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Core concept of compound process fuel cycle
Progress in Nuclear Energy, Vol. 47, N o . 1-4, pp. 2 3 1 - 2 3 8 , 2005 Available online at www.sciencedirect.com s =, E N c E ~ d ) o , ~ E c 1- o ELSEVIER www.elsevier.com/locate/pnucene
© 2 0 0 5 E l s e v i e r Ltd. A l l r i g h t s r e s e r v e d P r i n t e d in G r e a t B r i t a i n 0 1 4 9 - 1 9 7 0 / $ - s e e front m a t t e r
doi: 10.1016/j.pnueene.2005.05.023
CORE CONCEPT OF COMPOUND
PROCESS FUEL CYCLE
TETSUO IKEGAMI O-arai Engineering Center, Japan Nuclear Cycle Development Institute (JNC) O-arai Ibaraki 31 I- 1393, Japan ABSTRACT This paper presents fast reactor core concept and its feasibility as a part of newly proposed compound process fuel cycle in which spent fuels of light water reactor are multi-recycled without conventional reprocessing but with only pyrochemical processing, fuel re-fabrication and reloading to the fast reactor core. Results of the core survey analyses in order to find out the feasibility o f this concept, taking example for BWR MOX spent fuel o f 60 GWd/t burn-up, show that four times recycling of LWR spent fuel with the burn-up of more than 300 GWd/t can be achieved without increasing MA content. Such benefits will be expected in this concept as reduction of fuel cycle cost due to simplified reprocessing procedure, reduction of environmental impacts due to reduced high level waste, efficient utilization of nuclear fuel resources, enhancement of nuclear non-proliferation, and suppression of LWR spent fuel pile-up. © 2005 Elsevier Ltd. All rights reserved KEYWORDS Fast reactor core; LWR spent fuel; Pyrochemical processing; Compound process fuel cycle; Effective utilization of LWR fuel 1. INTRODUCTION Recently, pile-up of spent fuels of light water reactor (LWR) is becoming one of the major issues of nuclear fuel cycle in Japan. Furthermore, the smooth evolution from LWR system to next-generation innovative nuclear energy systems known as "Generation IV" system is another key issue, although few studies relevant to it have been reported (for example;Takaki et al., 2002) A new fuel cycle concept named "Compound Process Fuel Cycle" which utilizes LWR spent fuel in fast reactor core is proposed in this paper as a possible candidate of future fuel cycle options for smooth evolution from LWR system to fast reactor system. The feasibility of the cycle has been studied focusing
231
232
~ Ikegami
on the core nuclear characteristics together with the evaluation of expected benefits of the cycle. 2. COMPOUND PROCESS FUEL CYCLE CONCEPT The compound process fuel cycle aims at the efficient utilization o f LWR spent fuel and the suppression of LWR spent fuel pile-up. LWR spent fuel are multi-recycled, in the cycle, without conventional reprocessing but with only pyrochemieal processing, fuel re-fabrication, and reloading to the fast reactor core as shown in Fig. 1.
Pyrochemical I_ h Processing ~______.~bLWR SpentFuel ~ ~ VolatileFP
T
I ReuseFuel Fabrication
U. Pu. MA. FP
ES
1
Loadingto H FR Core
Fuel Uo,o.in,
~
I~I Repr°cessing I
Ooo,,n,,
f
Fresh FR Fuel Fabrication
U/~ I
FR : fast reactor
U, Pu, MA Fig.1.
Compound process fuel cycle concept
The pyrochemical processing corresponds to the pre-process procedure, consisting of only de-cladding and pulverization, of the conventional reprocessing o f mixed oxide (MOX) fuel. Spent fuel pins are oxidized at high temperature after being cut to small pieces or being hole-punched at cladding. The de-cladding and the pulverization are conducted utilizing the volume expansion, about 30%, at the process of oxidation from UO2 to U308. Volatile fission products (FP) are removed at the process. Reduction under the hydrogen added atmosphere enables U308 returning to UO2. FP removal rates at the pyrochemical processing assumed in this study are presented in Table 1. Table 1.
