8,670 8,670
2040 4340 7020 N.T.** N.T.** N.T.** N.T.** N.T.**
Transformation voi. AV/Vo (%)
Density
Perma- Compressinent bility vol. (X 106/ change* atm) AV/V o (%)
Before ¢ompression (g/cm 3)
After compression (g/cm 3)
16.0 11.8 6.8
16.0 10.9 6.7 -
4.1 3.8 4.0 3.4 4.5 3.9 3.4 3.1
15.73 15.66 15.60 15.50 15.31 15.38 15.04 14.87
18.67 17.70 16.71 15.49 15.26 i5.48 15.07 14.87
-
Pu-Zn
1.51 a/o 1.79 a/o 2.16 a/o 2.92 a/o 3.35 a/o 3.89 a/o
Zn Zn Zn Zn Zn Zn
10,000 9,250 9,250 9,100 9,880 9.250
1200 950 2520 4210 5290 6650
17.3 16.7 16.2 15.3 15.8 13.8
17.1 16.6 15.7 14.8 15.3 12.4
4.7 2.4 2.0 3.8 4.0 3.2
15.94 15.85 15.75 15.71 15.70 15.64
19.08 19.08 19,08 18.53 18.29 17.82
Pu-ln
3.4 a[o In
9,100
1520
13.1
I2.4
2.5
15.56
17.83
10,600 10,600 9,880 9,880 9,250 9,250 11,000 I 1,000 I0,000 10,000 10,000 10,000
1 ~ 60 11 3000 1 500 11 4380 I 1460 II 6470 I 1920 Ii 8220 1 3230 II N.T.** i 4400 ii N.T.**
8.6 9.t 8.4 8.3 7.9 7.8 7.8 6.2 6.9
-16.3 15.5 15.8 14.6 -
-1.9 4.2 1.9 3.0 6.0 5.4 6.5 8.4 6,8
15.63 15.56 15.46 15.31 15.13
18.76 18.55 18.02 17.86 15.16
Pu-Ce
3.4 3.4 4.0 4.0 5.0 5.0 60 6.0 8.0 8.0 19.0 10.0
a/oCe a/o Ce a/o Ce a/o Ce a/o Ce a/o Ce a/oCe a/o Ce a/o Ce afoCe a/oCe afoCe
* Values obtained by extrapolation of pressure-volume curve,~. '~* N.T. means no transformation.
-
5.7
-
-
I lI i I il I !1 1 11
-
-
14.96
14.93
-
-
S.H.Kittel et al., Plutonium and plutonium alloys
389
Table 15 " PIoperties of U-Pu-X alloys (20% Pu and 10% "X") [ 117 ] Composition
U-Pu
U-Pu-Mo
U-Pu-Nb
Linear coef. o f expansion from 20°C-=500°C(X 10-6/°C)
21
16
17.8
16
17.3
Density at 20°C (g/cm 3)
18.8
17.15
16.5
14.57
15.64
3.7
3.4
3.3
3.9
3.1
Pu density (g/cm 3 of alloy) Resistivity at 23°C(p~Zem)
80
Therntal cop.duc*ivity (watts/cm/cm2/°K at 23°C) (calculated)
77
9.0 X 10-2
while the latter proposal accounts for zinc it does not hlclude thallium [56]. Addition of any of the delta soluble elements causes an absolute increase in the thermal expansion coefficient and all of them ultimately expand on heating with sufficient alloy content [108,109]. Assuming a single valence for delta plutonium, 4.8! 5, it is found that the alloys change from negative to
o.,
z {---.--.-T~ ~ 1
1
I
F"
t
-I
U-Pu-Ti
U-Pu-Zr
103
9.4 X 10-2
86
7.0 X 10-2
8.4 X
10 - 2
positive expansion coefficients at compositions corresponding to 4.74 electrons/atom [ 109]. Delta-stabilized alloys have resistivity temperature plots similar to those for pure alpha and beta plutonium (see fig. 13). The resistivity maximum shifts to lower temperatures with increasing alloy content (188 to 100°K with aluminum decreasing from 1.2 to 10 a/o). The effect, alloying additions on a number of properties is giv in table 13o Table 14 summarizes some data obtau 1 from pressure studies [114] (also see ref. [106]).
t
20 F
i
i
'-~~,
O. IO
i
o,,I /,f!
~!0.0~
,2
i
0.06
coo , G
//
-I
s Z J/
0.O4
.
0.02
....
,
,
200
t
,
.
t
,
4oo
6e~o
soo
~
o0
200
400
500
800
T E M P E R A T U R E , °C
TEMPERATURE (=C)
Fig. 15. Thermal conductivity of U and U-Pu-Base alloys (w/o). (Reprinted from ref. [ 115].)
Fig. 16. Thermal expansion of U-19Pu-6Mo, U-25Pa-10TL and U-Pu-Fs alloys (a/o). (Reprinted from ~ef. [1171 .)
S.H. Kittcl et ai., Plutonium and plutonium a~loys
390
Table 16 Properties of U-Pu-Zr and U-Pu-Ti alloys [ 115].
U
Nominal composition: w/o a/o .
.
o
Approx. hqmdus temp,(C) Approx. solidus t e m p . ( C ) Solid transformation temp. range (of;.) Density at 25°C as-cast (g]cm3)
Thermal expansion Avg. coef. X 106 (°C-l} 25°C to 1st trans. End of trans, to 950°C In trans, range
-~X
103(°C -1)
Thermal cycling density change (%) H~dness at 25°C as-cast (DPH)
U
U
U
Pu
Zr
Pu
Zr
Pu
11.1 10
6.3 15
i5 12.9
10 22.5
18.5 14A 15 30
1200 1120 595680
1250 I ~55
Zt
! 290 1170 595~i60
595665
U
U
Pu
Ti
Pu
17.1 I5
3.4 15
15 10 10.7 35'.6
1206 1075
Ti
~340 120~;
585780
680850
Pu
Ti
?2 15
11,8 40
1360 !225 650815
16,8
15.8
14,8
17.5
14.7
14.0
18.3 18.1
17.6 20.1
17.5 20.0
2!.2. 16.4*
19.2 19,2
17.4 21.5
5.1
5,2
5.0
9.3
13.7
11.9
0 470
-0.1 540
-
+0.1 410
430
+0.1
-
400
360
* to 860°C,
Epsilon: This phase dissolves small amounts of a number of elements, and forms complete solid solutions with "r-Npand ~/-U. Compositions of 70 to 73 a/o U and 8 to 10 a/o fissium can stabilize the phase to room temperature [54]. The lattice parametercomposition curve for 3,Np-ePu has a slight negative deviation from Vegard's law at 550°C [ 103]. 3.4. Uranium-plutonium alloys Although this alloy system forms the basis for fast reactor metallic fuels containing plutonium, few physical property studies have been made of the binary system alone. This is because of the extremely poor properties of samples containing even small amounts of the zeta phase (see fig. 5). Fig. 15 shows the thermal conductivity of a uranium-10 a/o plutonium alloy in comparison to a number of alloys [ 115]. Plutonium is seen to decrease the thermal conductivity of uranium. Figs. 1 5 - 1 7 and tables 1 5 - 1 7 summarize a n u m b e r
of properties of alloys of U-Pu-X, where X may be "fizzium", "fissium", zirconium, titanium, molybdenum, or niobium. For a given fizzium content, the rate of transformation for "I,-U(e-Pu) ~ ~ U + 6' is constant for alloys widi up to 10% plutonium (see fig. 16)but increases significantly between 10 and 20% plutonium [ 117 ] Transformation is essentially complete at 450°C in 30 mip for a i 0% plutonium alloy and in 5 min for a 20% plutonium alloy. Other relevant properties of U-Pu-X alloys may be found in refs. [115-118], and i~ papers referenced therein. Mach of this work is reported in other sections of this article.
3.5. A luminum-based alloys The properties of alaminum-based, plutonium alloys have been studied for use in thermal reactors [119-121 ]. Table 18 :smnmar[zes the data. In general, plutonium additions up to 15 w/o cause a nearly linear degradation of the properties of the host metal.
S.H.Kittel eta!., Pl:~tonitan and ph~tonium alloys
391
Table 17 Prnp=rties of uranium-plutonkm~-fizzium alloys [ 115]. U Composition: w/o a/o
g
U
~t
U
Pu
Fz
U
Pu
Fz
90 90
10 I0
90 69.9
S0 8.7
I0 2i.4
75 65.5
i5 13.1
10 21.4
"U
Pu
60 20 61.1. 17.5
Liquidus temperature (°C) Solidus temperature (°C)
!133" 1133
1060 1025
1010 910
1000 865
990 820
Traasformation temp. ~ ( ~ Start Complete to
668 775
585
550 630
520 605
510 605
Density at 25°(2 (g/~~a- 3 Thermal expansion Avg. coel. X 106 (°c - ~) 25°(2 to 1st. trans. End of trans, to 7 2~'flC In trans, range - ~ X 103(OC - t ) Thermal cycling Density change (%) Length change (%)
7411
19. i
18.7
16.8
16.5
16.8
19.4 25.6
19.3 23.8
16.3 20.5
16.5 22.5
21.7
4.5
2.8
4.5
3.6
3.3
-2 -7
--30 + 25
+ 1 0
17.5
0 -1
- ! +2
Thermal conductivity (cai/sec- 1[ c m - I / ° c - ! )
2oo°c 400°C
600% 800% Enthalpy, 25°C to mp (cal/gm - l ) Hardness, DPN (kg/mm-2) "~quenched Oztransformed
0.071 0.080 0.094 0.115
0.071 0.069 0.0~.7 0.100
0.046 0.057 0.070 0.084
0.046 0.057 9.070 0.084
0.047 0.056 0.069 0.086
52
46
44
43
42
290
205
255 410
435
215 430
42 27 6
3
Tensile strength (kg[ m m - 2 )
200% 400°(2
600% 800%
37 17 5. 1
26 19 9 0.5
58* 40 8
27** 27 8
2
2
1
* As quenched. ** Transformed below 500°C. Table 18 Properties of aluminum-based, plutonium alloys*
Density (g/cm a) [ 119] Thermal expansion coef. (cm/cm/°C X 106) { 120} Thermal conductivity (cal/cm- I _scc.OC) Electrical conductivity ( o h m - ! -cm - ! ;/, 10- s ) [ 1211
A!
AI-5 w/o Pu
Al-15 ~vlo Pu
2.70 28.,t 0.5 ~ 3.60
2.76 27.7 0.43 2.8
3.07 26.4 0.13 0.6
* Some data are estimated from specific compositions other than those given here.
I:z i0 21.4
392
S.H.Kittel et al.. Plutonium and p/utonhtm alloys
2" I 1
]
I
I
I /f~15
t |
Pu-IO Ti
U-185 Pu-14.1Zr ]
20--
~-t6 ~o x z~ o
8--
4
[
0
0
L
0
I
200
I
I
ZOO 400 6)30 U-Pu-Zr AND U-Pu-Fz
I
I
400
600 U-Pu-Ti
.,I 800
[ 800
I
1000
1000
I
1200
TEMPERATURE |*C)
Fig. 17. Typical expansion of some U-Pu-basealloys (w/o). (Reprinted from ref. [ 1151.) 4. Mechanical properties 4.1. httroductivn Since, the previous edition of the Reactor Handbook was published, extensive information has beco~le available on the mechanical properties o f unallc.yed plutonium and delta plutonium stabilized with either aluminum or gallium. However, very limited in r :rmation exists on alloys of low plutoaium content. In the Plutonium Handbook [ 122 ] Gardner gii~,es a very complete presentation of the mechanical property data obtained prior to 1964. Because more information is now available on the tensile and creep properties, fracture behavior, strain hardening, and recovery of plutonium, a suzmnary of the mechanical properties of unalloyed plutonium will be discussed first, fol.~owed by these of plutonium-rich alloyed, and alloys of low plutonium content.
4.2. Unalloyed plutonium Because of Gardner's thorough analysis [122] only a summary of the mechanical properties of unalloyed plutonium is needed here. The specific properties discussed are hardness, tensile properties, compressive properties, creep, roiling characteristics, torsion, impact, fatigue, deformation modes, and recovery and recrystallization. 4.2. r. Hardness Hardness is the mechanical property of plutonium that ismeasured most frequently. The hardness of a-Pu depends upon the metal's prior thermal and mechanical history; apparently, more so than upon the metal's quality. The hardness of as-cast a-Pu containing 300 to 1000 ppm total impurities is 260 to 285 DPH [56, 122-125]. Gardner [122] gives the most probable average hardness as 265 DPH for 0t-Pu at room temperature, having a density of 19.50 to 19.70 g/cm 3 and a total impurity content of less than 1000 ppm. The hardness of as-cast electrorefined plutonium is about 255 to 265 DPH; whereas, the hardness of recrystallized electrorefined a-Pu is 235 DPH [124]. The hardness of a-Pu is about 375 DP[t at -80°C and about 180 DPH at the a ~/3 phase change (fig. 18). When alpha transforms to beta, the hardness decreases to about 60 DPH at 125°C and decreases to about 25 DPH at 180°C. The hardness of beta transformed from gamma, however, is higher than beta formed from alpha [125]. The hardness of 7-Pu is less than 20 DPH and that of 8-Pu is less than 10 DPH. 4.2.2. Tensile properties The ultimate tensile strength of t~-Pu cal~ vary between 35,000 and 85,000 psi, depeading upon the metal's prior thermal and mechanical history [56, 126--128]. Pavlick [126] found that a large variation in the ultimate tensile strength is caused primarily by microcracks, which form during the ~ t~ transformation [129]. Neither grain size nor ,urity influence the ultimate tensile strength as much as microcracks. The ductility ofet-Pu is less than 1% at room temperature at a testing speed of 0.015 in./min; however, 200% elongation can be obtained above 100°C. Gardner and Mann [56] studied the effect of temperature on the tensile properties of
393
S.H,Kittel et aL, Plutonium and plutonium alloys
ductility of delta as the temperature is increased; strength, however, decreases with increasing test temperature. Gardner [56] observed that testing speed influences the tensile properties. Between 30 and 100°C (alpha phase), the ultimate strength increases to a maximum (which obviously depends upon the metal and temperature) at about 0.250 in.[min testing speed and then decreases. He attributed the increase to strain hardening, and the decrease to an increase in the notch sensitivity with testing speed.
I 400 l I
I I
100
I I
I -200 -100
t 0
,I'll 100
2o0
I 300
Fig. 18. Effect of temperature on hardness of unalloyed plu.
tonium [ 124].
unalloyed plutonium in the alpha, beta, gamma, and delta phases (fig. 19). The ductility of ~-Pu can vary wide!y, depending on the metal's thermal history. Elongations up to 680% have been obtained when the beta phase is formed from the alpha phase; however, the total elongation is less than 20% when beta is formed from gamma. Dahlgren [130] studied the plasticity of unalloyed plutonium by evaluating the strain hardening exponent, m, in the equation o = ~'dm. Values of m up to 0.33 and elongations up to 680% are obtained for beta plutonium formed directly from the alpha phase. Metal cycled between the alpha and beta phases has a lower flow stress and a higher value for m (m ~ 0.45); the total elongations are not as great as for uncycled metal because of the premature failure at voids which form during cycling. Beta plutonium formed from the gamma phase has a higher flow stress and a lower value of m (m -~ O. 15) than beta metal formed from the alpha phase, and m is relatively insensitive to changes in temperature and strain rate. The decrease in ultimate strength with increasing temperature is much smaller in the gamma phase than in the alpha and beta phases (fig. 17). The gamma phase strength is higher than the beta phase strength, while the strength of the delta phase is 50% lower and the ductility is 34% higher than the corresponding values for the gamma phase. There is little change in
4.2.3. Elastic modulus H.L.Laquer [ 123] used a pulse sound-velocity technique to establish the elastic constants of unalloyed plutonium that had a density 19.772 g/cm 3 . A value of 14.40 X 106 and 6.29 × 106 psi was obtained for the modulus of elasticity and shear modulus, respectively. Gardner and Mann [56] used a microformer-type extensometer to determine the elastic modulus in the alpha phase, while Kay and
70
'i
"
40
ol,, -50 0
.50 ICO 150 ~
250 300 350 400 450
TEMPERATUREC
Fig. 19. Effect of temperature on tensile strength of unalloyed
plutonmm at a testing speed of 0.015 in./min. * Taken at point of departure from linearity on load-platen displacement curve - - approximates a 0.2% effect yield strength [ 122].
394
S.H.Kittei et aL, Plutonium and plutonium alloys
Table 19 Elastic constants of unalloyed plutonium. TernPhase perature (°C)
Modulus Shear Poisson's of elas- modulus ratio ticity (10 6 psi) (106psi)
-250 - 170 80 0 20 60 100 140 170 200 220 260 300 330 380 430
18.9 17.35 16.00 14.65 14.00 13.30 12.40 5.90 5.58 5.37 5.28 4.94 4.58 2.49 2.45 2.39
-
Ot o~ Ct tx o~ a ~ /3 # ~ ~, ~ "V 5 6 6
0.17 0.20 0.20 0.20 0.16 0.15 0.14 0.29 0.27 0.27 0.24 0.25 0.25 0.43 0.45 0.42
7.26 6.69 6.17 6.08 5.80 5.45 2.29 2.20 2.12 2.13 1.97 1.52 0.87 0.84 0.81
Bulk modulus (106 psi)
9.63 8.90 8.18 6.88 6.33 5.76 4.68 4.05 3.89 3.38 3.29 3.06 5.9 8.1 4.9
4.2.4. Poisson's ratio H.L.Laquer [123] calculated a value of 0.!5 + 0.01 for Poisson's ratio from elastic and shear moduli data determined by a pulse technique. Konobeevsky [84] calculated a value of 0.21 from moduli determined by resonance techniques for plutonium extruded at 230°C in the gamma phase. Kay and Linford [56, 131 ] using an ultrasonic resonance method, derived values of Poisson's ratio ranging from 0.I 75 for low quality plutonium and 0.186 for high quality plutonium. The effect of temperature on Poisson's ratio is shown in table 19.
[LIO.
oL] I -1.0
Linford [56, 131 ] used an ultrasonic resonance method up to 430°C. Lallement [ 133] and Linford [132] measured the temperature dependency of the modulus of elasticity between 4.2°Kand room temperature. Their data are comparable except that Lallement noted at -213°C a minimum, which wa~ not detected by Linford. The temperature dependence of the elastic moduh~s is given in table 19. The change of modulus with temperature shows that the alpha phase from 20 to 110°C exhibits a large change of modulus with temperature, i.e., it is 2 X 104 psi/°C betweeh 20 and 100°C. A higher metal quality, as indicated by density, results in a slight increase in the elastic constants (table 20). Lintord [ i 31 ] observed a slight increase in the elastic modulus at the /3 - 3' phase change similar to the strength increase observed by Gardner and Mann [56]. Room temperature elastic constant data from several sources are compared in table 20, with the agreement of the elastic constants being quite good for corresponding densities.
00
~ -2.0 I llO ~ -3.0
-5~0 -60
,
5OO
I 1.0
1.5
, 2.0
2.5
3.0
lO00/T, g-1
Fig. 20. Temperature dependence of the steady-state creep of unalloyed plutonium [57]. The indicated values are compressive stresses of psi
4.2.5. Compressive properties The deformation of unalloyed plutonium in compression have been studied by Gardner and Mann [56], Bronisz [127], Pavlick [135], and Nelson [ 136]. The large variation of the data among the authors can be attributed to metal purity. Gardner and Mann [56] made a very extensive study of the effects of temperature and testing speed on the compressive properties of unalloyed plutonium with a purity of 500 to 1000 ppm. They found that the general effect of temperature is quite similar to that observed in the tensile work, except the ultimate and yield strengths in compression are
S.H.Kittel etal., Plutonium and l~lutonium alloys
395
Table 20 Room temperature elastic constant data from various sources for unalloyed plutonium [ 13 ! ]. Source
Density (g/cm 3)
Modulus of elasticity (106psi)
Shear modulus (106 psi)
Poisson's ratio
Bulk mod,alus (106 psi)
Adiabatic compressibility ( 10 - 7 in.:'/Ib)
lsoMethod lhermal compressibility (10 - 7 in.2/Ib)
Linford [131]
19.49
14.15
6.01
0.176
7.29
i.36
1.51
Resonance
Linford [131] (high density)
19.71
14.60
6.13
0.186
7.75
1.30
1.44
Resonance
Laquer [ 56 ] (high density)
19.72
14.40
6.30
0.15
6.77
1.48
1.62
Pulse
DeCadenet [56]
19.35
14.25
5.93
0.199
7.90
1.27
1.41
Pulse
Bridgman [ 134]
.
1.38
Compressibility
Robinson [ 122]
19.6
.
1.32
Compressibility
Gardner [56]
19.53
14.32
.
Lallement [1331
-
13.6
-
0.23
-
-
-
Resonance
Linford [1321
19.65
14.50
-
0.18
-
-
-
Resonance
(mean as-cast)
(as-cast)
.
.
. .
. .
. .
.
.
.
considerably higher than those in tension. For example, at room temperature the ultimate compressive strength (175,000 psi) is three times as high as the ultimate tensile strength. Although the ultimate tensile strengths of the beta, gamma, and delta phases were not obtained because of the very large plasticity of these phases, the yield strengths do decrease - similar to tensile work - with increasing test temperature. They observed that increased testing speed increased the beta yield strength essentially the ~ame as it did in tension, but that yield strength in compression was independent of testing speed. Bronisz [ 127] studied the effect of temperature, testing speed, and purity on the compression properties of only the alpha phase. The total impurity contents of his metal were i 15, 185,227 and 480 ppm. He observed approximately the same dependency of yield strength on temperature and testing speed as Gardner and Mann [56], but he also noticed that temperature dependency is greater for purer plutonium, and (contrary to behavior of ether metals) that the testing speed sensitivity is less at higher testing temperatures.
.
.
Tensile test
Strain hardening of alpha up to at least 5% plasticity has been obselved; for example, Pavlick [ 135] reported a strain hardening exponent of 0.07. The hardness of deformed grains is about 310 DPH compared to 265 DPH for as-cast grains and 235 DPH for recry~tallized grains [ 136]. Strain hardening studies in compression have not been performed on the higher temperature allotropes. Nelson's [ 136] compression tests were on electrorefined plutonium containing less than 300 ppm total impurities, and these tests showed that recrystallization occurred concurrently with deformation. Deformation and recrystallization occurs very rapidly at the high alpha temperatures; for example, at 30,000 psi, 75% deformation with concurrent recrystallization occurs within five minutes at 115°C. Deformation with concurrent recrystalliation occurs at 20°C, but at a much slower rate and a much higher stress; more specifically, 80% reduction requires about 150 hr at 90,000 psi. 4.2.6. Creep Creep of plutonium has been the most extensively
396
S.H.Kittel et aL, Plutonium and plutonium alloys
studied in compression [57]. Creep curves of the/3, % 8, 6', and e phases are typical in that they consist initially of primary creep followed by secondary or steady-state creep. Creep curves of alpha plutonium, however, show recrystallization. Fig. 20 permits a comparison of the logarithm of the steady-state creep rate versus reciprocal temperature ior all plutonium allotropes. The creep rates of % 6,6', and e vary less than 10%, regardless of the transformation rate or the present phase. For example, at the same temperature and stress, the creep rate of ~, formed from/3 is the same as the creep rate of ~' formed from/i, but the creep rate of/3t~ 03 formed from or) is 50 to 500 times greater than the creep rate of 13.r 03 formed from ~). Sufficient creep data have been obtained for the 13,~, and 8 allotropes to conclude that the steady-state creep is related to stress, o, by the proportionality ~ 0 '1. Between steady-creep rate of 10 - 4 and 10- 1/hr, n equals about 6 for 8 and about 5 for 3, and/3; however, for most metals n is 5. 4.2.7. Rolling characteristics Alpha plutonium can be rolled successfully even though it is brittle, lanniello [ 137, 138] successfully rolled it by (I) rolling it about 15% reduction in the beta phase (which deforms easily)at 150 to 160°C; (2) rolling continuously during cooling, i.e., the roll separation was decreased 0.001 in. every 5°C until the temperature was 50°C; and (3) rolling at room temperature decreasing the thickness 0.001 in. each pass. The alpha phase can also be rolled from a thickness of 0.150 in. to 0.010 in. at 70 to 100°C by decreasing the roll separation 0.010 in. between passes. The deformability is most influenced by (1) amount of microcracks, (2) grain size, (3) prior mechanical history, (4) thickness, and (5) internal stresses. Metal that contains a very fine grain size, severe microcracking, and large amounts of internal stresses cannot be rolled. Strain hardening is very low because the hardness increase by rolling is less than 10% for deformation less than 40% reductions. The hardness decreases for large amounts of deformation. Rolled o~-Pu contains a two component texture, which was determined by Berndt and Lloyd [83]. One texture has the (010) aligned approximately parallel to the rolling direction, and the other texture has the t'010) nearly parallel to the cross direction.
The important texture is the one having the (010) nearly parallel to the rolling direction. 4.2.8. Torsion properties Only preliminary torsion data exist on as-cast plutonium. A group of five tubular specimens was tested by Gardner at room temperature [ 139]. The average ultimate shear strength was 53,200 psi for plutonium having a density of 19.55 g/cm 3 and 600 ppm total impurities. The shear strength of brittle material cannot be determined in a torsion test because failure actually occurs in diagonal tension before the shear strength is reached. By using a ratio of 1.2 and a value of 50,900 psi for the true tensile strength of plutonium, Gardner estimated a value of 61,100 psi for the true shear strength. A shear strength value of 80,000 psi was calculated based on compression test results; however, during tensile testing of threaded joints, shear strengths varying from 35,000 to 45,000 psi were observed. No direct determinations of the shear modulus or modulus of rigidity have been reported for plutonium, although pulse and resonance techniques have been used to determine shear modulus values of 5.93 X 106 psi [132], 6.29 X 106 psi [56], and 5.4 X 106 psi [841. 4.2.9. Impact Alpha-phase plutonium behaves in a brittle manner during a tensile impact test [56]. A group of eight, 0.250 in. gage diameter, 1.5 in. gage length, threaded specimens tested at room temperature gave impact energy values ranging from 1.3 to 4.8 ft-lb - with typical brittle fractures obtained in each case. Coffinberry [123] using Charpy keyhole notch type impact specimens, found that at 22°C the impact strength of alpha plutonium ranged from 1.5 to 2.0 ftqb. In addition, this analysis of the general mechanical behavior of plutonium suggests that impact strength approaches zero at lower temperatures and that there is some slight increase at temperatures above 75°C. Gardner, who made a study of the unnotehed and Charpy V-notched impact properties of plutonium [140], found that impact energies increase with in. creasing temperatures in the alpha phase. A further increase was observed as test temperature was increased
S.H.Kittel et al., Plutonium and plutonium alloys
to 130°C in the beta phase; however, at the 175°C test temperature the impact energy decreased. Essentially no plastic defo,mation was observed in the alpha and beta phases; while in the gamma phase, extremely ductile behavior was observed. These data confirm observations made on strain rate effects during tensile testing in the beta and gamma phases; i.e., the beta phase is quite strain-rate sensitive while the gamma phase is relatively insensitive to strain rate. The impact energies for the Sharpy V-notched specimens are much lower than the unnotched values at corresponding temperatures. As suggested by Coffinberry [ 123], the V-notched impact strength actually increases as temperature is increased in the alpha phase. Brittle fractures are obtained in the alpha and beta phases. Relatively ductile fractures are obtained in the gamma phase, and extremely ductile behavior occurs in the delta phase [140]. From a comparison of the unnotched and notched impact energies at 100 and 130°C it can be concluded that the beta phase is, in addition to being strain-rate sensitive, quite notch sensitive. 4.2.10. Fatigue Gardner [ 141 ] studied the fatigue of unalloyed plutonium of a wide range of quality. The total impurity content ranged from 277 to 2063 ppm, the densities varied from 19.40 to 19.64 g/cm3; microcracking varied from severe to none, which was due to a large amount of iron. He obtained two fatigue curves (fig. 21) by two methods - both pneumatic. One method produced a complete stress reversal during each cycle and the other produced an incomplete stress reversal. A large scatter in the data was produced by the difference in metal quality; severe microcracking caused failure during the first stress cycle. 4.2.11. Deformation modes The modes of deformation of plutonium have been studied for only the alpha phase [57, 142]. Slip has been observed most frequently and appears to be the most prevalent mode of deformation at room temperature under compression stresses. The most likely slip plane is (020) because this plane has a high atomic density and contains all of the atoms at y =¼ and y --3 - ~ . Bronisz and Tate [57], however, state
397
60
40 c,D
z
2O
0 0
I
I
104
105
-
I
I
106
107
I ~
108
REVERSED STRESSCYCLESTO INC IP IU',ITI:AILURE
Fig. 21. Fatigue curves for unalloyed plutonium I 1221.
that slip planes near (114-), (213), and (323 ) probably are more operative at room temperature than the
(020). While twinning has been obser,~ed infrequently. grain boundary sliding has been seen more frequently, especially as the available plutonium becomes purer. Grain boundary sliding is most common at the high alpha temperatures (80 to 1 !5°C) and at the slow deformation rates. 4.2.12. Recovery and recrystallization Recovery of residual stresses introduced by deformation and by phase transformations can occur by annealing between 100 and 115°C. Pavlick and Hanson [ 135 ] showed that recovery, which was monitored by measuring the decrease in yield strength with annealing time, occurred at 109°C of specimens that had been deformed 3 to 5% by compression. X-ray diffraction patterns are much sharper and the 0t ~/3 transfonnation rates are much slower for annealed c~-Pu than they are for del'ormed a-Pu. Even though recovery of a-Pu is very common, recrystallization (as observed by a change of microstructure) has not been reported for annealing of deformed a-Pu. laniello [1431 postulated that the recrystallization temperature is near the transfonnalion temperature. Nelson 11361 found that a decrease in grain size - to 1 micron or less occurs concurrently with deformation by compression. The decrease in grail~ size was attributed to recrystallization. They both measured hardnesses of 235 DPlt, which is about 30 DPH less than as-cast a-Pu.
S.H.Kittel et al., Plutonium and plutonium alloys
398
Table 21 Temperaturevs. hardness for a homogenizedPu-3 a/o Ga alloy [ 1461.
300
g
Temperature (°C)
Hardness (DPH)
25 121 172 196 254 323 385 415
40.5 30.8 26.0 23.6 19.5 14.5 5 3
200
~
~u-Ga
e,,,
100
~ ~tpu-AI
Pu-Ga
Pu-Ai Pu-Ce
j/
0 0
I
I
I
2
4
6
1, 10
I S
12
SOLUTECONCENTRATION,AT.%
Fig. 22. The compositional dependence of hardness for Pu-AI, Pu-Ga, and Pu-Ce alloys [ 144, 145].
4.3. Delta-stabilized alloys Since the three most common elements for stabilizing the delta phase of plutonium are aluminum, cerium, and gallium the discussion of the mechanical properties of delta stabilized alloys will include only these three elements. Specific mechanical properties to be discussed are hardness, tensile properties and compression properties, creep, torsion, and fatigue. Because these properties markedly depend upon thermal and mechanical treatments and upon composition, they can be discussed only in generalities.
15-0.2~
/
I 10 -
/
x ,=
/
I
/
[ [
5
ULTIMATE STRENGTH,18,600psi PROPORTIONAL LIMIT. 4500psi 0.2~ YIEEDSTRENGTH,ll,50~psi ELONGATION, 25.0% RED. IN AREA, 31.3~ 6 ELASTICMODULUS.6.2X 10 psi TESTSPEED.0.015~N.IMIN TESTTEMPERATURE,30 C
/ i
! / I
/ I
i
r 0
, 0
I
fi¢ 0.002
,
I
,
0.004
I 0.006
,
4.3.1. Hardness Hardness data have been determined as a function o~ composition by Miller and White for Pu-AI [144], Pu-Ce [144], and Pu-Ga [145] alloys. The Pu-Ce and Pu-Ga alloys were homogenized 50 hr at 450°C and the Pu-AI alloys were homogenized 200 hr to obtain fully homogenized alloys. Alloys that were believed to contain two phases (t~ and 5) were annealed an additional 50 hr at 250°C to produce an equilibrium structure. The hardness decreases from about 265 DPN for unalloyed plutonium to the 5-phase solid solution values, which depend upon the additive (fig. 22). The linear decrease in hardness as the amount of alloying element is increased is caused by a decrease in the amount of alpha, but the linear increase is caused by solid solution hardening. Ga!lium and aluminum show more solid solution hardetdng than does cerium. Miller and White [144] expressed the rate of hardening as 0.53 DPN/a/o for cerium and 4.75 DPN/a/o for aluminum and gallium. Gardner [122] on the other hand, obtained a rate of hardening of about 8.5 DPH/a/o Al. Hays [ 146] determined the hardness of a homogenized Pu-3 a/o Ga alloy as a function of temperature by using a 578-gram load (table 21). Miller and White [ 145 ] also reported a temperature dependence of hardness up to 5 a/o Ga.
I 0.008
STRAIN
Fig. 23. Stress-strain curve tot plutonium-3.0 a/o gallium
delta-stabilized plutonium, 0.250 in. diameter specimen [122].
4.3 .'2.. Tensile and compressive properties Most of the tensile and compressive properties have been on alloys containing 3.0 a/o Ga. The tensile properties on this alloy vary considerably due to variations in the impurity content, particularly iron.
S.H.Kittel et ai., Plutonium and plutonium alloys
P.J
I0
X
/
39
4O
-" t\ 30 5
x
Pu-AI
20
-AI
Pu'-.Ce
10
Pu-Ce
_
/
% _
0
t
1
2
4
I 6
I 8
I 10
12
A typical stress-strain curve (fig. 23) shows that stress is proportional to strain up to 4500 psi and that there is no well defined yield point. The ultimate strength decreases from 17,000 psi at room temperature, 2000 psi at 400°C. Correspondingly, the yield strength decreases from 10,000 to 1500 psi. The ductility increases from about 40% at room temperature to about 80% at 400°C. The effect of aluminum, cerium, and gallium compositions on the 0.1% yield strength (fig. 24), ultimate strength (fig. 25), and Young's modulus (fig. 26) is similar to the effect of solute concentration on hardness. The decrease in strength is because there is due to lesser amounts of alpha and the increase in strength is caused by solid solution hardening. 4.3.3. Creep The only creep work of delta-stabilized alloys has been the compressive creep studies by Robbins and Wheeler [57, 147] of a Pu-3.0 a/o Ga alloy. Creep was evaluated at 20~ ~,~psi between 234°C and 3870C. The alloys deform~a initially by primary creep, then by steady-state creep, and finally by a recrystaUization process, similar to high purity :alpha plutonium, that caused most of the deformation. The average activation energy was determined to be 33.7 +--2.57 kcal/g atom for strains of 0.05, 0.10, and 0.15. They found a marked influence of raetal purity on the creep
1
I
I
~,
4
6
8
10
.....
12
SOLUTECONCENTRATION.AT.%
SOLUTECONCENTRATIf,,N,AT.~
Fig, 24. The compositional dependence of the 0.0% yield strength for Pu-AI, Pu4[:e, and Pu.
l 2
Fig, 25. The compositional dependence of the ultimate ten~ile strength of Pu-AI, Pu-Ga, and Pu-Ce alloys 1144, 145],
rates of the alloy. They also noticed that the amount of primary creep increases with increasing temperatures. Fatigue The only fatigue work has been on the Pu-3 a/o Ga
4.3.4.
m
ii
10
°
8
---
4
I I I
t
x
i
0
1 .....
~
P
6
'1
I
S
10
12
SOLUTECONCENIRATION, AT.%
Fig. 26. The variation of Young's modulus with composition for Pu-AI alloys [ 1441 .
S.H.Kittel et al., Plutonium and plutonium alloys
400
Table 22 Tensile properties of plutonium-iron alloys [ 122]. Test
Ultimate
Yield strength
Modulus of
0.01% offset
elasticity (%)
iron
temperature ~°c)
strength (psi)
(psi)
(10 6 psi)
7.0 7.0 7.0 8.7 8.7 8.7 8.7
30 125 127 30 127 220 318
54,500 29,700 24,500 35,900 34,100 14,150 4,260
26,700
7.1
0.23
0
8,720 25,700 10,750
3.8 6.7 .5.0
0.59
0
0.044
0.43
0 0
-
-.
1.0
0
-
-
Atomic percent
Elongation
<
12.5
Reduction
in area (%)
5.9
Gage length : 1 in.
Diameter ,0.250 in. Testing speed: 0.015 in./min. alloy by Gardner [57] who used the same technique that he used for unalloyed plutonium. The fatigue strength was determined with a superimposed mean stress of 5,400 to 6,700 psi at a frequency of stress reversal of 215 cycles/see. The metallurgical conditions included: (1) as-cast, (2) with coring, i.e., with alpha phase present, (3) cold rolled, and (4) homogenized. The 0.1% yield strength ranged from 10,300 to 30,4(~0 psi due to the variations in metallurgical conditions. The fatigue limits ranged only from 10,000 to 15,000 psi (107 to 108 cycles) regardless of metallurgical condition; the presence of alpha phase apparently increased resistance to fatigue failure. 4.3.5. Torsion Robbins and Wheeler [148] also studied the torsional ductility of a Pu~3 a/o gallium alloy containing 231 ppm total metallic impurities that had been cast, swaged, and then heat treated 24 hr at 460°C. The specimens (0.200 in. diameter and 1.00 in. long) were deformed at a single constant tensional strain rate of 4.16%/see at temFeratures ranging from 20 to 576°C. The alloy exhibits a ductility transition region between 150 and 2S0°C, that leads to very high ductility between 200 and 500°C. Between 500 and 560°C, a sharp decrease in ductility occurs that is probably associated with the 8 --, e transformation. No torsional sheaz stresses have been determined but the strength decreases continuously with increasing
temperature. No abrupt changes in strength occur where the ductility increase occurs. 4.4. Plutonium-rich alloys 4.4.1. Plutonium-uranium A limited amount of hardness, tensile, and compressive data are available on Pu-U alloys containing 3, 7, and 14 a/o U [149]. The hardnesses were 240 to 270 DPI~ for 3% alloy, 180 to 215 DPH for the 7% alloy: ~nd 200 DPH for the as-cast 14% alloy. It should be noted that the as-cast alloys had the largest hardness values. The hardnesses were lowest when the alloys were heat treated at 270°C and quenchc~! to room temperature. The hardness increased with increasing uranium addition because the beta phase becomes retained at room temperature. The ultimate yield strength of the as-cast 3% alloys was 55,000 psi and the 0.01% yield strength was 41,200 psi. The compressive strength was 185,000 psi for the 7% alloy that had been heat treated 2.5 hr at 270°C and oil quenched to room temperature. 4.4.2. Plutonium-iron Gardner [ 122] obtained some tensile data (table 22) on Pu-Fe alloys containing 7.0 and 8.7 a/o Fe. At room temperature these alloys are weaker than unalloyed plutonium (50,000-85,000 psi) containing no microcracks. Although the ductility of each alloy is very low and comparable to unalloyed plutonium,
S.H.Kittei et ai., Plutonium and plutonium alloys
401
Table 23 Room temperature microhardness values for plutonium-rich alloys, Alloying
Amount
element
(a/o)
ol-Pu o~-Pu ot.Pu AI AI AI AI A! Al Ai Ce Ce Ce Ce Ce
< 300 ppm '< 300 ppm < 300 ppm 0.5 1 2 4 6 8 12 1 2 4 8 12 18 20 7 10 0.5 I 2
Ce Ce
Fe Fe Ga Ga Ga Ga Ga Hf Hf Hf Ti Th Th Th U U
U Zn ~r, Zr Zr Zr Zt Zr
2
5 3 9 12 0.3 3 5 10 3 7
14 2 4 3 to 7 3 6 10 20
Description
Hardness (DPH)
As-cast Recrystailized Deformed ol+ 6 ~+ 6 8 8 6 ~ ~ + PuAla 0~+ 6 (homogenized) 5 (homogenized) 6 (homogenized) 6 (homogenized) 6 (homogenized) 6 (homogenized) ~ + Ce ,~+ Pu6Fe 0~+ Pu6Fe Or+ 6 (homogenized) 0~+ ~ (homogenized) 5 (homogenized) 0~4 6 (as-cast) s (homogenized) 0 0 + PuHfx ~+ PuHfx /~ Notgiven Not given Notgiven 0t+ l' (as-cast) or+ f (as-cast) r~+ ~-(as-cast) 6 (homogenized) 6 (homogenized) fl (quenched) f + 0 (homogenized) ~' ~ O (homogenized) f + 0 (homogenized) ~i
255 to 235 265 to 160 60 32 45 62 76 85 150 31 32 34 36 38 45 to 218 230 165 65 36 50 50 i00 to ~ 46 50 to 100 to 35 to 45 to 40 to 270 215 200 37 68 100 to i 17 157 170 60
it is considerably lower than unalloyed plutonium at elevated temperatures. The compression strength o f the 8.7 a/o alloy is 112,000 to 115,000 psi compared to 175,000 psi t0r unalloyed plutonium; the total deformation is ~,pproximately 7% at failure.
265 315
55
105 55 105 50 55 70
105
Ref.