FP removal rates at pyrochemical processing
Br
Kr
1.00
1.00
Xe 1.00
Cs 0.98
0.98
Te 1.00
Mo 0.44
Pd 0.01
Ru 1.00
Rb 0.98
Cd 1.00
In 0.98
I
Sb 1.00
Significant simplification of the process and significant reduction of high level waste (HLW) compared with the conventional reprocessing can be expected in the pyrochemical processing. More homogeneous burning of fuel, both in radial and axial direction, can also be expected in a core design view point through the pyrochemical processing and re-fabrication compared to the simply long-lived
Proceedings' of INES-1, 2004
233
fuel. A lot of research and development works for the pyrochemical processing used to be conducted at Oak Ridge National Laboratory (ORNL method (Goode, 1973)), and Atomic International (AIROX method (Asquith and Grantham, 1978; Thomas, 1973)) in 1970's. Recently, DUPIC (Direct use o f spent PWR fuel in CANDU) concept which adopts the pyrochemical processing has been developed in Korea (Chun and Tayler, 1993; Choi, et al. 1997; Song et al., 2003).
Major differences of the compound
process fuel cycle from the DUPIC are followings; -
-
-
Fast reactor is used in stead of CANDU (CANadian Deuterium Uranium). LWR spent fuel is partially loaded in the radial heterogeneous core in stead of fully loaded. Multi recycling (up to 4 times) is possible. More than 300 GWd/t of burn-up can be achieved in the case o f L W R MOX spent fuel.
The multi-recycled LWR spent fuels are finally reprocessed by the method conventionally applied for FBR fuels. This concept utilizes the flexibility of fast reactor core in terms of relatively abundant surplus neutrons, since the multi-recycled LWR spent fuels dealt with in this concept possess some amount of FP in them.
3. CORE FEASIBILITY STUDY 3.1 Calculation Method Core nuclear calculation has been carried out by the CITATION code in two dimensional R-Z geometry using 70 group cross section set JFS3-J3.2 based on the nuclear data library JENDL3.2 (Nakagawa et al., 1995). Treatment of residual FP is supposed to be very important in this analysis since some amount of FP remains in the recycled LWR spent fuel. Both of neutron absorption effect and volume effect of FP have been taken into account. Top 30 FP nuclides for the neutron absorption effect, which is expressed by the product of neutron capture cross section by mass of each FP, cover about 90% of neutron absorption effect of all FPs. Therefore, only the top 30 FP nuclides have been considered in a neutron absorption effect view point. The volume effect of FP, which causes the reduction of heavy metal volume fraction, has been taken into account by considering the FP volume fraction which is approximately assumed to correspond to FP weight fraction multiplied by 1.5. An evaluation has also been carried out, as an extreme case, for a case where no FP are assumed to be removed at the pyrochemical processing, since there exists some sort of uncertainty in the FP removal rates presented in Table 1. 3.2 Core Specification A radial heterogeneous core configuration, consists of fast reactor fuel region, (2n-l) time recycled LWR fuel region, and 2n time recycled LWR fuel region as shown in Fig. 2, has been adopted in order to accept reuse fuels fabricated from LWR spent fuels. Fuel assemblies in (2n-l) time recycled LWR fuel region, and those in 2n time recycled LWR fuel region are identical so as to keep the smooth recycle fuel flow.
~ Ikegami
234
i
i I
<~ <~
Fast Reactor Fuel (2n-1) time Recycled LWR Fuel 2n time Recycled LWR Fuel
Fig. 2.
@ ~ @
Control Rod (Main) Control Rod (Buck up) Radial Shield
Core configuration
Core specifications, fixed after survey calculations under such conditions as reactor thermal power (2600 MWt), maximum linear heat rate (less than 400 W/cm*), maximum fast neutron fluence (less than 5X10 27
/m2*), and burn-up reactivity loss (less than 4%Ak/kk'*) taking boiling water reactor (BWR)
MOX spent fuel (60 GWd/t) as LWR spent fuel, are shown in Table 2.
( * : These conditions are taken
following most of the FBR core design.) Table 2.
Core specifications
Item reactor thermal output (MWt) coolant core height (fast reactor fuel / LWR fuel) (cm) axial blanket height (fast reactor fuel / LWR fuel) fuel element diameter (mm) fuel elements in an assembly P/D Fuel volume fraction (%) Refueling batch Cycle length (day)
(cm)
Specification 2600 sodium 100/160 60/0 9.0 397 1.12 41.0 3 730
The fast reactor fuel has following initial Pu isotope ratio and contains 1.0 wt% MA of following composition.
238pU/239pU/240pH/Z41pU/242pH = 3/53/25/12/7 237Np/239Np/241Am/242Am/243Am/242Cm/244Cm/245Cm = 5.4/1.8/29.9/3.0/3 1.6/2.0/22.6/3.7 4. CORE CHARACTERISTICS Major nuclear characteristics of the compound process fuel cycle core for the case of taking BWR MOX spent fuel (60 GWd/t) as LWR spent fuel are presented in Table 3. The given conditions for
235
Proceedings of INES-1, 2004
maximum linear heat rate, maximum fast neutron fluence, and burn-up reactivity loss described above are satisfied up to 4 time recycles. The burn-up reactivity loss exceeds 4%Ak/kk' in more than 5 time recycles. Therefore, it is possible to continue recycling up to 4 times in a core nuclear characteristics view point. Table 3.
Major core nuclear characteristics
item burn-up reactivity loss (%Ak/kk') maximum linear heat rate (W/cm) maximum fast neutron fluence (n/m 2) breeding ratio (EOC) Pu enrichment of fast reactor fuel (wt%)
1~t & 2 "d time recycle 3.78 383 3.9x 1027 1.08 26.2
3 rd & 4 th time recycle 3.95 371 3.9x 1027 0.99 23.9
Figure 3 shows the burn-up evolution of the multi-recycled BWR MOX spent fuel up to 4 time recycles. The fuel burn-up reaches, after 4 th recycle, 330 GWd/t which corresponds to more than five times of that of BWR MOX fuel. The fuel burn-up evolution for the assumed case of without FP removal at the pyrochemical processing, also presented in Fig. 3, shows about 20% reduction of fuel burn-up after 4 th recycle. The reduction is caused by shorter cycle length, 640 days, in order to keep the burn-up reactivity loss condition. ~-~
2.5
350,000
100.0
s
-o 300,000
~ 2.0
60.0
g
,
~& 250,000 ?
60.0
,= 200,000 ..Q
1.o
150,000 o
> 100,000
~= 0.5
a~
-5 E O
40.0
removal
50,000 m i
0
• i
=
FP removalJ i
Q
--m--
]
i
0.0
~=
eu mass
20.0
P u fissile(%)
~-
-ResidualFPvolumefTaction*5.0
[~
0.0
i
BWR After 1st After 2nd After 3rd After 4th MOX S/F recycle recycle recycle recycle
Fig. 3.
Fuel burn-up evolution
Fig. 4.
Pu mass/Pu fissile content/FP volume fraction changes
The changes, up to 4 time recycles, of Pu mass and Pu fissile content together with the residual FP volume fraction in the multi-recycled BWR MOX spent fuel are shown in Fig. 4. Both Pu mass and Pu fissile content increase at first but reach to equilibrium state after I st or 2 ~d recycle, while residual FP volume fraction increases monotonically and reaches to about 20% at 4 th recycle. This fact limits the multi-recycle of the BWR MOX spent fuel up to 4 times. Figure 5 presents the changes of MA mass and MA composition in the multi-recycled BWR MOX spent fuel up to 4 time recycles. It can be noticed that the MA mass shows quite small change giving rather less amount than that of BWR MOX spent fuel after 4 th recycle.
Ikegami
236
QNp237 INp239
LWR MOX S/F =
I
[]Am241
!
Q Am242m
After 1st recycle I
r~Am243
After 2nd recycle |
E3Cm242
I
After 3rd recycle
I~ICm244 !
D Cm245
1
After 4th recycle I
I
0.0
Fig. 5.
I
5.0
10.0
I
150
I
20.0
I
(Kg/bateh) 25.0
MA mass and MA composition changes (after 4 year cooling)
The fact that both Pu and MA reach to equilibrium state after 4 th recycle implies that the compound process fuel cycle proposed in this paper utilizes the LWR spent fuel quite well.
5. DISCUSSIONS The compound process fuel cycle proposed in this paper has following features. 1) Economic competitiveness The pyrochemical processing corresponds to merely the pre-process procedure of the conventional reprocessing of mixed oxide (MOX) fuel. Consequently, it is expected that the process is significantly simplified resulting in qualitatively significant reduction in fuel cycle cost compared with the conventional reprocessing, although quantitative evaluation is not available at present. 2) Reduction of environmental burden Actinide mass flow of the LWR spent fuel which is recycled 4 times in the compound process fuel cycle is shown in Fig. 6. The total actinide mass (MW), which leaks out of the system while the LWR spent fuel is recycled 4 times through the pyrochemical processing and finally through the conventional reprocessing, can be expressed in equation (1). M w = MWl+ M w2+ M w3+ MW4+ M wS= L2Mo { L1/L2 + (I-B) LI/L2(1-L1) + ( l - B ) 2 L1/L2 (l-L]) 2 + (l-B) 3 L]/L2 (I-L1) 3 + (l-B) 4 (l-L1) 4 }
(1)
where, L1 : actinide loss rate at the pyrochemical processing L2 : actinide loss rate at the conventional reprocessing B : fuel burn-up M0 : actinide mass in LWR spent fuel M w~: actinide mass which leaks out of the system at the i-th time pyrochemical processing or conventional reprocessing
Proceedings of INES-1, 2004
237
Energy :BM m, BM R2, BM R3, BM R4 (B:burn-up)
A
MR4
LWR S/F : M0 loss :
M wl= L I M o "
Mm
Li
(1-B)M
( 1-B) MRI ( 1-B) MR2
R4
• loss : L 2
( l - B ) MR3
,
Mw2=(1-B)L1 Me Mw3=(1-B)L1 MR2
Mw4=(1-B)L~ MR3
Fig. 6.