[ 136] [ 136] [ 136] 1144] [ 144] [ 144] [ 144] [ 144] [ 144 ! [ ]22] [144] [ 144] [ 144] 1144] [ 144] [ t44] [ 122] [ 122] [68] [ 145] [ 145] [ 145] [57] [ 145 ] ] 122] [ 122] ]122] [ 122] [122] [ 122] . [122] [ 122] [ 122] [ 122] [ 21 ] [ 21 ] [ 149] [ 149] [ 149] {149] [ 149]
4.4.3. Plutonium-zirconium Taylor [ 149] determined the mechanical properties of Pu-Zr alloys between 1.0 and 10 a/o Zr. He found that the beta phase cannot be stabilized at room temperature but that it is metastable when the
S.H. gittel et al., Plutonium and plutonium alloys
402
Table 23 Room temperature microhardnessvalues for plutonium compounds [ 122]. Hardness (DPN) 25 g load
Compound
Hardness (DPN) 25 g load
Compound
Hardness (DPN) 25 g load
Compound
.'uAg3 PU3AI PuAI PuA[2 PuA!3 PuAI4 PuAs PuAu PuBet3 PuBi PuBi2 PuBi3
~ 180 "" 125 ~ 340 500 to 600 450 to 550 300 to 500 140 to 170 170 to 220 510 to 590 85 to 110 60 to 100 145 to 200 6? to 110 500 to 900 1000 to 1200 150 to 200 130 to 200 230 to 27~3 580 to 690 350 to 550 610 to 720 230 to 260 160 to 240 260 1431 530 to 630 636 [43l
Pu3Ge Pu2Ge3 Pu2Ge PuGe2 PuGe3 Pull2 PU31n Puln Pu2ln3 Puln3 PuMn2 PuN PuNi PuNi PUNiz ~,tNi2 PuNi3 PuNi3 PUNi4 PuNi4 PUNis PuNis I~'-.gli9 PuNi9
"" ~ ~ ~_ ~
PuO2 PuP ~ PUIgRu PuaRu PusRu3 PuRu PURu2 ~ PusSi3 Pu3Si2 ~ PuSi Pu3Sis PUSi2 PU2Th PuZn2 Pu2Zn9 PuZna PU2Zn17 PuCeCo ternary phases: Pha~ A-, (PuCe)-~Co3 Phase B-, (PUCe)-/Co3 Phase C-, (PuCe)sCo3
Pu3C2 PUC PuzC3 PU6Co Pu3Co Pu2Co PuCo2 PuCo3
PU2COl7 PUCu2 Pu6Fe PU6Fe PuFe2 PuFe2
Pu203 Pu~O-I
360 405 450 450 335 120 to 180 75 to 140 75 to 215 130 to 375 155 to 275 440 to 500 ~ 580 220 to 270 ~ 250 520 to 630 505 to 634 [46] 440 to 550 388 to 550 [46] 200 to 290 196 to 292 [46] 460 to 550 442 to 580 [46] 420 to 560 416 to 560 146] 200 tO 300 ~ 1020
2 to 7% alloys ale quenched from either the delta or epsilon phase regions. The hardness of the metastable beta is 100 to 105 DPH. The hardnesses of the Pu-Zr alloys continuously decrease from the unalloyed value of 265 DPH for the alpha phase to a minimum of 117 DPH for the zeta phase; they then continuously increase to 170 DPH a: 8.5 a/o Zr for the theta phase. The only tensile and compressive data.are for the Pu-2.4 a/o alloy. The ultimate tensile strength decreases essentially linearly from 50,000 psi at 30°C to 18,000 psi at 2O0°C, and ther, decreases to 7800 psi at 260°C. The yield streogth decreases from 28,000 psi at 30°C to 14,000 psi at 2000C and then to 7000 psi at 260°C. While the di~ctility is less than 1% below 230°C, it is 6.3 at 260°C. The ultimate compression strength decreases from 67,000 psi at 60°C to 29,000 psi at 220°C and the yield str*,ngth
500 to 850 240 140 to 190 180 to 220 230 to 330 170 to 250 390 350 to 480 660 600 to 1000 680 to 850 420 to 505 I70 to 230 370 to 420 340 to 460 320 to 480 280 to 400 180 to 200 175 to !95 230 to 260
decreases from 60,000 psi at 60°C to 27,000 psi at 220°C. Brittle shear-type failure occurs at all test temperatures. The ultimate compression strength decreases from 67,000 psi at 60°C to 29,000 psi at 220°C and the yield strength decreases from 60,000 psi to 27,000 psi at 220°C. 4.3.4. Hardness data Hardness is the most common mechanical property that has been measured for plutonium rich alloys and plutonium compounds. Representative values are given in tables 23 and 24 for many of the materials. The hardness values for the alloys generally depend upon heat treatment. 4.5. Dilute plutonium alloys Information on the mechanical properties of binary alloys consists primarily of hardnesses and
S.H.Kittel et al., Plutonium and pluton&m alloys
Table 25 Hardness data of binary alloys of plutonium. Composition (w/o)
/vlechanicaland thermal treatment
;lard- Ref. hess (DPH)
Al-l.7 Pu AI-5 Pu
Extruded at 400°C As-cast Annealed I hr at 585°C As-cast Extruded at 400°C Annealed 1 hr at 585°(" As-cast Annealed 1 hr at 585°C As-cast Extruded at 400°C Arc cast Arc cast Are cast Are cast Horn. 2 days at 1000°(7 Arc cast Arc cast Horn. 2 days at 1000°C Arc cast Horn. 2 days at 1000°C Arc cast Arc cast Are cast Are cast Rolled As-east Rolled Rolled Rolled Rolled Rolled Rolled Rolled Rolled
31 35 22 42 41 23 58 43 92 24 t06 184 223
Al-10 Pu AI-15 Pu AI-20 Pu Fe-I 1.7 Pu Fe-18.4 Pu Fe-25.7 Pu Fe-32.2 Pu Fe-38.9 Pu Fe-43.0 Pu Fe-51.7 Pu Th-lO Pu Th-20 Pu Th-30 Pu Th-40 Pu U-5 Pu U-I 0 Pu U-15 Pu U-Z0 Pu
Zr-12.1 Pu Zr-22.5 Pu Zt-39.6 Pu Zr-52.9 Pu Zr-63.6 Pu
222
286 318 293 423 365 105 130 148 133 261 205 300 400 300 207 209 139 108 97
156l [56] 1561 [56] [56l [561 [56] [56] [56] [56] [561 [561 [56] [56] [561 [56] [56] [56] [ 561 [561 ! 122] I 122] [ 122] [ 1221 [561 [ 151 ] [561 [561 [t 171 [56] [561 156] [561 [561
tensile properties. For the ternary alloys there are hardness values, tensile properties, some compression properties, and some creep data. 4.5.1. Binary alloys Hardness values (table 25) have been published for A1.Pu, Fe-Pu, Th-Pu, U-Pu, and Zr-Pu alloys. The hardness increases virtually linearly up to about 20 w]o Pu for extruded and annealed AI-Pu alloys [56]. Annealed AI-Pu alloys are much softer than cast alloys; more specifically, the hardness for an
403
as-cast 80A120Pu alloy is 92 DPH, whereas it is about 44 DPH after it is annealed 1 hr at 585°C 156]. Some tensile data are shown in table 26 for the Pu-AI alloys. The hardness of the Fe-base alloys rapidly increases with Pu content due to the greater amount of PuFe 2 in the a-Fe matrix (table 25). The hardness of the Th.Pu alloys increases only slightly as the Th content is increased. The hardness of the U-Pu alloys, however. increases from 261 DPH at 5% Pu to 300 at 10~ Pu, where the phase boundary between single phase t~-U and the two phase (a-U + ~') region exists. The hardnesses continue to increase as Pu is added; for example, it is 400 DPH for the U 15Pu alloy. The hardness, which is about 210 DPH, of ot-Zr is little influenced by Pu, but as tke Pu content increases ab6ve about 22 w/o Pu the amount of retained delta increases and eonsequentiy the hardness decreases; the hardness of 97 for the 63.6 w/o Pu (40 a/o Pu) alloy is due to a completely retained delta phase alloy. 4.5:2. Ternary alloys The mechanical properties have been somewhat determined for U-Pu-Fz, U-Pu-Mo, U-Pu-Ti, and U.Pu-Zr alloys. Some tensile properties are given in table 2~, hardnesses are tabulated in table 27, some compressive properties for U-Pu.Ti and U-I~j-Zr alloys are listed in table 28, and some creep characteristics for U.Pu-Ti and U-Pu-Zr alloys are givel, in table 29. Essentially no meclmnical properties data are available on U-Pu-Th alloys. 1"he room temperature hardness values [56] of arc-cast and roiled U-Pu-Mo alloys varied between 160 and 492 DPH depending upon the composition, but large discrepancies were also reporled for similarly treated material of the same composition; the discrepancies were attributed either to the rate of cooling from the rolling temperature or to contamination during rolling. Pool et al. [56] stated that in general, arc-east, hot-rolled, and 3'-quenched alloys show similar hardness values. However, there are exceptions, particularly in alloys that lie in either the 3% (soft) or the 3' fields [1221 ;these alloys are hardest when they are rolled or slowly cooled. The hardness of retained 3' varied between 264 and 399 DPH depending primarily on the molybdenum con, tent; alloys containing the most molybdenum were the hardest. Alloys containing retained 3' + free
S,H.Kittel et aL, Plutonium and plutonium alloys
404
Table 26 Temperature dependence of the tensile properties of alloys containing plutonium. Composition
(w/o)
Temperature (°C)
Ultimate tensile strength (kg/mm 2)
Yield strength 2% offset (kg/mm 2)
25 25 25 200 400 600 8O0 200 400 6OO 800 200 400 600 60O 80O 25 500 625 675 25 25 500 625 700 25 25 650 7oq 25 500 625 675 25 675 25 500 625 675 25 675 25 500 625 675 25 675 700 800
46.7 74.1 78"5 26 19 9 O.5 58 40 8 2 42 27 6 3 I 18.1 30.1 9.5 1.2 4.9 4.0 15.8 8.9 1.2 7.7 14.7 4.6 1.7 6.7 13.3 8.1 2.1 14.7 26.3 30.8 15,7 6.4 5.5
7.2 36.8 53.5
3.6 4.5 19.7 6.8 2.6 6.5 7.0 4.4 4.0
3.2
f
AI-1.7Pu* AI-10 Pu AI-20 Pu U-10Pu**
U-IO Pu-lO Fz
U-15 Pu-10 Fz
U-20-Pu-IO Fz U-I I.I Pu-6.3 Zrt
U-12.3 Pu-14.1 Zr U-16.6 Pu-6.3 Zr
U-18.5 Pu-14.1 Zr
U-15Pu-10 Zr
U-9.1 Ti U-I 1.4 Pu-3.4 Ti
U-17.1 Pu-3.4 Ti U-! 5 Pu-6.5 Ti
O-15 Pu-lO Ti
8.7 1.1
4.1 1.6
Modulus of elasticity_ (kg/mm 2 X 10 "-3)
17.4 6.8 3.0 1.4 10.2 10.6
2.1 1.7 13.0
4.1 1.6
7.2 1.7
11.6 5.8 5.2
17.3 4.3 2.1 6.5 4.3
11.4 2.1 1.7 12.5 6.6 1.6 3.3 25.5 3.0 17.9 7.2 3.6 2.4 2.1 14.7 1.8 1.6 1.4 7.9 3.0 0.8
Reduction of area (%)
Total elongation
77.8 81.7 82.4
37.5 27.4 11.7
(%)
< 1 < 1 > 5 > 10
< 1 < l >10 >2O
<
1
<
1
< I < 1 < 1 >10 < 1 < 1 >25 > 20
< 1 > 10 < 1 < 1 >10 >10 <
1
>10 < 1
< 1 >5 >10 < 1
< l < 1 >5 >5
< 1 > 1 >S >5
< <
< I < J > 10 >5 < J > 20 > 2O
>5
< >10 >I0
I I 3.5 2.0 1
405
S.H.Kittel et aL, Plutonium and plutonium alloys
Table 26 (cont.)
Composition (w/o)
U-22 Pu-I 1.8 Ti
Temperatute (°C)
Ultimate tensile strength (kg/mm2)
500 625 675
8.2 7.5 7.3
Yield strength 2% offset (i~g/mm2)
Modulus of Reduction elasticity of area (%) (kg/mm2 X 10-3 )
Total elongation (%)
* AI-Pu alloys extruded at 400°(2 [561. ** U-Pu-Fz alloys as-cast 11511. ÷ U-Pu-Ti and U-Pu-Zr alloys homogenized i week at 950°(2 and oil quenched [ 153].
molybdenum had hardnesses between 305 and 393 DPH. Alloys in the 3' field had hardness between 174 and 283 DPH; the higher hardnesses are due to greater plutonium content. The mechanical properties of U-Pu-Fz alloys have been determined by Kelman and Dunworth [57, 151] ; the composition of the fizzium was 2.80 w/o Zr, 2.75 w]o Mo, 2.95 2/o Ru, 0.50 w/o Rh, and 1.00 w/o Pd. Some of the ultimate strengths for the alloys homogenized I week at 850°C and oil quenched are shown in table 2.26. They report [57] that the quenched fizzlum alloys are stronger than uranium but that the alloys transformed to alpha are considerably weaker. Their hardness data [ 151 ], however, show that the alpha transformed metal is considerably hardel than the 3,-quenched alloys. The strength of these alloys depends on the proportion of t~, b, and 3, phases. The U-Pu-Fz alloys are brittle at room temperature with increased plutonium content causing greater brittleness. The total elongation of the U-Pu-Fz alloys is near 50% at 650°C but it is limited above 650°C by hotshortness. The U-Pu-Ti, U-Pu-Mo, and U-Pu-Zr alloys have a high ductility above 600°C without the hot shortness of the. U.Pu-Fz alloys. The alloys, however, have very little strength at these high temperatures. The strength decrease and the ductility increase are shown in tables 27-29. These alloys show somewhat more plasticity at lower temperatures when tested i~ compression than in tension. For example, the U-Pu-Ti alloys have appreciable compressive ductility at 600°C but they have no significant tensile ductility below 750°C. It has also been noted that the ratio of compressive to tensile strength varies from 3 : 1 to 1 : 1 depending on whether the
alloy is brittle or ductile in tension [ 57.153 }. Homogenization (table 28) decreased the compressive strengths of the U-Pu-Zr and U-Pu-Ti alloys.
5. Preparation and fabrication 5.1. Introduction
The fabrication of plutonium alloys involves many of the techniques and operations that are used in working the more common metals. However, all operations are directly affected by the extreme toxicity of plutonium in any form, by the tendency of the metal to oxidize rapidly at elevated temperatures c,r when finely divided, and by the obvious necessity of avoiding inadvertent criticality. The toxic properties of plutonium necessitate the use of devices and equipment that enable work to be done without any direct contact between plutnium and the operator. This requirement is ordinarily met by housing all machine tools, melting furnaces, etc., in gloveboxes tb.at provide physical barriers between personnel and plutonium. When plutonium oxidizes, it ordinarily forms powdery PuO 2 , which is highly mobile and constitutes the principal health hazard in most operations. It is therefore necessary to protect the metal against more than superficial oxidation not only tc maintain its metallurgical integrity but as a contribution to safe practice. Consequently, all operations at temperatures appreciably higher than ambient (or when finely.divided metal is involved) should be conducted in atmospheres substantially free from oxygen and moisture. The most effective means of achieving this end is through use of high
$.H'.Kittel et al., Plutonium and plutonium alloys
406
Table 27 Hardness data of U-Pu based ternary alloys. Composition (w/o) U-10
Pu-10
Fz
U-15 U-20
Pu-10 Pu-10
Fz Fz
U-123 Pu-6.6 Mo U-I 3.0 Pu-11.8 Mo U-21.6 Pu-5.2 Mo
U-22.8 Pu-9.1 Mo U-10.8 Pu-5.5 Mo U-23.5 U-5.2 U-15.S U-5.4 U-10.7 U-16.1 U-5.5 U-16.6 U-5.7 U-I 1.4 U-17.1 U-3.0 U-5.9 U-5.9 U-8.9 U-6.2 U-I 2.3 U-232 U-17.1 U-15 U-15
Pu-10.2 Mo Pu-2.1 Mo Pu-2.1 Mo Pu-4.3 Mo Pu-4.3 Mo Pu-4.3 Mo Pu-6.6 Mo Pu-6.6 Mo Pu-9.2 Mo Pu-9.2 Mo Pu-9.2 Mo Pu-! 1.8 Mo Pu-! 1.8 Mo Pu-I 1.8 Mo Pu-ll.8 Mo Pu-14.7 Mo Pu-14.7 Mo Pu-10.0 Nb Pu-3.4 Ti Pu-6.5 Ti Pu-10 Ti
U-22 U-20
Pu.l 1.8 Ti Pu-10 Ti
U-I 1.1 Pu-6.3 gr U-15 Pu-10 Zr
U-20
Pu-10
Zr
U..18.5 Pu-14.1 Zr
Mechanical and thermal treatment
Hardness (DPH)
Ref.
-rquenched o~-transformed or-transformed "f-quenched c~-transformed hQmogenized and forged homogenized and forged homogenized and rolled homogenized and forged homogenized and rolled a~ast homogenized and forged homogenized and rolled as-cast homogenized and rolled as-cast rolled rolled rolled rolled rolled rolled arc cast rolled rolled arc cast rolled rolled arc cast rolled rolled arc cast as-cast as-cast as-casl hom. 50hratS00°C,O.Q. hom. 5 hrat620°C~O.Q. horn. 2 h r a t 9G0°C,O.Q. as-cast hom. 50hrat500°C,O.Q. horn. 5 hr at 620°C, O.Q. horn. 2 hr at 900°(7, O.Q. as-cast as-cast horn. 50 hr at 500°C, O.Q. horn. 5 hr at 620°C, O.Q. horn. 2 hr at 900°C, O:Q. horn. 50 hr at 500°(?, O.Q. horn. 5 hr at 620°C, O.Q. horn. 2 hr at 900°C, O.Q. as-cast
255 433
[152] [ 151 l [151] [151l [ 151 ] [1221 [ 122] [122] [122] [ 122] [ 122] [122] [ 122] [122] [ 122] [ 122] [56] [56] [56] [56] [56] [56] [56] [56] [56] [56] [56] [56] [56] [56] [56] [56] [ 1221 [ 150] {1501 [117] 11171 [117] [ 150] [117] [ 117] [ 117 !
* Large diffczencc presumably due to variation in cooling rate.
215 430 258 318 365 236 273 278 324 410 283 290 320 492 413 160 252 351 266,400* 303 272,423* 259,308* 325 442 426 327 408 282 308 360 428 396 400 410 400 357 355 364 355 465 539 426 428 488 417 415 480 406
11501 [150] i 1171 | 117] [ 117] [ 1171 [ 1171 [ 1171 [ 150]
S.H.Kittel et al., Plutonium and plutonium alloys
407
Table 28 Temperature dependence of the ultimate compressive strength of U-Pu-Ti and U-Pu-Zr alloys [56 ]. Composition (w/o)
Heat treatment
Ultimate compressive strength ( k g / m m
2)
25°C
500°C
164 166 164 127 129
-
12
4.0
-
-
6.9
U-16.6 Pu-6.3Zr U-15 P u - 1 0 Z r
horn.* horn.** as-cast as-cast a~cast
'( 55 < 55 48
12 11 l 1
5.2 2.5 5.6
--
U-I 8.5 Pu- 14. l Zr
horn.
116
-
-
5.6
-
horn.** as-cast horn.* horn.* horn.* as-cast horn.* as-cast as-cast
145 150 96 96 !30 158 90 120 141
U.Pu.Zr alloys U-11.1 Pu-6.3 Zr U-12.3 Pu-14.1 Zr
IU.Pu-Ti alloys I3-91. Ti U-I 1.1 Pu-3.4Ti O-17.1 Pu-3.4Ti U-15 Pu-6.5 Ti U-15 Pu-10 Ti U-22.1 Pu-11.8 Ti
i 15 95 -
625°(?
80 65 -
37
27 45 40 55
13 12 20 30
675°(?
65 50 6.3 3.8
6.3 9.0 10 20
750°C
4.2
35 30 -
4.2 7 10
* I week at 950°(=,oil quenched. ** 1 week at 1050°C, oil quenched. vacuums; but gases such as helium and argon are commonly used as protective atmospheres in those cases to which high-vacuum techniques do not apply. A third means of achieving protection against oxidation during fabrication is canning or cladding, which can be used in special instances.
5.2. Unalloyed plutonium 5.2.1. Melting and casting The melting and casting of unaUoyed plutonium presents few difficulties. The low melting point of plutonium (640°C) permits considerable latitude in the choice of melting equipment and techniques; the only restrictions are those imposed by the necessities of providing a nonreactive environment for plutonium and nonplutonium environment for operating personnel. The furnaces most commonly used for melting unalloyed plutonium are of either the wirewound resistor type or the inductive type. Arc furnaces can be used when it is desired to avoid contact with crucible materials at elevated temperatures. The induction furnace is the faster and more versatile, but it is less easily controlled.
The fluidity of molten plutonium metal is high but its affinity for oxygen causes formation of a tough oxide film even in relatively good vacuums (about 10-5 mm mercury). The mechanical strength of the oxide film can cause conditions which superficially resemble those resulting from a viscous melt, e.g., temperatures necessary to obtain satisfactory pouring may be several hundred centigrade degrees above the melting point. However, once the oxide film has been ruptured, molten plutonium will flow readily. Unalloyed plutonium has the general characteristics of a very castable metal. The low melting point, high fluidity, high density, and small volume change on freezing are all favorable characteristics for casting. But the differences in densities of the various solid phases cause volume changes that make pLoduction of intricate castings impracticable. Simple =,,!id shapes such as cylinders or spheres, in which there is no restraint of shrinkage, present very few casting problems provided dimensional tolerances are generous. Unrelieved restraint will invariably result in fracture, but molds that can be dismantled at temperatures sufficiently high to permit the beta-to-
408
$.H.Kittel et al., Plutonium and plutonium alloys
Table 29 Time (in minutes) to attain 2% creep strain in U-Pu-Ti and U-Pu-Zr alloys [56]. Alloy composition (w/o)
$lsess (k~mm 2)
U-11.1 Pu-6.3 Zr
0.5 1.0
U-16.6 Pu-6.3 Zr
650°C
-
-
-
15
-
-
-
5
---
-
2.0
-
-
0.5
-
1.0
-
4.0
U-18.5 Pu-14.1 Zr
625°(2
4.0
2.0
U-15 Pu-lO Zr
600°C
-
1.0 2.{3 4.0
-
0.5
100,000
0.5
0.5 1.0 2.0 4.0 0.5 2.0 4.0
. .
-
-
10
-
-
l
-
-
-
5,000 80 1 -
-
-
.
400 20
1.0
--
1
-
.
. 20,000 350 5
.
.
.
alpha transformation (and preferably also the gammato.beta transformation) to proceed without restraint can be devised. An interrupted cooling cycle, which permits isothermal transformation to the gamma pbase by holding for several hours at about 275°C, has been found useful in minimizing differential stressing and consequent warping. However, the difficulties and expense involved usually suggest that mechanical fabrication is preferred for producing complex shapes. Gardner and Mann [154] have determined that geometrically simple cast shapes o f plutonium have microcracking to varied degrees. The plutonium purity was generally 99.9+ percent with respect to metallic contaminants and less than 200 ppm total oxygen, hydrogen, and nitrogen. Iron in the plutonium in amounts greater than about 500 ppm was found to inhibit mierocracking, presumably due to the presence o f the Pu-Pu6Fe eutectic. The
.
11P 5
. .
2,000 60 1
-
-
45
-
. .
55 10 3
.
.
.
60 10 2
-
-
.
.
5,000 80 2 .
-
.
3
10
-
. -
-
-
.
5,000 210 !0
800 70
7000C
210 -
10,000
2.0 4.0
U-t5 Pu-10 Ti
5,000
1.0
U-I 1.4 Pu-3.4 Ti
5
675°C
5
. .
mechanism by which microcracking o f plutonium castings is inhibited is dependent " n the ductility of the eutectic [53]. Ostensibly the strain accompanying the phase transformations during cooling are relieved h y deformation o f the Pu-Pu 6 Fe phase rather than the p~utonium matrix. Since microcracks in a billet carry tluough to the detriment of mechanically worked products, introduction o f iron to achieve sound cast b~llets can be a distinct benefit. At this point one must recognize that 1,000 ppm o f iron in plutonium represents nearly 0.5 w/o, and the use o f "unalloyed" as a descriptive term becomes questionable. A wide variety o f refractory materials is suitable for use as crucibles and molds for unalloyed plutonium, although the, strong affinity o f plutonium for oxygen, carbon, :nitrogen, etc., restricts use to the more stable compounds of the oxide, carbide, nitride, boride, and sfliei,rle types. Bare graphite can be used for crucibles and molds if the times o f contact with
S.H.Kittel etal., Plutonium and plutonh~m allo),.~
molten plutonium do not exceed a few minutes and if some ca, ben pickup can be tolerated. Otherwise graphite crucibles should be coated with a less reactive ~uaterial. (MgO and A120 3 have been used as wash materials.) High-fired, high.purlty magnesia has come to be the almost universal refractory material for ordinary use. At temperatures above 1400°C some magnesium metal is introduced into the melt by reduction, but because of its high vapor pressure the amount retained is extremely small. High-purity calcium oxide is perhaps the best refractory known for the melting of unalloyed plutonium but it is not extensively used because it is more costly and more difficult to store than magnesium oxide. Of the refractory metals, tungsten is probably the least reactive with respect to plutonium. However, it is difficult to fabricate and to secure free from porosity; therefore, tantalum has been used much more extensively as a crucible material. Miley and Anderson [ i 55 ] report success in the use of tantalum and calcium fluoride-coated steel crucibles for melting plutonium and plutonium-rich alloys.
20[-
409
I, Calculated from Pearson and Parkins. The Fxtrusior, Of Metals, 2 nd ed, pp 194.
.
Wiley. New York 1960
Pu
® HW- 65019
o. 15,
--36
"~o
0
x
-
_~
IZ).
~lo
,
28 = I g
-
Z
¢.gl
.
~,
5
z
le -
\ o
J00
20o
\ 300
400
,~
8 50o
s00
"too
rEMPERATUr'E C
5.2•2. Mechanical fabrication Although mechanical fabrication of unalloyed plutonium holds little interest in power reactor concepts, some rather unique requirements derive from reactor physics and engineering studies. In the main such work requires foils, plates, or complex shapes that are not easily obtained by casting. Consequently, studies of the mechanical properties as related to fabricability have practical importance. At temperatures above 300°C, the yield strength of plutonium in tension is very low (less than 2,000 psi) and the compressive yield strength is only slightly influenced by testing speed. For these reasons, deformation processes usually employ compression loading. Thus extrusion, hot-pressing, or rolling are useful methods for fabrication of thin or elongated shapes of either simple or complex secti,)n. Los Alamos Scientific Laboratory has had considerable experience in the extrusion of unalloyed plutonium and has used the process in a rather unique manner to generate 0.005 to 0.055 in. thick sheet of area up to 24 in. square from plutonium or plutonium-I w/o gallium [ 156]. Satisfactory products are produced by direct extrusion past
Fig. 27. Extrusion constant and ultimate tensile strength of Sn, C(!. Pu, and AI vs. temperature. (Submitted by Argonne National Laboratory, November 1967•
streamline dies or shear dies with sharp edges. Undercutting of dies is necessary to provide clearance for the formed section. Working ternperatures between 300 and 400°C are coinmt~n for plutonium, although wire of 0.187 and 0.040 in. diameter has been extruded at temperature :,s high as 450°C [157]. A tendency toward galling is overctm~t" by die design and lubrication of die surfaces that contact plutonium with solid lubricants such as Aquadag or Molykote. A comparison between the extrt, sion constants fol plutoniu,n, tin, cadmium, and alt, mint, m is shown in fig.. 27. Although comparison of constants derived from different experiments is risky due to the wlrymg effects of die design, friction factors, and extrusion speeds, one may find some confidence in comparison if the extrusion constants are similar at temperatures where ultimate yield strengths are similar. Such is the case sl,~own in fig. 27, where the tensile strength of tin, plutonium, and ahtminum at several temperatures
410
~i tt K~ett't e~ af Ph~toni~tm and ph~tonfi~m alloys
is indicated by c~)sses ( ~ t 1 ~ ' ~.he ~tlength of the several elemen~ ~equ~,e~ e~i~l~ properties becau~ of tile dearth ~ ,:~n~pressive strength at the vari('~!~ t e m ~ , ~ Ih~wevet. m Ihe range of trdere~t~ the v~htes ~d ~ . . ~i.v:~ yield and ultim~,~~tensile ~trer~gth ~ exp,, ~ed to be about the same One ¢~nchld¢~ fro|l| thi~ fi~|l'e that the forces required for lhe ext[||$lO|l ~i |r~utt~niulll are significantly smaller th:m those neces~ry fin alu1111flLlrll eXtrllSlOn at ct)|vvparable ~emperature The rolling ot unalloyed plulonmun htls been reported by tiovton and Ward I 1581 Sheel lrom 0.048 to 0.01(~ m. thick v~,asformed at reductions of "~
e'¢
I 0 to .,3 ~, at 175°C. Since the room lerllperature
(monoclinic ~) phase is brittle, the rolling schedules were carried out in the ductile ~3phase. Roll surfaces and ingots were maintained at 175°C, and reduced from 0.225 In 0.048 in. in 15 phases. A specimen flom the above sheet was reheated to 175°C and r(~lled to 0.016 in. thickness in 5 passes with only slight edge cracking. Distortion during the phase changes was significantly reduced by clamping the sheet between warm steel plates. Alpha plutonium has excellent machining characteristics that resemble those of gray cast iron. However, the combination of high coefficient of expansion, low thermal conductivity, and low transformation temperature { 123°C) makes necessary a high degree of care if precision is desired. Plutonium is machined with standard metal working tools. Tools of high-speed steel can be used to machine unalloyed plutonium, but carbide-tipped tools are preferable because of their superior resistance to abrasion. 5.2.3. Heat treatment Because of its complex solid-state transformations, the benefits to be derived from the heat treatment of unalloyed plutonium are quite limited. Partial relief of stresses generated by the beta-to-alpha transformation can be accomplished through holding in the high-alpha range {1 I0 to 115°C) for extended periods of time (of the order of thousands of hours). Dimensional stability can be increased by subzero treatment, and controlled cooling of castings can significantly reduce stress levels. However, most of the considerations that lead to heat-treating programs • for pure metals are absent in the case of plutonium. Since there is no known practicable method for
cold working plutonium, there is no need for ordinary stress-relieving or recrystallization heat treatments. Becau~ of the low temperature phase transformations, ureatments for control of grain size are of little con~quence, although some degree of influence can be exercised through variations of beta-grain sizes and transformation conditions.
5.3. Plutonium alloys for power reactor use Plutonium alloy fabrication development for power reactors has been almost entirely associated with alloys for fast breeder reactors. This application requires a plutonium content on the order of 15 w/o. As much 238U must be in the alloy as possible in order to enhance internal breeding ratios. The remaining alloying elements in the alloy are normally those that improve the properties of the alloy. For example, zirconium is added to uranium-plutonium atloys to increase their melting points and to improv(! their compatibility with austenitic stainless steel, in another class of alloys, ~he uranium-plutoni,amfissium alloys, several fission product eleme~ts are left in the alloy as a result of the type of reprocessing cycle. 5.3. I. U-Pu-Fs alloys The initial fuel loading for EBR-Ii was U-5 w/o Fs [ 159]. Development of U-Pu-Fs alloys for EBR41 was also considered attractive [ 1601. Although processes to yield a wrought product were considered, injection casting [ 161] was finally selected ~s the fabrication procedure that satisfied fuel requirements on a economical basis [I 62]. As a result, nearly all experience in fabrication of U-Pu-Fs alloy fuels has been based upon injection casting. (a) Alloying. The preparation of alloy fi.;r injection casting is a relatively simple procedure. Predetermined weights of each of the alloying elements are charged to a weighed bottom.pour crucible with a stopper rod closure. The crucibles used at ANL are yttriacoated graphite. Although such materials as magnesia, calcium oxide, and zirconia are acceptable, good fits between stopper rod and crucible bottom are more difficult to achieve with such materials than with graphite. The yttria coating is applied to limit carbon contamination of the melt, The charged crucible is heated in an induction furnace to 1350 to 1400°C and maintained for
S.H.Kittel et al., Plutonium and plutonium alloys
periods up to one hour at a pressure of about 50 microns of mercury. Holding times of this order have been found necessary to out-gas the metal and to permit dross to come to the surface. After melting and holding, the stopper rod is withdrawn from its seat in the crucible bottom and the metal drains into an yttria-coated graphite mold of cylindrical shape. The dross formed during melting clings to the crucible side and is thereby separated from the ingot. The ingot resulting from the described procedure is weighed, sampled for analysis, and charged upside down to a crucible preparatory to injection casting. Losses on oxidation result in a slight increase of fissium content [163] but do not significantly affect ithe relative proportions of the fissium elements with the exception of zirconium, which is lost disproportionately to the dross. In the case of fissium alloys, analysis agrees with charge calculations within the limits of the analytical method, and no problems arise from inhomogeneity. (b) Injection casting. Injection casting has as a basis the elementary physical concept of support of a liquid column by the impression of a differential pressure across a liquid interface within and without a tube [164]. This phenomenon is characteristic of a closed tube manometer. One may readily calculate the height of an alloy column that can be supported by a pressure of one atmosphere in a previously evacuated tube; for an alloy of density 18.2 g/cm 3 this height is about 22 in. The above calculation assumes a static condition that cannot reflect the influence of hydraulic effects, casting cooling rate, mold filling rate, and the changing density of the casting during cooling. The importance of these effects is minimized by control of the casting parameters. Casting temperatures exceed the liquidus temperature by about 300°C and molds are heated before casting to insure against solidification during the injection of metal. In order to negate the effects of cooling during casting, pressurizing times are low - about 1 to 3 see - and the furnace pressure after casting is about one atmosphere. Adequate control of these variables results in successful casting of right circular cylinders of length to diameter ratios greater than 100 to 1. Fig. 28 is a plot of the influence of some casting parameters upon fuel pin length limited by 17 in. long molds. This process is particularly sensitive to changes in
Moll' No.
411
Mill
3CI 302 303 4D2
Tamp C
Costing Pressure psi
Initial
Prall~l~r,zmgTfa~ see
1320
53
3
1320 1325 1325
42 45 45
2 2 2
!
~s Denote Ave Ltngth ~B
E
!4D2
14
IS CASTING L[NGTH IN INCHES
16
1
I?
Fig. 28. Distribution versus casting length for conditions noted. (Submitted by Argonne National Laboratory, November 1967). casting parameters. Low melt or mold temperatures and long pressurizing times yield short pins. High melt temperatures and failure to maintain the melt in contact with the open ends of the molds for a sufficiently long peried promotes dripping of metal from the molds or hot shortness. The hot short condition is aggravated by the temperature difference between liquidus and solidus that is characteristic of U-Pu-Fs alloys (about 170°C for U-20 w/o Pu-10
w/o Fs). A typical injection casting furnace of the type used in the Plutonium Fabrication Facility at ANL is shown hi fig. 29. The furnace is housed in a glovebox that contains a helium atmosphere. The furnac proper consists of a covered induction heater assembly surrounded by radiation shields, a movable platform that holds the crucible, a mold suppert stand and the furnace envelope. Injection casting is accomplished by evacuating the fi~rnace; heating the metal charge, which is held in an yttria-coated graphite crucible, to casting temperatures; opening the heater cover; raising the crucible to submerge tl~e open end of yttria.coated Vycor molds; and pressurizing the furnace with helium. After an appropriate time the crucible is lowered and the furnace is cooled preparatory to removal of gravid molds. By this method uranium.plutonium-fissium/fizzium pins of diameters from 0.130 to 0.160 in. are made to lengths up to 18 in. Mold replication is very precise
412
S.tt.Kittel et al.. Phttonium and plutonium alloys
Iig. 29. Injection ca~ting furnace i~ glovebox.
S.lt.Kittel et al., Ph~tonium and phaonhon allto's
and diameter variation less than + 0.001 in. is a con> mon occurrence. During the casting of about 400 pins of U-lO w/o Pu-I 0 w/o Fz, U.I 5 w/o Pu-lO w/o Fz, and U-20 w/o Pu-lO w/o Fz diametral shrinkage of the castings was found to be about 1.5%. Gamma radiography showed internal shrinkage, similar to that occurring in U.Fs alloys, ,m doubt due to the inability to feed the mold cavity during solidification. Although plutonium-bearing fizzium alloys are more brittle than the uranium-fissium counterpart, they are not too fragile for routine handling. The fabrication of injection cast fuel into acceptable sodium-bonded fuel elements has been described in detail [ 165-167] and will not be repeated here. The bonding step, however, deserves special mention. In this process, as presently conceived, a continuous liquid metal annulus between fuel and jacket is achieved by heating the jacket, fuel, and liquid-metal (usually sodium) to about 500°C while the assembly is under vibration, in the case of U-5 w/o Fs alloy, specimens quenched from above the gamma eutectoidal temperature retain the lower density gamma phase in a metastable condition. Upon soaking at 500°C, a 3, -+ o~transformation occurs resulting in an increase in density of about 1%. Injection cast U-Pu-Fs alloys, upon heat treatment achieved by sodium-bonding, show ,,similar dilatometric effects [168]. The change in density manifests itself in a smaller diameter fuel pin than is found in the as-cast measurement. Where precise liquid-metal cover over a fuel pin is desired, one must adjust the sodium charge to compensate for the change in fuel pin dimension occasioned by the metallurgical transformations accompanying bonding. 5.3.2. U-Pu-Zr and U-Pu-Ti alloys The fabrication experience with l_l.Pu-Zr and U-Pu-Ti alloys at ANL has been contined to injection casting as described in the preceding section. The zirconium and titanium ternaries ale discussed under a common heading because of similar behavior during fabrication by injection casting. The following discussion, although restricted to U-Pu-Zr alloys, is also typical of U-Pu-Ti systems. (a) Alloying. During 1965 about 100 fuel pins of U-Pu-Ti and U-Pu-Zr alloys were fa0ricated [169]. The higher melting point of zirconium (1852°C) and titanium (1675°C) impresses extreme conditions on
413
alloying over fllose required to make fissmm alloys. The low density of zirconium and titanium ((,.5 and 4.5 g/cm 3 , respec,ively, at room lemperaturel retali~e to that of uranium or plutonium is cause for additional problems oll alloying lhat result in il:htmlogeneity. Alloying at temperatures below the melting point of either zirconimn or lit:lnilllll requires holding times sufficient to promote dissolu. tion followed by liquid-liqmd diffusion of the zirconium or titaniunl into the ur:mium o r plulonit|lll. Long holding time at temperature compromises allox quality by the tendency of zirconium to oxidize or carburize at the expense of c,ucible or ~ash materials. Alloying to achieve the COlnposition U-I 5 ~v/o Pu-10 w/o Zr has been accomplished wi~ll a measure of success by maki1~.g separate uranium-10 w/~ zirconium and plutonium-12 w/o zirconium melts. Melting is carried out under eacuum in yttriastabilized zirconia crucibles at 1450°C for holding times of one hour. Bottom-pouring of the meh into a mold is employed to separate the metal from lhe dross. The alloys are analvzed and later charged to an injection casting crucible in a 5 : 1 ratio ~1 U-Zr to Pu-Zr with sufficient zirconium to make up drossing losses that resulted during alloying. The liquidus temperature of Pu-] 2 w/o Zr is about 1000°C and that of U-lO w/o is about 1200°C. ('~lllbin:.tlioll tq" these alloys permits melting and dissolution al temperatures below those required for rejection casting, thereby, the final step of alloying is carried out during the melting operation incidental Io injection casting. Erosion of yttria-coated graphite and vttriastabilized zirconia crucibles is a characteristic of alloying by the technique described above and oxygen coPlanlinalion to the extent of I000 to 2000 pptn is common in the resulting alloy. An alternate method of alloying is to process a tnaqer alloy of Pu-40 w/o Zr by arc-nlelting. By this method smaller quantities of binary alloy are required to make a U-15 w/o Pu-10 w/o Zr ternary and at) crucible is necessary. The ternary alloy is made by charging master alloy and uranimn in the ratio 1 : 3 to an ytlria-stabilized zirconia crucible and induclion melting. Since the liquidtts temperature of Pu-40 w/o Zr is about !400°C and that of tl-I 5 w/o Pu-lt) w/o Zr is about 1250°C. homogeneity may be attained
414
S.H.Kittel et al., Plutonium and plutonium alloys
and crucible erosion limited by first meltingat about 1400°C and then holding at about 1300°C for times up to one hour. (b) Injection casting. The injection casting process is unaffected in principle by the alloys cast. However, the liquidus temperature o f the alloy to be processed does alter the values of controlling parameters. Since "~he liquidus for U-15 w/o Pu.lO w/o Zr is about 1250°C the rates of heat loss from castings is greater and casting temperatures are higher thanfor U-15 w/o Pu-lO w/o Fz whose liquidus occurs at about 1000°C. Since injection casting of U-15 w/o Pu-10 w/o Zr requires a melt temperature near the softening point of Vycor, the duration of immersion of molds is maintained at a minimum. The effect of this requirement is off-set somewhat by the high rate of heat loss after casting. Castings made in Vycor by this method are slightly larger at the open end of the mold due to slower cooling and improved feeding, softening of the Vycor and distortion due to pressure effects. Cropping of the ends of the castings, which is normally necessary to meet fuel pin length requirements, remedies this condition, Acceptable fuel pins of 0.144 in. diameter by 14 in;long are made by the injection casting process. Problems related to the softening point of Vycor, which occurs at about 1500°C, have been solved by the use of quartz molds, which melt above 1700°C, but are much more expensive. The injection casting of alloys containing larger quantities of zirconium th~n 15 w/o will, no doubt, dictate the need for mold materials other than Vycor due to the elevation in melting and casting temperatures. 5.3.3. AI-Pu alloys Research and development in the United States on AI-Pu alloys related to application as a power reactor fuel has been carried on largely at the Pacific Northwest Laboratory. This work was initiated in mid1956 with authorization of the plutonium recycle program. Fabrication has included loadings for the Materials Testing Reactor (MTR), Plutonium Recycle Critical Facility (PRCF), and Plutonium Recycle Test Reactor (PRTR) [ i 70]. Extensive fabrication experience with Pu-AI alloys also exists as a result of work done in Canada [171 ]. The techniques employed for fabrication of AI-Pu fuels has included
roll cladding with aluminum, coextrusion with alu: minum, injection casting, and encapsulation of unbonded AI-Pu bondies. • (a) Alloying. Aluminum-plutonium alloys con. taining up to 20 w/o plutonium are not subject to serious oxidation and the melting and casting operationsmay be carried out in air. At PNWL alloying is accomplished bycharging metallic plutonium and other desirable elements, such as nickel and silicon, directly into molten aluminum that is contained in graphite or clay-graphite crucibles [172,173]. An open tilt-pour furnace that is heated by induction is used in the melting operation. Alloying temperature about 950°C is normal and sufficient stirring results from induction heating that homogeneity is attained within ten minutes at temperature. When resistance heated furnaces are used manual stirring is required to achieve melt homogeneity. By such methods 25 It) charges of alloy containing 1.8 w/o Pu were prepared for the spike fuel elements for PRTR. Because AI-Pu alloys have-poor corrosion resistance in high temperature water, similar alloying procedures with equally good results were conducted on AI-1.8 w/o Pu.1.3 w/o Ni.1.1 w/o Si alloy, which exhibits improved corrosion qualities. Sampling of alloy melts is normally performed by ladling directly from the melt or using a small protmsion that is cast into a rod c r billet. The alloying procedure described above yields excellent agreement between analyses taken on samples by either method and analyses from fabricated elements. (b) Casting. Aluminum-plutonium alloys have been injection cast [ 174], cast by top-pouring [172] and vacuum cast [ 175]. The alloys, generally, are cast from the crucible used during alloying employing techniques described above. In the case of casting small cylinders for fuel elements and extrusion billets, melt temperatures 30 to 75°C above the liquidus are normal. Alloys containing up to 20 w/o Pu have been cast within ± 5% of nominal composition and three mil diametral tolerance by this technique. Injection casting has been proven feasible [ ! 74] through the casting of 90.in. long AI-2 w/o Pu.2 w/o Ni alloy into 0.035 in. thick zircaloy cladding. Cored billets of alloy were charged to a clay-gr~uhite crucible in an injection casting furnace, the furnace closed, and a shroud tube assembly containing the zircaloy molds was attached to the furnace top.
S.H.Kittel et aL, Plutonium and plutonium alloys
Soaking for 15 to 30 min at 900 to 950°C was required to limit plutonium segregation to 2.5 + 0.1 w/o Pu. Although feasibility was demonstrated by the method described, the control of casting defects such as porosity and hot tearing remains to be treated. (c) Mechanical fabrication. Aluminum-plutonium alloys have been fabricated into prototypic fuel elements and monitoring foils by rolling, extrusion, and coextrusion. Over 200 fuel rods were fabricated by extrusion at PNWL [ 175 ]. Extrusion was petformed on billets of Al-1.8 w/o Pu prepared by the alloying and casting techniques discussed above. Bare cylindrical billets approximately 2½ in. in diameter and 10 in. long were extruded through nonlubricated flat face shear dies. At die and billet temperatures of 500°C, 80,000 psi was required to achieve an extrusion ratio of 25 to 1 at a ram speed of 20 in./min. In this manner, rods about 9 ft long and 0.500 + 0.001 in. in diameter were made. Coextrusion of aluminum-plutonium cores with aluminum cladding is exemplified in the fabrication of 144 fuel elements for the Transplutonium Program of the Savannah River Laboratory [ 176]. This work consisted of fabrication of A1-7.35 w/o Pu into fuel rods 0.94 in. in diameter by 5 ft long with cladding thickness from 0.040 to 0.120 in. The coextrusion billet was macle up of a 0.350 in. thick X-8001 aluminum alloy shell containing an aluminum7.35 w/o plutoqium core that was 1.80 in. in diameter. The ektsusion program consisted of an average extrusion pressure of 64,200 psi and extrusion die temperature of 100°C. Since the core was harder than the cladding, the extrusion program resulted in reduction ratios of 5.9 : 1 for the core and 11 : 1 for the clad at a ram speed of 20 in./min using lubricated streamline dies with a 90 ° entrance
angle. 5.4. Zero power reactor fuel alloys The demands of reactor physicists for fabricated configurations containing plutonium alloys to be used in zero power reactors are limited only by the experimentafist's imagination. The alloys and shapes made for this purpose are indeed myriad. As a result this section will be confined to alloys made in large quantity or to the response of an alloy to a particular fabrication process. Zero power reactor fuels are used for a number of
415
purposes from complete matrices for large scale mock-up critical experiments to single elements for reactivity worth determinations of various kinds. In general, plutonium-alloy zero power reactor fuels are made in the form of jacketed right circular cylinders or thin flat plates. To meet safety requirements at the critical facilities, the compositions are chosen such that the pyrophoric properties of plutonium and uranium-plutonium alloys are minimized by alloying with elements of low neutron capture cross-section. The elements should withstand the rigors of repeated handling without effect to the core or distortion of the jacket. The requirement that pyrophoricity be limited stems from the obvious consequences of an element that develops a breach in its jacket during its lifetime. Alloying constituents of low neutron capture cross-section are desirable to permit criticality for a particular geometry to be reached with a minimum number of elements. 5.4.1. U-Pu-Fe alloys Early in 1964 experiments were performed at ANL to establish the feasibility of manufacturing Masurca elements by centrifugal casting [177]. The Masurca element is a right circular cylinder ~ in. diameter by 4 in. long containing a fuel section of U-25 w/o Pu-1.5 w/o Fe alloy. The fuel core is surrounded by a close-fitting Type 304 stainless steel jacket of 10 rail wall thickness. The technique employed is properly called centrifuged casting. In this method of centrifugal casting, molds are spaced with their axis along the radii of a rotor at the center of which is a distributor that acts as a downgate. Centrifugal force is applied, through the spinning rotor, to the metal as it is cast onto the distributor. This method of casting was used because maximum metal density was desired in the Masurca element. Maximum metal density can be achieved by centrifugal casting because the molten metal is quickly forced into the molds thus preventing premature freezing and consequent laps, surface irregularities, and if done under vacuum, voids formed by entrapped gases. The centrifuged casting furnace esed for the manufacture of the prototype Masurca fuel rods was an induction-heated vacuum furnace equipped for bottom-pour casting by the use of crucible with a removable stopper rod. The crucible stool was cored to permit the falling metal to impinge directly upon a
S.H, Kittel et al., Plutonium and phttonium atlovs
spinning distributor and be conducted by centrifugal force into the molds. The distributor was equipped with heaters to permit close control of the temperature of casting metal. The core alloy was cast directly into the stainless steel jacket. To prevent bonding of the core to the jacket, the jackets, which served as mold liners, were clamped between close-fitting split copper molds. During casting the molds act as heat sinks that conducted heat away from the thin steel jacket fast enough to prevent reaction of the plutonium alloy with the steel. The solidus-liquidus range for the Masurca alloy composition is from 665 to 825°C. Alloying was accomplished by holding the alloying constituents for one hour at a temperature about 400°C above the liquidus and a pressure of 1 X 10 - 3 tort. Holding at temperature and reduced pressure dcgassed the metal and insured against undesirable poro~i,y in the castings. Casting conditions for crucible charges of about one kilogram of met,~l were: 1340 g Charge weight 1230°C Temperature of metal cast I X 10 -3 torr Vacuum Temperature of distributor 450-500°C Rotor speed 350 rpm. A rotor speed of 350 rpm applies a force of about ten pounds at the center of a Masurca element w h i c h results in a pressure of about 50 psi at that point. The castings resulting from the application of this technique showed no evidence of reaction between the jacket and core. A radial shrinkage gap of about 0.001 in. between the jacket and core at room temperature made it possible to "demold" the casting by simply pushing the cast slug out of the jacket. The establishment of feasibility of manufacture by centrifuged casting was followed by implementation of the process. In the period 1965 to 1967 this process was used to fabricate over 700 kg of depleted U-25 w[o Pu-1 w[o Fe alloy into Masurca fuel elements [178]. Fig. 30 is a photograph of the internal components of the centrifugal casting furnace used at the European Institute for Transuranium Elements, Karlsruhe, Germany, to cast the Masurca fuel alloy. !