~I~ MwS= (1-B)L2M R4
Actinide mass flow in the compound process fuel cycle
It can be considered that the fuel burn-up (B) is nearly equal to 0.06 from Fig. 3, and that the actinide loss rate at the pyrochemical processing (L1) is nearly equal to zero. Therefore, M w= LzM0 (0.78 + 3.76 LI/L2 )
(2)
If F is defined as the ratio o f the total actinide mass which leaks out of the system to the actinide mass which leaks from the conventional reprocessing, F is expressed as F = 0.78 + 3.76 L1/Lz
(3)
F < 4.54
(4)
Then (since L1/L2< 1.0 )
Therefore, the actinide mass which leaks out o f the system can be reduced surely since F is equal to 5.0 in the case where the recycle is carried out only by the conventional reprocessing. L1 can be considered to be quite small. Consequently, if L~/L2 is assumed to be 0.1, the actinide mass which leaks out of the system becomes less than 1/4 of that of the conventional reprocessing. It is also a favorable fact in terms of reduction of environmental burden that the MA mass after 4 th recycle is rather reduced than that of the BWR MOX spent fuel as shown in Fig. 5. 3) Efficient utilization of nuclear fuel resources The compound process fuel cycle enables the B W R MOX spent fuel of 60 GWd/t burn-up to achieve 330 GWd/t. This fact shows about 5 times more efficient utilization of nuclear fuel resources. Moreover, further efficient utilization of nuclear fuel resources would be possible since the recycled fuel, reaching 330 GWd/t bum-up, can be further recycled through the conventional reprocessing, multiplying the fact that the actinide loss rate is small as described above. 4) Enhancement of nuclear non-proliferation All actinides including most of FPs are processed all together in a lumped state in the compound process fuel cycle and Pu is never treated separately. Consequently, the compound process fuel cycle can be considered to have higher characteristics of nuclear non-proliferation.
238
Z
Ikegami
5) Others It can be expected that the LWR spent fuel pile-up would be suppressed since the compound process fuel cycle selectively consumes LWR spent fuel. Fuels in a same batch are mixed up through the pyrochemical processing, resulting in homogenization of fuel both in radial and axial direction. Accordingly, more homogeneous depletion would be possible than such fuel that achieves high burn-up without recycling. 6. CONCLUSION A new fuel cycle concept named "Compound Process Fuel Cycle" is proposed in which LWR spent fuels are multi-recycled without conventional reprocessing but with only pyrochemical processing. The feasibility o f the cycle has been studied focusing on the core nuclear characteristics taking example for BWR MOX spent fuel. The BWR MOX spent fuel o f 60 GWd/t burn-up can be recycled 4 times achieving more than 330 GWd/t of burn-up. Therefore, efficient utilization of nuclear fuel resources can be expected. Reduction of environmental burden would be achieved through the facts that actinide mass leaking out of the system is reduced and that MA mass stays almost in same level after multi-recycled. Furthermore, such benefits can be expected as economic competitiveness, enhancement of nuclear non-proliferation, and suppression of LWR spent fuel pile-up. REFERENCES Asquith
J.
G.
and
Grantham
L.