417
5.4.2. U-Pu-Mo alloys Zero power reactor requirements involving large quantities of plutonium are characterized by Ihe Zero Power Plutonium Reactor (ZPPR) experiments. The reference design for the fuel body was established as a plate 0.200 in. thick, 1.930 in. wide, of several lengths from 0.940 to 8.940 in. in one-inch increments. The fuel composition was chosen on the basis of acceptable behavior in a neutron environment, physical properties, oxidation rate. ~md fabricability. The alloy selected was U-28 w/o Pu-25 w/o Me. U-Pu-Mo alloys have a coefficient of expansion greater than 20 × I0- 6/°C at 600°C which is sufficiently high to insure contact of the fuel with a closefitting Type 304 slainless steel jacket upon healing [179]. This requirement was necessary to assure prompt expansion of the jacketed fuel element in response to external as well as internal (nuclear) heating and consequent prompt reactivity change. Ignition tests by Fischer and Schnizlein [ 1801 and oxidation rate determinations by Kelman et al. [ 179] indicated that the reference a!loy oxidized slowly, 0.3% weight gain after 120 days in zn air atmosphere at room temperature, and sustained ignition in air takes place above 600°C. (a) Alloying and casting. Alloying of U-Pu-Mo may be accomplished by first producing a binary of U.Mo. Since molybdenum has a density of 10.2 g/cm 3 , compared with l 8.7 ~ c m 3 for uranium. inhomogeneity due to partition of molybdenum can be a problem. The melting point of molybdenum is 2625°C and that of uranium is 1133°C. The difference in melting po~,nt means that, at temperatures between the melting points of molybdenum and uranium, the molybdenum must be dissolved fron~ the solid state by the uranium and time at alloying temperature must be sufficient to affect the dissolution. The binary alloy of uranium and molybdenum has been produced by charging pelleted molybdenum powder and chunks of uranium to an yttria.coaled graphite crucible of the stopper-rod variety [ ! 811. It has been found that pelleted molybdenum powders show taster dissolution rates than either powders or solid forms. Powder~ have a tendency to separate by flotation and solid chunks dissolve much more slowly than porous pellets due to the decreased surface area.
418
S.ILKittel et al,, Plutonium andplutonium alloys
The crucible is heated by induction under a pressure of 10-~2 rtO lO~ 5 torr to 1450 to 1475°C in about one hour and held at temperature for about 40 min. Molybdenum is lost during the binary alloying process to the extent that a final alloy composition containing 3.54 w/o Mo results from 3,85 w/o Mo charge. The melting point o f the resulting binary alloy is about 1200°C. The binary alloy is cast into yttria. coated graphite molds to form cylinders that are broken into pieces as charging stock for the ternary alloying process. The ternary U-28 w/o Pu-2.5 w/o Ivloalloy is produced from the binary alloy by charging several large pieces of U.3.5 w/o Mo to a yttria coated graphite bottom-pour crucible. Plutoniura is placed on top of the binary alloy along with sufficient uranium to adjust for excess molybdenum occurring in the binary alloy. Ternary alloying and casting are accomplished simultaneously. The alloying constituents are brought to 1380°C by induction heating under a 10 - 2 to 10-5 tort pressure in about one hour and held at this temperature for 30 rain. The molds into which the castings were made consisted of graphite plates into one side of which was milled a cavity 1.973 in. wide, 943-in. long, and 0.206 in. deep. The milled plates were stacked together to form a book-type mold. The inside surfaces of the mold cavity were coated with yttria and the mold components were assembled and held together by tie-bolts and spring washers. The entrance to the molds was a trough or header that was heated to about 1000°C to insure against "pipe" at the top of the casting. At the above conditions acceptable castings resulted from pouring w~en a thermocouple, centrally located in the mold assembly, indicated a temperature of 450°C. (b) Mechanical fabrication. Some experiments to determine the feasibility of producing ZPPR core elements by secondary metal working methods have been carried out by Carson [ 181 ] at ANL. Attempts were made to roll slabs of U-28 w/o Pu-2.5 w/o Mo on a 5 in. diameter by 8 in. wide two.high laboratory rolling mill enclosed in a helium atmosI.~:~ereglovebox. Compressive yield determinations [179] have shown that this alloy system shows low yield characteristics below 550°C. For this reason rolling was carried out on billets at temperatures between 575 and 650°C. It was found that, for reductions of as little as five
which this alloymay be rolled without complete hil. ure of the work piece:It was possible to achieve a fifty percent reduction in five passes ona-~ in. thick billet heated to 650°C and fed between rolls heated to 300°C. Although no serious edge cracking resulted from this rolling schedule, the effect of temp ~:l~ature in the helium atmosphere containing up to 1500 ppm oxygen and 70ppm moisture was to severely oxidize the metal surfaces. Machining of U.28 w/o Pu.2.5 w/o Mo alloy has been accomplished both at room temperature and at elevated temperature. The knowledge that this alloy contains significant quantities of the zeta phase and the experience with rolling prompted an investigation of hot milling characteristics. Electrically heated fixtures held in a horizontal milling machine were used to raise the temperature of the work piece. At 200°C clean cuts were produced without evidence of chipped edges. Although the surfaces were acceptable, dimensional control was a problem due to the different thermal expansions and temperatures of the work piece, jigs, and milling machine components. At room temperature satisfactory machined surfaces were obtained by using carbide.tipped milling saws. The life of the carbide-tipped saws can be extended by a factor of four by chamfering the sides of the teeth to remove that portion of the tooth that is first to dull. The chamfered saws are less prone to cause chipping of the brittle fuel alloy and provide machined sur. faces that have a polished appearance.
6. Compatibility behavior The extent to which a metallic fuel and cladding material interact in a nuclear reactor is a primary consideration in their selection. Clearly to be avoided are fuel.cladding combinations that interact to affect either melting of the fuel or the formation of reaction layers that may lead to failure or penetration of the cladding and consequent release of fission products into the reactor coolant. Walter et al. [182, 183] surveyed by means of diffusion couple studies the out-of.reactor compat~ility of U-Pu-Zr, U-Pu-Ti and U-Pu-Fz alloys with a wide variety of materials. Their results, which show file extents to which uranium and plutonium penetrate
S.H.Kittel et al., Plutonium and plutonium alloys
419
Table 30 Fuel penetration into commercial Fe- and Ni-base alloys Cladding
Fuel alloy
Penetration (microns)
(w/o) 5000 ht at 700°C
1000 hr at at 750°C
168 tit at 800°C
Tin*
(°0
U-17 Pu~6 Zr
304 SS Hastelloy
12 (400 ht) 50 (400 hr)
Melted Melted
Melted Melted
725 4"25 725 + 25
U-15 Pu-10 Zr
16-15-6"* Haynes 56 16-25-6"* 304 SS N-155 Incoloy 800 Hastelloy-X
2 2 4 7 30
<
<
825 -+ 25 825 -+ 25
16-15-6"* Haynes 56 304 SS 16-25.6"* N-155 Incoloy 800 Hastelloy-X
U.18 Pu-14 Zr
U-10Zr
304 SS
U-10 Ti U-I 5 Pu-10 Ti U-22 Pu-12 Ti
304 SS 304 SS 304 SS
5 8
<85o
-
70 < -
5 15
6 4 2 80
30 (1000 hr)
12 > 40 27 Melted
Melted Melted
5 5 9 15 20 ~> 40 Melted
<: 6 4 12 20 70 Melted
3
30
9
Melted Melted at 650°C
28
12 (168 hr)
Melted
825 -+ 25 < 850 775 + 25 725 +- 25 > 825 825 -+ 25 825 + 25
< 850 825 -+25 825 -+25 725 +25 835 -+ 15 775 +25
< 700 <650
* Temperature at which liquid phases occur in diffusion layers. ** Timken 16 Ni-15 Cr-6 Mo and 16Ni-25Cr-6Mo.
Table 31 Fuel penetrations into V-20 w/o Ti and V-15 w/o Ti-7.5 w/o Cr alloys (microns). Fuel alloy
Anneal time
(w/o)
(hr)
6oo%
?oo°c
800%
V-20 w/o Ti U-18Pu-14ZI
168 1000 5000
U-22Pu-12Ti
168
<1
to2 1.5 to 3 3 to5 1
to3
5to 9 9 to 16 17 to 23 6to
9
V-15 w/o Ti-'l.5 w/o Cr U-18Pu-14Zr
168 1000 5000
<~1 1 2
tol.5 to3 to4
U-22 Pu-12Ti
168
~. 1
to 2
4to 6 9toll~ 15to17
15 to 17
$.H.Kittel.et aL, Plutoniam and plutoniumalloys
420
Table 32 U-Pu-Fz alloy fuel penetrations (calculated) into variouspure metals and alloys in one year (microns). Combination
--r'-------r----
I
'
I
,
I
Temperature (°C)
(w/o)
V-20 Ti/U-10 Pu-lO Fz V-20 Ti/U-15 Pa-10 Fz V-IO Ti/U-10 Pu-lOFz Cr/U-10 Pc-10 Fz Mo/U-IOPu-10 Fz Mo/U-I$ Pu-10 Fz 304 SS/U-IOPu-lO Fz 304 SS/U-15 Pu-lO Fz Hast-X/U.l0 Pu-lO Fz Hast-X/U-l$ Pu-lO Fz Nb/U.I 0 Pu-lO Fz Nb/U-20 Pu-lO Fz Nb-I Zr/U-IO Pu-lO Fz
500
600
650
700
750
3
15 15 20
30 50
75 100
4
6 6 10
15
10 15 25
25
50
20 30 25
45 75 35
15 25 60 100 110 190 700 1300 600
V12OTl IN U[ISPu,/I.STi O.~K
30 25 35
/ / : i
0,21 ~
TYPE~
/17
$$ I#
,f
/
/
/ // /
/
~- ~J~T, ,u
U~|SPu/iQZr
o.,o
--
the materials in the range 600 to 800°C, are summarized in tables 30-33. Above approximately 650°C the use of iron- and nickel,base alloys as claddings for the U-Pu-Ti and U-Pu-Fz alloys is inadvisable because of either marked cladding penetration or melting resulting from the transport of the eutecticforming elements iron and nickel into the fuel alloys. The use of nickel-base cladding alloys, e.g., lncoloy 800 and Hastelloy-X, for the U-Pu.Zr alloys has a similar limitation. Several commercial iron-base alloys, however, exhibit a high compatibility in laboratory tests to at least 750°C with U-Pu-Zr alloys containing 14 to 17 w/o plutonium and 10 to 14 w/o zirconium. The particular iron-base alloys include Type 304 stainless steel, Haynes 56, and steels containing 16 w/o nickel, 6 w/o molybdenum, and either 15 or 25 w/o chronium. With these combinations, cladding penetration is limited to 7 microns or less in 5,000 hr (1-2year) at 700°C and liquid-phase formation in diffusion layers occurs only above 800°C. The restricted diffusion is attributed to the formation of a diffusion layer that consists of one or more zirconium. rich phases which are stabilized by diffusing oxygen. The phases act effectively to restrict the transport of iron and nickel into the fuel alloys as well as the diffusion of uranium and plutonium into the cladding. The presence of from 100 to 450 ppm (by weight) of
1200
I/'s
llO0 IDIIIIlITUIE, ¢
i ? l 30q.IS IN
IIO0
1500
Fig, 31, Penetration rate vadalion with temperalul~ for Type
304 stainlesssteel abd V-IOTiin both U-15 Pu-10 Zr and U-15 Pu-6.5 Ti (maximum rates). oxygen in the iron-base alloys is seen to be a beneficial if not necessary factor affecting the compatibility. At temperatures to 800°C the use of the V-Ti and V-Ti.Er alloys as claddings for the U-Pu-base alloys is limited solely by the extent to which uranium and plutonium penetrate the dadddings and form brittle phases. The V.20 w/o Ti alloy is highly compatible with the U.pu.Zr and U-Pu-Fz alloys up to approximately 650°C. Above 650°C its use is limited because of pronounced penetration of uranium and plutonium. Substitution of chromium for some of the titanium in the alloy has little if any effect upon the diffusion behavior. Savage [184] has determined the rates of penetrao tion into Type 304 stainless steel and into V-20 w/o Ti alloy of molten U-15 w/o Pu-10 w/o Zr and U.15 w/o Pu~6.5 w/o Ti alloys in the temperature range 1200 to 1450°C. The rates are plotted versus temperature in fig. 31.
3.8 X 10 - t 3 1.6 X 10 -13
X 10 - 1 4
8
3.6 X 10 - 1 4
304 SS/U-15 Pu-lO Zr
304 SS/U-18 Pu-14 Zr
* No cladding penetration. K's represent band on the fue~ side believed to be (U, Pu)O 2. Vanadium contained 1300 ppm oxygen. ** Calculated from only one datum point assuming an X: = Kt law. t Obeyed the X = Kt rather tb~n X 2 = Kt rate law. t÷ Total band width. Also calculated from only one datum point ossuming an X 2 = Kt law.
2.0 X 10 - 1 3 1.5 X 10 -14
1.8 X 10 -13
8 . 0 X I0 -Is
V-15 Ti-7.5 Cr/U-18 Pu-14 Zr
304 SS/U-10 Zr
3.5 X 10 -13
1.5 X 10 -14
V-20 Ti/U-18 Pu-14 Zr
"['~'2.3X 10 -13
t l . 9 X 10 - 9 cm/sec
304 SS/V-20 Ti
4.0 X 10 -13
1.6 X 10 -13
Nb-I Zr/U-IO Pu-lO Fz
t4.2 X 10 - 9 cm/sec
t?3.4 X 10 -13
1.8 X 10 - 1 2
2.3 X 10 -13
Nb/U-20 Pu-lO Fz
t2.2 X 10 - 9 cm/sec
**1.1 X 10 - 1 !
3.6 X 10 -12
**3.4 X 10 -12
1.1 X 10 - 1 2
304 S$/V
6.3 X 10 -13
8.0 X 10 -13
1.3 X 10 -13
1.8 X l 0 -13
Nb/U-10 Pu-lO Fz
Hast-X/U-15 Pu-10 Fz
Hast-X/PU-10 Pu-10 Fz
304 SS/U-15 Pu-lO Fz
2.2 X 10 -13
**4.0 X 10 -13
**2.0 X 10 -13
**7.5 X 10 -14
Mo/U-15 Pu-10 Fz
304 SS/U-IO Pu-lO Fz
1.9 X 10 -13
!,2 X 10 - 1 3
6.9 X 10 -14
**3.0 X 10 - t 2
**8.0 X 10 -13
**3.5 X 10 -13
*'1.7 X 10 - 1 2
750
3.1 X 10 -13
70~
4,5 X 10 -14
1.i X 10 -13
8.1 X 10 - 1 4
*'1.3 X 10 - 1 4 2.3 X 10 -14
6.4 X 10 - 1 4
1.3 X 10 - 1 4
**2.3 X I 0 - I s
4.7X I0 -Is
*4.0X 10 - i s
650
"1.5 X 10 - l a
600
*7.5 X 10 -14
550
Temperature (°C)
Mo/U-10 Pu-10 Fz
Cr/U-IO Pu-10 Fz
V-10 Ti/U-IO Pa-lO F~
V-20 Ti/U-15 Pu-10 Fz
V-20 Ti/U-IO Pu-IO Fz
V/U-IO Pu-lO Fz
(w/o)
Combination
Table 33 Cladding penetration coefficients (K) in cm2/sec (except where noted).
9.8 X 10 -13
6 . 0 X 10 -12
800
i
422
S.H.Kittel et al.. Plugton!urn and plutonium alloys
7. In.reactor behavior 7.1. Introduction The properties of ultimate interest for any reactor material are those that apply when the material is in actual use in a reactor. Furthermore, in-reactor properties of greatest interest are those that exist in the complete reactor environment of stress, temperature, corrosion, and irradiation-induced property changes. In the case of fuels, the property normally of greatest importance is resistance to high temperature swelling. Fuel swelling is undesirable for several reasons. It can cause high stresses in the cladding tliat are difficult to predict, particularly under transient conditions. Axial fuel swelling can cause reactivity losses, and radial swelling can cause loss of inherent shutdown mechanisms that depend on unhampered rapid axial fuel expansion. The development of porosity in the fuel, asa result of swelling, lowers the effective thermal conductivi.ty of the fuel. The allowable linear power rating of the fuel element may thereby be adversely affected. In the sections that follow, much attention is devoted to the use of cladding restraint to control fuel swelling. Most of the initial discussion is on uranium-plutonium-fissium alloy, because of the greater preponderance of work on that alloy system. With the more recent shift to work on higher.melting alloys, in particular U-Pu.Zr alloys, marked improvements were obtained in metallic fuel element performance. U-Pu-Zr alloy offers promise as a major fuel candidate foi the LMFBR program. Further studies, now in progress, are expected to more clearly establish the comparative advantages of U-PU-Zr alloy and the leading ceramic fuels, such as oxide and carbide. 7.2. Uranium-plutonium binary alloys The irradiation behavior of alloys based on uranium and plutonium is of greatest interest because of the potential use of these alloys as fuel in fast breeder reactors. Ideally, from physics considerations, the best fuel for fast breeder reactors is an alloy of U 238 and Pu 239. Such a fuel would have the highest possible metal atom density and would
thereby enable the highest possible breeding ratios to be achieved. However, early irradiation resuRs on U-Pu binary alloys showed that they swelled badly under irradiation [ 185]. More recently, binary alloys were irradiated under conditions where restraint of swelling was achieved by use of strong cladding [ 186]. AI. though gross fuel swelling was prevented, the fuel elongated and separated into segments. Further studies of the performance of U.Pu binary alloys under irradiation is unlikely, primarily because of their relatively low melting points and because of their poor compatibility with austenitic stainless steel cladding alloys. 7.3. Uranium.plutonium.fissium alloys The experimental breeder reactor EBR-II was built and initially operated to demonstrate a closed fuel cycle based on pyrometallurgical reprccessing of uranium alloy fuel. The reprocessing scheme leaves in the fuel certain fission products (primarily Mo, Ru, and Tc, with smaller amount of other elements inchding Zr, Rh, and Pd). These fission products are termed "fissium", with the symbol "Fs". Although the reactor has been operated only with U-Fs alloy, original plans called for eventual operation with U.Pu-Fs alloy. Much effort, therefore, was expended in determining the in-reactor behavior of various U-Pu-Fs alloys under prototypical conditions. The first irradiations of U-Pu-Fs alloys were on unclad specimens [187]. A total of 35 specimens were irradiated at maximum fuel temperatures of 230 to 470°C and total bumups from ! .O to !.8 a/o. Emphasis was placed ca injection-cast, uranium-20 w/o plutonium-lO w/o fissium alloy. It was found that this material begins to swell rapidly at temperatures above 370°C. The ability of the fuel to resist swelling did not appear to vary appreciably with minor changes in fissium or zirconium. Decreasing the plutonium to 10 w/o improved the swelling behavior. Since these results were obtained on specimens irradiated 300°C or more below normal operating temperatures in EBR-II, it was apparent that considerable reliance would have to be placed on restraint of fuel sweill~ by strong cladding. An additional complicating feature of U.Pu.Fs
S.H.Kittel et al., Plutonium and plutonium alloys
alloy is its tendency to form a liquid eutectic with iron. or nickel.base cladding alloys at temperatures as low as 550°C. This temperature would be experienced at the fuel-cladding interface in the hotter regions of the EBR,II core during normal reactor operation. The cladding must therefore be made of the refractory metals that do not form low-melting eutectics with the fuel alloy. Alternatively, a thin barrier of a refractory metal could be placed between the fuel and the iron or nickel alloy cladding. A total of 78 specimens were irradiated in instrumented capsules in the initial investigations of refractory aUoy-clad [J-Pu-Fs alloy [ 138]. Table 34 summarizes the irradiation conditions and the results obtained. The main experimental parameter in the irradiations was the cladding composition. The cladding materials selected for these experiments were those that were known to be compatible with the fuel material and to have relatively high rupture strengths. The clad specimens measured approximately 3.5 in. in length and 0.175 in. in diameter. The cladding thickness was principally 0.009 in. A group of six specimens had claddings that were either 0.015 or 0.025 in. thick. The fuel pin was 0.144 in. OD and 2 in. long and was sodium.bonded to the jacket. The sodium annulus was 0.006 in. thick. The effec:ive (smeared) fuel density was 85%. The irradiations were performed in instrumented temperature-controlled capsules in the CP-5 reactor. The cladding materials that were evaluated are listed below: (l) Niobium. (2) Niobium-I w/o zirconium (3) Niobinm-33 w/v tantalum-I w/o zirconium (4) Niobium-4 w/o vanadium (5) Vanadium (6) Molybdenum (7) Tantalum-O.l w/o tungsten (8) Duplex tubing (a) Inconel-X (vanadium liner) (b) Type 304 stainless steel (vanadium line~) (c) Hastelloy-X (tungsten-coated). Most of the irradiations were made with niobium alloy cladding. The attainable burnups before cladcling failure ranged from 0.9 to > 3.0 a/o, The cladding failures were usually brittle, with no measurable elongation before fracture. An exception was
423
Nb-4 V alloy, which showed significant cladding strain without fracture. Unalloyed vanadium cladding hi the recrystallized condition was found to be satisfactory to bumups in excess of 2.0 a/o. The cladding retained its ductility during irradiation. Specimens clad in unalloyed molybdenum tubing failed at 0.4 a/o burnup. The failures were of a very brittle nature, with cracks extending the full length of the specimen. The poor performance is attributed to the poor quality of the cladding. The Ta-O.l W alloy cladding behaved similarly to the niobium alloy. Fuel pins clad in Type 304 stainless steel with vanadium liners as well as the Hastelloy-X with vapor deposited tungsten on the ID of the cladding were satisfactory to burnups in excess of 3.0 a/o. The majority of failures were attributed to undetected flaws in the liners. In addition to the irradiations listed in table 2.34, a number of instrumented capsule irradiations were performed on several full-length (18 in. long) EBR-il fuel elements of U-Pu-Fs alloy in refractory alloy cladding. The results were similar to those obtained for the CP-5 irradiations. Several series of instrumented capsule irradiations were also made in CP-5 to investigate certain design or operating parameters. The results of these irradiation experiments are summarized as follows: 1
7.3.1. Effect of plutonium content on the irradiation behavior of U-Pu-Fs alloys Comparison irradiations conducted on U-Pu-!0 Fs alloy specimens with plutonium concentrations between 10 and 20 w/o and clad in Nb-I Zr tubing having a wall thickness of 0.009 in. failed to show signifi~-ant increase in achievable burnup as the plutonium concentration was reduced from 20 to 15 w/o (table 35). Tile fuel with 10 w/o plutonium had not reached the burnup values of the other alloys and could not be directly compared. Increasing the plutonium concentration resulted in an increase in swelling rate, as anticipated. 7.3.2. Irradiations of U-Pu.Fs spechnens clad in duplex tubing Twenty-one specimens were irradiated in cladding of Type 304 stainless steel and Hastelloy-X lined with
S.H.Kittel et at,, Plutonium andpiutoniumalloys
424
Table 34 Effects of irradiation on cast U-20 w/o Pu-10 w]o Fs specimens [ !88]. Specimen No.
Melt No.
Jacket composition
Plenum vol.
(w/o)
(%)
Burnup (a/o)
Max. temp. ( P C )
Condition
Jacket surface
Fuel center
speeimen**
1.8 -2.0 2.1 2.5
655 790 780 680
760 920 910 790
B B B B
17-2 17-6 16-4 18-2
R21-10B R21-10C R21-10A R21-1OD,
Niobium Niobium Niobium Niobium
13 13 13 13
22-5 22-2 19-1 19-6 19-4 17-1 23-1 23-4 20-2 20-4 2O-6 16-2 17-4 16-5 18-1 21-4 21-1 21-2 27-4 27-1 25-4 25-1 28-1 28-4 32-1 32-2 32-3 32-4 32-5 32-6
$2-3-2 $2-3-1 R21-19C R21-20C R21-21C R21-15D $2-3-4 R21-11A R21-21F R21-22A R21-22D R21-15B R21-15E R21-15C R21-17B R21-17A $2-1-1 R21°22B R21-24B R2 I-11 E R21-1 IC R2 I-7B R2 I-7A R21-11B R21-11D R21-3B R21-3C R21-3D R21-3E R21-3F R2 I-4A
Nb-I Zr Nb-I Zr Nb-1 Zr Nb-I Zr Nb-I Zr Nb-I Zr Nb-1 Zr Nb-I Zr Nb-I Zr Nb-I Zr Nb-I Zr NbdZr Nbol Zr Nb-I Zr Nb-I Zr Nb-I Zr Nb-1 Zr Nb-I Zr Nb-I Zr Nb-I Zr Nb-i Zr Nb-! Zr Nb-I Zr Nb-1 Zr Nb-1 Zr Nb-I Zra Nb-I Zra Nb-I Zrb Nb-! Zrb Nb-I Zrb Nb-I Zr
36* ~6" 28 28 28 13 50 50 28 28 28 !3 13 13 13 13 25 25 25 Vented Vented 50 50 57 57 23 24 24 22 23 17
0.9 0.9 1.5 1.5 !.5 1.8 !.8 1.8 1.9 1.9 1.9 2.0 2.0 2.1 2.5 2.5 2.6 2.6 2.6 2.6 2.5 2.5 2.5 3.2 3,2 5.3 5.3 5.3 5.3 5.3 5.3
615 655 520 535 535 655 560 630 555 580 580 695 790 780 680 680 520 520 520 570 570 575 580 580 580 590 590 590 615 ,615 615
715 760 595 615 615 760 650 730 640 67,9 670 810 920 910 790 790 600 600 600 660 660 670 670 670 670 690 690 690 720 720 720
C C B B B B D A B B B B B B A B B B B C A B C B C A C A A A A
22-4 21-1 23-3 23-6 27-6 27-3 25-6 25-3
$2-2-3 $2-2-2 R21-9A R21-9B R21-25 F R21-25E R21-26D R2 !-26C
Nb-33 Ta-! Nb-33 Ta-I Nb-33 Tad Nb-33 Ta-! Nb-33 Ta-! Nb-33 Ta-! Nb-33 Ta-! Nb-33 Ta-!
36* 36* 50 50 yented Vented 50 50
0.9 0.9 1.8 1.8 2.6 2.6 2.6 2.6
615 655 560 630 570 570 575 590
715 760 650 730 660 660 670 680
A B B A A A B A
29-1 29-5 29-4
R21-29E R21-3A R2 i-29F
Nb-4 V Nb-4 V Nb-4 V
57 57 57
3.8 3.8 3.8
490 500 500
560 570 570
A A A
18-4
Zr Zr Zr Zr Zr Zr Zr Zr
$~H.Kittel et aL, Pluto~dum and plutonium alloys
425
Table 34 (cont.) Specimen No.
Melt No.
Jacket composition (w/o)
Plenum vol. (%)
Burnup (a/o)
Max.temp. (°C) Jacket surface
Fuel center
Condition of specF men**
22-6 17-3 16-3 18-5 18-3
$2~2-4 R21-17E R21-ITD R21-18B R21-I7E
Vanadium Vanadium Vanadium Vanadium Vanadium
50* 13 13 13 13
0.9 1.8 2.0 2.5 2.5
615 655 695 680 680
715 760 810 790 790
G B B G B
19-3 20-1
R21-20E R21-21B
Molybdenum Molybdenum
30 30
1.5 1.9
520 555
595 640
B C
22-3 19-2 19-5 23-2 23-5 20-3 20-5 21-5 21-6 21-3 27.2 27-5 25-5 25-2
$2-2-6 +21-20A R21-20B R21-9D $2-3-3 R21-27B R21-27D R21-H9 $2-2-$ R21-24E R21-25A R21-25B R21-14A R21-TD
Ta-O.l W Ta-0.1 W Ta-0.1 W Ta-0.1 W Ta-0.1 W Ta-0A W Ta-0.1 W Ta-0.1 W Ta-0.1 W Ta-0.1 W Ta-0.1 W Ta-0.! W Ta-0.! W Ta-0.I W
36* 28 28 50 50 28 28 25 36* 25 Vented Vented 50 50
0.9 1.5 1.5 1.8 1.8 1.9 1.9 2.6 2.6 2.6 2.6 2.6 2.6 2.6
655 520 535 560 630 555 590 520 520 520 570 570 575 590
760 595 615 650 740 640 670 600 600 600 660 660 670 680
B C C B A A B C B B A A B A
16-1
R21-18B
13
2.0
695
810
E
17-5
R21-18E
13
2.0
790
920
E
16-6
R21-18C
13
2.1
780
910
E
18-6
R21-18F
lnconel X V Barrier 304 SS V Barrier 304 SS V Barrier 304 SS V Barrier
13
2.5
680
790
A
28-3
R21-28F
57
3.2
590
670
E
28-2
R21-28B
57
3.2
590
670
F
28-5
R21-28C
57
3.2
590
670
A
28-6
R21-28D
57
3.2
590
670
A
29-3
R21-29D
57
3.8
490
560
A
29-2
R21-29C
57
3.8
490
560
A
29-6
R21-29B
Hastelloy-X W Lined Hastelloy-X W Lined Hastelloy-X W Lined Hastelloy-X W Lined Hastelloy-X W Lined Hastelloy-X W Lined Hastelloy-X W Lined
57
3.8
500
570
A
* No sodium bond. ** A. Specimen straight and intact. B. Longitudinal split in jacket with protrusion of fuel. C. Longitudinal split in jacket without protrusion of fuel. D. Several small cracks around center section of specimen. E. Fuel penetrated barrier and fomled extensive eutectic with jacket. F. Fuel penetrated barrier and formed small hole in jacket. G. Specimen bowed but intact. a Jacket thickness 0.38 mm (0.015 in.); b Jacket thickxless 0.64 mm (0.025 in.)
S.H.Kittel et al.. Plutonium and plutonium alloys
426
Table 35 Design parameters and operatin8 conditions for U-Pu, U-Pu-Fs comparison irradiations. Specimen Numbet
Opiating conditions
Designparameters Fuel composition
(w/o)
Effectire density
Cladding composition
(~;
(w/o)
Clad. OD (in.)
Clad. thick (in.)
Plenum col. (%)
Burnup
Max. clad. temp.
Max. fuel temp.
(°c)
(°c)
a/o (U+Pu)
fiss/cc XIO- 2 0 .
30-2 30-6 34-6
U-IO Pu-lO Fs U-IO Pu-lO Fs U-IO Pu-10 Fs
82.8 81.7 82.9
Nb-1 Zr Nb-I Zr Nb-I Zr
0.174 0.174 0.174
0.009 0.009 0.009
58.1 58.4 23.4
525 525 600
600 600 690
3.1 3.2 2.5
9.8 10.0 7.9
30-3 ~0-5 34-5
U-15 Pu-lO Fs U-15 Pu-lO Fs U-15 Pu-lO Fs
83.1 83.4 82.1
Nb-1 Zr Nb-1 Zr Nb-1 Zr
0.174 0.174 0.174
0.009 0.009 0.009
57.4 56.5 24.5
560 525 635
640 600 730
4.5 4.6 3.2
14.3 14.7 10.0
34-4
U-20 Pu-lO Fs
86.5
Nb-I Zr
0.174
0.009
23.4
625
720
3.6
11.9
* Based on effective density.
Table 36 Design parameters and operating conditions for U*Pu-Fs irradiated in duplex type cladding [ 188]. Specimen num bet
Operating conditions
Design parameters Fuel composition (w/o)
Effectire density (%)
Cladding composition (w/o)
Clad. OD (.in.)
Clad. thick. (in.)
Plenum vol. (%)
Bumup
Max. clad. temp. (°C)
Max. fuel temp. (°C)
a/o
fisslcc
(U+Pu)
XIO-2°*
34-3
U-10 Pu-10 Fs
88.4
304 SS-WLined
0.175
0.012
22.1
575
660
2.2
7.5
37-1 37-2 37-3 37-4 37-5 37-6 34-2
U-15 Pu-10Fs U-15 Pu-lOFs U-15 Pu-lO Fs U-15 Pu-lO Fs U-15 Pu-lO Fs U-15 Pu-lO Fs U-15 Pu-lO Fs
85.1 82.1 83.9 83.9 83.9 83.9 83.9
304 SS-WLined 304 SS-WLined 304 SS-WLined 304 SS-WLined 304 SS-WLined 304 SS-W Lined 304 SS-W Lined
0.175 0.175 0.175 0.175 0.175 0.175 0.175
0.010 0.010 0.010 0.010 0.010 0.010 0.011
Vented Vented 19.8 22.4 22.2 Vented 22.9
660 660 630 590 590 590 590
780 780 750 680 680 680 680
2.3 2.3 2.3 2.3 2.3 2.3 2.5
7.5 1.3 7.4 7.4 7.4 7.4 8.0
34-1
U-20 Pu-lO Fs
86.5
304 SS-W Lined
0.175
0.010
22.9
590
680
2.8
9.2
38-1 38-2 38-4 38-5 36-1 36-2 36-3 36-4 36-5 36-6 38-3 38.6
U-15 Pu-lO Fs U-15 Pu-10Fs U-15 Pu-lO Fs U-15 Pu-10 Fs U-15 Pu-lO Fs U-15 Pu-10Fs U-15 Pu-10 Fs U-15 Pu-10 Fs U-15 Pu-IO Fs U-15 Pu-IO Fs U-15 Pu-lO Fs U-15 Pu-lO Fs
82.8 82.8 74.2 74.2 88.5 88.5 88.5 88.5 88.5 88.5 73.2 73.2
304 SS-V Lined 304 SS-V Lined 304 SS-V Lined 304 SS-V Lined Hast.-X-WLined !'~st.-X-WLined Hast.-X-WLined Hast.-X-WLi~.ed Hast.-X-WLtned Hast.-X-WLined , Hast.-X-VLined Hast.-X-VLined
0.186 0.186 0.196 0.196 0.i74 0.174 0.174 0.174 0.174 0.174 0.184 0.184
0.015 0.015 0.015 0.015 0.011 0.011 0.011 0.011 0.Ol I 0.011 0.009 0.009
Vented Vented 54.0 Vented 23.0 Vented 21.0 22.0 22.0 20.0 Vented 58.0
580 580 630 630 645 645 645 600 600 635 580 630
660 660 710 710 750 750 750 695 695 740 660 710
3.2 3.-'2 3.2 3.2 2,2 2.2 2.2 2.3 2.3 2.3 3.2 3.2
10.3 10.3 9.1 9.1 7.5 7.5 7.5 7.8 7.8 7.8 8.9 8.9
* Based on effective density,
S.H.Kittel et al., Plutonium and plutonium alloys
427
Table 37 Design parameters and operating conditions for U-Pu-Fs irradiated to high burnup [ 188]. Specimen number
Design parameters
Fuel composition (w/o)
Operating condition~
Cladding tire composidensit> tion (%) 'w/o)
Clad. OD (in.)
Clad. thick, (in.)
Plenum voL (%)
Max. clad. temp. (°C)
Max.
fuel temp. (°C)
a/o " (U+Pu)
fm/cc XI0 -2°*
C-II5A U-10 Pu-10 Fs C-116B U-10 Pu-10 Fs C-120C U-10 Pu-10 Fs
81.6 78.6 79.7
Nb-I Zr Nb-I Zr Nb-I Zr
0.186 0.199 0.209
0.015 0.020 0.025
22.2 23.2 24.3
510 530 530
590 610 610
7.I 7.1 7.1
22.2 21.4 21.7
C-II9A C-II7A C-118C
85.2 84.0 87.4
Nb-I Zr Nb-1 Zr Nb*l Zr
0.186 0.186 0.209
0.015 0.015 0.025
23.2 29.9 23.9
545 545 545
625 625
8.7 8.7
28.4
625
8.7
U-15 Pu-10Fs U-15 Pu-10 Fs U-15 Pu-10 Fs
E, "'c-
Burnup
27.9 29.1
* Based on effective density.
tlmgsten or vanadium (table 36). The tungsten lining was achieved by vapor deposition on the ID o f the cladding. The vanadium liner was a 0.0005 ha. thick foil wrapped on the specimen. O f the 12 specimens that failed, nine failures were directly attributable to defects in the barrier layer, as evidenced b y eutectic formation, and three failures
were due to fracture o f the clad from fuel swelling. Variations in clad thickness or effective density of the fuel did not have significant effect o n the fuel bumup at which clad failure occurred. 7.3.3. U-Pu-Fs alloys irradiated in thicker cladding Six specimens were irradiated in Nb-1 w/o Zr
Table 38 Design parameters and operating condtions for U-Pu-Fs sPeciraens having increased plenum volume and reduced effective density of fuel [ 188]. Design parameters
Specimen
Operating conditions
Fuel composition (w/o)
Effectire density (%)
Cladding composition (w/o)
Clad. OD (in.)
Clad. thick, (in.)
Plenum vol. (%)
Max. clad temp. (°C)
Max. fuel temp. (°C)
ado {UtPu)
Fiss/cc X10 -20*
41-4 41-5 41-6
U-I0 Pu-10 Fs U-10 Pu-IO Fs U-10 Pu-10 Fs
76.0 79.9 84.1
V-20 Ti V-20 Ti V-20 To
0.197 0.193 0.189
0.016 0.016 0.016
41.1 39.9 36.7
630 630 630
740 740 740
8.2 8.2 8.2
23.9 25.1 26.4
40-1 40-2 40-3 40-4 40-5 40-6 41-1 41-2 41-3 43-1
U-15 Pu-10 Fs U-15 Pu-10 Fs U-15 Pu-10 Fs U-15 Pu-10 Fs U-15 Pu-10 Fs U-15 Pu.10 Fs U-15 Pu-10 Fs U-15 Pu-10 Fs U-15 Pu-10 Fs U-I 5 Pu-10 Fs
82.9 82.9 74.0 78.8 78.8 71.6 75.1 79.9 86.3 69.0
V-20 Ti V-20 Ti V-20 Ti V-20 Ti V-20 Ti V-20 Ti V-20 Ti V-20 Ti V-20 Ti V-20 Ti
0.189 0.189 0.197
0.016 0.016 0.016 0.016 0.016 0.016 0.016 0.016 0.016 0.015
23.5 23.6 26.5 25.0 25.0 27.5 41 ! 39.9 36.7 56.0
620 620 620 620 620 620 630 630 630 600
720 720 720 720 720 720 740 740 740 770
6.1 6.1 6.1
19.4 19.4 17.3
6.1 6.1 6.1 7.3 7.3 7.3 12.0
18.4 18.4 16.7 21.0 22.4 24.1 31.7
hum
-
ber
* Based on effective density.
0,193
0.193 0.201 0.197 0.193 0.187 0.203
Bumup
428
S.H.Kittel et al., Plutonium and plutonium alloys
Table 39 Fission gas relez~efrom U-Pu-Fsalloy with variable amounts of swelling.The specimenswere irradiated to 3.0 a]o burnup at
740% 11881. Specimen no.
39-1 39-2 39-3 39-4 39-5 39,6
Design parameters
Experimental results
Fuel composition (w/o)
Effective density (%)
Cladding composition (w/o)
C l a d d i n g Thickness Plenum OD (in.) vol. (in.) (%) ....
Fuel vol. in~rease (%)
Fission, gas release (% of theotetical yield)
U-15 Pu-lO Fs U-15 Pu-lO Fs U-15 Pu-lO Fs U-15 Pu-lO Fs U-15 PwlO Fs U-15 Pu-10 Fs
79.6 74. l 67.8 61.1 52.4 44.2
Nb-I Zr Nb-I Zr Nb-I Zr Nb'-I Zr Nb-1 Zr Nb-I Zr
0.202 0.204 0.209 0.220 0.237 0.260
23 30 43 57 97 133
-* 37 -** 63 76 83
0.021 0.019 0.018 0,019 0.021 0.022
29 39 74 89 124 168
* Jacket failed during irradiation. ** Gas sample lost due to equipment failure. tubing having a wall thickness between 0.015 and 0.025 in. (table 37). The selection o f increased cladding thickness was to preclude failures experienced because o f fabrication defects in refractory tubing having a wall thickness of 0.009 in, The specimens were irradiated to a maximum 8.7 a/o burnup (2.9 X 1021 fiss/cc) at maximum ternperatures o f 545°C. Maximum fuel pin elongation occurred ~t 5 a/o burnup. This was followed by a gradual reduction in fuel length which may be due to high plenun~ pressures that gradually increased as the fission gas released. The post-irradiation examination sl,ow:~d that only one specimen had failed. The average fission gas release to the specimen plenums was 4.8%. 7.3.4. Irradiations of prototype fuel elements having increased plenum volumes and reduced effective density of fuel An analysis was made by F.G.Foote [189] to determine the relationships between jacket stress in sodium-bonded metallic fuel elements with various fuel burnups, cladding dimensions, and mechanical properties. A series of 13 irradiations was then performed to verify the results predicted by the analysis. Table 38 summarizes the irradiation conditions and specimen design, One group of six specimens was assembled that was predicted by the analysi~ to develop cladding failures at 3.1 a/o burnup. Tl~te first cladding failures
were not observed until 5 a/o bumup. Examination of the specimens at 6.1 a/o burnup showed that four out of the six pins had ruptured or deformed the cladding. A second group was assembled with configurations which were calculated to result in cladding failures at bumups ranging from 5.9 to 6.4 a/o. No failures were noted until the specimens w,,~reexamined at a max/. mum bt~rnup of 8.2 a/o when it was observed that four had deformed cladding. A specimen was designed such that cladding faOure was anticipated at- 10.9 a/o burnup. Cladding failure did not occur until 12 a]o burnup. The significant conclusion that was drawn from these series of experiments is: (1) The specimens achieved burnups without cladding failure that were higher than that predicted by the analytical approach. (2) Specimens that did not fail generally had a lower effective fuel density, indicating that radial clearance is more effective than axial clearance in extending fuel burnup. 7.3.5. Effects o f enhanced fission gas disengagement from metal fuels Metal fuels are normally characterized by relatively low release of fission gas. For high burnup fuels, where the forces exerted on the cladding by fissiongas bubbles in the fuel become excessively high, it can be seen that release of the gas from the fuel into
429
S.H.Kittel et al., Plutonium and plutonium alloys
the plenum above the fuel pin would be advantageous. Pressure in the gas bubbles in the fuel matrix would thereby be reduced, and, in the ideal case, only volume expansion from solid fission products would exert significant pressure on the cladding, Three methods of enhancing fission gas release were investigated: (i) subdivision of the fuel to provide shorter paths of gas release and provide more surface for fission-recoil escape, (ii) use of an axial hole for release of fission gas migrating to the center of the specimen, and (iii) use of larger annuli between the fuel and cladding to permit the fuel to swell to such an extent that intedinking of bubbles could occur and fission gas would be released from the surface of the fuel. It was found that method (iii) was most effective in disengaging fission gas from the fuel alloy. Table 39 summarizes results. The specimens were irradiated to 3.0 a/o burnup before they were examined. The postirradiation examination showed that all specimens were intact except 39.1, which had been allowed a radial fuel volume expansion of only 26%. All the other specimens had allowable radial expansions of 30% or greater and were intact. The fuel length changes varied from 0% for specimen 39-2 which had an effective density of 74.1 to -7.4% for specimen 39-4 which had an effective density of 61.1%. It was observed that the specimens that had
90
80
I
|
"-
I
"
I
I
w
v
o
70
! •
2
50
40
M ~rJ
30 V
U-Fo
0
U- Pu-Fs
O U-Pu-Z¢ IO
, 20
0 ~
! 40
-
I
l
I
60
aO
I00
FUEL VOLUk~
IlfREASE . ' / .
Fig. 32. Fission gas release vs. fuel vo|ume increase in metallic fuei~ experienced volume increases in excess of 30% had released a significant amount of fission gas. These results supported the theoretical model by Barnes [190] which predicts that interconnection of bubble~
Table 40 Design parameters and operating conditions for U-Pu-Zr prototype elements [ 191]. Operating conditions
Design parameters
Spec~ men
Fuel composition (w/o)
Effectire density (%)
Cladding composition (w/o)
Clad. OD (in.)
Clad. thick, (in.)
Plenum Max. vol. clad. (%) temp. (°C)
Max. fuel temp. (~C)
48-2 48-5 28-3 48-6 48-1 48-4
U-15 Pu-12 Zr U-15 Pu-12 Zr U-15 Pu-12 Zr U-!5 Pu-12 Zr U-15 Pu-12 Zr U-15 Pu-12 Zr
75 75 75 75 75 75
304 SS 304 SS 316 SS 316 SS Hast.-X Hast.-X
0.196 0.196 0.196 0.196 0.196 0.196
0.015 0.015 0.015 0.015 0.015 0.015
96 92 97 97 95 98
610 660 610 660 610 660
700 810 700 810 700 810
2.4 2.4 2.4 2.4 2.4 2.4
6.2 6.2 6.2 6.2 6.2 6.2
45-1
U-18.5 Pu.14.1 Zr
63
V-20 Ti
0.208
0.016
73
655
840
12.5
28.0
no.
* Based on effective density.
Burnup
a/o fhs/cc ( U + P u ) XIO-2°*
430
S.H.Kittel et al.. Plutonium and pluton&m alloys
iii!
j
Fig. 33. Transversesection of U-IS w/o Pu-I 2 w/o Zr alloy jacketed in Hastelloy-X.The concentric bands in the fuel are related to phase distributions in the alloy during irradiation [ 191 ]. should occur after fuel volume increases of 33~%. The interlinked bubbles provide a continuous path for fission gas release lo the surface of the fuel. Fig. 32 which shows, in addition to the U-Pu-Fs data, additional results from U-Fs and U-Pu-Zr irradiations [ 191 ]. The results from this experiment support the view that fission release is largely independent of burnup and irradiation temperature, and depends principally
on the amount of fuel swelling. The points that are plotted in fig. 32 represent buh,ups between 2.7 and 12.5 a/o and maximum fuel temperatures between 450 and 840°C. The successful demonstration of gas release from metallic fuels has provided the key to obtaining high fuel burnups with cladding of normal thickness, as will be described in the following section.
S.H.Kittel et aL, Plutonium and plutt, nmm alloys
7.4. Uranium-plutonium-zirconiumalloys Interest has shifted from developing U-Pu-Fs alloy for EBR-II to developing high-melting uraniumplutonium alloys for use in liquid metal cooled fast breeder reactors for central station power generation. The U-Pu.Zr system has proved to be of greatest interest because of the excellent compatibility between U-Pu-Zr alloys and austenitic stainless steel [llS]. The first irradiations were performed on seven 13-15 w/o Pu.12 w/o Zr fuel alloy specimens clad in Type 304 stainless steal, Type 316 stainless steel, Hastell0y-X, and V-20 Ti alloy [191 ] (see table 40). The specimens were irradiated in instrumented, temperature-controlled capsules in vertical thimbles of the CP-5 reactor. The metallographic examination of the specimens in iron- and nickel-base alloy cladding that operated at maximum temperatures of 610°C showed excellent compatibility between the fuel and the cladding. The transverse macrosections of the fuel showed three distinct bands which are believed to be related to phase distributions during irradiation (see fig. 33). The outer zone is believed to correspond to the alpha-uranium + delta + zeta phase, the second
431
band to the alpha-uranium + zeta + gamma phase and the central area to the gamma phase. As anticipated, the fuel had swelled to the internal diameter of the cladding and the bond sodium was entirely displaced into the gas plenum. Fig. 33 also shows that original void volume, which had existed as a sodium-filled annulus around the solid metal fuel pin at the start 6f irradiation, became redistributed throughout the fuel volume in the form of finely-divided porosity. The U-Pu-Zr specimen jacketed in V-20 Ti alloy successfully reached an analyzed 12.5 a/o bumup (2.8 X 1021 fiss/cm 3) at a maximum clad temperature of 655°C. Periodic neutron radiography of the capsule during irradiation showed that the pin attained a maxinmm elongation of 3% within the cladding, which occurred at 4.2 a/o burnup. This dimension did not change throughout ~he remainder of the irradiation. Diameter changes in the cladding were calculated from volume changes measured byimmersion. An average 0.0002 in. diameter increase was observed. No measurable length increase of the cladding was noted. It was determined that 74% of the fission gas had been released to the plenum. Following these experiments on small prototype
Table 41 Irradiation conditions for U-Pu-Zr alloy fuel elements irradiated in EBR-Ii in subassembly XA07 [ 1921 . Specimen no.