E
(1978),
"A
Low-Decontamination
Approach
to
a
Proliferation-Resistant Fuel Cycle", Nucl. Tech. Vol.41,137. Choi H., Rhee B. W. and Park H. (1997), "Physics Study on Direct Use o f Spent Pressurized Water Reactor Fuel in CANDU (DUPIC)", Nnclear Science and Engineering, 126, 80-93. Chun K. S. and Tayler E (1993), "Basic Concept of Radioactive Waste Management for DUPIC Fuel Cycle in Korea", GLOBAL'93, 201. Goode J. H. (1973), "VOLOXIDATION - Removal o f Volatile Fission Products from Spent LMFBR Fuels", ORNL-TM-3723. Nakagawa T., Shibata K., Chiba S., Fukahori T., Nakajima Y., Kikuchi Y., Kawano T., Kanda Y., Ohsawa T., Matsunobu H., Kawai M., Zukeran A., Watanabe T., Igarasi S., Kosako K. and Asami T. (1995)., "Japanese Evaluated Nuclear Data Library Version 3 Revision 2: JENDL-3.2", Journal of Nuclear Science and Technology 32, p. 1259 Song K. C., Lee J. W. and Yang M. S. (2003), "Performance Evaluation of DUPIC FUEL using a Research Reactor", GLOBAL'03, 1325-1328. Takaki N., Shinoda Y., Watanabe M. and Yoshida K. (2002), "ORIENT-CYCLE - An Evolutional Recycle Concept with Fast Reactor for Minimizing High Level Waste -", Proc. 7 th Information Exchange Meeting, Jeju, Republic of Korea 14-16 Oct. Thomas T. R. (1973), "AIROX Nuclear Fuel Recycling and Waste Management", GLOBAL'93,722.
© 2 0 0 5 E l s e v i e r Ltd. A l l r i g h t s r e s e r v e d P r i n t e d in G r e a t B r i t a i n 0 1 4 9 - 1 9 7 0 / $ - s e e front m a t t e r
doi: 10.1016/j.pnueene.2005.05.023
CORE CONCEPT OF COMPOUND
PROCESS FUEL CYCLE
TETSUO IKEGAMI O-arai Engineering Center, Japan Nuclear Cycle Development Institute (JNC) O-arai Ibaraki 31 I- 1393, Japan ABSTRACT This paper presents fast reactor core concept and its feasibility as a part of newly proposed compound process fuel cycle in which spent fuels of light water reactor are multi-recycled without conventional reprocessing but with only pyrochemical processing, fuel re-fabrication and reloading to the fast reactor core. Results of the core survey analyses in order to find out the feasibility o f this concept, taking example for BWR MOX spent fuel o f 60 GWd/t burn-up, show that four times recycling of LWR spent fuel with the burn-up of more than 300 GWd/t can be achieved without increasing MA content. Such benefits will be expected in this concept as reduction of fuel cycle cost due to simplified reprocessing procedure, reduction of environmental impacts due to reduced high level waste, efficient utilization of nuclear fuel resources, enhancement of nuclear non-proliferation, and suppression of LWR spent fuel pile-up. © 2005 Elsevier Ltd. All rights reserved KEYWORDS Fast reactor core; LWR spent fuel; Pyrochemical processing; Compound process fuel cycle; Effective utilization of LWR fuel 1. INTRODUCTION Recently, pile-up of spent fuels of light water reactor (LWR) is becoming one of the major issues of nuclear fuel cycle in Japan. Furthermore, the smooth evolution from LWR system to next-generation innovative nuclear energy systems known as "Generation IV" system is another key issue, although few studies relevant to it have been reported (for example;Takaki et al., 2002) A new fuel cycle concept named "Compound Process Fuel Cycle" which utilizes LWR spent fuel in fast reactor core is proposed in this paper as a possible candidate of future fuel cycle options for smooth evolution from LWR system to fast reactor system. The feasibility of the cycle has been studied focusing
231
232
~ Ikegami
on the core nuclear characteristics together with the evaluation of expected benefits of the cycle. 2. COMPOUND PROCESS FUEL CYCLE CONCEPT The compound process fuel cycle aims at the efficient utilization o f LWR spent fuel and the suppression of LWR spent fuel pile-up. LWR spent fuel are multi-recycled, in the cycle, without conventional reprocessing but with only pyrochemieal processing, fuel re-fabrication, and reloading to the fast reactor core as shown in Fig. 1.
Pyrochemical I_ h Processing ~______.~bLWR SpentFuel ~ ~ VolatileFP
T
I ReuseFuel Fabrication
U. Pu. MA. FP
ES
1
Loadingto H FR Core
Fuel Uo,o.in,
~
I~I Repr°cessing I
Ooo,,n,,
f
Fresh FR Fuel Fabrication
U/~ I
FR : fast reactor
U, Pu, MA Fig.1.
Compound process fuel cycle concept
The pyrochemical processing corresponds to the pre-process procedure, consisting of only de-cladding and pulverization, of the conventional reprocessing o f mixed oxide (MOX) fuel. Spent fuel pins are oxidized at high temperature after being cut to small pieces or being hole-punched at cladding. The de-cladding and the pulverization are conducted utilizing the volume expansion, about 30%, at the process of oxidation from UO2 to U308. Volatile fission products (FP) are removed at the process. Reduction under the hydrogen added atmosphere enables U308 returning to UO2. FP removal rates at the pyrochemical processing assumed in this study are presented in Table 1. Table 1.