Fuel composition (w/o)
ND-28 ND-41 ND-32 ND-43
U-15 Pu-9 U-15 Pu-9 U-15 Pu-9 12-15 Pu-9
Zr Zr Zr Zr
ND-25 ND-27 ND-26 ND-29 ND-30 ND-31 ND-33 ND-34 ND-35 ND-37 ND-39 ND-44
U-15 Pu-12 U-15 Pu-12 U-15 Pu-12 U-15 Pu-12 U-15 Pu-12 U-15 Pu-12 U-15 Pu-12 U-15 Pu-12 U-15 Pu-12 U-15 Pu-12 U-15 Pu-12 U-15 Pu-12
Zr Zr Zr Zr Zr Zr Zr Zr Zr Zr Zr Zr
Cladding alloy
Effective density (%)
Cladding OD (in.)
Cladding thick, (in.)
Max. kw/ft
Max. fuel • temp.
Max. clad. temp.
t°O
~°c)
Burnup (a/o)
304SS 304 SS 316 SS Hast.-X
73.1 73.8 73.8 74,5
0,205 0.205 0.196 0.196
0.019 0.019 0.015 0.015
10.9 10.4 9.9 10.4
745 735 715 725
630 625 605 615
4.6 4.4 4.2 4,4
304 SS 304 SS 316 SS 316 SS 316 SS 316 SS Hast,-X [tast.-X Hast.-X Hast.-X-280 Hast.-X-280 Hast.-X-280
73.5 73.1 73.9 72.2 72.3 74.1 72.8 72.6 74.9 63.8 65.4 66.4
0.205 0.205 0.196 0.196 0.196 0.196 0,196 0.196 O. 197 0.207 0.207 0.208
0.019 0.019 0.015 0.015 0.015 0.015 0.015 0.015 0.015 0.015 0.015 0.015
9.5 9.7 9.5 9.5 10.4 9.9 9,9 9.9 10.4 10.4 10.2 9.9
710 715 695 700 700 720 715 720 725 720 720 710
600 605 590 595 615 610 605 610 615 610 610 600
4.0 4.1 4.0 4.0 4.4 4.2 4.2 4.2 4.4 4.4 4.3 4.2
S.H.Kittel et al., Plutonium and plutonium alloys
432
Table 42 Irradiation of U-Mo-Pualloys [ 194].
U23s
Mo
Pu
U23s
Before After irradiation irradiation
Percent Burnup increase MWD/Te in vol. (AV)
66.9 66.9 69.6 69.6 57.2 57.2 59.7 59.7
15.0 15.0 15.0 15.0 25.0 25.0 24.9 24.9
7.6 7.6 14.9 14.9 7.5 7.5 15.0 15.0
10.5 10.5 0.5 0.5 10.4 10.4 0,4 0.4
17.72 17.69 17.78 17.78 17.06 17.05 16.99 17.03
53.8 81.1 77.4 91.6 26.5 45.4 11.6 63.4
Composition, atomic percent
Density (g/cm3)
11.52 9.77 10.02 9.2~ 13.49 11.73 15.22 10.42
fuel elements, irradiations were started on full-length elements of U-Pu-Zr alloy in EBR-II. The first irradiations were on 16 elements irradiated in special subassembly XA07 [192]. Table 41 summarizes the irradiation. External dimensional measurements of the elements showed no significant changes as a result of irradiation. Fuel pin length dimensions within the cladding were determined by neutron radiography and disclosed an average fuel length increase of 1.9%. The fuel pins were not seated on the bottom closures of the jackets, but were elevated an average o f 0.20 in. The elements had been intentionally assembled without fuel restrainers to observe possible axial fuel movement. The neutron radiographs of the elements revealed one or two partial axial separations in most of the fuel pins within the cladding which varied from "~ 0.020 in. to 0.060 in. in width. Fission gas recovery data established that "- 57% of the fission gas had been released from each fuel pin to the plenum above the bond sodium. A calcula. tion of the plenum pressures in the specimens revealed that, at reactor operating temperatures, the average gas pressure was 458 psi. Transverse as well as longitudinal metallographic sections o f the fuel elements showed no penetration of the fuel into the cladding materials. A detailed metallographic and microprobe examination of the fuel/clad interfaces showed a reaction zone that had a depth of 150/~ in the Hastelloy-X, 140t~ in the Type 304 stainless steel, and 20/~ in the Type 316 stainless steel. The fuel adjacent to the Type 304 stainless steel
7,639 14,760 8,170 14,880 7,880 14,440 8,720 16,300
S-
51 55 70 59 25 29 10 41
AV
percent burnup
Rating (w/g)
73 103 78 110 75 103 85 119
and HasteHoy-X was U.15 w/o Pu-9 w/o Zr while the fuel adjacent to the Type 316 stainless steel was U.15 w/o Pu-I 2 w/o Zr. 7.5. Uranium-plutonium-titanium alloys The U-Fu-Ti system is o f interest because of the high melting points of alloys containing ~ 10 and "-" 15 w/o Ti and Pu, respectively. A high bumup experiment was performed on a U-15 Pu-10 Ti alloy pin sodium-bonded to V-20 Ti alloy cladding [ 186]. The specimen was examined at an analyzed 10.7 a/o burnup (2.5 X 1021 fiss/cm 3) at a maximum clad temperature of 630°C. Periodic nondestructive examination of the capsule by neutron radiography showed a maximum fuel elongation of 14% which occurred at 4.6 a/o bumup. This dimension remained the same throughout the remainder of the irradiation. An average clad diameter increase of 0.0016 in. was calculated from volume changes by immersion. No measurable length change was noted. The metallographic examination of the specimen shows that there was no significant penetration of the fuel into the cladding. In isolated areas there was occasional evidence of surface reaction in the fuel to a depth of ~ 0.005 in. A central area that is microstructurally different from the rest of the fuel[ is believed to be associated with the (U, Pu)~T~+ 7 phase that is stable above 710°C. 7.6. Uranium-plutonium.molybdenum alloys Investigations o f U.Pu-Mo alloys were a natural development based on prior selection of U-Me alloys
S.H.Kittei et al., Plutonium and plutonium alloys
433
Table 43
Specimendata on uraniam-plutonium-molybdenumalloys [ 196].
Speci-
Comp.
men
CF-I CF-2
U-20 Pu-5 Mo U-20 Pu-5 M,~
CF-3 CF-4 CF-5 CF-6 CF-7 CF-8
U-20 Pu-5 Mo U-20 Pu-5 Mo U-20 Pu-5 Mo U-20 Pu-5 Mo U-20 Pu-5 Mo U-20 Pu-5 Mo
Calculated flux (lO s
Approx. central metal temp.
Calculated burnup of all
nv)
(°C)
2.07 1.64 1.56 1.48 1.01 0.55 1.56 1.22
340 280 270 260 190 120 270 220
Length increase
Dia. increase
atom~ (%)
(%)
0.27 0.43 0.20 0.38 0.28 0.07 0.40 0.15
0.74 0.67 0.79 1.26 0.83 1.05 0.77
for the FERMI and Dounreay fast breeder reactors. In one early UK study, cast specimens of U-6.5 w/o Pu-13 w/o Me and U-18 w/o Pu-13 w/o Me alloys were irradiated to burnups up to 0.4 a/o at temperatures between 500 and 700°C [193]. The density changes were very large in some cases, with volume increases greater than 100%. It was suspected that the specimens were heavily segregated during fabrication. A second set of homogenized specimens was therefore irradiated at burnups ranging from 0.4 to 1.6% burnup of all atoms at surface temperatures of 600°C [194] (see table 42). The performance of this group of specimens was considerably better than the first group. The rate of volume change showed a maximum of about 70% increase in volume per a/o burnup. However, the results were disappointing when compared to the behavior of U.Mo binary alloys. In an extensive study of U-Pu-Mo alloys for possible use in the Rapsodie reactor, a number of specimens were irradiated at temperatures between 400 and 600°C to burnups ranging from 0.4 to 0.8 a/o [195]. The specimens were all found to have swelled extensively. In order to determine whether cladding was capable of restraining the welling, U-Pu.Mo alloy specimens were inserted into tightlyfitting tubes of niobium with wall thicknesses of 0.012, 0.016, and 0.020 in. A void space of 5 or 10% of the fuel volume was left in one end of the can for longitudinal fuel expansion. It was found that can failures resulted if the can temperature exceeded
Calc. vol.
(%)
Hardness change increase (RA)
Weight change (%)
Density decrease (%)
0.00 0.56 0.48 0.40 0.48 0 0.96 0.16
0.74 1.80 1.76 2.07 1.80 3.00 0.40
- 4 - 16 2 1 1 0 0
0.74 1.45 0.68 0.6~ 1.08 1.39 0.23
(%)
- 8.3 - 8.3 - 8.3 - 2~.9 - 17.2 - 7.0 - 7.7
400°C or if the burnup exceeded 1.0 a/o. The size of the expansion space at the end of the fuel appeared to be of little importance. On the other hand, the thickness of the can was found to have a significant effect. Under conditions of identical irradiation temperature and bumup, the 0.012 in. thick cans were found to have burst, whereas the 0.016 and 0.020 in. cans were intact and showed no deformation. A group of eight U-20 w/o Pu-5 w/o Me specimens was irradiate d by ANL in the MTR reactor [ 196]. Four of the molybdenum alloys were heat treated at 560°C for 25 min and slowly cooled. The specimens were irradiated at maximum central temperature~ of 340¢C to a maximum burnup of 0.43% of total atoms. The results are summarized in table 43. Low swelling rates were observed for all specimens. 7.7. A luminum-plutonium alloys Fuel elements of aluminum containing 5 to 20 w/o plutonium and sheathed in Zircaloy-2 cans have been irradiated successfully in the NRX reactor [ 197]. Six of the elements were assembled with a slip fit between the sheath and fuel so that the fuel underwent irradiation at " 400°C. Volume changes and sheath/fuel interaction were insignificant after 0.25% of the total atoms present had fissioned. Four dements were assembled with significant diametral clearances between the fuel and sheath. Initially these elements were irradiated at fuel temperatures near 600°C but this temperature was reduced during irra-
434
S,H.Kitrel et al., Plutonium and plutoniura alloys
diation due to swelling. The cores in those elements increased in volume by up to 6%. Four Pu-I w/o AI alloy fuel elements sodiumbonded to Zircaloy.2 cladding were irradiated in EBR-! [198]. The elements were operated with measured central temperatures ranging from 332 to 386°C to 0.1 a/o bt~rnup. Diameter changes of the fuel rods were less than 0.002 in.
7.8. A luminum-nickel-plutonium alloys Seventy-five AI-2 w/o Ni-1.8 w/o Pu alloy rods jacketed in Zircaloy cladding were irradiated as spike elements in the PRTR reactor [ 199]. The spike elements measured 224 cm in length and were separated from the cladding by a 0.1 to 0.2 mm gap which partially closed during operation by differential thermal expansion. The performance of the AI-Pu elements was excellent to 0.74 X 1020 fiss/cc (83% burnup of the initial fissile atoms) at rod powers to 492 w/cm. Rods o f AI-2 w/o Ni-2.1 w/o Pu were irradiated under more severe conditions in the ETR reactor [200]. The maximum bumup was 8.3 X 1019 fiss/cm 3 atoms at linear heat ratings up to 25 kw/ft. Some evidence of plutonium and fissionproduct migration was noted in autoradiographs. 7.9. Zirconium-plutonium alloys Zr-5 w/o Pu and Zr.7 w/o Pu alloys were irradiated in the MTR reactor at 500°C to burnups from 0.8 to 1.8 total a/o [201 ]. The postirradiation examination showed that the specimens had increased their length from 2 to 4 times. The anisotropic growth of the specimens was due to preferred orientation caused by the cold rolling of the hexagonal close packed alphazirconium alloy.
References [ 1} R.D.Moellerand F.W.Schonfeld,Alloys of pluton:um with aluminum, USAEC Report LA-1000 (Los Alamos Scientific Laboratory, February 13, 1950).[2J M.B.Waldronet aL, The physical metallurgy of plutonium, Proc. of the Second United Nations International Conference on the Peaceful Uses of Atomic Energy, Vol. 6 (United Nations, Geneva, 1958). [3] A.A.Bochvaret al., Interaction between plutonium and other metals in connection with their arrangement in
Mendeleev's periodic table, Proc. of the Second United Nations International (~onferenceon the PeacefulUses of Atomic Energy, VoL 6 (United Nations, Geneva, 1958). [4] F.H,Ellinger et al., The solubility limits of aluminum in delta plutonium and some revisions of the plutoniumaluminum phase diagram, J. Nucl. Mater. 5 (2) (1962) 165-172. [i] O.J.C.Rnnnalls,Phase equilibria studies on the aluminum-plutonium system, in: Plutonium 1965, eds.: A.E.Kay and M.B.Waldron(Chapman and Hall, London, 1967) pp. 341-357. [6 ] R.O.EUiottand K,A.GschneidnerJr., Behavior of some delta-stabilized plutonium alloys at high pressures, in: Extractive and PhysicalMetallurgyof Plutonium and Its Alloys, ed.: W.D.WUkinson(Interscience Publishers, New York, 1960) pp. 243-262. [7] R O.Elliott and A.C.Larson,Delta-Prime Plutonium, Chapter XXIV in: The Metal Plutonium, eds.: A.S.Cof.finberry '~ndW.N.Miner(The Universityof Chicago Press, Chicago, 1961) pp. 265-280. [8] A.E.Hall,Plutonium-aluminumsolid solubility and diffusion studies, Nucl. Sci. Eng. 8 (1959) 283-288. [9 ] P.R.Roy, Determination of Ol-aluminumsolid solubility limits in the aluminum-uraniumand aluminum-plutonium systems, J. Nucl. Mater. 11 (1) (1964) 59-66. [101 D.Calaiset al., Diffusionof plutonium in the solid state, in: Plutonium 1965, eds.: A.E.Kay and M.B.Waldron (Chapman and Hall, London, 1967). [ 11] O.J.C.Runnalls, The crystal structures of some intermetallic compounds of plutonium, Can. J. Chem. 34 (1956) 133-145. [ 12] F.H.Ellinger,A reviewof the hatermetalliccompounds of plutonium, Chapter XXV in: The Metal Plutonium, eds.: A.S.Coffinberryand W.N.Miner(The Universityof Chicago Press, Chicago, 1961) pp. 281-308. [ 13] J.Singer, Los Alamos ScientificLaboratory, unpublished data. [ 14] A.C.Larson, D.T.Cromer and C.K.Stambaugh,The crystal structure of PnAI3, Acta Cryst. 10 (1957) 443-446. [ 15] S.T.Konobeevsky,Equilibrium diagrams of certain systems of plutonium, Session on the PeacefulUses of Atomic Energy, Section on ChemicalSciences, Iii (USSR Academy of Sciences, Moscow, 1955) pp. 3623"/4. [ 16] P.G.Mardonet al., The plutonium-iron system, J. Inst. Met. 86 (1957) 166-171. [17] F.W.Schonfeld,Plutonium phase diagrams studied at Los Alamos,Chapter XXli in: The Metal Plutonium, eds.: A.S.Coffinberryand W.N.Miner(The University of Chicago Press,Chicago, 1961) p. 240-254. [ 18] C.C.Land, in: Quarterly Status Report on Plutonium Reactor Fuel Development for Period Ending February 20, 1964, USAEC Report LAMS-3057 (Los Alamos Scientific Laboratory, March 25, 1964) p. 13.
S.H.Kittel et al., Plutonium and plutonium alloys
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$.H.Kittel et al., Plutonium and plutonium alloys [171] Od.C.Runnels, Plutonium fuel program in Canada, Proc. of the Conference on Plutonium as a Power Reactor Fuel, USAEC Report HW-75007, (Pacific Northwest Laboratory, December 1962). [ 172] C,H.Bloomster, Casting aluminum-plutonium alloys, USAEC Report HW-63166 (Pacific Northwest Labor~tory, March 21, 1960). [ 173 ] M.B.Freshley, Plutonium spike fuel elements for the PCTR - P a r t I - The Mark I-G, USAEC Report HWo 69200 Pt 1 (Pacific Nortltwest Laboratory, Match 1961). [174] P.K.Koler, Pneumatic injection casting of aluminumplutonmm fuel elements, USAEC Report 1tW-69204 (Pacifk; Northwest Laboratory, April 1961). [175] J.B.Burnham, Fabrication ofaluminum-l.8 w/o plutonium PCTR loading, USAEC Report HW-62821 (Pacific Northwest Laboratory, November 11, 1959). [ 176] W.J.Bailey, C.H.Bloomster, Y.B,Katayama, and W.T.Ross, Fabrication of aluminum-plutonium alloy fuel ele.rnents by coextrusion, USAEC Report HW63151 (Pacific Northwest Laboratory, December 1, 1959). [177] R.L.Lesser and J,E.Ayer, The feasibility of centrifugal casting for manufacturing Masurea elements, USAEC Report ANL-6876 (Argonne National Laboratory, May 1964). [ 178] R.L.Le.,~ser,private communication with J.E.Ayer, (June 23, 1967). [ 179] L.R.Kelman, H.V.Rhude, J.G.Schnizlein, and H.Savage, Metallic plutonium alloys for fast critical experiments, in: Plutonium 1965, ist Edition (Chapman and Hall, London, 1967) pp. 510-524. [180] D.F.Fis~her and J.G.Schnizlein Jr., Uranium-plutonium alloy ignition studies, Chemical Engineering Division Semi-a~nual Report, January-June 1964, USAEC Report ANL-6900 (Argonne National Laboratory). [ 181 ] A.B.Schuek et al., The development of a design and fabrication method for plutonium-bearing zero-power reactor fuel elements, USAEC Report ANL-7313 (Argonne National Laboratory, to be published). [ 182] C.M.Walter and J.A.Lahti, Compatibility of U'Pu-Fz fuel alloys with potential cladding materials, Nuclear Applications, VoL 2 (1966) 308-319. [183] C.M.Walter, J.A.Lahti, and L.R.Kelman, Compatibility of commercial cladding alloys with improved metallic fast rea,'tor fuels, Trans. Am. Nucl. Soc. 8 (1966) 348-349. [ 184] H.Savage, Argonne National Laboratory, to be publish,~d. [185] J,H.Kittel and L.R.Kelman, Effects of irradiation on some uranium-plutonium alloys, USAEC Report ANL5706 (Argonne National Laboratory, June 1958). [ 186] W.N.Beck et al., The irradiation behavior of highburnup uramum-plutonium alloy prototype fuel elements, USAEC Report ANL-7388 (Argonne National Laboratory, in preparation). [ 188] W.N.Be:k et al., Irradiations of U-20 Pu-I 0 Fs alloy
439
fuel rods, USAEC Report ANL-6750 (Argonne National Laboratory, February 1970). [ 1891 W.N.Beck et al., Irradiation behavior of plutonium alloy fuels for fast reactors, Third International Conferertce on plutonium, London (November 22-- 26. 1965). [ 190 I R.S.Barnes, A theory of swelling and gas release for reactor materials, J. Nucl. Mater. ! 1 (1864) 1 3 : i 148~ [ 191 ] W.N.Beck et al., Irradiation performance of fast reactor uranium-plutonium metal fuels, AIME Nuclear Metallurgy Symposium, Phoenix, Arizona (October 4-6. 1967). [192] W.N.Beck et al., Performance of advanced U-Pu-Zr alloy fuel elements under fast reactor conditions, Trans. Am. Nucl. Soc. 10(1967) 106. 1193] M.B.Waldron et al., Plutonium technology for fast reactors, Proc. Second International Conference on the Peaceful Uses of Atomic Energy 6 (1958) 690-696 [ 194] B.R.T.Frost et al., Research on the fabrication, properties, and i~radiation behavior of plutoniam fuels for the U.K. Reactor Programme, USAEC Report HW75007 (Pacific Northwest Laboratory, 15.1 - i 5. i 7, 1967). [ 195] J.P.Mustelier, Quelques r~sultats d'irradiation sur les combustibles envisag6s pour Rapsodie, New N.aclear Materials Including Non-Metallic Fuels, !i. IAEA (1963) 163-183. [ 196] K.F.Smith and L.R.Kelman, Irradiation of cast uranium-plutonium base alloys, USAEC Report ANL5677 (May 1957). [ 197] T.I.Jones, The irradiation of aluminum-plutonium alloys in zirealoy-2 sheathing, AECL-1589 (Atomi.: Energy of Canada Limited, 1962). [ 198] R.Carlander et at., Postirradiation examination of EBR-I Core IV prototype fuel rods, USAEC Report ANL-6670 (Argonne NatiGnal Laboratory, September 1963). [ 199] M.D.Freshley et al., PRTR fuel element experience, Trans. Am. Nucl. Soc. 7 (1964) 388-389. [200] R.K.Koler et al., Irradiation testing of injection-casl AI/Pu/Ni alloys fuel rods, Trans. Am. Nucl. Soc 6 (1963) 159. [ 201 ] J.A.Horak and H.V.Rhude, Irradiation growth of zirconium-plutonium alloys, J. Nucl. Mater. 3 (1961) 111-112. Selected 'reading list (1) F.H.Ellinger, W.N.Miner, D.R.O'Boyle, and F.W.Schonfeld, Constitution of plutonium alloys, USAEC Report LA3870 (Los Alamos Scientific Laboratory, 1968). (2) O.J.Wick (ed.), Ph.,t~nium Handbook (Gordon and Brcuch, New York, 1967). (3) H.Blank, G.Brossman, and M.Kemmerich, Zwei- und Mehrstoffsysteme mit Plutonium, Tell 1. Pu-Ag his Pu-Su. Report KFK-105, Kernforschungszentmm, Karlsn~he ~June 1962);
440
S,H.KitteletaL, Plutonium and plutonium alloys
($) Er.GriSotkW.H.B~Lord and R.D.Fowler (ecls.),Plutonium 1960 (Cleaver-flume Pgeu, London, 196D. ' (6) A+.Kayand M!B.mimon (ods.)~mtonium 1965 (Chapmln-Hnn' London,+1967)( (7) AEC Reactor Handbook on Maleria|+, Second Edilion, Chapters I and 11 (1960).
Northwest Laboratory, September 1965).
PLIJTONIUM ANDPLUTONI'JMALLOYSAS NUCLEAR FUEL MATERIALS* 3.H.KITTEL, J. E. AYER, W. N. BECK, M. B. BRODSKY,D. R. O’BOYLE,and S. T. ZEGLER Argonne hlational Laboratory, Argonne, Illinois, USA
F. H. ELLINGER, W. N. MINER, and F. W. SCHONFELD Los Alamos Scientific Laboratu.;
Los.4 Iamos. New Mexico, USA
R. D. NELSON
FncificNorthwest Laboratorv.
Richland. Washington, USA
Received28 August1970
1. Introduction The second edition of the AEC Reactor Materials Handbook (RMH-2)presented in Chapter 11 an excellent summary of the early history of plutonium. The health hazards of handling and staring plutonium are also discussed in detail in Chapters 1 and 11 of RMH-2and will not be repeated here. Interest in plutonium, its alloys, and its compounds has increased at an accelerating rate in the intervening decade since preparation of RMH-2.Furthermore, it is clear that interest in plutonium fuels will continue unabated for at least the next decade. The widespread interest in plutonium fuels is due primarily to the
emergence of the fast breeder reactor as the principal long-range development objective of the civilian reactor programs of the United Statzs and of the other major nuclear powers. Aside from the technical importance of plutonium, the metal witi always intrigue metallurgists, and others interested in materials behavior, because of its many strange properties. Tc mention some of its more interesting properties, it is the only man-made element being used routinely in tonnage quantities, in the sense that “man-made” means that man must * Chapter2 of the projectedthirdeditionof the U.S.A.E.C. ReactorMaterials Handbook.
provide the proper conditions for nature to create plutonium from uranium; it undergoes an ugprece& dented number of phase transformations between room temperature and its relatively low melting point; it has a negative coefficient of expansion in two of its h&-temperature crystallographic forms. This article summarizes present knowledge on plutonium and its alloys. The material in this chapter is in many respects an updating of Chapter 11 in RMH-2. However, those parts of Chapter I 1 in RMH-2 that are still applicable without revision have not been repeated. The reader should, if possible, read that chapter as well as this article to be more completely informed on important aspects of plutonium and its alloys.
2. Phase relationships and crystal structures 2.1. rntroc!uction
Information is availablein the literature on the phase relationships and crystal structures of approximately 65 binary and 17 ternary systems of plutonium with other metals. Space limitations prevent even a limited presentation and discussion of all these alloy systems. The piutonium alloys discussed, therefore, have been restricted to those alloy systems judged to be of greatest present
374
S.H.Kittel et al., Plutonium and plutonium alloys
interest to those engaged in the development of reactor fuel elements. The alloy systems discussed here are also limited to those that are normally in the solid state at ordinary reactor operating temperatures. The phase relationships of plutonium with nonmetallic elements such as carbon and oxygen are not discussed herein. The information given is mainly in the form of constitutional diagrams and crystal structure tables. Only brief descriptions accompany the diagra~ns. In general, these descriptions are intended to document information sources, point out any significant differences that may exist between different versions of the diagrams, and clarify certain details of the phase relationships that are known but may not be readily apparent from the diagrams. Most of the diagrams are composites based on the results of more than one group of investigators. All binary systems in thiis chapter have been drawn with Pu as the base, i.e., at the left, and compositions are given in atomic percent (a/o). Standard nomenclature has been retained for the terminal phases; Greek letters are used to designate intermediate phases in order of increasing content of the nonplutonium alloying elements. 2.2. Bina~ systems
2.2.1. Plutonium-aluminum The phase diagram shown in fig. 1 is based on the thermal, microstructural, and X-ray data contained in refs. [ 1-5]. Most of the solid-state phase relationships were identified by Moeller and Schonfeld [ 1 ] and by Waldron et al. [2], but they did not obtain data adequate to locate the solidus and liquidus boundaries accurately. The results reported by Bochvar et al. [3] are in agreement with the diagram shown here, with five exceptions: (1) eutactoid decomposition of 5 at 175°C; (2) temperatures of 530 and "-'540°C, respectively, for the PuAl and Pu3Al peritectoid horizontals; (3) a eutectic temperature of 635 °C; (4) some indicated solubility of A1 in the 3' and/3 phases; and (5) absence of phase transformations in PuAl 3 and PuAl4. ltigh-pressure work [6] supports the conclusion that/i does not decompose eutectoidally, and other results [7] show that less than 0.25 a/o Al is soluble in 6'. Hall [8] has suggested that the solid solubility of Pu in Al is approximately 0.26 w/o (0.03 a/o) at 600°C, whereas Roy [9] has
1600
. . . . .
--7-
,:e'"xt
i400 1200 I000 800
I-
600 |'
~."~,A
*
I r~
V-_-'-I
', I
~°
I
!
_4
~',..
;
z ~AI
4OO
200 -4
0
0
i
~14b lI
I0
~J
O.
20
I i
!
! 4P0 I
!
30 40 50 60 70 80 ATOMIC PERCENT ALUMINUM
90
J
I00
Fig. 1. Plutonium-aluminum phase diagram. (Submitted by LASL July 1, 1967.)
reported a maximum solubility of 0.05 w/o (0.0056 a/o) at 650°C. Calais et al. [ 10] have confirmed the result of Roy. In phase equilibria studies, Runnalls [5J has observed a phase transformation in PuAI 4 and several polymorphic transformations in PuAI 3, and has provided crysta~ographic data. Runnalls [11 ], Ellinger [12], Singer [13] and Larson et al. [ 14] have also provided crygtallographic data on the iniermediate eonipounds (see table 1). 2.2.2. Plutonium-iron Phase diagrams for this system have been proposed by Konobeevsky [ 15 ], Mardon et al. [ 16] and Schonfeld [ 17]. In addition, the phase relationships in the 5'Pu region have been studied [7], liquidus points for alloys containing between 15 and 30 a/o Fe have been determined [18] and Avivi [19] has suggested minor modifications to the published diagrams in the Fe-rich region between Pu2Fe and Fe. In general, the results of the various investigators differ only in details. Konobeevsky did not report the inverse peritectie decomposition of the ePu solid solution, as observed by Mardon et al. and confirmed by Elliott and Larson [7]. Mardon et al. placed the Pu-Pu6Fe e'atectic temperature at 413°C, rather than at 410°C, the eutectic temperature tbund by Konobeevsky and Schonfeld. Also, Mardon et al. found somewhat higher solubilities of Fe iv : and ~1~ (~ 2.5 and 1.5 a/o) than did Elliott at,:, ~,rson
S.H. Kittel et al., Plutonium and plutonium alloys
375
Table 1 Crystal structure data for plutonium-aluminum alloys. Phase
Pu3AI
Strutture type
Symmetry
SrPbs
tetragonal
Space group a P4/mmm
cubic
Unit cell dimension, (A) b c 4.499 4.499 4.500
4.536 4.538 .
cubic
PuAI 77 PuA!2 0
PuAI3
PuMa K 0t-PuAl4 ~-PuAI4
Cu2Mg cubic
PuAI3
UA14
I... Fd3m
hexagonal
P63]mmc
cubic (3H) hexagonal (6H) rhombohedral (9HB) rhombohedral (9H~)
Pm3m P63/mmc R3M
orthorhomblc
Imma
orthorhombic orthothombic
R3M
lmma lmma
Formula units per unit cell
.
.
.
.
.
.
Ref.
13.45 13.45
[ 3l 1121 [41
1
.
.
.
.
.
.
.
.
.
10.76 10.769 7.831 7.840 (Pu-rich) 7.836 (Al-rich) 7.874 7.838 (Pu-rich) 7.848 (Al-tieh) 7.833
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
29
10.25 10.253
[ 3] 14]
8
8.09
Ill] 131 131
.
.
.
.
.
14.40 14.427 14.47
6.08 6.084 6.10 4.262 6.083 7.879; = 45.94 ° 7.901 ; ot = 45.81 °
.
.
.
.
.
.
.
.
.
.
13.66 13.71a
4.41 4.396 4.396
6.29 6.266 6.266
13.79 ~.';0~ t3..~'~: .
.
.
141 1121
S.095
[12] 151
.
.
.
.
.
.
.
.
.
.
6.604 6.643 6.657
Illl 13} 1141 i5] [51 151
6.634
15]
6.8
14.410
6.26 6.262
8.06
.
6
4.42 4.387
(> 2 and 9.6 a/o). The temperature of the peritectic formation o f Pu6Fe has been reported variously, as 430°C by Konobeevsky, 428°C by Mardon et al., and 4250C by Miner [20]. Avivi has reported the existence of a hexagonal modification of PuFe 2 between 760 and 1020°C and has provided solubility data with respect to Pu ~ ~/Fe and Fe in PuFe 2. The diagram shown in fig. 2 is a composite based on the results of the various investigators. The crystal structure data shown in table 2 have been taken from references [11, 12, 15, 16, 19].
X-ray density (g/cma)
[lll 4
.
6.02 6.11
[31 [131 151 [51
5.680 5.680 .
.
.
.
.
.
.
.
.
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.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
2.2.3. Plutonium-nickel Complete phase diagrams for tiffs system have been published [ 15, 21 ] and the effect of Ni additions on the phase equilibria associated with 5'Pu has been reported [7 ]. The diagram of Konobeevsky [ 15 ] is in general agreement with that of Wensda and Whytc [21 ], except that it did not include the intermediate phase Pu2Nil7. The diagram given in fig. 3 is based on refs. [7 and 21]. There are two eutectics: one at 12.5 a/o Ni and 465°C, the other at 92 a/o Ni and 1210°C. ePu dissolves a maximum of 4.3 a/o Ni at
$.H.Kittel et aL, Plutonium and plutonium alloys
376
Table 2 Crystal structure data for plutonium.iron alloys. Structure type
Symmetry
Pu6Fe
UeMn
tetsagonal
PuFe 2
Cu2Mg cubic
Phase
Space group
Unit cell dimensions, (,~) b c
a
14/mcm
10.404 10.403 10,405 7.150 (preparation '~'3 7.190 (preparation "b") 7.191 7.178 7.189 7,184 (Pu~ich) 7.189
Fd3M
n
(cubic)
hexagonal
PuF~
5,355 5.347 5.349
Formula units per unit cell
X-ray density (g/cm~)
ReL
4
17.07 17.10
[121 [15] [16]
12.74
[lll
12,53
[I11
12.53 12.59
[12] [15] [16] [16]
8
[19]
5.64
18.37
[19]
11
(hexagonal)
450°C. The solubility of Ni in the other Pu allotropes is very restricted. The maximum solubility of Pu in Ni is about 1.8 a/o Pu at 1210°C. Crystal structure data have been determined for all six of the intermediate phases and are given in table 3.
from the combined results of Bochvar et al. [3], Schonfeld [17] and Poole et al. [25]. The B-Th solid solution field described by Bochvar et al. has not been reported by Schonfeld or Poole etal., however, and thus is not shown. The composition of the single Pu-Th intermediate phase, ~', (see table 4) in the system has been bracketed between 30 and 33 a/o Th [25,26]. Under equilibrium conditions, ~"is fon~aed
2.2.4. Plutonium-thorium The phase diagram shown in fig. 4 was constructed
°6o0F - - T i ' ; ,~,--V--T --- F I 4BO,'-~'-~:Y_ - - ~
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l 200
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20
30 40 ATOMIC
50 60 PERCENT
70 IRON
i
80
t /
90
I00
Fig. 2. Plutonium-ironphase diagram. (Submitted by LASL July 1, 1967.)
0
I0
20
30 40 60 60 TO 80 ATOMIC PERCENT NICKEL
90
I00
Fig. 3. Plutonium-nickelphase diagram.(Redrawn from tel [21].)
377
S.H.Kittel et al., Plutonium and plutonium alloys
Table 3 Cryst',d structure data for plutonium-nickel alloys. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Phase .
.
.
.
.
Structure type .
.
.
.
.
.
.
.
.
.
.
.
.
.
Symmetry
Space group
Unit cell dimensior, s, (fl~) b c
a .
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
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.
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.
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.
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.
.
.
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.
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.
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.
.
.
.
.
.
.
.
.
.
.
.
.
10.21
.
.
.
.
.
.
.
Formula units per unit cell .
.
.
.
.
.
.
.
.
.
.
.
Ref.
4
,12.9
[ 22]
13.1
I 1i l l 121
.
.
.
.
.
.
.
PuNi
TII
orthorhombic
Cmem
3.59
PuNi2 r/
Cu2Mg
face-centered cubic
Fd3m
7.16 7.141 ~Pu-fich) 7.115 (Ni-rich) 7.14
8
3
! 1.8
[ 231
6
11.3
1241
t 151 [151
PuNi 3 0
PuNi 3
rhombohedrai
R3m
8.6 i 5; or: 33°44 '
PuNi4 t
PuNi 4
monoclinic
C 2/m
4.87
8.46
100 ° + 0,1
Pu2Nil7 h
CaZn s
P6/mmm
hexagonal
Th2Nil7 hexagonal
P63/mmc
10.27
1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PuNis
4.22
X-ray density (g/cm 3 )
4.875 4.872 (Pu-rich) 4.861 (Ni-rich)
3.970 3.980
8.30 8.29
8.00 8.01
by the peritectie reaction, L + a T h * ~" Under normal conditions, however, the peritectic reaction is suppressed on cooling, and ~"is formed by a nonequilibrium peritectoid reaction subsequent to eutectic solidification. 2.2.5. Plutonium-uranium C o m p l e t e phase diagrams for this system have been reported [3, 2 7 28]. All are in agreement as to the general f o r m o f the diagram b u t some o f the phase boundaries reported b y Bochvar et al. [3] are quite
1
10.8
3.982
[111 [ 12] t l2l
'
10.3
[ 11 ] 1121
different from the corresponding boundaries determined by Ellinger et al. [27] and b y Waldrou [28 ]. The diagram shown in fig. 5 is based on the thermal, dilatometric, X-ray and microstructural studies of Ellinger et al. and of Waldron. A major disagreement concerns the ~-Pu field, which Bochvar found to extend from about 4 a/o U in the vicinity of 120°C to roughly 17 a/o U at about 300°C. The data of Ellinger et al., on tile other hand, show the ~-Pu field extending from essentially 0 a/o U at 125°C t~ about 2 a/o U at 280°C. These latter result:; appear
Table 4 Crystal structure data for plutonium-thorium alioys. Phase
Structure type
Symmetry
Space group
.............................
orthorhombic (?)
a 9.820 7.90
Unit cell dimensions, ~A) b c
Formula u nits per unit ceil
X.ray density (g/'cma ,~
Ref.
' ...............................................................
8.164 8.43
6.681 9.79
6 8
[ 25 ] 13l
S.H.Kittel et al., Plutonium and plutonium alloys
378
eoc ..... 700
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...... i-
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s
:,
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~. . . . . . .
~
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........
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Y+g
200 ~_
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'
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.......~~--~--~ ....
=.,,v
s*I 300r
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L.;-T.
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PERCENt
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-
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1
3
.......
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-aoo~__--.J~;~_J-----~-------- -
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~oo
THORIUM
i
='-, I; ! I0
~
\~
_-'~_
i ,~'5 "t
--
-
-
i_ ~.. . ..... c ........
I ~ I . - L . . . . . [~. _ . _ _ L _ _ 20 30 40 50 60 1'0 ATOMIC PERCENT URANIUM
I 80
90
I00
Fig. 4. Plu~:onium-thorium phase diagram. (Submitted by LASL July 1, 1967.)
Fig. 5. Plutonium-uranium phase diagram. (Submitted by LASL July 1, 1967.)
to be confirmed by the work of Waldron. Also, Bochvar et al. found the ~"field to extend to higher U contents from about 6 a/o U at 120°C, whereas Ellinger et al. found the corresponding point to be at about 25 a/o U and 278°C. There is better agreement among the three groups of investigators concerning the U-rid-, portion of the diagram. Work by Berndt [29] places the ~U/(aU + ~')boundary at about 85 a/o U at 400°C, which agrees reasonably well with the results of Ellinger et al. and Waldron as well as with revised work of Bochvar et al. as mentioned by Schonfeld [30]. Also, the solubility data of Calais et al. [10] between 410 and 546°C fall within "-1 a/o of the boundaries established by Ellinger et al. and
Waldron for the ~ + aU field. Crystal structure data are given in table 5. 2.2.6. Plutonium-zirconium Complete diagrams, which differ in several details, have been published by 8ochvar et al. [3] and Marples [31 ], additional work on Pu-lich alloys has been rei~orted by Ellinger [32] and Kutaitsev et al. [33 ], alloys containing between 30 and 60 a/o Pu have been studied by Robillard [34] and solubility data for Zr in liquid Pu between 700 and 950°C have been obtained by Bowersox and Leary [35 ]. The diagram given in fig. 6 is largely that of Marples but has been modified to show the ~ phase ("Pul9Zr) as
Table 5 Crystal structure data for plutonium-uranium alloys. Phase
Structure type
Symmetry
Space group a
Pu-U ~-
cubic (at room temp.)
Pu-U r~
tetragonal (?)
P...
Unit cell dimensions, (A) b c
10.692 (35 a/o U) 10.651 (70 a/o U) 10.57
10.76
10.73
10.44
Formula units per unit cell
X-ray density (g/cm 3)
Ref.
58 atoms
18.95
[27]
52 atoms 56 atoms
17.2
[27] [3l
S.H.Kittel et al,, Plutonium and phttonium alloys
2°°°I--~----:--- .......r....
o * "'
ix:
i
|
i
/
i
15OOl-"/-~ _ l
I,
!
i
i
~
1 I.
r ........
~
i
,
;J"
I
V"~'F/
~
4~
! , ....
i
i ~;..7/i
,
, ~-~ ~-~
,
.~-'L.a-z,/!
/ i I ,oooi.---4 ~-"
~
:.
i
' -I:I
~-
-~ ..... q ..... l
I-
-
.fi
! I ~ .... ~-.
a tetragonal unit cell [36]. Although K is believed to correspond stoiehiometrically to about PuZr3, its structure is based on the hexagonal A1B2 type. The maximum solubility of Pu in otZr was found to be at about 16 a/o Pu at 618°C and ! 1 a/o at 150°(" [3]. Crystal structure data are given in table 6.
-T---~ ,I
i./"
]
..., -" I ;..........
/
/
2.3. Ternary systems 2.3.1. Plutonium-iron-uranium Boucher et al. [37] have studied mainly two compositions, 74 U-25Pu-1 Fe and 73.5 U-25 Pu-l.5 Fe (in w/o). The cast alloys were composed predominantly of the Pu-U ~"phase togethe7 with U6 Fe and Pu6 Fe. The latter compounds tended to form (U, Pu)6 Fe on homogenization of the alloys. Dilatometric examination of these alloys revealed, respectively, transformations at 595 ° -+-3°C and 590 ° +--3°C, and fusion points at 705 ° +- 5°C and 680 ° +--5°C. Treating the alloys above the transformation temperatures resulted in the formation and retention of some Pu-U r/phase. Treating the alloys below the transformation temperatures resulted in the formation of some aU. Ellinger [ 12 ] reported that continuous solid solutions exist between Pu6Fe and U6F,z and between PuFe 2 and UFe 2. Also, he gives lattice parameter versus composition data.
i i ~ ..... 1
750
E--L-,,4, 250
--"
v
I0
;~0
30
ATOMIC
50 PERCENT
40
60 70 80 ZIRCONIUM
90
379
I00
Fig. 6. Plutonium-zirconium phase diagram. (Submitted by LASL Aug. 1, 1967.)
found by Ellinger and the solubility data ~ " Bowersox and Leafy. The solidus curve de mined by Boehvar et al. is consistently higher than th~. of Marples, being as much as 100°C higher at 50 a/o Zr. There is better agreement between their liquidus curves. ~', which has a complex crystal structure, was found to exist between "--3 and 5 a/o Zr and to decompose to ~ and O at ~220°C, although under conventional cooling it is stated that it is readily supercooled and may exist as a metastable phase at room tem~rature [33]. The O phase was reported to be formed at about 14 a/o Zr (Pu6Zr) and 350°C, and to have a homogeneity range from 12.1 to 20.6 a/o Zr [3]. The X-ray powder pattern for the O phase at 21 a[o Zr has been indexed on the basis of
2.3.2. Hutonium-fissium (or fizziurn)-uranium Phase studies in the Pu-Fs-U an~ l?u-.Fz-U quasiternary alloy systemsby means ot metallography and X-ray diffraction have been reported by Kruger I38, 39]. The source of interest in these alloys is given in sect. 7. Alloys investigated contained 20 w/o Pu and either 5, 10 or 15 w/o Fs or Fz*. The phases found in equilibrium after isothermal annealing are shown in the
Table 6 Crystal structura data for plutonium-zirconium alloys.
Phase
Structure
Symmetry
Space group
type
Pu4Zr
a
tetragonal
P4/ncc
hexagonal
P6/mmm
Unit cell dimensions, (.~) b
10.893
16.889
5.060 5.055
3.119 3.123
Formula units per unit cell
X-ray density (g/cm 3 )
Ref.
16
15.76
1361
0
P.z~
PuZr3 g
AIB2
131 1311
380
S.H.Kittel
~ooo~-, 900~-
,
,
,
~
. . . .
~
~
. . . .
o
•
l
•
r u
[ o q),3~ o & u ÷ oo 600 - - - - ~ - - e ' - , . - - o c . , -UeO h;-u+~-U÷oC • - . ~ 7 ~ .o 1 ,~"-~o- • cr"~ ~-'" ' - - - - ~ - - -
soo~+#-~8 ~ I o I ,-u.,-r'÷t
i.ooIil
o
•
o
,
1
.o
o Too u + B ~ . ~ \ ~ r - u + ~
400
, ,
L+),-U
oootr;u+~'~' "
=
~-,
e t al,, P l u t o n i u m
• • , .r-u+r+C ~--'/--
"~-~-~r~-V~-oo
-e\ \
ONormol flssium olloyg 200~- oFissium o l l o y , . . i l h odditionol Zr 0
5 no 15 WEIGHT PERCENT FnssIUM
20
Fig. 7. lsopleth showing equilibrium phases and transformations in the pseudo-ternary plutonium-fissium-uranium system at 20 w/o plutonium. (Reprinted from ref. 138] .) isopleth presented in fig. 7. The nomenclature used for the aU, ~U, 7U, ~'(U-Pu), and 17(U-Pu) phases is the same as that adopted by Ellinger et al. [27] for phases in the U-Pu system. Six other phases occur in the system: Alpha-prime (a'): A metastable modification of aU that is also referred to as "distorted alpha". Gamma-naught (`/0): A tetragonal modification of the `/phase having a c/a ratio of approximately 0.98. Gamma-prime (`/'): A tetragonal phase based on the binary U2Mo phase but which may take Pu in solution. Theta (O): A phase containing U, Pu and Pd that is present between room temperature and the solidus temperature in all alloys studied. Crystal structure type not identified.
* The term fissium (Fs) denotes the equilibrium concentration of second long period elements (Mo, To, Ru, Rh, Pd) that build up as fission products in the fuel during irradiation and which are not removed during the pyrometallurgical fuel reprocessing scheme presently in use at EBR-II. Fizzium (Fz) denotes the same group of solid fission products with the addition of Zr in approximately the same amount as Ru. The nominal composition of U-20 w/o Pu-5 w/o Fs is: 20 w/o Pu, i.90 w/o Mo, 2.02 w/o Ru, 0.72 w/o Pd, and 0.28 w/o Rh, balance U (stx components) and the nominal composition of U-20 w/o Pu-5 w/o Fz is: 20 w/o Pu, 1.31 w/o Mo, 1.38 w]o Ru, 1.45 w/o Zr, 0.53 w/o Pd, and 0.26 w/o Rh, balance U (seven components).
and plutonium
alloys
U2Ru: A monoclinic phase found in the Fs alloys. ZrRu: A CsCl-type phase found only in the Fz alloys. In addition to the phases shown in fig.7, allalloys contained the O phase at all temperatures below the solidus.U 2 R u was found in all Fs alloys and increased in stabilitywith an increasein Fs content. In all Fz alloys ZrRu was stablebetween room temperature and the solidus. 2.3.3. Plutonium-molybdenum-uranium Constitutional studies of this ternary alloy system, mainly by Mardon et al. [40] have been directed toward determining the boundaries of the `/-U solid solution region and the phase equilibria associated with its decomposition. Alloys containing 35 to 100 a/o U solidify either as the `/-U solid solution or as a mixture of 7-U and Mo. With decreasing temperatures the 7-13 region expands toward increasing Pu contents. A typical isothermal section (for 900°C) is shown in fig. 8. At about 630°C the 7-U solid solution splits into a U-rich region and a Pu-rich region, termed 3'] and "/2 U, respectively. Below about 700°C, where the Pu-U phases, 77 and ~', first appear, the ternary equilibria become comple, and have not been fully worked out. Six 4-phase invariant reactions occur between 610°C and 525°C. The `/1-U phase decomposes eutectoidally, `/1 -+ aU + `/' + ~, with the
u/
7
v
I0
v
20
v
30
/
/ v
4O
,,
50
\
,,\
60
ATOMIG PERGENT MOL.YBOENUM
Fig. 8. Plutonium-molybdenum-uranium 900°C partial isothermal section. (Redrawn from tel [40] .)
S.H.K~ttel et aL, Plutonium and plutonium alloys
381
eutectoid point lying in ~he neighborhood of 10 to 14 a/o Mo and 17 to 20 a/o Pu. This reaction has been observed to be very sluggish and to proceed in two stages [41]. Alloys quenched from the 3' phase show retained 3'1 and 72 phases plus the metastable phases designated 3'0 and oq. Anselin [41] has determined the lattice parameter-composition relationships of the 3' phase preserved to room temperature by quenching from 900°C. He also reported that the 3'0 phase has a tetragonally-deformed 3'-U structure, but the identity of the true unit cell is uncertain. The phase labelled (X1 has a distorted 0~-Utype of structure. Transformations in homogenized and as-cast alloys containing 20 w/o Pu and 8, 10, and 12 w/o Mo, and 30 w/o Pu and 10 w/o Mo were studied by Boucher [42].
peritectoid reaction/~U + ?U -~ r/at 710°C and the other two 3-phase regions remain in the ternary. The otTh + 7U + L three-pt'.ase region continues moving toward the Pu comer as the temperature decreases. The ~"phase is formed by a peritecto~d invariant reaction at 610°C. The phase relationships in the Pu corner of the system are complex and have not been experimentally def'med. The isopleth given as fig. 9 is a section through the Pu-Th-U system at 10 a/o Pu and shows the effect of U in decreasing the liquidus and solidus temperatures. As shown in the figure, an increase in U from 0 to 2 a/o reduces the solidus temperature from about 1300 to 905°C. Transformation temperatures indicated in the figure were determined by DTA and dilatometric analysis.
2.3.4. Plutonium-thorium-uranium Phase studies in the Pu-Th-U system have been reported by Blumenthal et al. [43 ]. Metallography, differential thermal analysis, and X-ray diffraction were used to establish solid-state phase transformations and to outline phase regions principally in the Th corner of the system. The L 1 + L 2 miscibility gap is believed to be restricted along the Th-U side of the ternary system below which/3Th is the first phase to crystallize. In the central region of the system o~This the first phase to crystallize from the melt. 7U(ePu) i.'~,the first phase to form from the liquid along the U-Pu side of the system, except for a small region near the Pu corner below 630°C where Pu2Th is the first phase to freeze. In constructing a liquidus projection, Blumenthal [43] assumed that otTh forms peritectically in the Th-Pu system ~ T h + L ~ o~That approximately 1400°C) and that the aTh +/~Th + L three-phase region crosses the Th corner of the system with decreasing temperature to exit along the Th-U side at 1265°C. Below 1086°C the offh + 3'U + L three-phase region enters the ternary system from the Th-U binary and moves toward the Th-Pu side with decreasing temperature. Below 760°C the aTh + flU + + 3'U three-phase region moves out from the Th-U binary and peritectoidally forms r/(U-Pu) at 714°C by the invariant reaction aTh + flU + 7U ~ rt(U-Pu). Of the three 3-phase regions formed at 714°C (aTh + ~U + rt, aTh + r / + 7U,/~U + 7U + rT), the flU + 3,U + rt region exits along the U-Pu side as the
2.3.5. Plutonium-titanium-uranium Alloys of interest as fast reactor fuels contain from 10 to 20 w/o Pu and from 7 to 14 w/o Ti, remainder U. Most phase studies in the ternary system have been restricted to alloys which contain more than
t60o
\1
I
I
F
I
\ o
a-TII+jg-Th'~L|
~" o -Th
-<~,ooo ~
I
'"
I ~oo
L
I
:
;
|
i
!
,
t
I
J:
!
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o-Th'I'L
i
-
i
! ----'-F-- ~ j" !
ATOMIC
!
~--~
° : ~ + L -U+L _ _ - ~ -I - - ~ - ~
!
o}~+~u+,~l . ~---'~
I a-Th+o-U
"
1
i
I
i
i
°-r~+,'-u,~-u
~---:--~" i I
~ -
_L__,,X
1
i
,',
'
II
i
|
/ T -=-
...... a-Th+o-U+~
.... t ....... ! ........ T I i i
PERCENT
i
| -i
~
........ ]
URANIUM
Fig. 9. Plutonium-thorium-uranium isopleth at I0 atomic percent plutonium. (Reprinted from ref. 143).1
I
382
S.H.Kittel et ai.. Plutonium and plutonium alloys
40 a/o U. The bcc high-temperature aUotropes of both Ti (~Ti) and Pu (elhl) form a complete series of solid solutions with bcc 7U. Similarly, in the U corner of the ternary system the bcc T phase is the first phase to freeze from the melt over a wide composition range. In the binary U-Ti system the hexagonal intermediate phase U2Ti forms by a congruent solid state reaction at 898°C (3' "~ U2Ti) [44]. U2Ti is capable of dissolving at least 17 a/o Pu in solid solution and extends sufficiently far into the ternary system as (U, Pu)2Ti to exert a strong influence on the properties and transformations of U-rich alloys. Solidus temperatures for alloys containing more than 40 a/o U, as based on binary-solidus data and the metallographic and differential thermal analysis results of Blumenthal [45] for a limited number of ternary alloys, are given in fig. 10. An increase in Ti at a constant Pu:U ratio causes a moderate increase in the solidus temperature whereas the solidus temperature of binary U-Ti alloys is strongly reduced by the addition of Pu. Pu stabilizes the 7 phase of U-Ti alloys, based on the DTA and dilatometric results [45,46]. An increase in Pu from 0 to 30 a/o at 33.3 a/o Ti stabilizes the 3' phase flora 898 to 745°C. Over the composition range 0 to 30 a/o Pu, with 33.3 a/o Ti, the ? phase is not retained by quenching. Limited me:allographic and X-ray evidence [46A] suggests that in the ternary system the single-phase
region corresponds to the hyperstoichiometric compound (U, Pu)2 Til +x. Solid state transformations along the Pu-Ti side of the ternary system are complex and have not been established. In addition to the equilibrium phases that occur in the system, a commonly observed white extraneous phase has been identified as 0-stabilized aTi [47]. 2.3.6. Plutonium-uranium-zirconium Early work on Pu-U-Zr alloys of interest as fast reactor fuels, containing 10 to 20 w/o Pu and 10 to 15 w[o Zr, was done at both Fontenay [48] and Argonne [48A]. Zr increases the solidus temperatures of alloys in the U corner of the system as shown in fig. 11, based on the work at Argonne [49, 50]. Solidus and liquidus temperatures in the Pu corner of the system have been determined by Mound Laboratory [51 ] and are shown in fig. 12. Both the solidus and the liquidus temperatures of binary U-Pu alloys are increased with the addition of Zr. As shown in fig. 12, the liquidus temperature increases more rapidly with an increase in Zr than does the solidus. The effect of the minimum point in the solidus and liquidus of binary U-Pu alloys at about 15 a/o U is shown in fig. 12 by the curvature of the ternary isotherms in the ternary system. The three binary systems show complete solid miscibility of the bcc high-temperature allotropes (~,U, ePu,/3Zr). Similarly, in the ternary system the
O
U
.o o I lOO°C
v 40¢ /
/
/
;
/
/
//
/
,'
/I
/
,~oo.c i
,
;
!
/I
~.4o o~.
\ %
IO00"C
" . .
,/ 60'
Fig. i0. Plutonium-titanium-uraniumsolidusprojection in the uranium comer of the system [45].
v
60
Fig. 11. Plutonium-uranium-zirconiumsolidusprojection in
the uranium corner of the system [49, 50].
S.H.Kittel et aL, Ph~tonium and plutonium allo),s
first phase to freeze over the entire range of compositions is the bcc 1' phase. In the U corner of the system both Pu and Zr are effective 1' stabilizers. As a result of the increase in solidus temperature in ternary alloys, the bee 3' phase is stable over a wide range of temperatures (300 to 400°C). As the temperature decreases, the 1' singlephase field moves toward the Zr-Pu binary and then pulls rapidly toward the Pu corner In the U corner of the system, invariant reactions at about 655 and 600°C have been observed [48, 49]. O'Boyle et al. [52] have suggested that these reactions are Class I1 type phase transformations: 655°C 600°C
3' +/3U ~ otU + ~'(U-Pu) aU + 3' -" cS(U-Zr) + ~'(U-eu).
In alloys annealed below the invariant reaction at 600°C, the aU + ~'(U-Pu) + 5(U-ZO phases have been identified by X-ray diffraction [48]. In addition to the ternary phases, a light-etching Zr-rich impurity phase has been identified as oxygen stabilized aZr [471.
3. Physical properties 3.1. Introduction
The second edition of the Reactor Handbook (RMH-2) presented an excellent discussion of the early history of plutonium metallurgy, and presented all of the information on the physical properties of plutonium and its alloys available up to early 1957. Most of that information had been presented at the First Geneva Conference 153], in a paper that covered many of the properties of the allotropes of pure plutonium, and presented a considerable amount of phase diagram information. Since that time, there have been four international conferences on plutonium, the proceedings of which have all been published [54-57 ]. Much additional material has appeared throughout the general literature as the properties of plutonium became interesting to chemists, metallurgists, physicists, etc., in each of the countries involved in plutonium work, i.e., the United States, United Kingdom, Soviet Union, and France. One development since that time has been the
....
383
COP4TOURS~~
SOLIDUS CONTOURS L/OUIDUS
\',,
,
\%..
\ Fig. 12. Plutonium-uranium-zirconiumsolidus and liquidus projections in the plutonium corner of lhe system. (Reprinted from ref. [511 .) routine production of high purity plutonium by electrorefining techniques [58, 59]. Surprisingly, use of the high purity metal (less than I O0 ppm tot~1 impurities) has had little effect on measurements of the properties of the metal. Lower residual electrical resistivities have been obtained (as low as 6.2/~ ~2cm), and varying transformation kinetics have been observed. But on the whole, the availability of this purer metal has not changed any of the "strange" properties of plutonium, e.g., electrical resistivity vs. temperature, allotropy, contraction of delta phase etc. (see below), The low melting temperature of pure plutonium, its large number of phase transformations, its anisotropy in the low temperature phases, and the large, 10% change in volume during the beta --, alpha transformation all work towards making pure plutonium an undesirable engineering material. It is not possible, however, to ignore the properties of unalloyed plutotuum since it is precisely those properties which ultimately limit the usefulness of particular alloy, cermet, and even ceramic fuel compositions. The alloys to be discussed are mainly of two types: those which retain the pure metal structure, and those based on U-Pu. Most of the former alloys are-in the face-centered-cubic delta phase, while the latter generally include one or more alloy additions to improve engineering properties.
S,H.Kittel et aL, Plutonium and plutonium alloys
384
Table 7 Properties of pure plutonium allotropes, Phase
Alpha
Beta
Gamma
Delta .
Delta-prime
Epsilon
Crystal structure
Monoclinic [60]
Body-centered monoclinic [60]
Face-centered orthorhombic 1621
Face-centered cubic [63]
Body-centered tetragonal
[631
Bodycentered cubic 163 ]
at 21°C
at 190°C
at 235°C
at 320°C
at 465°C
at 490°C
a = 6.183 b = 4.822 c = 10.963 = 101.79 °
a = 9.284 b = 10.463 c = 7.859 # = 92.13 °
a = 3.1587 b = 5.7682 c = 10.162
a = 46371
a = 3.327 c = 4.482
a = 3.6361
No. of atoms/unit cell
16
34
X-ray density t~'cm 3 )
19.86
17.70
17.14
15.92
16.00
16.51
Bulk expansion coefficient ( l ( l " cm/cmf~(} *
47 to 76
26 to 38
28 tO 35
- 8 t O - 33
- 50 t o - 1 0 0
20 tO 36
Magnetic susceptibility lemu/g/106) *
2.22 1671 2.38 1681
2.29 2.50
2.22 2.42
2.12 2.36
2.12 2.36
2.15 2.38
Specific heat, ('p (cal'mol°(") [ 691
8.66 at 47°(7
8.28 at 160°C
8.67 at 250°C
9.0 ~.t 377°("
24 at 473°C
8.4 at 500-600
Absolute thermoelectric power (mvl°C) 1701
+ 15.5 a t 27°61
Thermal conductivity (cal/cm-~ec ~C,~[711
0.005 at - 123°C to 0.032 at + 120~'C
Unit cell dimensions, (A)
8
4
2
2
oc
+ I0.0 at 127°(7
*9.2at227°C
+3.7at327°C
+2.3at452°C
+4.2at 527°c
0.037 at + 140~C
* Near rrAd-point of temperature range.
3.2. Unallo.w'd Plutonium Table 7 summarizes m u c h o f the data for the pure phases. A considerable a m o u n t o f detail exists for each o f the properties listed and the references shoul6! be consulted, where appropriate. In addS.lion t o the bulk thermal-expansion coefficients listed in the table, thermal expansion data are available for the unit cell dimensions for each o f the allotropes. N o a t t e m p t has been made t o choose a "best value" for the bulk expansion data because o f the large emisotropy in several o f tl~e phases, The negative
expansion o f the delta and delta-prone phases are very n o t e w o r t h y . Delta p l u t o n i u m is unique a m o n g face-centered-cubic metals in this respect, and considerable experimental and theoretical effort has been e x p e n d e d on the causes o f the p h e n o m e n o n . The various suggestions for this effect have been electronic p r o m o t i o n [72] ; special band-structure effects [73 ] ', and elimination o f traces o f covalent b o n d i n g [74]. The electrical resistivity data for all o f the phases are summarized in fig. 13 [67, 75, 7 6 ] . The negative slopes in the alpha, beta, g a m m a , and perhaps epsilon
S.H.Kittel etal., Plutonium and plutonbon alloys
,
osC(~
' ....i
I
'
I
'
t
I00~
ALPHA
K
DELTA-
ILON
DELTA-PRIME -]
l~
50 0
200
I
40(}
,
600
1
aoo
TEMPERATURE, =K
Fig, 13. Electrical resistivity o f plutonium allotropes.
phases are not understood, although a discussion has been presented based on band structure effects [77]. Much work has been directed towards the explanation of the resistivity maxima in alpha and supercooled beta plutonium. The proposed mechanisms have been atomic order-disorder, a combination of band structure effects, or antiferromagnetic ordering. The latter model is supported by thermal expansion, 700
I
600
oU
~ ...... ~
'
~
I"
L
.
° E ~ . . . ~
50U
4o0
./°
7"
, ~
.,//~
n ILl I--
'~
I/ iOt~_//~ 0
y
"
•
L_- SI'EPHENS
/° o
t
.
t
I
__ I
I
,I
I
I0
20
30
40
50
60
PRESSURE,
7O
k bars
Fig. 14. Pressure-temperature diagram for plutonium.
80
385
thermoelectric power, radiation damage, Hall effect, and magnetoresistivity measurements at low temperatures. Unfortunately no corroboration has been obtained in magnetic susceptibility, specific heat, or neutron diffraction studies [57]. The ttall coefficients near, or above room temperature, are + 3.5 and + 2.5 X 1 0 - 13 v-cm/amp-gauss for pure alpha and bets, respectively. These results led to a band picture with a nearly full 7s band and the remaining 6+ electrons in 5f or 6d bands. The pressure-temperature diagram is given in fig. 14 [78, 79]. Although the alpha-beta-liquid triple point indicated from the earlier work was not found by Liptai and Friddle, the latter workers have had some success in using high pressures and temperatures to grow usable single crystals of alpha plutonium. They find that best results are obtained near the zero-slope portion of the beta ~ alpha phase boundary, viz. at 55 kbars [80]. Preferred orientation may be introduced into alpha plutonium by rolling in the alpha phase [81 ] or by cooling through the beta -~ alpha transformation under compression [82]. In the latter approach. the (020) planes align perpendicularly to the pressing direction, which is consistent with a (201) rolling plane, [01 O] rolling direction texture found in the former [83]. In both cases, the resistivity-telnperature slopes are nearly zero, and the resistivity maximum is shifted t?om 100 K to about 130 K when measured in the [010] direction. The transformation behavior is summarized in table 8. Temperatures for the a , . 13and 13~ 1, transformations are very dependent on heating/cooling rates and on sample size. The parenthetic temperatures are for moderate heating rates, while the quoted results are from Hill's studies of transformation temperature as a function of rate of temperature change. The transformation mechanisms have been the subject of much study, and the results are summarized in table 9. Selle's measurements of internal friction have allowed a determination of the mechanisms for all of tile transformati~ms. His results which are based on a new hypothesis agree with the models most generally accepted. The retero ences should be checked to get a full bibliography for these studies. A new. interesting property of beta plutonium has been studied at Pacific No,.ttlwest Laboratories. They find that the mechanical
386
S.H.Kittel et aL, Plutonhtm and plutonnon alloys Table 8 Phase transformation data for pure plutonium.
"lran~ition
Or-+/3
~-+~
"y"+,8
6 -+6'
6' -+e
e -+liquid
Temperature of trans, on heating I°C) 164--66. It, 841
112 [85] (122-126)
184 [85] (202-213)
314-319
440-464
460-484
635-641
150
280
469
490
637
Temperature of trans, on • .o , cooling | ( ) [ 6 5 . 661 Volume change (9;-) [ 86 ! Ileat of transforma~.ion lcal/g-atom} [69. 841
91
2.4
8.9 880
146
properties of beta depend on whether it is formed from the alpha or gamma phases. Their explanation is based on stacking faults in the/3~ (beta formed from gamma) while Selle [87] suggests that the difference is due to the different mechanisms of beta formation in a ~/3 and 7 "+/3. this is discussed in greater detail in sect. 4. A property which has been extensively studied in the last few years, primarily for basic understanding but whizh has some application to engineering problems, is self-radiation damage [57, 9 4 - 9 8 ] . The effect has been studied by electrical resistivity, thermal conductivity, lattice parameter, thermoelectric power, and specific heat methods. A saturation is found at high damage levels in alpha plutonium and is thougllt to be related to the proposed magnetic transivion. Damage studies with highly enriched pu238show a decrease in resistivity after saturation for reasons not fully understood. Similar behavior has Table 9 Transformation mechanisms for plutonium. Transformation
Mechanism
o~--*~3 ~'~ 3' -" ~ ,5 -~-6 ~'~'e e -"6' 6' -+ 6 -*3" "r ~ ¢ -+~x
Shear [ 87.88] D~ffusional [89] Diffu~ional [87, 88, 90, 91 ] Diffusional [ 87, 91 ] Shear [ 871 Shear [871 Diffusional [87] Diffusional [ 87 ] Shear [87, 90, 911 Diffusionai [87, 88, 90, 91] Shear [87, 88,921 Mixed [931
6.8 152
-0.1 15
-3.0 434
-2.4 732
been observed in supercooled beta and alloy-stabilized delta. Table 10 summarizes the results. Data are available at ofl~er temperatures and also on compounds. It should be noted that some of the radiation damage is not annealed out at room temperature. Results of tracer and mechanical testing studies have been used to calculate the activation energies for self-diffusion in the ailotropes. The data, listed in table 11, are not in good agreement. However, Nelson [99] found that his results depend on the stress-.strain exponent, and Selle [87 ] surmised that his activation energies may be low. Seile has also separated the results into vacancy formation and migration contributions. Several systems have been studied for chemical diffusion coefficient determinations. Results are in table 12. 3.3. Alloys with plutonium structure Alpha: Alpha plutonium may dissolve 75 a/o neptunium and very small amounts of uranium, in general, the addition of 2 a/o uranium shrinks the lattice parameters by about 0.1 to 0.3% and has little effect on the angle,/L The thermal expansion coefficients are also changed with the expansion in the a direction increased, and in the b and c directions both decreased and made nearly equal. There is a monotonic decrease in each of the lattice parameters with neptunium additions and the density at 75 a/o Np is 20.1 g/cm 3, compared to 19.86 g/cm 3 for pure plutonium [ 103]. Additions of neptunium to alpha plutonium eliminated the maximum in the resistivity-temperature curves above 4 a/o Np and all compositions up to 50 a/o Np have a negative slope in these plots [ 104].
S.H.Kittel eta'.. Plutonium and plutonium alloys Table 10 Effect of self-radiation damage on the electrical resistivity of plutonium.
387
Table 11 Activation energies for self-diffusion of the plutonium allotropes*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Alpha Initial damage rate at 4K (u s2 em/hr) Temperature of annealing stages (K) Damage remaining at room temperature (%)
Beta
0.06 75; 150
5
0.10 ' ( 4.2; 30-180
**
Delta 0.01
Selfdiffusion
Ot
3
"f
~
aef.
20.9 23
19.4 27
21.0 31 16.7
21.2 30 23.8
1~71 l ~9 J [ 1(10. loll
50*; 150
Vacancy formatien
15.7
11.0
12.7
10.0
[87}
10
Vacancy migration
5.2
8.4
8.3
11.2
1871
* In kcal/mole * This stage is a function of cornposition of delta-stabilizer. ** Metastable beta transforms to alpha phase on heating above 180°K. Beta: This phase may be retained with zirconium or titanium additions. The phase can dissolve uranium, aluminum, and neptunium also. Neptunium additions decrease the beta lattice parameters with a larger decrease per atom percent than for the alpha phase [103]. The electrical resistivity of a 4 a/o Ti alloy was found to lie about 3 / a ~ c m above the curve for pure beta plutonium, and with a negative slope, also, No maximum was found in the resistivity-temperature curve down to ~5 K [75]. Time-temperature-transformation data have been obtained on titanium-stabilized alloys. The results are interpreted to suggest two transformation mechanisms; martensitic at low temperatures and massive at higher temperatures. The "nose" of the T-T-T curve is near 0°C, and 2.5 a/o Ti alloys begin their transformation at 20 sec near the nose [ 105 ]. A study of the effects o f pressure on the Pu-Ti phase boundaries shows no beta ~ alpha transformation above 1 a/o Ti at pressures up to 50 kbar [1061. Gamma: Very small amounts of uranium, neptunium, zinc, zirconium, and perhaps :aluminum are soluble. The phase has not been retained at room temperature and no physical property measurements exist. Delta: A large number of elements dissolve in this phase, retain the structure on cooling, and/or stabilize the phase to very low temperatures. Among these are: aluminum, americium, cerium, gallium, indium, scandium, zinc and a large number o f rare
earths. Aluminum. gallium, and zinc contract the del~: cell, while the other elements mentioned expand the unit cell. Gschneidner et al. have considered the factors which cause delta-retention and concluded that only trivalent and tetravalent metals (zinc is an exception) with a favorable size factor are delta retainers [107]. Other models such as the influence of alloying on stored elastic energy or electronegativity considerations have been proposed, and
Table 12 Chemical diffusion in plutonium [ 102]. System
Pu-Mg (Mg)
Pu-Zr (6-Pu)
Pu-U (0t-U)
Comp. (a/o Pu)
Do (cm2/sec)
Q tkcal/ mole~
0.045 0.562 1.124
1 X 104 2.45 X 10-2 1.05 X 10-- 2
35 28.32 28.30
1.686
3.6
_~..38
X 10 - 4
38.5 46.2 61.6 69.3
7,70 X 10 -e 3.56 X 10-" 8.86 X 10 -9 9.60X 10- 9
23.50 15.05 11.80 12.65
1.75 3.50 5.25 7.00 8.75 10.50 12.25 14.00 15.75
O.14X 1(I-7 O.15X 10-7 0.18X 10--7 0.28X I 0 7 C44 X 10 - 7 0.88X 10-7 1.18X !q--7 290X 1 0 - 7 2.57)'. I0- 7
13.4 13.7 14.1 15.2 16,3 17.9 If,.8 20.0 20.6
S.H.Kittel et eL, Plutonium and plutonium alloys
388
Table 13 Effects of deRa-stabilizer additions on physical properties* 1
Thermal expansion coeff. (X 106 cm/cm°C) [107,108] Residua| resistivity (u 1-1cm) [ 110] Temperature of resistivity maximum (°K) [ 110] Thermoelectric power at (uV/°K) [ 1111 Magnetic susceptibility (emu/g X 106) [ 1121 Hall coefficient at room temperature t V cm/amp gauss X 1013) [ 113]
a/o
AI
5 a/o AI
10 a/o AI
+
+ 13.4 131 100 "~ 5 2.22 2.0
7.7 122 145 "~ 5 2.40 2.8
-
6 103 190 > 5.5 2.41 3.6
* E xtrapolaled when necessary
Table 14 Summary of data on delta-stabilized Pu-dch binary alloys at high pressures [114]. System
Pu-AI
Composition
1.7
2.5 3.4 4.0 5.0 7.5 10.0 12.5
a]o AI a/o AI a{o AI a/o Ai a/o AI a/o AI a/o AI a/o AI
Max. press, (alto)
Transformation press, (atm)
8,880 8,920 8,920 10,060 8,670 8,470 8,670 8,670
2040 4340 7020 N.T.** N.T.** N.T.** N.T.** N.T.**
Transformation voi. AV/Vo (%)
Density
Perma- Compressinent bility vol. (X 106/ change* atm) AV/V o (%)
Before ¢ompression (g/cm 3)
After compression (g/cm 3)
16.0 11.8 6.8
16.0 10.9 6.7 -
4.1 3.8 4.0 3.4 4.5 3.9 3.4 3.1
15.73 15.66 15.60 15.50 15.31 15.38 15.04 14.87
18.67 17.70 16.71 15.49 15.26 i5.48 15.07 14.87
-
Pu-Zn
1.51 a/o 1.79 a/o 2.16 a/o 2.92 a/o 3.35 a/o 3.89 a/o
Zn Zn Zn Zn Zn Zn
10,000 9,250 9,250 9,100 9,880 9.250
1200 950 2520 4210 5290 6650
17.3 16.7 16.2 15.3 15.8 13.8
17.1 16.6 15.7 14.8 15.3 12.4
4.7 2.4 2.0 3.8 4.0 3.2
15.94 15.85 15.75 15.71 15.70 15.64
19.08 19.08 19,08 18.53 18.29 17.82
Pu-ln
3.4 a[o In
9,100
1520
13.1
I2.4
2.5
15.56
17.83
10,600 10,600 9,880 9,880 9,250 9,250 11,000 I 1,000 I0,000 10,000 10,000 10,000
1 ~ 60 11 3000 1 500 11 4380 I 1460 II 6470 I 1920 Ii 8220 1 3230 II N.T.** i 4400 ii N.T.**
8.6 9.t 8.4 8.3 7.9 7.8 7.8 6.2 6.9
-16.3 15.5 15.8 14.6 -
-1.9 4.2 1.9 3.0 6.0 5.4 6.5 8.4 6,8
15.63 15.56 15.46 15.31 15.13
18.76 18.55 18.02 17.86 15.16
Pu-Ce
3.4 3.4 4.0 4.0 5.0 5.0 60 6.0 8.0 8.0 19.0 10.0
a/oCe a/o Ce a/o Ce a/o Ce a/o Ce a/o Ce a/oCe a/o Ce a/o Ce afoCe a/oCe afoCe
* Values obtained by extrapolation of pressure-volume curve,~. '~* N.T. means no transformation.
-
5.7
-
-
I lI i I il I !1 1 11
-
-
14.96
14.93
-
-
S.H.Kittel et al., Plutonium and plutonium alloys
389
Table 15 " PIoperties of U-Pu-X alloys (20% Pu and 10% "X") [ 117 ] Composition
U-Pu
U-Pu-Mo
U-Pu-Nb
Linear coef. o f expansion from 20°C-=500°C(X 10-6/°C)
21
16
17.8
16
17.3
Density at 20°C (g/cm 3)
18.8
17.15
16.5
14.57
15.64
3.7
3.4
3.3
3.9
3.1
Pu density (g/cm 3 of alloy) Resistivity at 23°C(p~Zem)
80
Therntal cop.duc*ivity (watts/cm/cm2/°K at 23°C) (calculated)
77
9.0 X 10-2
while the latter proposal accounts for zinc it does not hlclude thallium [56]. Addition of any of the delta soluble elements causes an absolute increase in the thermal expansion coefficient and all of them ultimately expand on heating with sufficient alloy content [108,109]. Assuming a single valence for delta plutonium, 4.8! 5, it is found that the alloys change from negative to
o.,
z {---.--.-T~ ~ 1
1
I
F"
t
-I
U-Pu-Ti
U-Pu-Zr
103
9.4 X 10-2
86
7.0 X 10-2
8.4 X
10 - 2
positive expansion coefficients at compositions corresponding to 4.74 electrons/atom [ 109]. Delta-stabilized alloys have resistivity temperature plots similar to those for pure alpha and beta plutonium (see fig. 13). The resistivity maximum shifts to lower temperatures with increasing alloy content (188 to 100°K with aluminum decreasing from 1.2 to 10 a/o). The effect, alloying additions on a number of properties is giv in table 13o Table 14 summarizes some data obtau 1 from pressure studies [114] (also see ref. [106]).
t
20 F
i
i
'-~~,
O. IO
i
o,,I /,f!
~!0.0~
,2
i
0.06
coo , G
//
-I
s Z J/
0.O4
.
0.02
....
,
,
200
t
,
.
t
,
4oo
6e~o
soo
~
o0
200
400
500
800
T E M P E R A T U R E , °C
TEMPERATURE (=C)
Fig. 15. Thermal conductivity of U and U-Pu-Base alloys (w/o). (Reprinted from ref. [ 115].)
Fig. 16. Thermal expansion of U-19Pu-6Mo, U-25Pa-10TL and U-Pu-Fs alloys (a/o). (Reprinted from ~ef. [1171 .)
S.H. Kittcl et ai., Plutonium and plutonium a~loys
390
Table 16 Properties of U-Pu-Zr and U-Pu-Ti alloys [ 115].
U
Nominal composition: w/o a/o .
.
o
Approx. hqmdus temp,(C) Approx. solidus t e m p . ( C ) Solid transformation temp. range (of;.) Density at 25°C as-cast (g]cm3)
Thermal expansion Avg. coef. X 106 (°C-l} 25°C to 1st trans. End of trans, to 950°C In trans, range
-~X
103(°C -1)
Thermal cycling density change (%) H~dness at 25°C as-cast (DPH)
U
U
U
Pu
Zr
Pu
Zr
Pu
11.1 10
6.3 15
i5 12.9
10 22.5
18.5 14A 15 30
1200 1120 595680
1250 I ~55
Zt
! 290 1170 595~i60
595665
U
U
Pu
Ti
Pu
17.1 I5
3.4 15
15 10 10.7 35'.6
1206 1075
Ti
~340 120~;
585780
680850
Pu
Ti
?2 15
11,8 40
1360 !225 650815
16,8
15.8
14,8
17.5
14.7
14.0
18.3 18.1
17.6 20.1
17.5 20.0
2!.2. 16.4*
19.2 19,2
17.4 21.5
5.1
5,2
5.0
9.3
13.7
11.9
0 470
-0.1 540
-
+0.1 410
430
+0.1
-
400
360
* to 860°C,
Epsilon: This phase dissolves small amounts of a number of elements, and forms complete solid solutions with "r-Npand ~/-U. Compositions of 70 to 73 a/o U and 8 to 10 a/o fissium can stabilize the phase to room temperature [54]. The lattice parametercomposition curve for 3,Np-ePu has a slight negative deviation from Vegard's law at 550°C [ 103]. 3.4. Uranium-plutonium alloys Although this alloy system forms the basis for fast reactor metallic fuels containing plutonium, few physical property studies have been made of the binary system alone. This is because of the extremely poor properties of samples containing even small amounts of the zeta phase (see fig. 5). Fig. 15 shows the thermal conductivity of a uranium-10 a/o plutonium alloy in comparison to a number of alloys [ 115]. Plutonium is seen to decrease the thermal conductivity of uranium. Figs. 1 5 - 1 7 and tables 1 5 - 1 7 summarize a n u m b e r
of properties of alloys of U-Pu-X, where X may be "fizzium", "fissium", zirconium, titanium, molybdenum, or niobium. For a given fizzium content, the rate of transformation for "I,-U(e-Pu) ~ ~ U + 6' is constant for alloys widi up to 10% plutonium (see fig. 16)but increases significantly between 10 and 20% plutonium [ 117 ] Transformation is essentially complete at 450°C in 30 mip for a i 0% plutonium alloy and in 5 min for a 20% plutonium alloy. Other relevant properties of U-Pu-X alloys may be found in refs. [115-118], and i~ papers referenced therein. Mach of this work is reported in other sections of this article.
3.5. A luminum-based alloys The properties of alaminum-based, plutonium alloys have been studied for use in thermal reactors [119-121 ]. Table 18 :smnmar[zes the data. In general, plutonium additions up to 15 w/o cause a nearly linear degradation of the properties of the host metal.
S.H.Kittel eta!., Pl:~tonitan and ph~tonium alloys
391
Table 17 Prnp=rties of uranium-plutonkm~-fizzium alloys [ 115]. U Composition: w/o a/o
g
U
~t
U
Pu
Fz
U
Pu
Fz
90 90
10 I0
90 69.9
S0 8.7
I0 2i.4
75 65.5
i5 13.1
10 21.4
"U
Pu
60 20 61.1. 17.5
Liquidus temperature (°C) Solidus temperature (°C)
!133" 1133
1060 1025
1010 910
1000 865
990 820
Traasformation temp. ~ ( ~ Start Complete to
668 775
585
550 630
520 605
510 605
Density at 25°(2 (g/~~a- 3 Thermal expansion Avg. coel. X 106 (°c - ~) 25°(2 to 1st. trans. End of trans, to 7 2~'flC In trans, range - ~ X 103(OC - t ) Thermal cycling Density change (%) Length change (%)
7411
19. i
18.7
16.8
16.5
16.8
19.4 25.6
19.3 23.8
16.3 20.5
16.5 22.5
21.7
4.5
2.8
4.5
3.6
3.3
-2 -7
--30 + 25
+ 1 0
17.5
0 -1
- ! +2
Thermal conductivity (cai/sec- 1[ c m - I / ° c - ! )
2oo°c 400°C
600% 800% Enthalpy, 25°C to mp (cal/gm - l ) Hardness, DPN (kg/mm-2) "~quenched Oztransformed
0.071 0.080 0.094 0.115
0.071 0.069 0.0~.7 0.100
0.046 0.057 0.070 0.084
0.046 0.057 9.070 0.084
0.047 0.056 0.069 0.086
52
46
44
43
42
290
205
255 410
435
215 430
42 27 6
3
Tensile strength (kg[ m m - 2 )
200% 400°(2
600% 800%
37 17 5. 1
26 19 9 0.5
58* 40 8
27** 27 8
2
2
1
* As quenched. ** Transformed below 500°C. Table 18 Properties of aluminum-based, plutonium alloys*
Density (g/cm a) [ 119] Thermal expansion coef. (cm/cm/°C X 106) { 120} Thermal conductivity (cal/cm- I _scc.OC) Electrical conductivity ( o h m - ! -cm - ! ;/, 10- s ) [ 1211
A!
AI-5 w/o Pu
Al-15 ~vlo Pu
2.70 28.,t 0.5 ~ 3.60
2.76 27.7 0.43 2.8
3.07 26.4 0.13 0.6
* Some data are estimated from specific compositions other than those given here.
I:z i0 21.4
392
S.H.Kittel et al.. Plutonium and p/utonhtm alloys
2" I 1
]
I
I
I /f~15
t |
Pu-IO Ti
U-185 Pu-14.1Zr ]
20--
~-t6 ~o x z~ o
8--
4
[
0
0
L
0
I
200
I
I
ZOO 400 6)30 U-Pu-Zr AND U-Pu-Fz
I
I
400
600 U-Pu-Ti
.,I 800
[ 800
I
1000
1000
I
1200
TEMPERATURE |*C)
Fig. 17. Typical expansion of some U-Pu-basealloys (w/o). (Reprinted from ref. [ 1151.) 4. Mechanical properties 4.1. httroductivn Since, the previous edition of the Reactor Handbook was published, extensive information has beco~le available on the mechanical properties o f unallc.yed plutonium and delta plutonium stabilized with either aluminum or gallium. However, very limited in r :rmation exists on alloys of low plutoaium content. In the Plutonium Handbook [ 122 ] Gardner gii~,es a very complete presentation of the mechanical property data obtained prior to 1964. Because more information is now available on the tensile and creep properties, fracture behavior, strain hardening, and recovery of plutonium, a suzmnary of the mechanical properties of unalloyed plutonium will be discussed first, fol.~owed by these of plutonium-rich alloyed, and alloys of low plutonium content.
4.2. Unalloyed plutonium Because of Gardner's thorough analysis [122] only a summary of the mechanical properties of unalloyed plutonium is needed here. The specific properties discussed are hardness, tensile properties, compressive properties, creep, roiling characteristics, torsion, impact, fatigue, deformation modes, and recovery and recrystallization. 4.2. r. Hardness Hardness is the mechanical property of plutonium that ismeasured most frequently. The hardness of a-Pu depends upon the metal's prior thermal and mechanical history; apparently, more so than upon the metal's quality. The hardness of as-cast a-Pu containing 300 to 1000 ppm total impurities is 260 to 285 DPH [56, 122-125]. Gardner [122] gives the most probable average hardness as 265 DPH for 0t-Pu at room temperature, having a density of 19.50 to 19.70 g/cm 3 and a total impurity content of less than 1000 ppm. The hardness of as-cast electrorefined plutonium is about 255 to 265 DPH; whereas, the hardness of recrystallized electrorefined a-Pu is 235 DPH [124]. The hardness of a-Pu is about 375 DP[t at -80°C and about 180 DPH at the a ~/3 phase change (fig. 18). When alpha transforms to beta, the hardness decreases to about 60 DPH at 125°C and decreases to about 25 DPH at 180°C. The hardness of beta transformed from gamma, however, is higher than beta formed from alpha [125]. The hardness of 7-Pu is less than 20 DPH and that of 8-Pu is less than 10 DPH. 4.2.2. Tensile properties The ultimate tensile strength of t~-Pu cal~ vary between 35,000 and 85,000 psi, depeading upon the metal's prior thermal and mechanical history [56, 126--128]. Pavlick [126] found that a large variation in the ultimate tensile strength is caused primarily by microcracks, which form during the ~ t~ transformation [129]. Neither grain size nor ,urity influence the ultimate tensile strength as much as microcracks. The ductility ofet-Pu is less than 1% at room temperature at a testing speed of 0.015 in./min; however, 200% elongation can be obtained above 100°C. Gardner and Mann [56] studied the effect of temperature on the tensile properties of
393
S.H,Kittel et aL, Plutonium and plutonium alloys
ductility of delta as the temperature is increased; strength, however, decreases with increasing test temperature. Gardner [56] observed that testing speed influences the tensile properties. Between 30 and 100°C (alpha phase), the ultimate strength increases to a maximum (which obviously depends upon the metal and temperature) at about 0.250 in.[min testing speed and then decreases. He attributed the increase to strain hardening, and the decrease to an increase in the notch sensitivity with testing speed.
I 400 l I
I I
100
I I
I -200 -100
t 0
,I'll 100
2o0
I 300
Fig. 18. Effect of temperature on hardness of unalloyed plu.
tonium [ 124].
unalloyed plutonium in the alpha, beta, gamma, and delta phases (fig. 19). The ductility of ~-Pu can vary wide!y, depending on the metal's thermal history. Elongations up to 680% have been obtained when the beta phase is formed from the alpha phase; however, the total elongation is less than 20% when beta is formed from gamma. Dahlgren [130] studied the plasticity of unalloyed plutonium by evaluating the strain hardening exponent, m, in the equation o = ~'dm. Values of m up to 0.33 and elongations up to 680% are obtained for beta plutonium formed directly from the alpha phase. Metal cycled between the alpha and beta phases has a lower flow stress and a higher value for m (m ~ 0.45); the total elongations are not as great as for uncycled metal because of the premature failure at voids which form during cycling. Beta plutonium formed from the gamma phase has a higher flow stress and a lower value of m (m -~ O. 15) than beta metal formed from the alpha phase, and m is relatively insensitive to changes in temperature and strain rate. The decrease in ultimate strength with increasing temperature is much smaller in the gamma phase than in the alpha and beta phases (fig. 17). The gamma phase strength is higher than the beta phase strength, while the strength of the delta phase is 50% lower and the ductility is 34% higher than the corresponding values for the gamma phase. There is little change in
4.2.3. Elastic modulus H.L.Laquer [ 123] used a pulse sound-velocity technique to establish the elastic constants of unalloyed plutonium that had a density 19.772 g/cm 3 . A value of 14.40 X 106 and 6.29 × 106 psi was obtained for the modulus of elasticity and shear modulus, respectively. Gardner and Mann [56] used a microformer-type extensometer to determine the elastic modulus in the alpha phase, while Kay and
70
'i
"
40
ol,, -50 0
.50 ICO 150 ~
250 300 350 400 450
TEMPERATUREC
Fig. 19. Effect of temperature on tensile strength of unalloyed
plutonmm at a testing speed of 0.015 in./min. * Taken at point of departure from linearity on load-platen displacement curve - - approximates a 0.2% effect yield strength [ 122].
394
S.H.Kittei et aL, Plutonium and plutonium alloys
Table 19 Elastic constants of unalloyed plutonium. TernPhase perature (°C)
Modulus Shear Poisson's of elas- modulus ratio ticity (10 6 psi) (106psi)
-250 - 170 80 0 20 60 100 140 170 200 220 260 300 330 380 430
18.9 17.35 16.00 14.65 14.00 13.30 12.40 5.90 5.58 5.37 5.28 4.94 4.58 2.49 2.45 2.39
-
Ot o~ Ct tx o~ a ~ /3 # ~ ~, ~ "V 5 6 6
0.17 0.20 0.20 0.20 0.16 0.15 0.14 0.29 0.27 0.27 0.24 0.25 0.25 0.43 0.45 0.42
7.26 6.69 6.17 6.08 5.80 5.45 2.29 2.20 2.12 2.13 1.97 1.52 0.87 0.84 0.81
Bulk modulus (106 psi)
9.63 8.90 8.18 6.88 6.33 5.76 4.68 4.05 3.89 3.38 3.29 3.06 5.9 8.1 4.9
4.2.4. Poisson's ratio H.L.Laquer [123] calculated a value of 0.!5 + 0.01 for Poisson's ratio from elastic and shear moduli data determined by a pulse technique. Konobeevsky [84] calculated a value of 0.21 from moduli determined by resonance techniques for plutonium extruded at 230°C in the gamma phase. Kay and Linford [56, 131 ] using an ultrasonic resonance method, derived values of Poisson's ratio ranging from 0.I 75 for low quality plutonium and 0.186 for high quality plutonium. The effect of temperature on Poisson's ratio is shown in table 19.
[LIO.
oL] I -1.0
Linford [56, 131 ] used an ultrasonic resonance method up to 430°C. Lallement [ 133] and Linford [132] measured the temperature dependency of the modulus of elasticity between 4.2°Kand room temperature. Their data are comparable except that Lallement noted at -213°C a minimum, which wa~ not detected by Linford. The temperature dependence of the elastic moduh~s is given in table 19. The change of modulus with temperature shows that the alpha phase from 20 to 110°C exhibits a large change of modulus with temperature, i.e., it is 2 X 104 psi/°C betweeh 20 and 100°C. A higher metal quality, as indicated by density, results in a slight increase in the elastic constants (table 20). Lintord [ i 31 ] observed a slight increase in the elastic modulus at the /3 - 3' phase change similar to the strength increase observed by Gardner and Mann [56]. Room temperature elastic constant data from several sources are compared in table 20, with the agreement of the elastic constants being quite good for corresponding densities.
00
~ -2.0 I llO ~ -3.0
-5~0 -60
,
5OO
I 1.0
1.5
, 2.0
2.5
3.0
lO00/T, g-1
Fig. 20. Temperature dependence of the steady-state creep of unalloyed plutonium [57]. The indicated values are compressive stresses of psi
4.2.5. Compressive properties The deformation of unalloyed plutonium in compression have been studied by Gardner and Mann [56], Bronisz [127], Pavlick [135], and Nelson [ 136]. The large variation of the data among the authors can be attributed to metal purity. Gardner and Mann [56] made a very extensive study of the effects of temperature and testing speed on the compressive properties of unalloyed plutonium with a purity of 500 to 1000 ppm. They found that the general effect of temperature is quite similar to that observed in the tensile work, except the ultimate and yield strengths in compression are
S.H.Kittel etal., Plutonium and l~lutonium alloys
395
Table 20 Room temperature elastic constant data from various sources for unalloyed plutonium [ 13 ! ]. Source
Density (g/cm 3)
Modulus of elasticity (106psi)
Shear modulus (106 psi)
Poisson's ratio
Bulk mod,alus (106 psi)
Adiabatic compressibility ( 10 - 7 in.:'/Ib)
lsoMethod lhermal compressibility (10 - 7 in.2/Ib)
Linford [131]
19.49
14.15
6.01
0.176
7.29
i.36
1.51
Resonance
Linford [131] (high density)
19.71
14.60
6.13
0.186
7.75
1.30
1.44
Resonance
Laquer [ 56 ] (high density)
19.72
14.40
6.30
0.15
6.77
1.48
1.62
Pulse
DeCadenet [56]
19.35
14.25
5.93
0.199
7.90
1.27
1.41
Pulse
Bridgman [ 134]
.