FP removal rates at pyrochemical processing
Br
Kr
1.00
1.00
Xe 1.00
Cs 0.98
0.98
Te 1.00
Mo 0.44
Pd 0.01
Ru 1.00
Rb 0.98
Cd 1.00
In 0.98
I
Sb 1.00
Significant simplification of the process and significant reduction of high level waste (HLW) compared with the conventional reprocessing can be expected in the pyrochemical processing. More homogeneous burning of fuel, both in radial and axial direction, can also be expected in a core design view point through the pyrochemical processing and re-fabrication compared to the simply long-lived
Proceedings' of INES-1, 2004
233
fuel. A lot of research and development works for the pyrochemical processing used to be conducted at Oak Ridge National Laboratory (ORNL method (Goode, 1973)), and Atomic International (AIROX method (Asquith and Grantham, 1978; Thomas, 1973)) in 1970's. Recently, DUPIC (Direct use o f spent PWR fuel in CANDU) concept which adopts the pyrochemical processing has been developed in Korea (Chun and Tayler, 1993; Choi, et al. 1997; Song et al., 2003).
Major differences of the compound
process fuel cycle from the DUPIC are followings; -
-
-
Fast reactor is used in stead of CANDU (CANadian Deuterium Uranium). LWR spent fuel is partially loaded in the radial heterogeneous core in stead of fully loaded. Multi recycling (up to 4 times) is possible. More than 300 GWd/t of burn-up can be achieved in the case o f L W R MOX spent fuel.
The multi-recycled LWR spent fuels are finally reprocessed by the method conventionally applied for FBR fuels. This concept utilizes the flexibility of fast reactor core in terms of relatively abundant surplus neutrons, since the multi-recycled LWR spent fuels dealt with in this concept possess some amount of FP in them.
3. CORE FEASIBILITY STUDY 3.1 Calculation Method Core nuclear calculation has been carried out by the CITATION code in two dimensional R-Z geometry using 70 group cross section set JFS3-J3.2 based on the nuclear data library JENDL3.2 (Nakagawa et al., 1995). Treatment of residual FP is supposed to be very important in this analysis since some amount of FP remains in the recycled LWR spent fuel. Both of neutron absorption effect and volume effect of FP have been taken into account. Top 30 FP nuclides for the neutron absorption effect, which is expressed by the product of neutron capture cross section by mass of each FP, cover about 90% of neutron absorption effect of all FPs. Therefore, only the top 30 FP nuclides have been considered in a neutron absorption effect view point. The volume effect of FP, which causes the reduction of heavy metal volume fraction, has been taken into account by considering the FP volume fraction which is approximately assumed to correspond to FP weight fraction multiplied by 1.5. An evaluation has also been carried out, as an extreme case, for a case where no FP are assumed to be removed at the pyrochemical processing, since there exists some sort of uncertainty in the FP removal rates presented in Table 1. 3.2 Core Specification A radial heterogeneous core configuration, consists of fast reactor fuel region, (2n-l) time recycled LWR fuel region, and 2n time recycled LWR fuel region as shown in Fig. 2, has been adopted in order to accept reuse fuels fabricated from LWR spent fuels. Fuel assemblies in (2n-l) time recycled LWR fuel region, and those in 2n time recycled LWR fuel region are identical so as to keep the smooth recycle fuel flow.
~ Ikegami
234
i
i I
<~ <~
Fast Reactor Fuel (2n-1) time Recycled LWR Fuel 2n time Recycled LWR Fuel
Fig. 2.
@ ~ @
Control Rod (Main) Control Rod (Buck up) Radial Shield
Core configuration
Core specifications, fixed after survey calculations under such conditions as reactor thermal power (2600 MWt), maximum linear heat rate (less than 400 W/cm*), maximum fast neutron fluence (less than 5X10 27
/m2*), and burn-up reactivity loss (less than 4%Ak/kk'*) taking boiling water reactor (BWR)
MOX spent fuel (60 GWd/t) as LWR spent fuel, are shown in Table 2.
( * : These conditions are taken
following most of the FBR core design.) Table 2.