1.38
Compressibility
Robinson [ 122]
19.6
.
1.32
Compressibility
Gardner [56]
19.53
14.32
.
Lallement [1331
-
13.6
-
0.23
-
-
-
Resonance
Linford [1321
19.65
14.50
-
0.18
-
-
-
Resonance
(mean as-cast)
(as-cast)
.
.
. .
. .
. .
.
.
.
considerably higher than those in tension. For example, at room temperature the ultimate compressive strength (175,000 psi) is three times as high as the ultimate tensile strength. Although the ultimate tensile strengths of the beta, gamma, and delta phases were not obtained because of the very large plasticity of these phases, the yield strengths do decrease - similar to tensile work - with increasing test temperature. They observed that increased testing speed increased the beta yield strength essentially the ~ame as it did in tension, but that yield strength in compression was independent of testing speed. Bronisz [ 127] studied the effect of temperature, testing speed, and purity on the compression properties of only the alpha phase. The total impurity contents of his metal were i 15, 185,227 and 480 ppm. He observed approximately the same dependency of yield strength on temperature and testing speed as Gardner and Mann [56], but he also noticed that temperature dependency is greater for purer plutonium, and (contrary to behavior of ether metals) that the testing speed sensitivity is less at higher testing temperatures.
.
.
Tensile test
Strain hardening of alpha up to at least 5% plasticity has been obselved; for example, Pavlick [ 135] reported a strain hardening exponent of 0.07. The hardness of deformed grains is about 310 DPH compared to 265 DPH for as-cast grains and 235 DPH for recry~tallized grains [ 136]. Strain hardening studies in compression have not been performed on the higher temperature allotropes. Nelson's [ 136] compression tests were on electrorefined plutonium containing less than 300 ppm total impurities, and these tests showed that recrystallization occurred concurrently with deformation. Deformation and recrystallization occurs very rapidly at the high alpha temperatures; for example, at 30,000 psi, 75% deformation with concurrent recrystallization occurs within five minutes at 115°C. Deformation with concurrent recrystalliation occurs at 20°C, but at a much slower rate and a much higher stress; more specifically, 80% reduction requires about 150 hr at 90,000 psi. 4.2.6. Creep Creep of plutonium has been the most extensively
396
S.H.Kittel et aL, Plutonium and plutonium alloys
studied in compression [57]. Creep curves of the/3, % 8, 6', and e phases are typical in that they consist initially of primary creep followed by secondary or steady-state creep. Creep curves of alpha plutonium, however, show recrystallization. Fig. 20 permits a comparison of the logarithm of the steady-state creep rate versus reciprocal temperature ior all plutonium allotropes. The creep rates of % 6,6', and e vary less than 10%, regardless of the transformation rate or the present phase. For example, at the same temperature and stress, the creep rate of ~, formed from/3 is the same as the creep rate of ~' formed from/i, but the creep rate of/3t~ 03 formed from or) is 50 to 500 times greater than the creep rate of 13.r 03 formed from ~). Sufficient creep data have been obtained for the 13,~, and 8 allotropes to conclude that the steady-state creep is related to stress, o, by the proportionality ~ 0 '1. Between steady-creep rate of 10 - 4 and 10- 1/hr, n equals about 6 for 8 and about 5 for 3, and/3; however, for most metals n is 5. 4.2.7. Rolling characteristics Alpha plutonium can be rolled successfully even though it is brittle, lanniello [ 137, 138] successfully rolled it by (I) rolling it about 15% reduction in the beta phase (which deforms easily)at 150 to 160°C; (2) rolling continuously during cooling, i.e., the roll separation was decreased 0.001 in. every 5°C until the temperature was 50°C; and (3) rolling at room temperature decreasing the thickness 0.001 in. each pass. The alpha phase can also be rolled from a thickness of 0.150 in. to 0.010 in. at 70 to 100°C by decreasing the roll separation 0.010 in. between passes. The deformability is most influenced by (1) amount of microcracks, (2) grain size, (3) prior mechanical history, (4) thickness, and (5) internal stresses. Metal that contains a very fine grain size, severe microcracking, and large amounts of internal stresses cannot be rolled. Strain hardening is very low because the hardness increase by rolling is less than 10% for deformation less than 40% reductions. The hardness decreases for large amounts of deformation. Rolled o~-Pu contains a two component texture, which was determined by Berndt and Lloyd [83]. One texture has the (010) aligned approximately parallel to the rolling direction, and the other texture has the t'010) nearly parallel to the cross direction.
The important texture is the one having the (010) nearly parallel to the rolling direction. 4.2.8. Torsion properties Only preliminary torsion data exist on as-cast plutonium. A group of five tubular specimens was tested by Gardner at room temperature [ 139]. The average ultimate shear strength was 53,200 psi for plutonium having a density of 19.55 g/cm 3 and 600 ppm total impurities. The shear strength of brittle material cannot be determined in a torsion test because failure actually occurs in diagonal tension before the shear strength is reached. By using a ratio of 1.2 and a value of 50,900 psi for the true tensile strength of plutonium, Gardner estimated a value of 61,100 psi for the true shear strength. A shear strength value of 80,000 psi was calculated based on compression test results; however, during tensile testing of threaded joints, shear strengths varying from 35,000 to 45,000 psi were observed. No direct determinations of the shear modulus or modulus of rigidity have been reported for plutonium, although pulse and resonance techniques have been used to determine shear modulus values of 5.93 X 106 psi [132], 6.29 X 106 psi [56], and 5.4 X 106 psi [841. 4.2.9. Impact Alpha-phase plutonium behaves in a brittle manner during a tensile impact test [56]. A group of eight, 0.250 in. gage diameter, 1.5 in. gage length, threaded specimens tested at room temperature gave impact energy values ranging from 1.3 to 4.8 ft-lb - with typical brittle fractures obtained in each case. Coffinberry [123] using Charpy keyhole notch type impact specimens, found that at 22°C the impact strength of alpha plutonium ranged from 1.5 to 2.0 ftqb. In addition, this analysis of the general mechanical behavior of plutonium suggests that impact strength approaches zero at lower temperatures and that there is some slight increase at temperatures above 75°C. Gardner, who made a study of the unnotehed and Charpy V-notched impact properties of plutonium [140], found that impact energies increase with in. creasing temperatures in the alpha phase. A further increase was observed as test temperature was increased
S.H.Kittel et al., Plutonium and plutonium alloys
to 130°C in the beta phase; however, at the 175°C test temperature the impact energy decreased. Essentially no plastic defo,mation was observed in the alpha and beta phases; while in the gamma phase, extremely ductile behavior was observed. These data confirm observations made on strain rate effects during tensile testing in the beta and gamma phases; i.e., the beta phase is quite strain-rate sensitive while the gamma phase is relatively insensitive to strain rate. The impact energies for the Sharpy V-notched specimens are much lower than the unnotched values at corresponding temperatures. As suggested by Coffinberry [ 123], the V-notched impact strength actually increases as temperature is increased in the alpha phase. Brittle fractures are obtained in the alpha and beta phases. Relatively ductile fractures are obtained in the gamma phase, and extremely ductile behavior occurs in the delta phase [140]. From a comparison of the unnotched and notched impact energies at 100 and 130°C it can be concluded that the beta phase is, in addition to being strain-rate sensitive, quite notch sensitive. 4.2.10. Fatigue Gardner [ 141 ] studied the fatigue of unalloyed plutonium of a wide range of quality. The total impurity content ranged from 277 to 2063 ppm, the densities varied from 19.40 to 19.64 g/cm3; microcracking varied from severe to none, which was due to a large amount of iron. He obtained two fatigue curves (fig. 21) by two methods - both pneumatic. One method produced a complete stress reversal during each cycle and the other produced an incomplete stress reversal. A large scatter in the data was produced by the difference in metal quality; severe microcracking caused failure during the first stress cycle. 4.2.11. Deformation modes The modes of deformation of plutonium have been studied for only the alpha phase [57, 142]. Slip has been observed most frequently and appears to be the most prevalent mode of deformation at room temperature under compression stresses. The most likely slip plane is (020) because this plane has a high atomic density and contains all of the atoms at y =¼ and y --3 - ~ . Bronisz and Tate [57], however, state
397
60
40 c,D
z
2O
0 0
I
I
104
105
-
I
I
106
107
I ~
108
REVERSED STRESSCYCLESTO INC IP IU',ITI:AILURE
Fig. 21. Fatigue curves for unalloyed plutonium I 1221.
that slip planes near (114-), (213), and (323 ) probably are more operative at room temperature than the
(020). While twinning has been obser,~ed infrequently. grain boundary sliding has been seen more frequently, especially as the available plutonium becomes purer. Grain boundary sliding is most common at the high alpha temperatures (80 to 1 !5°C) and at the slow deformation rates. 4.2.12. Recovery and recrystallization Recovery of residual stresses introduced by deformation and by phase transformations can occur by annealing between 100 and 115°C. Pavlick and Hanson [ 135 ] showed that recovery, which was monitored by measuring the decrease in yield strength with annealing time, occurred at 109°C of specimens that had been deformed 3 to 5% by compression. X-ray diffraction patterns are much sharper and the 0t ~/3 transfonnation rates are much slower for annealed c~-Pu than they are for del'ormed a-Pu. Even though recovery of a-Pu is very common, recrystallization (as observed by a change of microstructure) has not been reported for annealing of deformed a-Pu. laniello [1431 postulated that the recrystallization temperature is near the transfonnalion temperature. Nelson 11361 found that a decrease in grain size - to 1 micron or less occurs concurrently with deformation by compression. The decrease in grail~ size was attributed to recrystallization. They both measured hardnesses of 235 DPlt, which is about 30 DPH less than as-cast a-Pu.
S.H.Kittel et al., Plutonium and plutonium alloys
398
Table 21 Temperaturevs. hardness for a homogenizedPu-3 a/o Ga alloy [ 1461.
300
g
Temperature (°C)
Hardness (DPH)
25 121 172 196 254 323 385 415
40.5 30.8 26.0 23.6 19.5 14.5 5 3
200
~
~u-Ga
e,,,
100
~ ~tpu-AI
Pu-Ga
Pu-Ai Pu-Ce
j/
0 0
I
I
I
2
4
6
1, 10
I S
12
SOLUTECONCENTRATION,AT.%
Fig. 22. The compositional dependence of hardness for Pu-AI, Pu-Ga, and Pu-Ce alloys [ 144, 145].
4.3. Delta-stabilized alloys Since the three most common elements for stabilizing the delta phase of plutonium are aluminum, cerium, and gallium the discussion of the mechanical properties of delta stabilized alloys will include only these three elements. Specific mechanical properties to be discussed are hardness, tensile properties and compression properties, creep, torsion, and fatigue. Because these properties markedly depend upon thermal and mechanical treatments and upon composition, they can be discussed only in generalities.
15-0.2~
/
I 10 -
/
x ,=
/
I
/
[ [
5
ULTIMATE STRENGTH,18,600psi PROPORTIONAL LIMIT. 4500psi 0.2~ YIEEDSTRENGTH,ll,50~psi ELONGATION, 25.0% RED. IN AREA, 31.3~ 6 ELASTICMODULUS.6.2X 10 psi TESTSPEED.0.015~N.IMIN TESTTEMPERATURE,30 C
/ i
! / I
/ I
i
r 0
, 0
I
fi¢ 0.002
,
I
,
0.004
I 0.006
,
4.3.1. Hardness Hardness data have been determined as a function o~ composition by Miller and White for Pu-AI [144], Pu-Ce [144], and Pu-Ga [145] alloys. The Pu-Ce and Pu-Ga alloys were homogenized 50 hr at 450°C and the Pu-AI alloys were homogenized 200 hr to obtain fully homogenized alloys. Alloys that were believed to contain two phases (t~ and 5) were annealed an additional 50 hr at 250°C to produce an equilibrium structure. The hardness decreases from about 265 DPN for unalloyed plutonium to the 5-phase solid solution values, which depend upon the additive (fig. 22). The linear decrease in hardness as the amount of alloying element is increased is caused by a decrease in the amount of alpha, but the linear increase is caused by solid solution hardening. Ga!lium and aluminum show more solid solution hardetdng than does cerium. Miller and White [144] expressed the rate of hardening as 0.53 DPN/a/o for cerium and 4.75 DPN/a/o for aluminum and gallium. Gardner [122] on the other hand, obtained a rate of hardening of about 8.5 DPH/a/o Al. Hays [ 146] determined the hardness of a homogenized Pu-3 a/o Ga alloy as a function of temperature by using a 578-gram load (table 21). Miller and White [ 145 ] also reported a temperature dependence of hardness up to 5 a/o Ga.
I 0.008
STRAIN
Fig. 23. Stress-strain curve tot plutonium-3.0 a/o gallium
delta-stabilized plutonium, 0.250 in. diameter specimen [122].
4.3 .'2.. Tensile and compressive properties Most of the tensile and compressive properties have been on alloys containing 3.0 a/o Ga. The tensile properties on this alloy vary considerably due to variations in the impurity content, particularly iron.
S.H.Kittel et ai., Plutonium and plutonium alloys
P.J
I0
X
/
39
4O
-" t\ 30 5
x
Pu-AI
20
-AI
Pu'-.Ce
10
Pu-Ce
_
/
% _
0
t
1
2
4
I 6
I 8
I 10
12
A typical stress-strain curve (fig. 23) shows that stress is proportional to strain up to 4500 psi and that there is no well defined yield point. The ultimate strength decreases from 17,000 psi at room temperature, 2000 psi at 400°C. Correspondingly, the yield strength decreases from 10,000 to 1500 psi. The ductility increases from about 40% at room temperature to about 80% at 400°C. The effect of aluminum, cerium, and gallium compositions on the 0.1% yield strength (fig. 24), ultimate strength (fig. 25), and Young's modulus (fig. 26) is similar to the effect of solute concentration on hardness. The decrease in strength is because there is due to lesser amounts of alpha and the increase in strength is caused by solid solution hardening. 4.3.3. Creep The only creep work of delta-stabilized alloys has been the compressive creep studies by Robbins and Wheeler [57, 147] of a Pu-3.0 a/o Ga alloy. Creep was evaluated at 20~ ~,~psi between 234°C and 3870C. The alloys deform~a initially by primary creep, then by steady-state creep, and finally by a recrystaUization process, similar to high purity :alpha plutonium, that caused most of the deformation. The average activation energy was determined to be 33.7 +--2.57 kcal/g atom for strains of 0.05, 0.10, and 0.15. They found a marked influence of raetal purity on the creep
1
I
I
~,
4
6
8
10
.....
12
SOLUTECONCENTRATION.AT.%
SOLUTECONCENTRATIf,,N,AT.~
Fig, 24. The compositional dependence of the 0.0% yield strength for Pu-AI, Pu4[:e, and Pu.
l 2
Fig, 25. The compositional dependence of the ultimate ten~ile strength of Pu-AI, Pu-Ga, and Pu-Ce alloys 1144, 145],
rates of the alloy. They also noticed that the amount of primary creep increases with increasing temperatures. Fatigue The only fatigue work has been on the Pu-3 a/o Ga
4.3.4.
m
ii
10
°
8
---
4
I I I
t
x
i
0
1 .....
~
P
6
'1
I
S
10
12
SOLUTECONCENIRATION, AT.%
Fig. 26. The variation of Young's modulus with composition for Pu-AI alloys [ 1441 .
S.H.Kittel et al., Plutonium and plutonium alloys
400
Table 22 Tensile properties of plutonium-iron alloys [ 122]. Test
Ultimate
Yield strength
Modulus of
0.01% offset
elasticity (%)
iron
temperature ~°c)
strength (psi)
(psi)
(10 6 psi)
7.0 7.0 7.0 8.7 8.7 8.7 8.7
30 125 127 30 127 220 318
54,500 29,700 24,500 35,900 34,100 14,150 4,260
26,700
7.1
0.23
0
8,720 25,700 10,750
3.8 6.7 .5.0
0.59
0
0.044
0.43
0 0
-
-.
1.0
0
-
-
Atomic percent
Elongation
<
12.5
Reduction
in area (%)
5.9
Gage length : 1 in.
Diameter ,0.250 in. Testing speed: 0.015 in./min. alloy by Gardner [57] who used the same technique that he used for unalloyed plutonium. The fatigue strength was determined with a superimposed mean stress of 5,400 to 6,700 psi at a frequency of stress reversal of 215 cycles/see. The metallurgical conditions included: (1) as-cast, (2) with coring, i.e., with alpha phase present, (3) cold rolled, and (4) homogenized. The 0.1% yield strength ranged from 10,300 to 30,4(~0 psi due to the variations in metallurgical conditions. The fatigue limits ranged only from 10,000 to 15,000 psi (107 to 108 cycles) regardless of metallurgical condition; the presence of alpha phase apparently increased resistance to fatigue failure. 4.3.5. Torsion Robbins and Wheeler [148] also studied the torsional ductility of a Pu~3 a/o gallium alloy containing 231 ppm total metallic impurities that had been cast, swaged, and then heat treated 24 hr at 460°C. The specimens (0.200 in. diameter and 1.00 in. long) were deformed at a single constant tensional strain rate of 4.16%/see at temFeratures ranging from 20 to 576°C. The alloy exhibits a ductility transition region between 150 and 2S0°C, that leads to very high ductility between 200 and 500°C. Between 500 and 560°C, a sharp decrease in ductility occurs that is probably associated with the 8 --, e transformation. No torsional sheaz stresses have been determined but the strength decreases continuously with increasing
temperature. No abrupt changes in strength occur where the ductility increase occurs. 4.4. Plutonium-rich alloys 4.4.1. Plutonium-uranium A limited amount of hardness, tensile, and compressive data are available on Pu-U alloys containing 3, 7, and 14 a/o U [149]. The hardnesses were 240 to 270 DPI~ for 3% alloy, 180 to 215 DPH for the 7% alloy: ~nd 200 DPH for the as-cast 14% alloy. It should be noted that the as-cast alloys had the largest hardness values. The hardnesses were lowest when the alloys were heat treated at 270°C and quenchc~! to room temperature. The hardness increased with increasing uranium addition because the beta phase becomes retained at room temperature. The ultimate yield strength of the as-cast 3% alloys was 55,000 psi and the 0.01% yield strength was 41,200 psi. The compressive strength was 185,000 psi for the 7% alloy that had been heat treated 2.5 hr at 270°C and oil quenched to room temperature. 4.4.2. Plutonium-iron Gardner [ 122] obtained some tensile data (table 22) on Pu-Fe alloys containing 7.0 and 8.7 a/o Fe. At room temperature these alloys are weaker than unalloyed plutonium (50,000-85,000 psi) containing no microcracks. Although the ductility of each alloy is very low and comparable to unalloyed plutonium,
S.H.Kittei et ai., Plutonium and plutonium alloys
401
Table 23 Room temperature microhardness values for plutonium-rich alloys, Alloying
Amount
element
(a/o)
ol-Pu o~-Pu ot.Pu AI AI AI AI A! Al Ai Ce Ce Ce Ce Ce
< 300 ppm '< 300 ppm < 300 ppm 0.5 1 2 4 6 8 12 1 2 4 8 12 18 20 7 10 0.5 I 2
Ce Ce
Fe Fe Ga Ga Ga Ga Ga Hf Hf Hf Ti Th Th Th U U
U Zn ~r, Zr Zr Zr Zt Zr
2
5 3 9 12 0.3 3 5 10 3 7
14 2 4 3 to 7 3 6 10 20
Description
Hardness (DPH)
As-cast Recrystailized Deformed ol+ 6 ~+ 6 8 8 6 ~ ~ + PuAla 0~+ 6 (homogenized) 5 (homogenized) 6 (homogenized) 6 (homogenized) 6 (homogenized) 6 (homogenized) ~ + Ce ,~+ Pu6Fe 0~+ Pu6Fe Or+ 6 (homogenized) 0~+ ~ (homogenized) 5 (homogenized) 0~4 6 (as-cast) s (homogenized) 0 0 + PuHfx ~+ PuHfx /~ Notgiven Not given Notgiven 0t+ l' (as-cast) or+ f (as-cast) r~+ ~-(as-cast) 6 (homogenized) 6 (homogenized) fl (quenched) f + 0 (homogenized) ~' ~ O (homogenized) f + 0 (homogenized) ~i
255 to 235 265 to 160 60 32 45 62 76 85 150 31 32 34 36 38 45 to 218 230 165 65 36 50 50 i00 to ~ 46 50 to 100 to 35 to 45 to 40 to 270 215 200 37 68 100 to i 17 157 170 60
it is considerably lower than unalloyed plutonium at elevated temperatures. The compression strength o f the 8.7 a/o alloy is 112,000 to 115,000 psi compared to 175,000 psi t0r unalloyed plutonium; the total deformation is ~,pproximately 7% at failure.
265 315
55
105 55 105 50 55 70
105
Ref.
[ 136] [ 136] [ 136] 1144] [ 144] [ 144] [ 144] [ 144] [ 144 ! [ ]22] [144] [ 144] [ 144] 1144] [ 144] [ t44] [ 122] [ 122] [68] [ 145] [ 145] [ 145] [57] [ 145 ] ] 122] [ 122] ]122] [ 122] [122] [ 122] . [122] [ 122] [ 122] [ 122] [ 21 ] [ 21 ] [ 149] [ 149] [ 149] {149] [ 149]
4.4.3. Plutonium-zirconium Taylor [ 149] determined the mechanical properties of Pu-Zr alloys between 1.0 and 10 a/o Zr. He found that the beta phase cannot be stabilized at room temperature but that it is metastable when the
S.H. gittel et al., Plutonium and plutonium alloys
402
Table 23 Room temperature microhardnessvalues for plutonium compounds [ 122]. Hardness (DPN) 25 g load
Compound
Hardness (DPN) 25 g load
Compound
Hardness (DPN) 25 g load
Compound
.'uAg3 PU3AI PuAI PuA[2 PuA!3 PuAI4 PuAs PuAu PuBet3 PuBi PuBi2 PuBi3
~ 180 "" 125 ~ 340 500 to 600 450 to 550 300 to 500 140 to 170 170 to 220 510 to 590 85 to 110 60 to 100 145 to 200 6? to 110 500 to 900 1000 to 1200 150 to 200 130 to 200 230 to 27~3 580 to 690 350 to 550 610 to 720 230 to 260 160 to 240 260 1431 530 to 630 636 [43l
Pu3Ge Pu2Ge3 Pu2Ge PuGe2 PuGe3 Pull2 PU31n Puln Pu2ln3 Puln3 PuMn2 PuN PuNi PuNi PUNiz ~,tNi2 PuNi3 PuNi3 PUNi4 PuNi4 PUNis PuNis I~'-.gli9 PuNi9
"" ~ ~ ~_ ~
PuO2 PuP ~ PUIgRu PuaRu PusRu3 PuRu PURu2 ~ PusSi3 Pu3Si2 ~ PuSi Pu3Sis PUSi2 PU2Th PuZn2 Pu2Zn9 PuZna PU2Zn17 PuCeCo ternary phases: Pha~ A-, (PuCe)-~Co3 Phase B-, (PUCe)-/Co3 Phase C-, (PuCe)sCo3
Pu3C2 PUC PuzC3 PU6Co Pu3Co Pu2Co PuCo2 PuCo3
PU2COl7 PUCu2 Pu6Fe PU6Fe PuFe2 PuFe2
Pu203 Pu~O-I
360 405 450 450 335 120 to 180 75 to 140 75 to 215 130 to 375 155 to 275 440 to 500 ~ 580 220 to 270 ~ 250 520 to 630 505 to 634 [46] 440 to 550 388 to 550 [46] 200 to 290 196 to 292 [46] 460 to 550 442 to 580 [46] 420 to 560 416 to 560 146] 200 tO 300 ~ 1020
2 to 7% alloys ale quenched from either the delta or epsilon phase regions. The hardness of the metastable beta is 100 to 105 DPH. The hardnesses of the Pu-Zr alloys continuously decrease from the unalloyed value of 265 DPH for the alpha phase to a minimum of 117 DPH for the zeta phase; they then continuously increase to 170 DPH a: 8.5 a/o Zr for the theta phase. The only tensile and compressive data.are for the Pu-2.4 a/o alloy. The ultimate tensile strength decreases essentially linearly from 50,000 psi at 30°C to 18,000 psi at 2O0°C, and ther, decreases to 7800 psi at 260°C. The yield streogth decreases from 28,000 psi at 30°C to 14,000 psi at 2000C and then to 7000 psi at 260°C. While the di~ctility is less than 1% below 230°C, it is 6.3 at 260°C. The ultimate compression strength decreases from 67,000 psi at 60°C to 29,000 psi at 220°C and the yield str*,ngth
500 to 850 240 140 to 190 180 to 220 230 to 330 170 to 250 390 350 to 480 660 600 to 1000 680 to 850 420 to 505 I70 to 230 370 to 420 340 to 460 320 to 480 280 to 400 180 to 200 175 to !95 230 to 260
decreases from 60,000 psi at 60°C to 27,000 psi at 220°C. Brittle shear-type failure occurs at all test temperatures. The ultimate compression strength decreases from 67,000 psi at 60°C to 29,000 psi at 220°C and the yield strength decreases from 60,000 psi to 27,000 psi at 220°C. 4.3.4. Hardness data Hardness is the most common mechanical property that has been measured for plutonium rich alloys and plutonium compounds. Representative values are given in tables 23 and 24 for many of the materials. The hardness values for the alloys generally depend upon heat treatment. 4.5. Dilute plutonium alloys Information on the mechanical properties of binary alloys consists primarily of hardnesses and
S.H.Kittel et al., Plutonium and pluton&m alloys
Table 25 Hardness data of binary alloys of plutonium. Composition (w/o)
/vlechanicaland thermal treatment
;lard- Ref. hess (DPH)
Al-l.7 Pu AI-5 Pu
Extruded at 400°C As-cast Annealed I hr at 585°C As-cast Extruded at 400°C Annealed 1 hr at 585°(" As-cast Annealed 1 hr at 585°C As-cast Extruded at 400°C Arc cast Arc cast Are cast Are cast Horn. 2 days at 1000°(7 Arc cast Arc cast Horn. 2 days at 1000°C Arc cast Horn. 2 days at 1000°C Arc cast Arc cast Are cast Are cast Rolled As-east Rolled Rolled Rolled Rolled Rolled Rolled Rolled Rolled
31 35 22 42 41 23 58 43 92 24 t06 184 223
Al-10 Pu AI-15 Pu AI-20 Pu Fe-I 1.7 Pu Fe-18.4 Pu Fe-25.7 Pu Fe-32.2 Pu Fe-38.9 Pu Fe-43.0 Pu Fe-51.7 Pu Th-lO Pu Th-20 Pu Th-30 Pu Th-40 Pu U-5 Pu U-I 0 Pu U-15 Pu U-Z0 Pu
Zr-12.1 Pu Zr-22.5 Pu Zt-39.6 Pu Zr-52.9 Pu Zr-63.6 Pu
222
286 318 293 423 365 105 130 148 133 261 205 300 400 300 207 209 139 108 97
156l [56] 1561 [56] [56l [561 [56] [56] [56] [56] [561 [561 [56] [56] [561 [56] [56] [56] [ 561 [561 ! 122] I 122] [ 122] [ 1221 [561 [ 151 ] [561 [561 [t 171 [56] [561 156] [561 [561
tensile properties. For the ternary alloys there are hardness values, tensile properties, some compression properties, and some creep data. 4.5.1. Binary alloys Hardness values (table 25) have been published for A1.Pu, Fe-Pu, Th-Pu, U-Pu, and Zr-Pu alloys. The hardness increases virtually linearly up to about 20 w]o Pu for extruded and annealed AI-Pu alloys [56]. Annealed AI-Pu alloys are much softer than cast alloys; more specifically, the hardness for an
403
as-cast 80A120Pu alloy is 92 DPH, whereas it is about 44 DPH after it is annealed 1 hr at 585°C 156]. Some tensile data are shown in table 26 for the Pu-AI alloys. The hardness of the Fe-base alloys rapidly increases with Pu content due to the greater amount of PuFe 2 in the a-Fe matrix (table 25). The hardness of the Th.Pu alloys increases only slightly as the Th content is increased. The hardness of the U-Pu alloys, however. increases from 261 DPH at 5% Pu to 300 at 10~ Pu, where the phase boundary between single phase t~-U and the two phase (a-U + ~') region exists. The hardnesses continue to increase as Pu is added; for example, it is 400 DPH for the U 15Pu alloy. The hardness, which is about 210 DPH, of ot-Zr is little influenced by Pu, but as tke Pu content increases ab6ve about 22 w/o Pu the amount of retained delta increases and eonsequentiy the hardness decreases; the hardness of 97 for the 63.6 w/o Pu (40 a/o Pu) alloy is due to a completely retained delta phase alloy. 4.5:2. Ternary alloys The mechanical properties have been somewhat determined for U-Pu-Fz, U-Pu-Mo, U-Pu-Ti, and U.Pu-Zr alloys. Some tensile properties are given in table 2~, hardnesses are tabulated in table 27, some compressive properties for U-Pu.Ti and U-I~j-Zr alloys are listed in table 28, and some creep characteristics for U.Pu-Ti and U-Pu-Zr alloys are givel, in table 29. Essentially no meclmnical properties data are available on U-Pu-Th alloys. 1"he room temperature hardness values [56] of arc-cast and roiled U-Pu-Mo alloys varied between 160 and 492 DPH depending upon the composition, but large discrepancies were also reporled for similarly treated material of the same composition; the discrepancies were attributed either to the rate of cooling from the rolling temperature or to contamination during rolling. Pool et al. [56] stated that in general, arc-east, hot-rolled, and 3'-quenched alloys show similar hardness values. However, there are exceptions, particularly in alloys that lie in either the 3% (soft) or the 3' fields [1221 ;these alloys are hardest when they are rolled or slowly cooled. The hardness of retained 3' varied between 264 and 399 DPH depending primarily on the molybdenum con, tent; alloys containing the most molybdenum were the hardest. Alloys containing retained 3' + free
S,H.Kittel et aL, Plutonium and plutonium alloys
404
Table 26 Temperature dependence of the tensile properties of alloys containing plutonium. Composition
(w/o)
Temperature (°C)
Ultimate tensile strength (kg/mm 2)
Yield strength 2% offset (kg/mm 2)
25 25 25 200 400 600 8O0 200 400 6OO 800 200 400 600 60O 80O 25 500 625 675 25 25 500 625 700 25 25 650 7oq 25 500 625 675 25 675 25 500 625 675 25 675 25 500 625 675 25 675 700 800
46.7 74.1 78"5 26 19 9 O.5 58 40 8 2 42 27 6 3 I 18.1 30.1 9.5 1.2 4.9 4.0 15.8 8.9 1.2 7.7 14.7 4.6 1.7 6.7 13.3 8.1 2.1 14.7 26.3 30.8 15,7 6.4 5.5
7.2 36.8 53.5
3.6 4.5 19.7 6.8 2.6 6.5 7.0 4.4 4.0
3.2
f
AI-1.7Pu* AI-10 Pu AI-20 Pu U-10Pu**
U-IO Pu-lO Fz
U-15 Pu-10 Fz
U-20-Pu-IO Fz U-I I.I Pu-6.3 Zrt
U-12.3 Pu-14.1 Zr U-16.6 Pu-6.3 Zr
U-18.5 Pu-14.1 Zr
U-15Pu-10 Zr
U-9.1 Ti U-I 1.4 Pu-3.4 Ti
U-17.1 Pu-3.4 Ti U-! 5 Pu-6.5 Ti
O-15 Pu-lO Ti
8.7 1.1
4.1 1.6
Modulus of elasticity_ (kg/mm 2 X 10 "-3)
17.4 6.8 3.0 1.4 10.2 10.6
2.1 1.7 13.0
4.1 1.6
7.2 1.7
11.6 5.8 5.2
17.3 4.3 2.1 6.5 4.3
11.4 2.1 1.7 12.5 6.6 1.6 3.3 25.5 3.0 17.9 7.2 3.6 2.4 2.1 14.7 1.8 1.6 1.4 7.9 3.0 0.8
Reduction of area (%)
Total elongation
77.8 81.7 82.4
37.5 27.4 11.7
(%)
< 1 < 1 > 5 > 10
< 1 < l >10 >2O
<
1
<
1
< I < 1 < 1 >10 < 1 < 1 >25 > 20
< 1 > 10 < 1 < 1 >10 >10 <
1
>10 < 1
< 1 >5 >10 < 1
< l < 1 >5 >5
< 1 > 1 >S >5
< <
< I < J > 10 >5 < J > 20 > 2O
>5
< >10 >I0
I I 3.5 2.0 1
405
S.H.Kittel et aL, Plutonium and plutonium alloys
Table 26 (cont.)
Composition (w/o)
U-22 Pu-I 1.8 Ti
Temperatute (°C)
Ultimate tensile strength (kg/mm2)
500 625 675
8.2 7.5 7.3
Yield strength 2% offset (i~g/mm2)
Modulus of Reduction elasticity of area (%) (kg/mm2 X 10-3 )
Total elongation (%)
* AI-Pu alloys extruded at 400°(2 [561. ** U-Pu-Fz alloys as-cast 11511. ÷ U-Pu-Ti and U-Pu-Zr alloys homogenized i week at 950°(2 and oil quenched [ 153].
molybdenum had hardnesses between 305 and 393 DPH. Alloys in the 3' field had hardness between 174 and 283 DPH; the higher hardnesses are due to greater plutonium content. The mechanical properties of U-Pu-Fz alloys have been determined by Kelman and Dunworth [57, 151] ; the composition of the fizzium was 2.80 w/o Zr, 2.75 w]o Mo, 2.95 2/o Ru, 0.50 w/o Rh, and 1.00 w/o Pd. Some of the ultimate strengths for the alloys homogenized I week at 850°C and oil quenched are shown in table 2.26. They report [57] that the quenched fizzlum alloys are stronger than uranium but that the alloys transformed to alpha are considerably weaker. Their hardness data [ 151 ], however, show that the alpha transformed metal is considerably hardel than the 3,-quenched alloys. The strength of these alloys depends on the proportion of t~, b, and 3, phases. The U-Pu-Fz alloys are brittle at room temperature with increased plutonium content causing greater brittleness. The total elongation of the U-Pu-Fz alloys is near 50% at 650°C but it is limited above 650°C by hotshortness. The U-Pu-Ti, U-Pu-Mo, and U-Pu-Zr alloys have a high ductility above 600°C without the hot shortness of the. U.Pu-Fz alloys. The alloys, however, have very little strength at these high temperatures. The strength decrease and the ductility increase are shown in tables 27-29. These alloys show somewhat more plasticity at lower temperatures when tested i~ compression than in tension. For example, the U-Pu-Ti alloys have appreciable compressive ductility at 600°C but they have no significant tensile ductility below 750°C. It has also been noted that the ratio of compressive to tensile strength varies from 3 : 1 to 1 : 1 depending on whether the
alloy is brittle or ductile in tension [ 57.153 }. Homogenization (table 28) decreased the compressive strengths of the U-Pu-Zr and U-Pu-Ti alloys.
5. Preparation and fabrication 5.1. Introduction
The fabrication of plutonium alloys involves many of the techniques and operations that are used in working the more common metals. However, all operations are directly affected by the extreme toxicity of plutonium in any form, by the tendency of the metal to oxidize rapidly at elevated temperatures c,r when finely divided, and by the obvious necessity of avoiding inadvertent criticality. The toxic properties of plutonium necessitate the use of devices and equipment that enable work to be done without any direct contact between plutnium and the operator. This requirement is ordinarily met by housing all machine tools, melting furnaces, etc., in gloveboxes tb.at provide physical barriers between personnel and plutonium. When plutonium oxidizes, it ordinarily forms powdery PuO 2 , which is highly mobile and constitutes the principal health hazard in most operations. It is therefore necessary to protect the metal against more than superficial oxidation not only tc maintain its metallurgical integrity but as a contribution to safe practice. Consequently, all operations at temperatures appreciably higher than ambient (or when finely.divided metal is involved) should be conducted in atmospheres substantially free from oxygen and moisture. The most effective means of achieving this end is through use of high
$.H'.Kittel et al., Plutonium and plutonium alloys
406
Table 27 Hardness data of U-Pu based ternary alloys. Composition (w/o) U-10
Pu-10
Fz
U-15 U-20
Pu-10 Pu-10
Fz Fz
U-123 Pu-6.6 Mo U-I 3.0 Pu-11.8 Mo U-21.6 Pu-5.2 Mo
U-22.8 Pu-9.1 Mo U-10.8 Pu-5.5 Mo U-23.5 U-5.2 U-15.S U-5.4 U-10.7 U-16.1 U-5.5 U-16.6 U-5.7 U-I 1.4 U-17.1 U-3.0 U-5.9 U-5.9 U-8.9 U-6.2 U-I 2.3 U-232 U-17.1 U-15 U-15
Pu-10.2 Mo Pu-2.1 Mo Pu-2.1 Mo Pu-4.3 Mo Pu-4.3 Mo Pu-4.3 Mo Pu-6.6 Mo Pu-6.6 Mo Pu-9.2 Mo Pu-9.2 Mo Pu-9.2 Mo Pu-! 1.8 Mo Pu-! 1.8 Mo Pu-I 1.8 Mo Pu-ll.8 Mo Pu-14.7 Mo Pu-14.7 Mo Pu-10.0 Nb Pu-3.4 Ti Pu-6.5 Ti Pu-10 Ti
U-22 U-20
Pu.l 1.8 Ti Pu-10 Ti
U-I 1.1 Pu-6.3 gr U-15 Pu-10 Zr
U-20
Pu-10
Zr
U..18.5 Pu-14.1 Zr
Mechanical and thermal treatment
Hardness (DPH)
Ref.
-rquenched o~-transformed or-transformed "f-quenched c~-transformed hQmogenized and forged homogenized and forged homogenized and rolled homogenized and forged homogenized and rolled a~ast homogenized and forged homogenized and rolled as-cast homogenized and rolled as-cast rolled rolled rolled rolled rolled rolled arc cast rolled rolled arc cast rolled rolled arc cast rolled rolled arc cast as-cast as-cast as-casl hom. 50hratS00°C,O.Q. hom. 5 hrat620°C~O.Q. horn. 2 h r a t 9G0°C,O.Q. as-cast hom. 50hrat500°C,O.Q. horn. 5 hr at 620°C, O.Q. horn. 2 hr at 900°(7, O.Q. as-cast as-cast horn. 50 hr at 500°C, O.Q. horn. 5 hr at 620°C, O.Q. horn. 2 hr at 900°C, O:Q. horn. 50 hr at 500°(?, O.Q. horn. 5 hr at 620°C, O.Q. horn. 2 hr at 900°C, O.Q. as-cast
255 433
[152] [ 151 l [151] [151l [ 151 ] [1221 [ 122] [122] [122] [ 122] [ 122] [122] [ 122] [122] [ 122] [ 122] [56] [56] [56] [56] [56] [56] [56] [56] [56] [56] [56] [56] [56] [56] [56] [56] [ 1221 [ 150] {1501 [117] 11171 [117] [ 150] [117] [ 117] [ 117 !
* Large diffczencc presumably due to variation in cooling rate.
215 430 258 318 365 236 273 278 324 410 283 290 320 492 413 160 252 351 266,400* 303 272,423* 259,308* 325 442 426 327 408 282 308 360 428 396 400 410 400 357 355 364 355 465 539 426 428 488 417 415 480 406
11501 [150] i 1171 | 117] [ 117] [ 1171 [ 1171 [ 1171 [ 150]
S.H.Kittel et al., Plutonium and plutonium alloys
407
Table 28 Temperature dependence of the ultimate compressive strength of U-Pu-Ti and U-Pu-Zr alloys [56 ]. Composition (w/o)
Heat treatment
Ultimate compressive strength ( k g / m m
2)
25°C
500°C
164 166 164 127 129
-
12
4.0
-
-
6.9
U-16.6 Pu-6.3Zr U-15 P u - 1 0 Z r
horn.* horn.** as-cast as-cast a~cast
'( 55 < 55 48
12 11 l 1
5.2 2.5 5.6
--
U-I 8.5 Pu- 14. l Zr
horn.
116
-
-
5.6
-
horn.** as-cast horn.* horn.* horn.* as-cast horn.* as-cast as-cast
145 150 96 96 !30 158 90 120 141
U.Pu.Zr alloys U-11.1 Pu-6.3 Zr U-12.3 Pu-14.1 Zr
IU.Pu-Ti alloys I3-91. Ti U-I 1.1 Pu-3.4Ti O-17.1 Pu-3.4Ti U-15 Pu-6.5 Ti U-15 Pu-10 Ti U-22.1 Pu-11.8 Ti
i 15 95 -
625°(?
80 65 -
37
27 45 40 55
13 12 20 30
675°(?
65 50 6.3 3.8
6.3 9.0 10 20
750°C
4.2
35 30 -
4.2 7 10
* I week at 950°(=,oil quenched. ** 1 week at 1050°C, oil quenched. vacuums; but gases such as helium and argon are commonly used as protective atmospheres in those cases to which high-vacuum techniques do not apply. A third means of achieving protection against oxidation during fabrication is canning or cladding, which can be used in special instances.
5.2. Unalloyed plutonium 5.2.1. Melting and casting The melting and casting of unaUoyed plutonium presents few difficulties. The low melting point of plutonium (640°C) permits considerable latitude in the choice of melting equipment and techniques; the only restrictions are those imposed by the necessities of providing a nonreactive environment for plutonium and nonplutonium environment for operating personnel. The furnaces most commonly used for melting unalloyed plutonium are of either the wirewound resistor type or the inductive type. Arc furnaces can be used when it is desired to avoid contact with crucible materials at elevated temperatures. The induction furnace is the faster and more versatile, but it is less easily controlled.
The fluidity of molten plutonium metal is high but its affinity for oxygen causes formation of a tough oxide film even in relatively good vacuums (about 10-5 mm mercury). The mechanical strength of the oxide film can cause conditions which superficially resemble those resulting from a viscous melt, e.g., temperatures necessary to obtain satisfactory pouring may be several hundred centigrade degrees above the melting point. However, once the oxide film has been ruptured, molten plutonium will flow readily. Unalloyed plutonium has the general characteristics of a very castable metal. The low melting point, high fluidity, high density, and small volume change on freezing are all favorable characteristics for casting. But the differences in densities of the various solid phases cause volume changes that make pLoduction of intricate castings impracticable. Simple =,,!id shapes such as cylinders or spheres, in which there is no restraint of shrinkage, present very few casting problems provided dimensional tolerances are generous. Unrelieved restraint will invariably result in fracture, but molds that can be dismantled at temperatures sufficiently high to permit the beta-to-
408
$.H.Kittel et al., Plutonium and plutonium alloys
Table 29 Time (in minutes) to attain 2% creep strain in U-Pu-Ti and U-Pu-Zr alloys [56]. Alloy composition (w/o)
$lsess (k~mm 2)
U-11.1 Pu-6.3 Zr
0.5 1.0
U-16.6 Pu-6.3 Zr
650°C
-
-
-
15
-
-
-
5
---
-
2.0
-
-
0.5
-
1.0
-
4.0
U-18.5 Pu-14.1 Zr
625°(2
4.0
2.0
U-15 Pu-lO Zr
600°C
-
1.0 2.{3 4.0
-
0.5
100,000
0.5
0.5 1.0 2.0 4.0 0.5 2.0 4.0
. .
-
-
10
-
-
l
-
-
-
5,000 80 1 -
-
-
.
400 20
1.0
--
1
-
.
. 20,000 350 5
.
.
.
alpha transformation (and preferably also the gammato.beta transformation) to proceed without restraint can be devised. An interrupted cooling cycle, which permits isothermal transformation to the gamma pbase by holding for several hours at about 275°C, has been found useful in minimizing differential stressing and consequent warping. However, the difficulties and expense involved usually suggest that mechanical fabrication is preferred for producing complex shapes. Gardner and Mann [154] have determined that geometrically simple cast shapes o f plutonium have microcracking to varied degrees. The plutonium purity was generally 99.9+ percent with respect to metallic contaminants and less than 200 ppm total oxygen, hydrogen, and nitrogen. Iron in the plutonium in amounts greater than about 500 ppm was found to inhibit mierocracking, presumably due to the presence o f the Pu-Pu6Fe eutectic. The
.
11P 5
. .
2,000 60 1
-
-
45
-
. .
55 10 3
.
.
.
60 10 2
-
-
.
.
5,000 80 2 .
-
.
3
10
-
. -
-
-
.
5,000 210 !0
800 70
7000C
210 -
10,000
2.0 4.0
U-t5 Pu-10 Ti
5,000
1.0
U-I 1.4 Pu-3.4 Ti
5
675°C
5
. .
mechanism by which microcracking o f plutonium castings is inhibited is dependent " n the ductility of the eutectic [53]. Ostensibly the strain accompanying the phase transformations during cooling are relieved h y deformation o f the Pu-Pu 6 Fe phase rather than the p~utonium matrix. Since microcracks in a billet carry tluough to the detriment of mechanically worked products, introduction o f iron to achieve sound cast b~llets can be a distinct benefit. At this point one must recognize that 1,000 ppm o f iron in plutonium represents nearly 0.5 w/o, and the use o f "unalloyed" as a descriptive term becomes questionable. A wide variety o f refractory materials is suitable for use as crucibles and molds for unalloyed plutonium, although the, strong affinity o f plutonium for oxygen, carbon, :nitrogen, etc., restricts use to the more stable compounds of the oxide, carbide, nitride, boride, and sfliei,rle types. Bare graphite can be used for crucibles and molds if the times o f contact with
S.H.Kittel etal., Plutonium and plutonh~m allo),.~
molten plutonium do not exceed a few minutes and if some ca, ben pickup can be tolerated. Otherwise graphite crucibles should be coated with a less reactive ~uaterial. (MgO and A120 3 have been used as wash materials.) High-fired, high.purlty magnesia has come to be the almost universal refractory material for ordinary use. At temperatures above 1400°C some magnesium metal is introduced into the melt by reduction, but because of its high vapor pressure the amount retained is extremely small. High-purity calcium oxide is perhaps the best refractory known for the melting of unalloyed plutonium but it is not extensively used because it is more costly and more difficult to store than magnesium oxide. Of the refractory metals, tungsten is probably the least reactive with respect to plutonium. However, it is difficult to fabricate and to secure free from porosity; therefore, tantalum has been used much more extensively as a crucible material. Miley and Anderson [ i 55 ] report success in the use of tantalum and calcium fluoride-coated steel crucibles for melting plutonium and plutonium-rich alloys.