Core specifications
Item reactor thermal output (MWt) coolant core height (fast reactor fuel / LWR fuel) (cm) axial blanket height (fast reactor fuel / LWR fuel) fuel element diameter (mm) fuel elements in an assembly P/D Fuel volume fraction (%) Refueling batch Cycle length (day)
(cm)
Specification 2600 sodium 100/160 60/0 9.0 397 1.12 41.0 3 730
The fast reactor fuel has following initial Pu isotope ratio and contains 1.0 wt% MA of following composition.
238pU/239pU/240pH/Z41pU/242pH = 3/53/25/12/7 237Np/239Np/241Am/242Am/243Am/242Cm/244Cm/245Cm = 5.4/1.8/29.9/3.0/3 1.6/2.0/22.6/3.7 4. CORE CHARACTERISTICS Major nuclear characteristics of the compound process fuel cycle core for the case of taking BWR MOX spent fuel (60 GWd/t) as LWR spent fuel are presented in Table 3. The given conditions for
235
Proceedings of INES-1, 2004
maximum linear heat rate, maximum fast neutron fluence, and burn-up reactivity loss described above are satisfied up to 4 time recycles. The burn-up reactivity loss exceeds 4%Ak/kk' in more than 5 time recycles. Therefore, it is possible to continue recycling up to 4 times in a core nuclear characteristics view point. Table 3.
Major core nuclear characteristics
item burn-up reactivity loss (%Ak/kk') maximum linear heat rate (W/cm) maximum fast neutron fluence (n/m 2) breeding ratio (EOC) Pu enrichment of fast reactor fuel (wt%)
1~t & 2 "d time recycle 3.78 383 3.9x 1027 1.08 26.2
3 rd & 4 th time recycle 3.95 371 3.9x 1027 0.99 23.9
Figure 3 shows the burn-up evolution of the multi-recycled BWR MOX spent fuel up to 4 time recycles. The fuel burn-up reaches, after 4 th recycle, 330 GWd/t which corresponds to more than five times of that of BWR MOX fuel. The fuel burn-up evolution for the assumed case of without FP removal at the pyrochemical processing, also presented in Fig. 3, shows about 20% reduction of fuel burn-up after 4 th recycle. The reduction is caused by shorter cycle length, 640 days, in order to keep the burn-up reactivity loss condition. ~-~
2.5
350,000
100.0
s
-o 300,000
~ 2.0
60.0
g
,
~& 250,000 ?
60.0
,= 200,000 ..Q
1.o
150,000 o
> 100,000
~= 0.5
a~
-5 E O
40.0
removal
50,000 m i
0
• i
=
FP removalJ i
Q
--m--
]
i
0.0
~=
eu mass
20.0
P u fissile(%)
~-
-ResidualFPvolumefTaction*5.0
[~
0.0
i
BWR After 1st After 2nd After 3rd After 4th MOX S/F recycle recycle recycle recycle
Fig. 3.
Fuel burn-up evolution
Fig. 4.
Pu mass/Pu fissile content/FP volume fraction changes
The changes, up to 4 time recycles, of Pu mass and Pu fissile content together with the residual FP volume fraction in the multi-recycled BWR MOX spent fuel are shown in Fig. 4. Both Pu mass and Pu fissile content increase at first but reach to equilibrium state after I st or 2 ~d recycle, while residual FP volume fraction increases monotonically and reaches to about 20% at 4 th recycle. This fact limits the multi-recycle of the BWR MOX spent fuel up to 4 times. Figure 5 presents the changes of MA mass and MA composition in the multi-recycled BWR MOX spent fuel up to 4 time recycles. It can be noticed that the MA mass shows quite small change giving rather less amount than that of BWR MOX spent fuel after 4 th recycle.
Ikegami
236
QNp237 INp239
LWR MOX S/F =
I
[]Am241
!
Q Am242m
After 1st recycle I
r~Am243
After 2nd recycle |
E3Cm242
I
After 3rd recycle
I~ICm244 !
D Cm245
1
After 4th recycle I
I
0.0
Fig. 5.
I
5.0
10.0
I
150
I
20.0
I
(Kg/bateh) 25.0
MA mass and MA composition changes (after 4 year cooling)
The fact that both Pu and MA reach to equilibrium state after 4 th recycle implies that the compound process fuel cycle proposed in this paper utilizes the LWR spent fuel quite well.