20[-
409
I, Calculated from Pearson and Parkins. The Fxtrusior, Of Metals, 2 nd ed, pp 194.
.
Wiley. New York 1960
Pu
® HW- 65019
o. 15,
--36
"~o
0
x
-
_~
IZ).
~lo
,
28 = I g
-
Z
¢.gl
.
~,
5
z
le -
\ o
J00
20o
\ 300
400
,~
8 50o
s00
"too
rEMPERATUr'E C
5.2•2. Mechanical fabrication Although mechanical fabrication of unalloyed plutonium holds little interest in power reactor concepts, some rather unique requirements derive from reactor physics and engineering studies. In the main such work requires foils, plates, or complex shapes that are not easily obtained by casting. Consequently, studies of the mechanical properties as related to fabricability have practical importance. At temperatures above 300°C, the yield strength of plutonium in tension is very low (less than 2,000 psi) and the compressive yield strength is only slightly influenced by testing speed. For these reasons, deformation processes usually employ compression loading. Thus extrusion, hot-pressing, or rolling are useful methods for fabrication of thin or elongated shapes of either simple or complex secti,)n. Los Alamos Scientific Laboratory has had considerable experience in the extrusion of unalloyed plutonium and has used the process in a rather unique manner to generate 0.005 to 0.055 in. thick sheet of area up to 24 in. square from plutonium or plutonium-I w/o gallium [ 156]. Satisfactory products are produced by direct extrusion past
Fig. 27. Extrusion constant and ultimate tensile strength of Sn, C(!. Pu, and AI vs. temperature. (Submitted by Argonne National Laboratory, November 1967•
streamline dies or shear dies with sharp edges. Undercutting of dies is necessary to provide clearance for the formed section. Working ternperatures between 300 and 400°C are coinmt~n for plutonium, although wire of 0.187 and 0.040 in. diameter has been extruded at temperature :,s high as 450°C [157]. A tendency toward galling is overctm~t" by die design and lubrication of die surfaces that contact plutonium with solid lubricants such as Aquadag or Molykote. A comparison between the extrt, sion constants fol plutoniu,n, tin, cadmium, and alt, mint, m is shown in fig.. 27. Although comparison of constants derived from different experiments is risky due to the wlrymg effects of die design, friction factors, and extrusion speeds, one may find some confidence in comparison if the extrusion constants are similar at temperatures where ultimate yield strengths are similar. Such is the case sl,~own in fig. 27, where the tensile strength of tin, plutonium, and ahtminum at several temperatures
410
~i tt K~ett't e~ af Ph~toni~tm and ph~tonfi~m alloys
is indicated by c~)sses ( ~ t 1 ~ ' ~.he ~tlength of the several elemen~ ~equ~,e~ e~i~l~ properties becau~ of tile dearth ~ ,:~n~pressive strength at the vari('~!~ t e m ~ , ~ Ih~wevet. m Ihe range of trdere~t~ the v~htes ~d ~ . . ~i.v:~ yield and ultim~,~~tensile ~trer~gth ~ exp,, ~ed to be about the same One ¢~nchld¢~ fro|l| thi~ fi~|l'e that the forces required for lhe ext[||$lO|l ~i |r~utt~niulll are significantly smaller th:m those neces~ry fin alu1111flLlrll eXtrllSlOn at ct)|vvparable ~emperature The rolling ot unalloyed plulonmun htls been reported by tiovton and Ward I 1581 Sheel lrom 0.048 to 0.01(~ m. thick v~,asformed at reductions of "~
e'¢
I 0 to .,3 ~, at 175°C. Since the room lerllperature
(monoclinic ~) phase is brittle, the rolling schedules were carried out in the ductile ~3phase. Roll surfaces and ingots were maintained at 175°C, and reduced from 0.225 In 0.048 in. in 15 phases. A specimen flom the above sheet was reheated to 175°C and r(~lled to 0.016 in. thickness in 5 passes with only slight edge cracking. Distortion during the phase changes was significantly reduced by clamping the sheet between warm steel plates. Alpha plutonium has excellent machining characteristics that resemble those of gray cast iron. However, the combination of high coefficient of expansion, low thermal conductivity, and low transformation temperature { 123°C) makes necessary a high degree of care if precision is desired. Plutonium is machined with standard metal working tools. Tools of high-speed steel can be used to machine unalloyed plutonium, but carbide-tipped tools are preferable because of their superior resistance to abrasion. 5.2.3. Heat treatment Because of its complex solid-state transformations, the benefits to be derived from the heat treatment of unalloyed plutonium are quite limited. Partial relief of stresses generated by the beta-to-alpha transformation can be accomplished through holding in the high-alpha range {1 I0 to 115°C) for extended periods of time (of the order of thousands of hours). Dimensional stability can be increased by subzero treatment, and controlled cooling of castings can significantly reduce stress levels. However, most of the considerations that lead to heat-treating programs • for pure metals are absent in the case of plutonium. Since there is no known practicable method for
cold working plutonium, there is no need for ordinary stress-relieving or recrystallization heat treatments. Becau~ of the low temperature phase transformations, ureatments for control of grain size are of little con~quence, although some degree of influence can be exercised through variations of beta-grain sizes and transformation conditions.
5.3. Plutonium alloys for power reactor use Plutonium alloy fabrication development for power reactors has been almost entirely associated with alloys for fast breeder reactors. This application requires a plutonium content on the order of 15 w/o. As much 238U must be in the alloy as possible in order to enhance internal breeding ratios. The remaining alloying elements in the alloy are normally those that improve the properties of the alloy. For example, zirconium is added to uranium-plutonium atloys to increase their melting points and to improv(! their compatibility with austenitic stainless steel, in another class of alloys, ~he uranium-plutoni,amfissium alloys, several fission product eleme~ts are left in the alloy as a result of the type of reprocessing cycle. 5.3. I. U-Pu-Fs alloys The initial fuel loading for EBR-Ii was U-5 w/o Fs [ 159]. Development of U-Pu-Fs alloys for EBR41 was also considered attractive [ 1601. Although processes to yield a wrought product were considered, injection casting [ 161] was finally selected ~s the fabrication procedure that satisfied fuel requirements on a economical basis [I 62]. As a result, nearly all experience in fabrication of U-Pu-Fs alloy fuels has been based upon injection casting. (a) Alloying. The preparation of alloy fi.;r injection casting is a relatively simple procedure. Predetermined weights of each of the alloying elements are charged to a weighed bottom.pour crucible with a stopper rod closure. The crucibles used at ANL are yttriacoated graphite. Although such materials as magnesia, calcium oxide, and zirconia are acceptable, good fits between stopper rod and crucible bottom are more difficult to achieve with such materials than with graphite. The yttria coating is applied to limit carbon contamination of the melt, The charged crucible is heated in an induction furnace to 1350 to 1400°C and maintained for
S.H.Kittel et al., Plutonium and plutonium alloys
periods up to one hour at a pressure of about 50 microns of mercury. Holding times of this order have been found necessary to out-gas the metal and to permit dross to come to the surface. After melting and holding, the stopper rod is withdrawn from its seat in the crucible bottom and the metal drains into an yttria-coated graphite mold of cylindrical shape. The dross formed during melting clings to the crucible side and is thereby separated from the ingot. The ingot resulting from the described procedure is weighed, sampled for analysis, and charged upside down to a crucible preparatory to injection casting. Losses on oxidation result in a slight increase of fissium content [163] but do not significantly affect ithe relative proportions of the fissium elements with the exception of zirconium, which is lost disproportionately to the dross. In the case of fissium alloys, analysis agrees with charge calculations within the limits of the analytical method, and no problems arise from inhomogeneity. (b) Injection casting. Injection casting has as a basis the elementary physical concept of support of a liquid column by the impression of a differential pressure across a liquid interface within and without a tube [164]. This phenomenon is characteristic of a closed tube manometer. One may readily calculate the height of an alloy column that can be supported by a pressure of one atmosphere in a previously evacuated tube; for an alloy of density 18.2 g/cm 3 this height is about 22 in. The above calculation assumes a static condition that cannot reflect the influence of hydraulic effects, casting cooling rate, mold filling rate, and the changing density of the casting during cooling. The importance of these effects is minimized by control of the casting parameters. Casting temperatures exceed the liquidus temperature by about 300°C and molds are heated before casting to insure against solidification during the injection of metal. In order to negate the effects of cooling during casting, pressurizing times are low - about 1 to 3 see - and the furnace pressure after casting is about one atmosphere. Adequate control of these variables results in successful casting of right circular cylinders of length to diameter ratios greater than 100 to 1. Fig. 28 is a plot of the influence of some casting parameters upon fuel pin length limited by 17 in. long molds. This process is particularly sensitive to changes in
Moll' No.
411
Mill
3CI 302 303 4D2
Tamp C
Costing Pressure psi
Initial
Prall~l~r,zmgTfa~ see
1320
53
3
1320 1325 1325
42 45 45
2 2 2
!
~s Denote Ave Ltngth ~B
E
!4D2
14
IS CASTING L[NGTH IN INCHES
16
1
I?
Fig. 28. Distribution versus casting length for conditions noted. (Submitted by Argonne National Laboratory, November 1967). casting parameters. Low melt or mold temperatures and long pressurizing times yield short pins. High melt temperatures and failure to maintain the melt in contact with the open ends of the molds for a sufficiently long peried promotes dripping of metal from the molds or hot shortness. The hot short condition is aggravated by the temperature difference between liquidus and solidus that is characteristic of U-Pu-Fs alloys (about 170°C for U-20 w/o Pu-10
w/o Fs). A typical injection casting furnace of the type used in the Plutonium Fabrication Facility at ANL is shown hi fig. 29. The furnace is housed in a glovebox that contains a helium atmosphere. The furnac proper consists of a covered induction heater assembly surrounded by radiation shields, a movable platform that holds the crucible, a mold suppert stand and the furnace envelope. Injection casting is accomplished by evacuating the fi~rnace; heating the metal charge, which is held in an yttria-coated graphite crucible, to casting temperatures; opening the heater cover; raising the crucible to submerge tl~e open end of yttria.coated Vycor molds; and pressurizing the furnace with helium. After an appropriate time the crucible is lowered and the furnace is cooled preparatory to removal of gravid molds. By this method uranium.plutonium-fissium/fizzium pins of diameters from 0.130 to 0.160 in. are made to lengths up to 18 in. Mold replication is very precise
412
S.tt.Kittel et al.. Phttonium and plutonium alloys
Iig. 29. Injection ca~ting furnace i~ glovebox.
S.lt.Kittel et al., Ph~tonium and phaonhon allto's
and diameter variation less than + 0.001 in. is a con> mon occurrence. During the casting of about 400 pins of U-lO w/o Pu-I 0 w/o Fz, U.I 5 w/o Pu-lO w/o Fz, and U-20 w/o Pu-lO w/o Fz diametral shrinkage of the castings was found to be about 1.5%. Gamma radiography showed internal shrinkage, similar to that occurring in U.Fs alloys, ,m doubt due to the inability to feed the mold cavity during solidification. Although plutonium-bearing fizzium alloys are more brittle than the uranium-fissium counterpart, they are not too fragile for routine handling. The fabrication of injection cast fuel into acceptable sodium-bonded fuel elements has been described in detail [ 165-167] and will not be repeated here. The bonding step, however, deserves special mention. In this process, as presently conceived, a continuous liquid metal annulus between fuel and jacket is achieved by heating the jacket, fuel, and liquid-metal (usually sodium) to about 500°C while the assembly is under vibration, in the case of U-5 w/o Fs alloy, specimens quenched from above the gamma eutectoidal temperature retain the lower density gamma phase in a metastable condition. Upon soaking at 500°C, a 3, -+ o~transformation occurs resulting in an increase in density of about 1%. Injection cast U-Pu-Fs alloys, upon heat treatment achieved by sodium-bonding, show ,,similar dilatometric effects [168]. The change in density manifests itself in a smaller diameter fuel pin than is found in the as-cast measurement. Where precise liquid-metal cover over a fuel pin is desired, one must adjust the sodium charge to compensate for the change in fuel pin dimension occasioned by the metallurgical transformations accompanying bonding. 5.3.2. U-Pu-Zr and U-Pu-Ti alloys The fabrication experience with l_l.Pu-Zr and U-Pu-Ti alloys at ANL has been contined to injection casting as described in the preceding section. The zirconium and titanium ternaries ale discussed under a common heading because of similar behavior during fabrication by injection casting. The following discussion, although restricted to U-Pu-Zr alloys, is also typical of U-Pu-Ti systems. (a) Alloying. During 1965 about 100 fuel pins of U-Pu-Ti and U-Pu-Zr alloys were fa0ricated [169]. The higher melting point of zirconium (1852°C) and titanium (1675°C) impresses extreme conditions on
413
alloying over fllose required to make fissmm alloys. The low density of zirconium and titanium ((,.5 and 4.5 g/cm 3 , respec,ively, at room lemperaturel retali~e to that of uranium or plutonium is cause for additional problems oll alloying lhat result in il:htmlogeneity. Alloying at temperatures below the melting point of either zirconimn or lit:lnilllll requires holding times sufficient to promote dissolu. tion followed by liquid-liqmd diffusion of the zirconium or titaniunl into the ur:mium o r plulonit|lll. Long holding time at temperature compromises allox quality by the tendency of zirconium to oxidize or carburize at the expense of c,ucible or ~ash materials. Alloying to achieve the COlnposition U-I 5 ~v/o Pu-10 w/o Zr has been accomplished wi~ll a measure of success by maki1~.g separate uranium-10 w/~ zirconium and plutonium-12 w/o zirconium melts. Melting is carried out under eacuum in yttriastabilized zirconia crucibles at 1450°C for holding times of one hour. Bottom-pouring of the meh into a mold is employed to separate the metal from lhe dross. The alloys are analvzed and later charged to an injection casting crucible in a 5 : 1 ratio ~1 U-Zr to Pu-Zr with sufficient zirconium to make up drossing losses that resulted during alloying. The liquidus temperature of Pu-] 2 w/o Zr is about 1000°C and that of U-lO w/o is about 1200°C. ('~lllbin:.tlioll tq" these alloys permits melting and dissolution al temperatures below those required for rejection casting, thereby, the final step of alloying is carried out during the melting operation incidental Io injection casting. Erosion of yttria-coated graphite and vttriastabilized zirconia crucibles is a characteristic of alloying by the technique described above and oxygen coPlanlinalion to the extent of I000 to 2000 pptn is common in the resulting alloy. An alternate method of alloying is to process a tnaqer alloy of Pu-40 w/o Zr by arc-nlelting. By this method smaller quantities of binary alloy are required to make a U-15 w/o Pu-10 w/o Zr ternary and at) crucible is necessary. The ternary alloy is made by charging master alloy and uranimn in the ratio 1 : 3 to an ytlria-stabilized zirconia crucible and induclion melting. Since the liquidtts temperature of Pu-40 w/o Zr is about !400°C and that of tl-I 5 w/o Pu-lt) w/o Zr is about 1250°C. homogeneity may be attained
414
S.H.Kittel et al., Plutonium and plutonium alloys
and crucible erosion limited by first meltingat about 1400°C and then holding at about 1300°C for times up to one hour. (b) Injection casting. The injection casting process is unaffected in principle by the alloys cast. However, the liquidus temperature o f the alloy to be processed does alter the values of controlling parameters. Since "~he liquidus for U-15 w/o Pu.lO w/o Zr is about 1250°C the rates of heat loss from castings is greater and casting temperatures are higher thanfor U-15 w/o Pu-lO w/o Fz whose liquidus occurs at about 1000°C. Since injection casting of U-15 w/o Pu-10 w/o Zr requires a melt temperature near the softening point of Vycor, the duration of immersion of molds is maintained at a minimum. The effect of this requirement is off-set somewhat by the high rate of heat loss after casting. Castings made in Vycor by this method are slightly larger at the open end of the mold due to slower cooling and improved feeding, softening of the Vycor and distortion due to pressure effects. Cropping of the ends of the castings, which is normally necessary to meet fuel pin length requirements, remedies this condition, Acceptable fuel pins of 0.144 in. diameter by 14 in;long are made by the injection casting process. Problems related to the softening point of Vycor, which occurs at about 1500°C, have been solved by the use of quartz molds, which melt above 1700°C, but are much more expensive. The injection casting of alloys containing larger quantities of zirconium th~n 15 w/o will, no doubt, dictate the need for mold materials other than Vycor due to the elevation in melting and casting temperatures. 5.3.3. AI-Pu alloys Research and development in the United States on AI-Pu alloys related to application as a power reactor fuel has been carried on largely at the Pacific Northwest Laboratory. This work was initiated in mid1956 with authorization of the plutonium recycle program. Fabrication has included loadings for the Materials Testing Reactor (MTR), Plutonium Recycle Critical Facility (PRCF), and Plutonium Recycle Test Reactor (PRTR) [ i 70]. Extensive fabrication experience with Pu-AI alloys also exists as a result of work done in Canada [171 ]. The techniques employed for fabrication of AI-Pu fuels has included
roll cladding with aluminum, coextrusion with alu: minum, injection casting, and encapsulation of unbonded AI-Pu bondies. • (a) Alloying. Aluminum-plutonium alloys con. taining up to 20 w/o plutonium are not subject to serious oxidation and the melting and casting operationsmay be carried out in air. At PNWL alloying is accomplished bycharging metallic plutonium and other desirable elements, such as nickel and silicon, directly into molten aluminum that is contained in graphite or clay-graphite crucibles [172,173]. An open tilt-pour furnace that is heated by induction is used in the melting operation. Alloying temperature about 950°C is normal and sufficient stirring results from induction heating that homogeneity is attained within ten minutes at temperature. When resistance heated furnaces are used manual stirring is required to achieve melt homogeneity. By such methods 25 It) charges of alloy containing 1.8 w/o Pu were prepared for the spike fuel elements for PRTR. Because AI-Pu alloys have-poor corrosion resistance in high temperature water, similar alloying procedures with equally good results were conducted on AI-1.8 w/o Pu.1.3 w/o Ni.1.1 w/o Si alloy, which exhibits improved corrosion qualities. Sampling of alloy melts is normally performed by ladling directly from the melt or using a small protmsion that is cast into a rod c r billet. The alloying procedure described above yields excellent agreement between analyses taken on samples by either method and analyses from fabricated elements. (b) Casting. Aluminum-plutonium alloys have been injection cast [ 174], cast by top-pouring [172] and vacuum cast [ 175]. The alloys, generally, are cast from the crucible used during alloying employing techniques described above. In the case of casting small cylinders for fuel elements and extrusion billets, melt temperatures 30 to 75°C above the liquidus are normal. Alloys containing up to 20 w/o Pu have been cast within ± 5% of nominal composition and three mil diametral tolerance by this technique. Injection casting has been proven feasible [ ! 74] through the casting of 90.in. long AI-2 w/o Pu.2 w/o Ni alloy into 0.035 in. thick zircaloy cladding. Cored billets of alloy were charged to a clay-gr~uhite crucible in an injection casting furnace, the furnace closed, and a shroud tube assembly containing the zircaloy molds was attached to the furnace top.
S.H.Kittel et aL, Plutonium and plutonium alloys
Soaking for 15 to 30 min at 900 to 950°C was required to limit plutonium segregation to 2.5 + 0.1 w/o Pu. Although feasibility was demonstrated by the method described, the control of casting defects such as porosity and hot tearing remains to be treated. (c) Mechanical fabrication. Aluminum-plutonium alloys have been fabricated into prototypic fuel elements and monitoring foils by rolling, extrusion, and coextrusion. Over 200 fuel rods were fabricated by extrusion at PNWL [ 175 ]. Extrusion was petformed on billets of Al-1.8 w/o Pu prepared by the alloying and casting techniques discussed above. Bare cylindrical billets approximately 2½ in. in diameter and 10 in. long were extruded through nonlubricated flat face shear dies. At die and billet temperatures of 500°C, 80,000 psi was required to achieve an extrusion ratio of 25 to 1 at a ram speed of 20 in./min. In this manner, rods about 9 ft long and 0.500 + 0.001 in. in diameter were made. Coextrusion of aluminum-plutonium cores with aluminum cladding is exemplified in the fabrication of 144 fuel elements for the Transplutonium Program of the Savannah River Laboratory [ 176]. This work consisted of fabrication of A1-7.35 w/o Pu into fuel rods 0.94 in. in diameter by 5 ft long with cladding thickness from 0.040 to 0.120 in. The coextrusion billet was macle up of a 0.350 in. thick X-8001 aluminum alloy shell containing an aluminum7.35 w/o plutoqium core that was 1.80 in. in diameter. The ektsusion program consisted of an average extrusion pressure of 64,200 psi and extrusion die temperature of 100°C. Since the core was harder than the cladding, the extrusion program resulted in reduction ratios of 5.9 : 1 for the core and 11 : 1 for the clad at a ram speed of 20 in./min using lubricated streamline dies with a 90 ° entrance
angle. 5.4. Zero power reactor fuel alloys The demands of reactor physicists for fabricated configurations containing plutonium alloys to be used in zero power reactors are limited only by the experimentafist's imagination. The alloys and shapes made for this purpose are indeed myriad. As a result this section will be confined to alloys made in large quantity or to the response of an alloy to a particular fabrication process. Zero power reactor fuels are used for a number of
415
purposes from complete matrices for large scale mock-up critical experiments to single elements for reactivity worth determinations of various kinds. In general, plutonium-alloy zero power reactor fuels are made in the form of jacketed right circular cylinders or thin flat plates. To meet safety requirements at the critical facilities, the compositions are chosen such that the pyrophoric properties of plutonium and uranium-plutonium alloys are minimized by alloying with elements of low neutron capture cross-section. The elements should withstand the rigors of repeated handling without effect to the core or distortion of the jacket. The requirement that pyrophoricity be limited stems from the obvious consequences of an element that develops a breach in its jacket during its lifetime. Alloying constituents of low neutron capture cross-section are desirable to permit criticality for a particular geometry to be reached with a minimum number of elements. 5.4.1. U-Pu-Fe alloys Early in 1964 experiments were performed at ANL to establish the feasibility of manufacturing Masurca elements by centrifugal casting [177]. The Masurca element is a right circular cylinder ~ in. diameter by 4 in. long containing a fuel section of U-25 w/o Pu-1.5 w/o Fe alloy. The fuel core is surrounded by a close-fitting Type 304 stainless steel jacket of 10 rail wall thickness. The technique employed is properly called centrifuged casting. In this method of centrifugal casting, molds are spaced with their axis along the radii of a rotor at the center of which is a distributor that acts as a downgate. Centrifugal force is applied, through the spinning rotor, to the metal as it is cast onto the distributor. This method of casting was used because maximum metal density was desired in the Masurca element. Maximum metal density can be achieved by centrifugal casting because the molten metal is quickly forced into the molds thus preventing premature freezing and consequent laps, surface irregularities, and if done under vacuum, voids formed by entrapped gases. The centrifuged casting furnace esed for the manufacture of the prototype Masurca fuel rods was an induction-heated vacuum furnace equipped for bottom-pour casting by the use of crucible with a removable stopper rod. The crucible stool was cored to permit the falling metal to impinge directly upon a
S.H, Kittel et al., Plutonium and phttonium atlovs
spinning distributor and be conducted by centrifugal force into the molds. The distributor was equipped with heaters to permit close control of the temperature of casting metal. The core alloy was cast directly into the stainless steel jacket. To prevent bonding of the core to the jacket, the jackets, which served as mold liners, were clamped between close-fitting split copper molds. During casting the molds act as heat sinks that conducted heat away from the thin steel jacket fast enough to prevent reaction of the plutonium alloy with the steel. The solidus-liquidus range for the Masurca alloy composition is from 665 to 825°C. Alloying was accomplished by holding the alloying constituents for one hour at a temperature about 400°C above the liquidus and a pressure of 1 X 10 - 3 tort. Holding at temperature and reduced pressure dcgassed the metal and insured against undesirable poro~i,y in the castings. Casting conditions for crucible charges of about one kilogram of met,~l were: 1340 g Charge weight 1230°C Temperature of metal cast I X 10 -3 torr Vacuum Temperature of distributor 450-500°C Rotor speed 350 rpm. A rotor speed of 350 rpm applies a force of about ten pounds at the center of a Masurca element w h i c h results in a pressure of about 50 psi at that point. The castings resulting from the application of this technique showed no evidence of reaction between the jacket and core. A radial shrinkage gap of about 0.001 in. between the jacket and core at room temperature made it possible to "demold" the casting by simply pushing the cast slug out of the jacket. The establishment of feasibility of manufacture by centrifuged casting was followed by implementation of the process. In the period 1965 to 1967 this process was used to fabricate over 700 kg of depleted U-25 w[o Pu-1 w[o Fe alloy into Masurca fuel elements [178]. Fig. 30 is a photograph of the internal components of the centrifugal casting furnace used at the European Institute for Transuranium Elements, Karlsruhe, Germany, to cast the Masurca fuel alloy. !
417
5.4.2. U-Pu-Mo alloys Zero power reactor requirements involving large quantities of plutonium are characterized by Ihe Zero Power Plutonium Reactor (ZPPR) experiments. The reference design for the fuel body was established as a plate 0.200 in. thick, 1.930 in. wide, of several lengths from 0.940 to 8.940 in. in one-inch increments. The fuel composition was chosen on the basis of acceptable behavior in a neutron environment, physical properties, oxidation rate. ~md fabricability. The alloy selected was U-28 w/o Pu-25 w/o Me. U-Pu-Mo alloys have a coefficient of expansion greater than 20 × I0- 6/°C at 600°C which is sufficiently high to insure contact of the fuel with a closefitting Type 304 slainless steel jacket upon healing [179]. This requirement was necessary to assure prompt expansion of the jacketed fuel element in response to external as well as internal (nuclear) heating and consequent prompt reactivity change. Ignition tests by Fischer and Schnizlein [ 1801 and oxidation rate determinations by Kelman et al. [ 179] indicated that the reference a!loy oxidized slowly, 0.3% weight gain after 120 days in zn air atmosphere at room temperature, and sustained ignition in air takes place above 600°C. (a) Alloying and casting. Alloying of U-Pu-Mo may be accomplished by first producing a binary of U.Mo. Since molybdenum has a density of 10.2 g/cm 3 , compared with l 8.7 ~ c m 3 for uranium. inhomogeneity due to partition of molybdenum can be a problem. The melting point of molybdenum is 2625°C and that of uranium is 1133°C. The difference in melting po~,nt means that, at temperatures between the melting points of molybdenum and uranium, the molybdenum must be dissolved fron~ the solid state by the uranium and time at alloying temperature must be sufficient to affect the dissolution. The binary alloy of uranium and molybdenum has been produced by charging pelleted molybdenum powder and chunks of uranium to an yttria.coaled graphite crucible of the stopper-rod variety [ ! 811. It has been found that pelleted molybdenum powders show taster dissolution rates than either powders or solid forms. Powder~ have a tendency to separate by flotation and solid chunks dissolve much more slowly than porous pellets due to the decreased surface area.
418
S.ILKittel et al,, Plutonium andplutonium alloys
The crucible is heated by induction under a pressure of 10-~2 rtO lO~ 5 torr to 1450 to 1475°C in about one hour and held at temperature for about 40 min. Molybdenum is lost during the binary alloying process to the extent that a final alloy composition containing 3.54 w/o Mo results from 3,85 w/o Mo charge. The melting point o f the resulting binary alloy is about 1200°C. The binary alloy is cast into yttria. coated graphite molds to form cylinders that are broken into pieces as charging stock for the ternary alloying process. The ternary U-28 w/o Pu-2.5 w/o Ivloalloy is produced from the binary alloy by charging several large pieces of U.3.5 w/o Mo to a yttria coated graphite bottom-pour crucible. Plutoniura is placed on top of the binary alloy along with sufficient uranium to adjust for excess molybdenum occurring in the binary alloy. Ternary alloying and casting are accomplished simultaneously. The alloying constituents are brought to 1380°C by induction heating under a 10 - 2 to 10-5 tort pressure in about one hour and held at this temperature for 30 rain. The molds into which the castings were made consisted of graphite plates into one side of which was milled a cavity 1.973 in. wide, 943-in. long, and 0.206 in. deep. The milled plates were stacked together to form a book-type mold. The inside surfaces of the mold cavity were coated with yttria and the mold components were assembled and held together by tie-bolts and spring washers. The entrance to the molds was a trough or header that was heated to about 1000°C to insure against "pipe" at the top of the casting. At the above conditions acceptable castings resulted from pouring w~en a thermocouple, centrally located in the mold assembly, indicated a temperature of 450°C. (b) Mechanical fabrication. Some experiments to determine the feasibility of producing ZPPR core elements by secondary metal working methods have been carried out by Carson [ 181 ] at ANL. Attempts were made to roll slabs of U-28 w/o Pu-2.5 w/o Mo on a 5 in. diameter by 8 in. wide two.high laboratory rolling mill enclosed in a helium atmosI.~:~ereglovebox. Compressive yield determinations [179] have shown that this alloy system shows low yield characteristics below 550°C. For this reason rolling was carried out on billets at temperatures between 575 and 650°C. It was found that, for reductions of as little as five
which this alloymay be rolled without complete hil. ure of the work piece:It was possible to achieve a fifty percent reduction in five passes ona-~ in. thick billet heated to 650°C and fed between rolls heated to 300°C. Although no serious edge cracking resulted from this rolling schedule, the effect of temp ~:l~ature in the helium atmosphere containing up to 1500 ppm oxygen and 70ppm moisture was to severely oxidize the metal surfaces. Machining of U.28 w/o Pu.2.5 w/o Mo alloy has been accomplished both at room temperature and at elevated temperature. The knowledge that this alloy contains significant quantities of the zeta phase and the experience with rolling prompted an investigation of hot milling characteristics. Electrically heated fixtures held in a horizontal milling machine were used to raise the temperature of the work piece. At 200°C clean cuts were produced without evidence of chipped edges. Although the surfaces were acceptable, dimensional control was a problem due to the different thermal expansions and temperatures of the work piece, jigs, and milling machine components. At room temperature satisfactory machined surfaces were obtained by using carbide.tipped milling saws. The life of the carbide-tipped saws can be extended by a factor of four by chamfering the sides of the teeth to remove that portion of the tooth that is first to dull. The chamfered saws are less prone to cause chipping of the brittle fuel alloy and provide machined sur. faces that have a polished appearance.
6. Compatibility behavior The extent to which a metallic fuel and cladding material interact in a nuclear reactor is a primary consideration in their selection. Clearly to be avoided are fuel.cladding combinations that interact to affect either melting of the fuel or the formation of reaction layers that may lead to failure or penetration of the cladding and consequent release of fission products into the reactor coolant. Walter et al. [182, 183] surveyed by means of diffusion couple studies the out-of.reactor compat~ility of U-Pu-Zr, U-Pu-Ti and U-Pu-Fz alloys with a wide variety of materials. Their results, which show file extents to which uranium and plutonium penetrate
S.H.Kittel et al., Plutonium and plutonium alloys
419
Table 30 Fuel penetration into commercial Fe- and Ni-base alloys Cladding
Fuel alloy
Penetration (microns)
(w/o) 5000 ht at 700°C
1000 hr at at 750°C
168 tit at 800°C
Tin*
(°0
U-17 Pu~6 Zr
304 SS Hastelloy
12 (400 ht) 50 (400 hr)
Melted Melted
Melted Melted
725 4"25 725 + 25
U-15 Pu-10 Zr
16-15-6"* Haynes 56 16-25-6"* 304 SS N-155 Incoloy 800 Hastelloy-X
2 2 4 7 30
<
<
825 -+ 25 825 -+ 25
16-15-6"* Haynes 56 304 SS 16-25.6"* N-155 Incoloy 800 Hastelloy-X
U.18 Pu-14 Zr
U-10Zr
304 SS
U-10 Ti U-I 5 Pu-10 Ti U-22 Pu-12 Ti
304 SS 304 SS 304 SS
5 8
<85o
-
70 < -
5 15
6 4 2 80
30 (1000 hr)
12 > 40 27 Melted
Melted Melted
5 5 9 15 20 ~> 40 Melted
<: 6 4 12 20 70 Melted
3
30
9
Melted Melted at 650°C
28
12 (168 hr)
Melted
825 -+ 25 < 850 775 + 25 725 +- 25 > 825 825 -+ 25 825 + 25
< 850 825 -+25 825 -+25 725 +25 835 -+ 15 775 +25
< 700 <650
* Temperature at which liquid phases occur in diffusion layers. ** Timken 16 Ni-15 Cr-6 Mo and 16Ni-25Cr-6Mo.
Table 31 Fuel penetrations into V-20 w/o Ti and V-15 w/o Ti-7.5 w/o Cr alloys (microns). Fuel alloy
Anneal time
(w/o)
(hr)
6oo%
?oo°c
800%
V-20 w/o Ti U-18Pu-14ZI
168 1000 5000
U-22Pu-12Ti
168
<1
to2 1.5 to 3 3 to5 1
to3
5to 9 9 to 16 17 to 23 6to
9
V-15 w/o Ti-'l.5 w/o Cr U-18Pu-14Zr
168 1000 5000
<~1 1 2
tol.5 to3 to4
U-22 Pu-12Ti
168
~. 1
to 2
4to 6 9toll~ 15to17
15 to 17
$.H.Kittel.et aL, Plutoniam and plutoniumalloys
420
Table 32 U-Pu-Fz alloy fuel penetrations (calculated) into variouspure metals and alloys in one year (microns). Combination
--r'-------r----
I
'
I
,
I
Temperature (°C)
(w/o)
V-20 Ti/U-10 Pu-lO Fz V-20 Ti/U-15 Pa-10 Fz V-IO Ti/U-10 Pu-lOFz Cr/U-10 Pc-10 Fz Mo/U-IOPu-10 Fz Mo/U-I$ Pu-10 Fz 304 SS/U-IOPu-lO Fz 304 SS/U-15 Pu-lO Fz Hast-X/U.l0 Pu-lO Fz Hast-X/U-l$ Pu-lO Fz Nb/U.I 0 Pu-lO Fz Nb/U-20 Pu-lO Fz Nb-I Zr/U-IO Pu-lO Fz
500
600
650
700
750
3
15 15 20
30 50
75 100
4
6 6 10
15
10 15 25
25
50
20 30 25
45 75 35
15 25 60 100 110 190 700 1300 600
V12OTl IN U[ISPu,/I.STi O.~K
30 25 35
/ / : i
0,21 ~
TYPE~
/17
$$ I#
,f
/
/
/ // /
/
~- ~J~T, ,u
U~|SPu/iQZr
o.,o
--
the materials in the range 600 to 800°C, are summarized in tables 30-33. Above approximately 650°C the use of iron- and nickel,base alloys as claddings for the U-Pu-Ti and U-Pu-Fz alloys is inadvisable because of either marked cladding penetration or melting resulting from the transport of the eutecticforming elements iron and nickel into the fuel alloys. The use of nickel-base cladding alloys, e.g., lncoloy 800 and Hastelloy-X, for the U-Pu.Zr alloys has a similar limitation. Several commercial iron-base alloys, however, exhibit a high compatibility in laboratory tests to at least 750°C with U-Pu-Zr alloys containing 14 to 17 w/o plutonium and 10 to 14 w/o zirconium. The particular iron-base alloys include Type 304 stainless steel, Haynes 56, and steels containing 16 w/o nickel, 6 w/o molybdenum, and either 15 or 25 w/o chronium. With these combinations, cladding penetration is limited to 7 microns or less in 5,000 hr (1-2year) at 700°C and liquid-phase formation in diffusion layers occurs only above 800°C. The restricted diffusion is attributed to the formation of a diffusion layer that consists of one or more zirconium. rich phases which are stabilized by diffusing oxygen. The phases act effectively to restrict the transport of iron and nickel into the fuel alloys as well as the diffusion of uranium and plutonium into the cladding. The presence of from 100 to 450 ppm (by weight) of
1200
I/'s
llO0 IDIIIIlITUIE, ¢
i ? l 30q.IS IN
IIO0
1500
Fig, 31, Penetration rate vadalion with temperalul~ for Type
304 stainlesssteel abd V-IOTiin both U-15 Pu-10 Zr and U-15 Pu-6.5 Ti (maximum rates). oxygen in the iron-base alloys is seen to be a beneficial if not necessary factor affecting the compatibility. At temperatures to 800°C the use of the V-Ti and V-Ti.Er alloys as claddings for the U-Pu-base alloys is limited solely by the extent to which uranium and plutonium penetrate the dadddings and form brittle phases. The V.20 w/o Ti alloy is highly compatible with the U.pu.Zr and U-Pu-Fz alloys up to approximately 650°C. Above 650°C its use is limited because of pronounced penetration of uranium and plutonium. Substitution of chromium for some of the titanium in the alloy has little if any effect upon the diffusion behavior. Savage [184] has determined the rates of penetrao tion into Type 304 stainless steel and into V-20 w/o Ti alloy of molten U-15 w/o Pu-10 w/o Zr and U.15 w/o Pu~6.5 w/o Ti alloys in the temperature range 1200 to 1450°C. The rates are plotted versus temperature in fig. 31.
3.8 X 10 - t 3 1.6 X 10 -13
X 10 - 1 4
8
3.6 X 10 - 1 4
304 SS/U-15 Pu-lO Zr
304 SS/U-18 Pu-14 Zr
* No cladding penetration. K's represent band on the fue~ side believed to be (U, Pu)O 2. Vanadium contained 1300 ppm oxygen. ** Calculated from only one datum point assuming an X: = Kt law. t Obeyed the X = Kt rather tb~n X 2 = Kt rate law. t÷ Total band width. Also calculated from only one datum point ossuming an X 2 = Kt law.
2.0 X 10 - 1 3 1.5 X 10 -14
1.8 X 10 -13
8 . 0 X I0 -Is
V-15 Ti-7.5 Cr/U-18 Pu-14 Zr
304 SS/U-10 Zr
3.5 X 10 -13
1.5 X 10 -14
V-20 Ti/U-18 Pu-14 Zr
"['~'2.3X 10 -13
t l . 9 X 10 - 9 cm/sec
304 SS/V-20 Ti
4.0 X 10 -13
1.6 X 10 -13
Nb-I Zr/U-IO Pu-lO Fz
t4.2 X 10 - 9 cm/sec
t?3.4 X 10 -13
1.8 X 10 - 1 2
2.3 X 10 -13
Nb/U-20 Pu-lO Fz
t2.2 X 10 - 9 cm/sec
**1.1 X 10 - 1 !
3.6 X 10 -12
**3.4 X 10 -12
1.1 X 10 - 1 2
304 S$/V
6.3 X 10 -13
8.0 X 10 -13
1.3 X 10 -13
1.8 X l 0 -13
Nb/U-10 Pu-lO Fz
Hast-X/U-15 Pu-10 Fz
Hast-X/PU-10 Pu-10 Fz
304 SS/U-15 Pu-lO Fz
2.2 X 10 -13
**4.0 X 10 -13
**2.0 X 10 -13
**7.5 X 10 -14
Mo/U-15 Pu-10 Fz
304 SS/U-IO Pu-lO Fz
1.9 X 10 -13
!,2 X 10 - 1 3
6.9 X 10 -14
**3.0 X 10 - t 2
**8.0 X 10 -13
**3.5 X 10 -13
*'1.7 X 10 - 1 2
750
3.1 X 10 -13
70~
4,5 X 10 -14
1.i X 10 -13
8.1 X 10 - 1 4
*'1.3 X 10 - 1 4 2.3 X 10 -14
6.4 X 10 - 1 4
1.3 X 10 - 1 4
**2.3 X I 0 - I s
4.7X I0 -Is
*4.0X 10 - i s
650
"1.5 X 10 - l a
600
*7.5 X 10 -14
550
Temperature (°C)
Mo/U-10 Pu-10 Fz
Cr/U-IO Pu-10 Fz
V-10 Ti/U-IO Pa-lO F~
V-20 Ti/U-15 Pu-10 Fz
V-20 Ti/U-IO Pu-IO Fz
V/U-IO Pu-lO Fz
(w/o)
Combination
Table 33 Cladding penetration coefficients (K) in cm2/sec (except where noted).
9.8 X 10 -13
6 . 0 X 10 -12
800
i
422
S.H.Kittel et al.. Plugton!urn and plutonium alloys
7. In.reactor behavior 7.1. Introduction The properties of ultimate interest for any reactor material are those that apply when the material is in actual use in a reactor. Furthermore, in-reactor properties of greatest interest are those that exist in the complete reactor environment of stress, temperature, corrosion, and irradiation-induced property changes. In the case of fuels, the property normally of greatest importance is resistance to high temperature swelling. Fuel swelling is undesirable for several reasons. It can cause high stresses in the cladding tliat are difficult to predict, particularly under transient conditions. Axial fuel swelling can cause reactivity losses, and radial swelling can cause loss of inherent shutdown mechanisms that depend on unhampered rapid axial fuel expansion. The development of porosity in the fuel, asa result of swelling, lowers the effective thermal conductivi.ty of the fuel. The allowable linear power rating of the fuel element may thereby be adversely affected. In the sections that follow, much attention is devoted to the use of cladding restraint to control fuel swelling. Most of the initial discussion is on uranium-plutonium-fissium alloy, because of the greater preponderance of work on that alloy system. With the more recent shift to work on higher.melting alloys, in particular U-Pu.Zr alloys, marked improvements were obtained in metallic fuel element performance. U-Pu-Zr alloy offers promise as a major fuel candidate foi the LMFBR program. Further studies, now in progress, are expected to more clearly establish the comparative advantages of U-PU-Zr alloy and the leading ceramic fuels, such as oxide and carbide. 7.2. Uranium-plutonium binary alloys The irradiation behavior of alloys based on uranium and plutonium is of greatest interest because of the potential use of these alloys as fuel in fast breeder reactors. Ideally, from physics considerations, the best fuel for fast breeder reactors is an alloy of U 238 and Pu 239. Such a fuel would have the highest possible metal atom density and would
thereby enable the highest possible breeding ratios to be achieved. However, early irradiation resuRs on U-Pu binary alloys showed that they swelled badly under irradiation [ 185]. More recently, binary alloys were irradiated under conditions where restraint of swelling was achieved by use of strong cladding [ 186]. AI. though gross fuel swelling was prevented, the fuel elongated and separated into segments. Further studies of the performance of U.Pu binary alloys under irradiation is unlikely, primarily because of their relatively low melting points and because of their poor compatibility with austenitic stainless steel cladding alloys. 7.3. Uranium.plutonium.fissium alloys The experimental breeder reactor EBR-II was built and initially operated to demonstrate a closed fuel cycle based on pyrometallurgical reprccessing of uranium alloy fuel. The reprocessing scheme leaves in the fuel certain fission products (primarily Mo, Ru, and Tc, with smaller amount of other elements inchding Zr, Rh, and Pd). These fission products are termed "fissium", with the symbol "Fs". Although the reactor has been operated only with U-Fs alloy, original plans called for eventual operation with U.Pu-Fs alloy. Much effort, therefore, was expended in determining the in-reactor behavior of various U-Pu-Fs alloys under prototypical conditions. The first irradiations of U-Pu-Fs alloys were on unclad specimens [187]. A total of 35 specimens were irradiated at maximum fuel temperatures of 230 to 470°C and total bumups from ! .O to !.8 a/o. Emphasis was placed ca injection-cast, uranium-20 w/o plutonium-lO w/o fissium alloy. It was found that this material begins to swell rapidly at temperatures above 370°C. The ability of the fuel to resist swelling did not appear to vary appreciably with minor changes in fissium or zirconium. Decreasing the plutonium to 10 w/o improved the swelling behavior. Since these results were obtained on specimens irradiated 300°C or more below normal operating temperatures in EBR-II, it was apparent that considerable reliance would have to be placed on restraint of fuel sweill~ by strong cladding. An additional complicating feature of U.Pu.Fs
S.H.Kittel et al., Plutonium and plutonium alloys
alloy is its tendency to form a liquid eutectic with iron. or nickel.base cladding alloys at temperatures as low as 550°C. This temperature would be experienced at the fuel-cladding interface in the hotter regions of the EBR,II core during normal reactor operation. The cladding must therefore be made of the refractory metals that do not form low-melting eutectics with the fuel alloy. Alternatively, a thin barrier of a refractory metal could be placed between the fuel and the iron or nickel alloy cladding. A total of 78 specimens were irradiated in instrumented capsules in the initial investigations of refractory aUoy-clad [J-Pu-Fs alloy [ 138]. Table 34 summarizes the irradiation conditions and the results obtained. The main experimental parameter in the irradiations was the cladding composition. The cladding materials selected for these experiments were those that were known to be compatible with the fuel material and to have relatively high rupture strengths. The clad specimens measured approximately 3.5 in. in length and 0.175 in. in diameter. The cladding thickness was principally 0.009 in. A group of six specimens had claddings that were either 0.015 or 0.025 in. thick. The fuel pin was 0.144 in. OD and 2 in. long and was sodium.bonded to the jacket. The sodium annulus was 0.006 in. thick. The effec:ive (smeared) fuel density was 85%. The irradiations were performed in instrumented temperature-controlled capsules in the CP-5 reactor. The cladding materials that were evaluated are listed below: (l) Niobium. (2) Niobium-I w/o zirconium (3) Niobinm-33 w/v tantalum-I w/o zirconium (4) Niobium-4 w/o vanadium (5) Vanadium (6) Molybdenum (7) Tantalum-O.l w/o tungsten (8) Duplex tubing (a) Inconel-X (vanadium liner) (b) Type 304 stainless steel (vanadium line~) (c) Hastelloy-X (tungsten-coated). Most of the irradiations were made with niobium alloy cladding. The attainable burnups before cladcling failure ranged from 0.9 to > 3.0 a/o, The cladding failures were usually brittle, with no measurable elongation before fracture. An exception was
423
Nb-4 V alloy, which showed significant cladding strain without fracture. Unalloyed vanadium cladding hi the recrystallized condition was found to be satisfactory to bumups in excess of 2.0 a/o. The cladding retained its ductility during irradiation. Specimens clad in unalloyed molybdenum tubing failed at 0.4 a/o burnup. The failures were of a very brittle nature, with cracks extending the full length of the specimen. The poor performance is attributed to the poor quality of the cladding. The Ta-O.l W alloy cladding behaved similarly to the niobium alloy. Fuel pins clad in Type 304 stainless steel with vanadium liners as well as the Hastelloy-X with vapor deposited tungsten on the ID of the cladding were satisfactory to burnups in excess of 3.0 a/o. The majority of failures were attributed to undetected flaws in the liners. In addition to the irradiations listed in table 2.34, a number of instrumented capsule irradiations were performed on several full-length (18 in. long) EBR-il fuel elements of U-Pu-Fs alloy in refractory alloy cladding. The results were similar to those obtained for the CP-5 irradiations. Several series of instrumented capsule irradiations were also made in CP-5 to investigate certain design or operating parameters. The results of these irradiation experiments are summarized as follows: 1
7.3.1. Effect of plutonium content on the irradiation behavior of U-Pu-Fs alloys Comparison irradiations conducted on U-Pu-!0 Fs alloy specimens with plutonium concentrations between 10 and 20 w/o and clad in Nb-I Zr tubing having a wall thickness of 0.009 in. failed to show signifi~-ant increase in achievable burnup as the plutonium concentration was reduced from 20 to 15 w/o (table 35). Tile fuel with 10 w/o plutonium had not reached the burnup values of the other alloys and could not be directly compared. Increasing the plutonium concentration resulted in an increase in swelling rate, as anticipated. 7.3.2. Irradiations of U-Pu.Fs spechnens clad in duplex tubing Twenty-one specimens were irradiated in cladding of Type 304 stainless steel and Hastelloy-X lined with
S.H.Kittel et at,, Plutonium andpiutoniumalloys
424
Table 34 Effects of irradiation on cast U-20 w/o Pu-10 w]o Fs specimens [ !88]. Specimen No.
Melt No.
Jacket composition
Plenum vol.
(w/o)
(%)
Burnup (a/o)
Max. temp. ( P C )
Condition
Jacket surface
Fuel center
speeimen**
1.8 -2.0 2.1 2.5
655 790 780 680
760 920 910 790
B B B B
17-2 17-6 16-4 18-2
R21-10B R21-10C R21-10A R21-1OD,
Niobium Niobium Niobium Niobium
13 13 13 13
22-5 22-2 19-1 19-6 19-4 17-1 23-1 23-4 20-2 20-4 2O-6 16-2 17-4 16-5 18-1 21-4 21-1 21-2 27-4 27-1 25-4 25-1 28-1 28-4 32-1 32-2 32-3 32-4 32-5 32-6
$2-3-2 $2-3-1 R21-19C R21-20C R21-21C R21-15D $2-3-4 R21-11A R21-21F R21-22A R21-22D R21-15B R21-15E R21-15C R21-17B R21-17A $2-1-1 R21°22B R21-24B R2 I-11 E R21-1 IC R2 I-7B R2 I-7A R21-11B R21-11D R21-3B R21-3C R21-3D R21-3E R21-3F R2 I-4A
Nb-I Zr Nb-I Zr Nb-1 Zr Nb-I Zr Nb-I Zr Nb-I Zr Nb-1 Zr Nb-I Zr Nb-I Zr Nb-I Zr Nb-I Zr NbdZr Nbol Zr Nb-I Zr Nb-I Zr Nb-I Zr Nb-1 Zr Nb-I Zr Nb-I Zr Nb-I Zr Nb-i Zr Nb-! Zr Nb-I Zr Nb-1 Zr Nb-1 Zr Nb-I Zra Nb-I Zra Nb-I Zrb Nb-! Zrb Nb-I Zrb Nb-I Zr
36* ~6" 28 28 28 13 50 50 28 28 28 !3 13 13 13 13 25 25 25 Vented Vented 50 50 57 57 23 24 24 22 23 17
0.9 0.9 1.5 1.5 !.5 1.8 !.8 1.8 1.9 1.9 1.9 2.0 2.0 2.1 2.5 2.5 2.6 2.6 2.6 2.6 2.5 2.5 2.5 3.2 3,2 5.3 5.3 5.3 5.3 5.3 5.3
615 655 520 535 535 655 560 630 555 580 580 695 790 780 680 680 520 520 520 570 570 575 580 580 580 590 590 590 615 ,615 615
715 760 595 615 615 760 650 730 640 67,9 670 810 920 910 790 790 600 600 600 660 660 670 670 670 670 690 690 690 720 720 720
C C B B B B D A B B B B B B A B B B B C A B C B C A C A A A A
22-4 21-1 23-3 23-6 27-6 27-3 25-6 25-3
$2-2-3 $2-2-2 R21-9A R21-9B R21-25 F R21-25E R21-26D R2 !-26C
Nb-33 Ta-! Nb-33 Ta-I Nb-33 Tad Nb-33 Ta-! Nb-33 Ta-! Nb-33 Ta-! Nb-33 Ta-! Nb-33 Ta-!
36* 36* 50 50 yented Vented 50 50
0.9 0.9 1.8 1.8 2.6 2.6 2.6 2.6
615 655 560 630 570 570 575 590
715 760 650 730 660 660 670 680
A B B A A A B A
29-1 29-5 29-4
R21-29E R21-3A R2 i-29F
Nb-4 V Nb-4 V Nb-4 V
57 57 57
3.8 3.8 3.8
490 500 500
560 570 570
A A A
18-4
Zr Zr Zr Zr Zr Zr Zr Zr
$~H.Kittel et aL, Pluto~dum and plutonium alloys
425
Table 34 (cont.) Specimen No.
Melt No.
Jacket composition (w/o)
Plenum vol. (%)
Burnup (a/o)
Max.temp. (°C) Jacket surface
Fuel center
Condition of specF men**
22-6 17-3 16-3 18-5 18-3
$2~2-4 R21-17E R21-ITD R21-18B R21-I7E
Vanadium Vanadium Vanadium Vanadium Vanadium
50* 13 13 13 13
0.9 1.8 2.0 2.5 2.5
615 655 695 680 680
715 760 810 790 790
G B B G B
19-3 20-1
R21-20E R21-21B
Molybdenum Molybdenum
30 30
1.5 1.9
520 555
595 640
B C
22-3 19-2 19-5 23-2 23-5 20-3 20-5 21-5 21-6 21-3 27.2 27-5 25-5 25-2
$2-2-6 +21-20A R21-20B R21-9D $2-3-3 R21-27B R21-27D R21-H9 $2-2-$ R21-24E R21-25A R21-25B R21-14A R21-TD
Ta-O.l W Ta-0.1 W Ta-0.1 W Ta-0.1 W Ta-0.1 W Ta-0A W Ta-0.1 W Ta-0.1 W Ta-0.1 W Ta-0.1 W Ta-0.1 W Ta-0.! W Ta-0.! W Ta-0.I W
36* 28 28 50 50 28 28 25 36* 25 Vented Vented 50 50
0.9 1.5 1.5 1.8 1.8 1.9 1.9 2.6 2.6 2.6 2.6 2.6 2.6 2.6
655 520 535 560 630 555 590 520 520 520 570 570 575 590
760 595 615 650 740 640 670 600 600 600 660 660 670 680
B C C B A A B C B B A A B A
16-1
R21-18B
13
2.0
695
810
E
17-5
R21-18E
13
2.0
790
920
E
16-6
R21-18C
13
2.1
780
910
E
18-6
R21-18F
lnconel X V Barrier 304 SS V Barrier 304 SS V Barrier 304 SS V Barrier
13
2.5
680
790
A
28-3
R21-28F
57
3.2
590
670
E
28-2
R21-28B
57
3.2
590
670
F
28-5
R21-28C
57
3.2
590
670
A
28-6
R21-28D
57
3.2
590
670
A
29-3
R21-29D
57
3.8
490
560
A
29-2
R21-29C
57
3.8
490
560
A
29-6
R21-29B
Hastelloy-X W Lined Hastelloy-X W Lined Hastelloy-X W Lined Hastelloy-X W Lined Hastelloy-X W Lined Hastelloy-X W Lined Hastelloy-X W Lined
57
3.8
500
570
A
* No sodium bond. ** A. Specimen straight and intact. B. Longitudinal split in jacket with protrusion of fuel. C. Longitudinal split in jacket without protrusion of fuel. D. Several small cracks around center section of specimen. E. Fuel penetrated barrier and fomled extensive eutectic with jacket. F. Fuel penetrated barrier and formed small hole in jacket. G. Specimen bowed but intact. a Jacket thickness 0.38 mm (0.015 in.); b Jacket thickxless 0.64 mm (0.025 in.)
S.H.Kittel et al.. Plutonium and plutonium alloys
426
Table 35 Design parameters and operatin8 conditions for U-Pu, U-Pu-Fs comparison irradiations. Specimen Numbet
Opiating conditions
Designparameters Fuel composition
(w/o)
Effectire density
Cladding composition
(~;
(w/o)
Clad. OD (in.)
Clad. thick (in.)
Plenum col. (%)
Burnup
Max. clad. temp.
Max. fuel temp.
(°c)
(°c)
a/o (U+Pu)
fiss/cc XIO- 2 0 .
30-2 30-6 34-6
U-IO Pu-lO Fs U-IO Pu-lO Fs U-IO Pu-10 Fs
82.8 81.7 82.9
Nb-1 Zr Nb-I Zr Nb-I Zr
0.174 0.174 0.174
0.009 0.009 0.009
58.1 58.4 23.4
525 525 600
600 600 690
3.1 3.2 2.5
9.8 10.0 7.9
30-3 ~0-5 34-5
U-15 Pu-lO Fs U-15 Pu-lO Fs U-15 Pu-lO Fs
83.1 83.4 82.1
Nb-1 Zr Nb-1 Zr Nb-1 Zr
0.174 0.174 0.174
0.009 0.009 0.009
57.4 56.5 24.5
560 525 635
640 600 730
4.5 4.6 3.2
14.3 14.7 10.0
34-4
U-20 Pu-lO Fs
86.5
Nb-I Zr
0.174
0.009
23.4
625
720
3.6
11.9
* Based on effective density.
Table 36 Design parameters and operating conditions for U*Pu-Fs irradiated in duplex type cladding [ 188]. Specimen num bet
Operating conditions
Design parameters Fuel composition (w/o)
Effectire density (%)
Cladding composition (w/o)
Clad. OD (.in.)
Clad. thick. (in.)
Plenum vol. (%)
Bumup
Max. clad. temp. (°C)
Max. fuel temp. (°C)
a/o
fisslcc
(U+Pu)
XIO-2°*
34-3
U-10 Pu-10 Fs
88.4
304 SS-WLined
0.175
0.012
22.1
575
660
2.2
7.5
37-1 37-2 37-3 37-4 37-5 37-6 34-2
U-15 Pu-10Fs U-15 Pu-lOFs U-15 Pu-lO Fs U-15 Pu-lO Fs U-15 Pu-lO Fs U-15 Pu-lO Fs U-15 Pu-lO Fs
85.1 82.1 83.9 83.9 83.9 83.9 83.9
304 SS-WLined 304 SS-WLined 304 SS-WLined 304 SS-WLined 304 SS-WLined 304 SS-W Lined 304 SS-W Lined
0.175 0.175 0.175 0.175 0.175 0.175 0.175
0.010 0.010 0.010 0.010 0.010 0.010 0.011
Vented Vented 19.8 22.4 22.2 Vented 22.9
660 660 630 590 590 590 590
780 780 750 680 680 680 680
2.3 2.3 2.3 2.3 2.3 2.3 2.5
7.5 1.3 7.4 7.4 7.4 7.4 8.0
34-1
U-20 Pu-lO Fs
86.5
304 SS-W Lined
0.175
0.010
22.9
590
680
2.8
9.2
38-1 38-2 38-4 38-5 36-1 36-2 36-3 36-4 36-5 36-6 38-3 38.6
U-15 Pu-lO Fs U-15 Pu-10Fs U-15 Pu-lO Fs U-15 Pu-10 Fs U-15 Pu-lO Fs U-15 Pu-10Fs U-15 Pu-10 Fs U-15 Pu-10 Fs U-15 Pu-IO Fs U-15 Pu-IO Fs U-15 Pu-lO Fs U-15 Pu-lO Fs
82.8 82.8 74.2 74.2 88.5 88.5 88.5 88.5 88.5 88.5 73.2 73.2
304 SS-V Lined 304 SS-V Lined 304 SS-V Lined 304 SS-V Lined Hast.-X-WLined !'~st.-X-WLined Hast.-X-WLined Hast.-X-WLi~.ed Hast.-X-WLtned Hast.-X-WLined , Hast.-X-VLined Hast.-X-VLined
0.186 0.186 0.196 0.196 0.i74 0.174 0.174 0.174 0.174 0.174 0.184 0.184
0.015 0.015 0.015 0.015 0.011 0.011 0.011 0.011 0.Ol I 0.011 0.009 0.009
Vented Vented 54.0 Vented 23.0 Vented 21.0 22.0 22.0 20.0 Vented 58.0
580 580 630 630 645 645 645 600 600 635 580 630
660 660 710 710 750 750 750 695 695 740 660 710
3.2 3.-'2 3.2 3.2 2,2 2.2 2.2 2.3 2.3 2.3 3.2 3.2
10.3 10.3 9.1 9.1 7.5 7.5 7.5 7.8 7.8 7.8 8.9 8.9
* Based on effective density,
S.H.Kittel et al., Plutonium and plutonium alloys
427
Table 37 Design parameters and operating conditions for U-Pu-Fs irradiated to high burnup [ 188]. Specimen number
Design parameters
Fuel composition (w/o)
Operating condition~
Cladding tire composidensit> tion (%) 'w/o)
Clad. OD (in.)
Clad. thick, (in.)
Plenum voL (%)
Max. clad. temp. (°C)
Max.
fuel temp. (°C)
a/o " (U+Pu)
fm/cc XI0 -2°*
C-II5A U-10 Pu-10 Fs C-116B U-10 Pu-10 Fs C-120C U-10 Pu-10 Fs
81.6 78.6 79.7
Nb-I Zr Nb-I Zr Nb-I Zr
0.186 0.199 0.209
0.015 0.020 0.025
22.2 23.2 24.3
510 530 530
590 610 610
7.I 7.1 7.1
22.2 21.4 21.7
C-II9A C-II7A C-118C
85.2 84.0 87.4
Nb-I Zr Nb-1 Zr Nb*l Zr
0.186 0.186 0.209
0.015 0.015 0.025
23.2 29.9 23.9
545 545 545
625 625
8.7 8.7
28.4
625
8.7
U-15 Pu-10Fs U-15 Pu-10 Fs U-15 Pu-10 Fs
E, "'c-
Burnup
27.9 29.1
* Based on effective density.
tlmgsten or vanadium (table 36). The tungsten lining was achieved by vapor deposition on the ID o f the cladding. The vanadium liner was a 0.0005 ha. thick foil wrapped on the specimen. O f the 12 specimens that failed, nine failures were directly attributable to defects in the barrier layer, as evidenced b y eutectic formation, and three failures
were due to fracture o f the clad from fuel swelling. Variations in clad thickness or effective density of the fuel did not have significant effect o n the fuel bumup at which clad failure occurred. 7.3.3. U-Pu-Fs alloys irradiated in thicker cladding Six specimens were irradiated in Nb-1 w/o Zr
Table 38 Design parameters and operating condtions for U-Pu-Fs sPeciraens having increased plenum volume and reduced effective density of fuel [ 188]. Design parameters
Specimen
Operating conditions
Fuel composition (w/o)
Effectire density (%)
Cladding composition (w/o)
Clad. OD (in.)
Clad. thick, (in.)
Plenum vol. (%)
Max. clad temp. (°C)
Max. fuel temp. (°C)
ado {UtPu)
Fiss/cc X10 -20*
41-4 41-5 41-6
U-I0 Pu-10 Fs U-10 Pu-IO Fs U-10 Pu-10 Fs
76.0 79.9 84.1
V-20 Ti V-20 Ti V-20 To
0.197 0.193 0.189
0.016 0.016 0.016
41.1 39.9 36.7
630 630 630
740 740 740
8.2 8.2 8.2
23.9 25.1 26.4
40-1 40-2 40-3 40-4 40-5 40-6 41-1 41-2 41-3 43-1
U-15 Pu-10 Fs U-15 Pu-10 Fs U-15 Pu-10 Fs U-15 Pu-10 Fs U-15 Pu-10 Fs U-15 Pu.10 Fs U-15 Pu-10 Fs U-15 Pu-10 Fs U-15 Pu-10 Fs U-I 5 Pu-10 Fs
82.9 82.9 74.0 78.8 78.8 71.6 75.1 79.9 86.3 69.0
V-20 Ti V-20 Ti V-20 Ti V-20 Ti V-20 Ti V-20 Ti V-20 Ti V-20 Ti V-20 Ti V-20 Ti
0.189 0.189 0.197
0.016 0.016 0.016 0.016 0.016 0.016 0.016 0.016 0.016 0.015
23.5 23.6 26.5 25.0 25.0 27.5 41 ! 39.9 36.7 56.0
620 620 620 620 620 620 630 630 630 600
720 720 720 720 720 720 740 740 740 770
6.1 6.1 6.1
19.4 19.4 17.3
6.1 6.1 6.1 7.3 7.3 7.3 12.0
18.4 18.4 16.7 21.0 22.4 24.1 31.7
hum
-
ber
* Based on effective density.
0,193
0.193 0.201 0.197 0.193 0.187 0.203
Bumup
428
S.H.Kittel et al., Plutonium and plutonium alloys
Table 39 Fission gas relez~efrom U-Pu-Fsalloy with variable amounts of swelling.The specimenswere irradiated to 3.0 a]o burnup at
740% 11881. Specimen no.
39-1 39-2 39-3 39-4 39-5 39,6
Design parameters
Experimental results
Fuel composition (w/o)
Effective density (%)
Cladding composition (w/o)
C l a d d i n g Thickness Plenum OD (in.) vol. (in.) (%) ....
Fuel vol. in~rease (%)
Fission, gas release (% of theotetical yield)
U-15 Pu-lO Fs U-15 Pu-lO Fs U-15 Pu-lO Fs U-15 Pu-lO Fs U-15 PwlO Fs U-15 Pu-10 Fs
79.6 74. l 67.8 61.1 52.4 44.2
Nb-I Zr Nb-I Zr Nb-I Zr Nb'-I Zr Nb-1 Zr Nb-I Zr
0.202 0.204 0.209 0.220 0.237 0.260
23 30 43 57 97 133
-* 37 -** 63 76 83
0.021 0.019 0.018 0,019 0.021 0.022
29 39 74 89 124 168
* Jacket failed during irradiation. ** Gas sample lost due to equipment failure. tubing having a wall thickness between 0.015 and 0.025 in. (table 37). The selection o f increased cladding thickness was to preclude failures experienced because o f fabrication defects in refractory tubing having a wall thickness of 0.009 in, The specimens were irradiated to a maximum 8.7 a/o burnup (2.9 X 1021 fiss/cc) at maximum ternperatures o f 545°C. Maximum fuel pin elongation occurred ~t 5 a/o burnup. This was followed by a gradual reduction in fuel length which may be due to high plenun~ pressures that gradually increased as the fission gas released. The post-irradiation examination sl,ow:~d that only one specimen had failed. The average fission gas release to the specimen plenums was 4.8%. 7.3.4. Irradiations of prototype fuel elements having increased plenum volumes and reduced effective density of fuel An analysis was made by F.G.Foote [189] to determine the relationships between jacket stress in sodium-bonded metallic fuel elements with various fuel burnups, cladding dimensions, and mechanical properties. A series of 13 irradiations was then performed to verify the results predicted by the analysis. Table 38 summarizes the irradiation conditions and specimen design, One group of six specimens was assembled that was predicted by the analysi~ to develop cladding failures at 3.1 a/o burnup. Tl~te first cladding failures
were not observed until 5 a/o bumup. Examination of the specimens at 6.1 a/o burnup showed that four out of the six pins had ruptured or deformed the cladding. A second group was assembled with configurations which were calculated to result in cladding failures at bumups ranging from 5.9 to 6.4 a/o. No failures were noted until the specimens w,,~reexamined at a max/. mum bt~rnup of 8.2 a/o when it was observed that four had deformed cladding. A specimen was designed such that cladding faOure was anticipated at- 10.9 a/o burnup. Cladding failure did not occur until 12 a]o burnup. The significant conclusion that was drawn from these series of experiments is: (1) The specimens achieved burnups without cladding failure that were higher than that predicted by the analytical approach. (2) Specimens that did not fail generally had a lower effective fuel density, indicating that radial clearance is more effective than axial clearance in extending fuel burnup. 7.3.5. Effects o f enhanced fission gas disengagement from metal fuels Metal fuels are normally characterized by relatively low release of fission gas. For high burnup fuels, where the forces exerted on the cladding by fissiongas bubbles in the fuel become excessively high, it can be seen that release of the gas from the fuel into
429
S.H.Kittel et al., Plutonium and plutonium alloys
the plenum above the fuel pin would be advantageous. Pressure in the gas bubbles in the fuel matrix would thereby be reduced, and, in the ideal case, only volume expansion from solid fission products would exert significant pressure on the cladding, Three methods of enhancing fission gas release were investigated: (i) subdivision of the fuel to provide shorter paths of gas release and provide more surface for fission-recoil escape, (ii) use of an axial hole for release of fission gas migrating to the center of the specimen, and (iii) use of larger annuli between the fuel and cladding to permit the fuel to swell to such an extent that intedinking of bubbles could occur and fission gas would be released from the surface of the fuel. It was found that method (iii) was most effective in disengaging fission gas from the fuel alloy. Table 39 summarizes results. The specimens were irradiated to 3.0 a/o burnup before they were examined. The postirradiation examination showed that all specimens were intact except 39.1, which had been allowed a radial fuel volume expansion of only 26%. All the other specimens had allowable radial expansions of 30% or greater and were intact. The fuel length changes varied from 0% for specimen 39-2 which had an effective density of 74.1 to -7.4% for specimen 39-4 which had an effective density of 61.1%. It was observed that the specimens that had
90
80
I
|
"-
I
"
I
I
w
v
o
70
! •
2
50
40
M ~rJ
30 V
U-Fo
0
U- Pu-Fs
O U-Pu-Z¢ IO
, 20
0 ~
! 40
-
I
l
I
60
aO
I00
FUEL VOLUk~
IlfREASE . ' / .
Fig. 32. Fission gas release vs. fuel vo|ume increase in metallic fuei~ experienced volume increases in excess of 30% had released a significant amount of fission gas. These results supported the theoretical model by Barnes [190] which predicts that interconnection of bubble~
Table 40 Design parameters and operating conditions for U-Pu-Zr prototype elements [ 191]. Operating conditions
Design parameters
Spec~ men
Fuel composition (w/o)
Effectire density (%)
Cladding composition (w/o)
Clad. OD (in.)
Clad. thick, (in.)
Plenum Max. vol. clad. (%) temp. (°C)
Max. fuel temp. (~C)
48-2 48-5 28-3 48-6 48-1 48-4
U-15 Pu-12 Zr U-15 Pu-12 Zr U-15 Pu-12 Zr U-!5 Pu-12 Zr U-15 Pu-12 Zr U-15 Pu-12 Zr
75 75 75 75 75 75
304 SS 304 SS 316 SS 316 SS Hast.-X Hast.-X
0.196 0.196 0.196 0.196 0.196 0.196
0.015 0.015 0.015 0.015 0.015 0.015
96 92 97 97 95 98
610 660 610 660 610 660
700 810 700 810 700 810
2.4 2.4 2.4 2.4 2.4 2.4
6.2 6.2 6.2 6.2 6.2 6.2
45-1
U-18.5 Pu.14.1 Zr
63
V-20 Ti
0.208
0.016
73
655
840
12.5
28.0
no.
* Based on effective density.
Burnup
a/o fhs/cc ( U + P u ) XIO-2°*
430
S.H.Kittel et al.. Plutonium and pluton&m alloys
iii!
j
Fig. 33. Transversesection of U-IS w/o Pu-I 2 w/o Zr alloy jacketed in Hastelloy-X.The concentric bands in the fuel are related to phase distributions in the alloy during irradiation [ 191 ]. should occur after fuel volume increases of 33~%. The interlinked bubbles provide a continuous path for fission gas release lo the surface of the fuel. Fig. 32 which shows, in addition to the U-Pu-Fs data, additional results from U-Fs and U-Pu-Zr irradiations [ 191 ]. The results from this experiment support the view that fission release is largely independent of burnup and irradiation temperature, and depends principally
on the amount of fuel swelling. The points that are plotted in fig. 32 represent buh,ups between 2.7 and 12.5 a/o and maximum fuel temperatures between 450 and 840°C. The successful demonstration of gas release from metallic fuels has provided the key to obtaining high fuel burnups with cladding of normal thickness, as will be described in the following section.
S.H.Kittel et aL, Plutonium and plutt, nmm alloys
7.4. Uranium-plutonium-zirconiumalloys Interest has shifted from developing U-Pu-Fs alloy for EBR-II to developing high-melting uraniumplutonium alloys for use in liquid metal cooled fast breeder reactors for central station power generation. The U-Pu.Zr system has proved to be of greatest interest because of the excellent compatibility between U-Pu-Zr alloys and austenitic stainless steel [llS]. The first irradiations were performed on seven 13-15 w/o Pu.12 w/o Zr fuel alloy specimens clad in Type 304 stainless steal, Type 316 stainless steel, Hastell0y-X, and V-20 Ti alloy [191 ] (see table 40). The specimens were irradiated in instrumented, temperature-controlled capsules in vertical thimbles of the CP-5 reactor. The metallographic examination of the specimens in iron- and nickel-base alloy cladding that operated at maximum temperatures of 610°C showed excellent compatibility between the fuel and the cladding. The transverse macrosections of the fuel showed three distinct bands which are believed to be related to phase distributions during irradiation (see fig. 33). The outer zone is believed to correspond to the alpha-uranium + delta + zeta phase, the second
431
band to the alpha-uranium + zeta + gamma phase and the central area to the gamma phase. As anticipated, the fuel had swelled to the internal diameter of the cladding and the bond sodium was entirely displaced into the gas plenum. Fig. 33 also shows that original void volume, which had existed as a sodium-filled annulus around the solid metal fuel pin at the start 6f irradiation, became redistributed throughout the fuel volume in the form of finely-divided porosity. The U-Pu-Zr specimen jacketed in V-20 Ti alloy successfully reached an analyzed 12.5 a/o bumup (2.8 X 1021 fiss/cm 3) at a maximum clad temperature of 655°C. Periodic neutron radiography of the capsule during irradiation showed that the pin attained a maxinmm elongation of 3% within the cladding, which occurred at 4.2 a/o burnup. This dimension did not change throughout ~he remainder of the irradiation. Diameter changes in the cladding were calculated from volume changes measured byimmersion. An average 0.0002 in. diameter increase was observed. No measurable length increase of the cladding was noted. It was determined that 74% of the fission gas had been released to the plenum. Following these experiments on small prototype
Table 41 Irradiation conditions for U-Pu-Zr alloy fuel elements irradiated in EBR-Ii in subassembly XA07 [ 1921 . Specimen no.
Fuel composition (w/o)
ND-28 ND-41 ND-32 ND-43
U-15 Pu-9 U-15 Pu-9 U-15 Pu-9 12-15 Pu-9
Zr Zr Zr Zr
ND-25 ND-27 ND-26 ND-29 ND-30 ND-31 ND-33 ND-34 ND-35 ND-37 ND-39 ND-44
U-15 Pu-12 U-15 Pu-12 U-15 Pu-12 U-15 Pu-12 U-15 Pu-12 U-15 Pu-12 U-15 Pu-12 U-15 Pu-12 U-15 Pu-12 U-15 Pu-12 U-15 Pu-12 U-15 Pu-12
Zr Zr Zr Zr Zr Zr Zr Zr Zr Zr Zr Zr
Cladding alloy
Effective density (%)
Cladding OD (in.)
Cladding thick, (in.)
Max. kw/ft
Max. fuel • temp.
Max. clad. temp.
t°O
~°c)
Burnup (a/o)
304SS 304 SS 316 SS Hast.-X
73.1 73.8 73.8 74,5
0,205 0.205 0.196 0.196
0.019 0.019 0.015 0.015
10.9 10.4 9.9 10.4
745 735 715 725
630 625 605 615
4.6 4.4 4.2 4,4
304 SS 304 SS 316 SS 316 SS 316 SS 316 SS Hast,-X [tast.-X Hast.-X Hast.-X-280 Hast.-X-280 Hast.-X-280
73.5 73.1 73.9 72.2 72.3 74.1 72.8 72.6 74.9 63.8 65.4 66.4
0.205 0.205 0.196 0.196 0.196 0.196 0,196 0.196 O. 197 0.207 0.207 0.208
0.019 0.019 0.015 0.015 0.015 0.015 0.015 0.015 0.015 0.015 0.015 0.015
9.5 9.7 9.5 9.5 10.4 9.9 9,9 9.9 10.4 10.4 10.2 9.9
710 715 695 700 700 720 715 720 725 720 720 710
600 605 590 595 615 610 605 610 615 610 610 600
4.0 4.1 4.0 4.0 4.4 4.2 4.2 4.2 4.4 4.4 4.3 4.2
S.H.Kittel et al., Plutonium and plutonium alloys
432
Table 42 Irradiation of U-Mo-Pualloys [ 194].
U23s
Mo
Pu
U23s
Before After irradiation irradiation
Percent Burnup increase MWD/Te in vol. (AV)
66.9 66.9 69.6 69.6 57.2 57.2 59.7 59.7
15.0 15.0 15.0 15.0 25.0 25.0 24.9 24.9
7.6 7.6 14.9 14.9 7.5 7.5 15.0 15.0
10.5 10.5 0.5 0.5 10.4 10.4 0,4 0.4
17.72 17.69 17.78 17.78 17.06 17.05 16.99 17.03
53.8 81.1 77.4 91.6 26.5 45.4 11.6 63.4
Composition, atomic percent
Density (g/cm3)
11.52 9.77 10.02 9.2~ 13.49 11.73 15.22 10.42
fuel elements, irradiations were started on full-length elements of U-Pu-Zr alloy in EBR-II. The first irradiations were on 16 elements irradiated in special subassembly XA07 [192]. Table 41 summarizes the irradiation. External dimensional measurements of the elements showed no significant changes as a result of irradiation. Fuel pin length dimensions within the cladding were determined by neutron radiography and disclosed an average fuel length increase of 1.9%. The fuel pins were not seated on the bottom closures of the jackets, but were elevated an average o f 0.20 in. The elements had been intentionally assembled without fuel restrainers to observe possible axial fuel movement. The neutron radiographs of the elements revealed one or two partial axial separations in most of the fuel pins within the cladding which varied from "~ 0.020 in. to 0.060 in. in width. Fission gas recovery data established that "- 57% of the fission gas had been released from each fuel pin to the plenum above the bond sodium. A calcula. tion of the plenum pressures in the specimens revealed that, at reactor operating temperatures, the average gas pressure was 458 psi. Transverse as well as longitudinal metallographic sections o f the fuel elements showed no penetration of the fuel into the cladding materials. A detailed metallographic and microprobe examination of the fuel/clad interfaces showed a reaction zone that had a depth of 150/~ in the Hastelloy-X, 140t~ in the Type 304 stainless steel, and 20/~ in the Type 316 stainless steel. The fuel adjacent to the Type 304 stainless steel
7,639 14,760 8,170 14,880 7,880 14,440 8,720 16,300
S-
51 55 70 59 25 29 10 41
AV
percent burnup
Rating (w/g)
73 103 78 110 75 103 85 119
and HasteHoy-X was U.15 w/o Pu-9 w/o Zr while the fuel adjacent to the Type 316 stainless steel was U.15 w/o Pu-I 2 w/o Zr. 7.5. Uranium-plutonium-titanium alloys The U-Fu-Ti system is o f interest because of the high melting points of alloys containing ~ 10 and "-" 15 w/o Ti and Pu, respectively. A high bumup experiment was performed on a U-15 Pu-10 Ti alloy pin sodium-bonded to V-20 Ti alloy cladding [ 186]. The specimen was examined at an analyzed 10.7 a/o burnup (2.5 X 1021 fiss/cm 3) at a maximum clad temperature of 630°C. Periodic nondestructive examination of the capsule by neutron radiography showed a maximum fuel elongation of 14% which occurred at 4.6 a/o bumup. This dimension remained the same throughout the remainder of the irradiation. An average clad diameter increase of 0.0016 in. was calculated from volume changes by immersion. No measurable length change was noted. The metallographic examination of the specimen shows that there was no significant penetration of the fuel into the cladding. In isolated areas there was occasional evidence of surface reaction in the fuel to a depth of ~ 0.005 in. A central area that is microstructurally different from the rest of the fuel[ is believed to be associated with the (U, Pu)~T~+ 7 phase that is stable above 710°C. 7.6. Uranium-plutonium.molybdenum alloys Investigations o f U.Pu-Mo alloys were a natural development based on prior selection of U-Me alloys
S.H.Kittei et al., Plutonium and plutonium alloys
433
Table 43
Specimendata on uraniam-plutonium-molybdenumalloys [ 196].
Speci-
Comp.
men
CF-I CF-2
U-20 Pu-5 Mo U-20 Pu-5 M,~
CF-3 CF-4 CF-5 CF-6 CF-7 CF-8
U-20 Pu-5 Mo U-20 Pu-5 Mo U-20 Pu-5 Mo U-20 Pu-5 Mo U-20 Pu-5 Mo U-20 Pu-5 Mo
Calculated flux (lO s
Approx. central metal temp.
Calculated burnup of all
nv)
(°C)
2.07 1.64 1.56 1.48 1.01 0.55 1.56 1.22
340 280 270 260 190 120 270 220
Length increase
Dia. increase
atom~ (%)
(%)
0.27 0.43 0.20 0.38 0.28 0.07 0.40 0.15
0.74 0.67 0.79 1.26 0.83 1.05 0.77
for the FERMI and Dounreay fast breeder reactors. In one early UK study, cast specimens of U-6.5 w/o Pu-13 w/o Me and U-18 w/o Pu-13 w/o Me alloys were irradiated to burnups up to 0.4 a/o at temperatures between 500 and 700°C [193]. The density changes were very large in some cases, with volume increases greater than 100%. It was suspected that the specimens were heavily segregated during fabrication. A second set of homogenized specimens was therefore irradiated at burnups ranging from 0.4 to 1.6% burnup of all atoms at surface temperatures of 600°C [194] (see table 42). The performance of this group of specimens was considerably better than the first group. The rate of volume change showed a maximum of about 70% increase in volume per a/o burnup. However, the results were disappointing when compared to the behavior of U.Mo binary alloys. In an extensive study of U-Pu-Mo alloys for possible use in the Rapsodie reactor, a number of specimens were irradiated at temperatures between 400 and 600°C to burnups ranging from 0.4 to 0.8 a/o [195]. The specimens were all found to have swelled extensively. In order to determine whether cladding was capable of restraining the welling, U-Pu.Mo alloy specimens were inserted into tightlyfitting tubes of niobium with wall thicknesses of 0.012, 0.016, and 0.020 in. A void space of 5 or 10% of the fuel volume was left in one end of the can for longitudinal fuel expansion. It was found that can failures resulted if the can temperature exceeded
Calc. vol.
(%)
Hardness change increase (RA)
Weight change (%)
Density decrease (%)
0.00 0.56 0.48 0.40 0.48 0 0.96 0.16
0.74 1.80 1.76 2.07 1.80 3.00 0.40
- 4 - 16 2 1 1 0 0
0.74 1.45 0.68 0.6~ 1.08 1.39 0.23
(%)
- 8.3 - 8.3 - 8.3 - 2~.9 - 17.2 - 7.0 - 7.7
400°C or if the burnup exceeded 1.0 a/o. The size of the expansion space at the end of the fuel appeared to be of little importance. On the other hand, the thickness of the can was found to have a significant effect. Under conditions of identical irradiation temperature and bumup, the 0.012 in. thick cans were found to have burst, whereas the 0.016 and 0.020 in. cans were intact and showed no deformation. A group of eight U-20 w/o Pu-5 w/o Me specimens was irradiate d by ANL in the MTR reactor [ 196]. Four of the molybdenum alloys were heat treated at 560°C for 25 min and slowly cooled. The specimens were irradiated at maximum central temperature~ of 340¢C to a maximum burnup of 0.43% of total atoms. The results are summarized in table 43. Low swelling rates were observed for all specimens. 7.7. A luminum-plutonium alloys Fuel elements of aluminum containing 5 to 20 w/o plutonium and sheathed in Zircaloy-2 cans have been irradiated successfully in the NRX reactor [ 197]. Six of the elements were assembled with a slip fit between the sheath and fuel so that the fuel underwent irradiation at " 400°C. Volume changes and sheath/fuel interaction were insignificant after 0.25% of the total atoms present had fissioned. Four dements were assembled with significant diametral clearances between the fuel and sheath. Initially these elements were irradiated at fuel temperatures near 600°C but this temperature was reduced during irra-
434
S,H.Kitrel et al., Plutonium and plutoniura alloys
diation due to swelling. The cores in those elements increased in volume by up to 6%. Four Pu-I w/o AI alloy fuel elements sodiumbonded to Zircaloy.2 cladding were irradiated in EBR-! [198]. The elements were operated with measured central temperatures ranging from 332 to 386°C to 0.1 a/o bt~rnup. Diameter changes of the fuel rods were less than 0.002 in.
7.8. A luminum-nickel-plutonium alloys Seventy-five AI-2 w/o Ni-1.8 w/o Pu alloy rods jacketed in Zircaloy cladding were irradiated as spike elements in the PRTR reactor [ 199]. The spike elements measured 224 cm in length and were separated from the cladding by a 0.1 to 0.2 mm gap which partially closed during operation by differential thermal expansion. The performance of the AI-Pu elements was excellent to 0.74 X 1020 fiss/cc (83% burnup of the initial fissile atoms) at rod powers to 492 w/cm. Rods o f AI-2 w/o Ni-2.1 w/o Pu were irradiated under more severe conditions in the ETR reactor [200]. The maximum bumup was 8.3 X 1019 fiss/cm 3 atoms at linear heat ratings up to 25 kw/ft. Some evidence of plutonium and fissionproduct migration was noted in autoradiographs. 7.9. Zirconium-plutonium alloys Zr-5 w/o Pu and Zr.7 w/o Pu alloys were irradiated in the MTR reactor at 500°C to burnups from 0.8 to 1.8 total a/o [201 ]. The postirradiation examination showed that the specimens had increased their length from 2 to 4 times. The anisotropic growth of the specimens was due to preferred orientation caused by the cold rolling of the hexagonal close packed alphazirconium alloy.
References [ 1} R.D.Moellerand F.W.Schonfeld,Alloys of pluton:um with aluminum, USAEC Report LA-1000 (Los Alamos Scientific Laboratory, February 13, 1950).[2J M.B.Waldronet aL, The physical metallurgy of plutonium, Proc. of the Second United Nations International Conference on the Peaceful Uses of Atomic Energy, Vol. 6 (United Nations, Geneva, 1958). [3] A.A.Bochvaret al., Interaction between plutonium and other metals in connection with their arrangement in
Mendeleev's periodic table, Proc. of the Second United Nations International (~onferenceon the PeacefulUses of Atomic Energy, VoL 6 (United Nations, Geneva, 1958). [4] F.H,Ellinger et al., The solubility limits of aluminum in delta plutonium and some revisions of the plutoniumaluminum phase diagram, J. Nucl. Mater. 5 (2) (1962) 165-172. [i] O.J.C.Rnnnalls,Phase equilibria studies on the aluminum-plutonium system, in: Plutonium 1965, eds.: A.E.Kay and M.B.Waldron(Chapman and Hall, London, 1967) pp. 341-357. [6 ] R.O.EUiottand K,A.GschneidnerJr., Behavior of some delta-stabilized plutonium alloys at high pressures, in: Extractive and PhysicalMetallurgyof Plutonium and Its Alloys, ed.: W.D.WUkinson(Interscience Publishers, New York, 1960) pp. 243-262. [7] R O.Elliott and A.C.Larson,Delta-Prime Plutonium, Chapter XXIV in: The Metal Plutonium, eds.: A.S.Cof.finberry '~ndW.N.Miner(The Universityof Chicago Press, Chicago, 1961) pp. 265-280. [8] A.E.Hall,Plutonium-aluminumsolid solubility and diffusion studies, Nucl. Sci. Eng. 8 (1959) 283-288. [9 ] P.R.Roy, Determination of Ol-aluminumsolid solubility limits in the aluminum-uraniumand aluminum-plutonium systems, J. Nucl. Mater. 11 (1) (1964) 59-66. [101 D.Calaiset al., Diffusionof plutonium in the solid state, in: Plutonium 1965, eds.: A.E.Kay and M.B.Waldron (Chapman and Hall, London, 1967). [ 11] O.J.C.Runnalls, The crystal structures of some intermetallic compounds of plutonium, Can. J. Chem. 34 (1956) 133-145. [ 12] F.H.Ellinger,A reviewof the hatermetalliccompounds of plutonium, Chapter XXV in: The Metal Plutonium, eds.: A.S.Coffinberryand W.N.Miner(The Universityof Chicago Press, Chicago, 1961) pp. 281-308. [ 13] J.Singer, Los Alamos ScientificLaboratory, unpublished data. [ 14] A.C.Larson, D.T.Cromer and C.K.Stambaugh,The crystal structure of PnAI3, Acta Cryst. 10 (1957) 443-446. [ 15] S.T.Konobeevsky,Equilibrium diagrams of certain systems of plutonium, Session on the PeacefulUses of Atomic Energy, Section on ChemicalSciences, Iii (USSR Academy of Sciences, Moscow, 1955) pp. 3623"/4. [ 16] P.G.Mardonet al., The plutonium-iron system, J. Inst. Met. 86 (1957) 166-171. [17] F.W.Schonfeld,Plutonium phase diagrams studied at Los Alamos,Chapter XXli in: The Metal Plutonium, eds.: A.S.Coffinberryand W.N.Miner(The University of Chicago Press,Chicago, 1961) p. 240-254. [ 18] C.C.Land, in: Quarterly Status Report on Plutonium Reactor Fuel Development for Period Ending February 20, 1964, USAEC Report LAMS-3057 (Los Alamos Scientific Laboratory, March 25, 1964) p. 13.
S.H.Kittel et al., Plutonium and plutonium alloys
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fuel rods, USAEC Report ANL-6750 (Argonne National Laboratory, February 1970). [ 1891 W.N.Beck et al., Irradiation behavior of plutonium alloy fuels for fast reactors, Third International Conferertce on plutonium, London (November 22-- 26. 1965). [ 190 I R.S.Barnes, A theory of swelling and gas release for reactor materials, J. Nucl. Mater. ! 1 (1864) 1 3 : i 148~ [ 191 ] W.N.Beck et al., Irradiation performance of fast reactor uranium-plutonium metal fuels, AIME Nuclear Metallurgy Symposium, Phoenix, Arizona (October 4-6. 1967). [192] W.N.Beck et al., Performance of advanced U-Pu-Zr alloy fuel elements under fast reactor conditions, Trans. Am. Nucl. Soc. 10(1967) 106. 1193] M.B.Waldron et al., Plutonium technology for fast reactors, Proc. Second International Conference on the Peaceful Uses of Atomic Energy 6 (1958) 690-696 [ 194] B.R.T.Frost et al., Research on the fabrication, properties, and i~radiation behavior of plutoniam fuels for the U.K. Reactor Programme, USAEC Report HW75007 (Pacific Northwest Laboratory, 15.1 - i 5. i 7, 1967). [ 195] J.P.Mustelier, Quelques r~sultats d'irradiation sur les combustibles envisag6s pour Rapsodie, New N.aclear Materials Including Non-Metallic Fuels, !i. IAEA (1963) 163-183. [ 196] K.F.Smith and L.R.Kelman, Irradiation of cast uranium-plutonium base alloys, USAEC Report ANL5677 (May 1957). [ 197] T.I.Jones, The irradiation of aluminum-plutonium alloys in zirealoy-2 sheathing, AECL-1589 (Atomi.: Energy of Canada Limited, 1962). [ 198] R.Carlander et at., Postirradiation examination of EBR-I Core IV prototype fuel rods, USAEC Report ANL-6670 (Argonne NatiGnal Laboratory, September 1963). [ 199] M.D.Freshley et al., PRTR fuel element experience, Trans. Am. Nucl. Soc. 7 (1964) 388-389. [200] R.K.Koler et al., Irradiation testing of injection-casl AI/Pu/Ni alloys fuel rods, Trans. Am. Nucl. Soc 6 (1963) 159. [ 201 ] J.A.Horak and H.V.Rhude, Irradiation growth of zirconium-plutonium alloys, J. Nucl. Mater. 3 (1961) 111-112. Selected 'reading list (1) F.H.Ellinger, W.N.Miner, D.R.O'Boyle, and F.W.Schonfeld, Constitution of plutonium alloys, USAEC Report LA3870 (Los Alamos Scientific Laboratory, 1968). (2) O.J.Wick (ed.), Ph.,t~nium Handbook (Gordon and Brcuch, New York, 1967). (3) H.Blank, G.Brossman, and M.Kemmerich, Zwei- und Mehrstoffsysteme mit Plutonium, Tell 1. Pu-Ag his Pu-Su. Report KFK-105, Kernforschungszentmm, Karlsn~he ~June 1962);
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S,H.KitteletaL, Plutonium and plutonium alloys
($) Er.GriSotkW.H.B~Lord and R.D.Fowler (ecls.),Plutonium 1960 (Cleaver-flume Pgeu, London, 196D. ' (6) A+.Kayand M!B.mimon (ods.)~mtonium 1965 (Chapmln-Hnn' London,+1967)( (7) AEC Reactor Handbook on Maleria|+, Second Edilion, Chapters I and 11 (1960).
Northwest Laboratory, September 1965).