5. DISCUSSIONS The compound process fuel cycle proposed in this paper has following features. 1) Economic competitiveness The pyrochemical processing corresponds to merely the pre-process procedure of the conventional reprocessing of mixed oxide (MOX) fuel. Consequently, it is expected that the process is significantly simplified resulting in qualitatively significant reduction in fuel cycle cost compared with the conventional reprocessing, although quantitative evaluation is not available at present. 2) Reduction of environmental burden Actinide mass flow of the LWR spent fuel which is recycled 4 times in the compound process fuel cycle is shown in Fig. 6. The total actinide mass (MW), which leaks out of the system while the LWR spent fuel is recycled 4 times through the pyrochemical processing and finally through the conventional reprocessing, can be expressed in equation (1). M w = MWl+ M w2+ M w3+ MW4+ M wS= L2Mo { L1/L2 + (I-B) LI/L2(1-L1) + ( l - B ) 2 L1/L2 (l-L]) 2 + (l-B) 3 L]/L2 (I-L1) 3 + (l-B) 4 (l-L1) 4 }
(1)
where, L1 : actinide loss rate at the pyrochemical processing L2 : actinide loss rate at the conventional reprocessing B : fuel burn-up M0 : actinide mass in LWR spent fuel M w~: actinide mass which leaks out of the system at the i-th time pyrochemical processing or conventional reprocessing
Proceedings of INES-1, 2004
237
Energy :BM m, BM R2, BM R3, BM R4 (B:burn-up)
A
MR4
LWR S/F : M0 loss :
M wl= L I M o "
Mm
Li
(1-B)M
( 1-B) MRI ( 1-B) MR2
R4
• loss : L 2
( l - B ) MR3
,
Mw2=(1-B)L1 Me Mw3=(1-B)L1 MR2
Mw4=(1-B)L~ MR3
Fig. 6.
~I~ MwS= (1-B)L2M R4
Actinide mass flow in the compound process fuel cycle
It can be considered that the fuel burn-up (B) is nearly equal to 0.06 from Fig. 3, and that the actinide loss rate at the pyrochemical processing (L1) is nearly equal to zero. Therefore, M w= LzM0 (0.78 + 3.76 LI/L2 )
(2)
If F is defined as the ratio o f the total actinide mass which leaks out of the system to the actinide mass which leaks from the conventional reprocessing, F is expressed as F = 0.78 + 3.76 L1/Lz
(3)
F < 4.54
(4)
Then (since L1/L2< 1.0 )
Therefore, the actinide mass which leaks out o f the system can be reduced surely since F is equal to 5.0 in the case where the recycle is carried out only by the conventional reprocessing. L1 can be considered to be quite small. Consequently, if L~/L2 is assumed to be 0.1, the actinide mass which leaks out of the system becomes less than 1/4 of that of the conventional reprocessing. It is also a favorable fact in terms of reduction of environmental burden that the MA mass after 4 th recycle is rather reduced than that of the BWR MOX spent fuel as shown in Fig. 5. 3) Efficient utilization of nuclear fuel resources The compound process fuel cycle enables the B W R MOX spent fuel of 60 GWd/t burn-up to achieve 330 GWd/t. This fact shows about 5 times more efficient utilization of nuclear fuel resources. Moreover, further efficient utilization of nuclear fuel resources would be possible since the recycled fuel, reaching 330 GWd/t bum-up, can be further recycled through the conventional reprocessing, multiplying the fact that the actinide loss rate is small as described above. 4) Enhancement of nuclear non-proliferation All actinides including most of FPs are processed all together in a lumped state in the compound process fuel cycle and Pu is never treated separately. Consequently, the compound process fuel cycle can be considered to have higher characteristics of nuclear non-proliferation.
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Ikegami
5) Others It can be expected that the LWR spent fuel pile-up would be suppressed since the compound process fuel cycle selectively consumes LWR spent fuel. Fuels in a same batch are mixed up through the pyrochemical processing, resulting in homogenization of fuel both in radial and axial direction. Accordingly, more homogeneous depletion would be possible than such fuel that achieves high burn-up without recycling. 6. CONCLUSION A new fuel cycle concept named "Compound Process Fuel Cycle" is proposed in which LWR spent fuels are multi-recycled without conventional reprocessing but with only pyrochemical processing. The feasibility o f the cycle has been studied focusing on the core nuclear characteristics taking example for BWR MOX spent fuel. The BWR MOX spent fuel o f 60 GWd/t burn-up can be recycled 4 times achieving more than 330 GWd/t of burn-up. Therefore, efficient utilization of nuclear fuel resources can be expected. Reduction of environmental burden would be achieved through the facts that actinide mass leaking out of the system is reduced and that MA mass stays almost in same level after multi-recycled. Furthermore, such benefits can be expected as economic competitiveness, enhancement of nuclear non-proliferation, and suppression of LWR spent fuel pile-up. REFERENCES Asquith
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