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The calibration of fast reactor irradiated silicon carbide temperature monitors using a length measurement technique
Journal of Nuclear Materials 92 (1980) 43-50 0 North-Holed Publish Company
THECALIBRATIONOFFASTREACTORIRRADIATEDSILICONCARBIDETEMPE~TU~ MONITORSUSINGALENGTHMEASUREMENTTECHNIQUE J.E. PALENTINE UKAEA, Springfields Nuclear Power Development Laboratories, Salwick, Preston PR4 ORR, UK Received 3 April 1980
Silicon carbide temperature monitors have been calibrated against thermocouples in the Dounreay Fast Reactor. Statistical confidence levels have been determined for future temperature estimates based on as-irradiated length change and on the post-irradiation annealing intersection temperature. Possible dose limitations are discussed.
monobloc, one at the mid-way position of each tier of specimens. The 12.7 mm long X 3.175 mm diameter monitors were made from ‘%rusilite” material ~orga~te Electroheat Ltd.) or from material manufactured internally at SNPDL. They were encapsulated in heliumfilled capsules of stainless steel, the Sic pellet being wrapped in molybdenum knit-mesh to prevent chemical interactions at higher temperatures. The silicon carbide pellets were prepared to the high standards of flatness and parellelism described in ref. [ 11, and had been accurately measured prior to encapsulation. In each monobloc, certain of the monitors were used for X-ray lattice parameter analysis at Dounreay [2], and the remainder, the analysis of which is reported herein, were examined at Springfields. The vehicle was irradiated in position 36/Ea5 during run 8 l/l for 31 days. During this period reactor power remained very steady at 60 MW, with no trips. The temperatures recorded throughout the period were as shown in table 1, and it is clear that these are appreciably lower than had been hoped. The dose attained by the monitors was 1.02 to 1.22 dpa (NRT) (Fe) [3] and the dose to damage saturation in the Sic, ca. 0.7 dpa (NRT) (Fe) was achieved in about 20 days. The temperature over the final 20 days is shown in table 1, and is seen to have been reasonably uniform over this period.
1. introduction In a previous paper [l] the present author described the development of improved techniques for the preparation and measurement of silicon carbide temperature monitors, and for the objective analysis of the measurement data. Calibration data from a thermal reactor irradiation were presented, but evidence was put forward to suggest that the use of such a calibration could seriously underestimate irradiation temperatures if applied to monitors from a fast reactor. A fast flux calibration experiment was recommended. This report describes just such an experiment performed in the Dounreay Fast Reactor (DFR) to calibrate SE temperature monitors against thermocouples in a f&t flux.
2. The calibration experiment The irradiation was carried out in an instrumented gamma-heated rig in the DFR breeder. The rig consisted of 4 stainless steel monoblocs mounted one on top of the other and designed to operate at temperatures of 450, 520, 590 and 660°C. Each monobloc had six lon~tud~~ holes for the specimen capsules, there being three tiers of specimens per monobloc, and hence 18 specimen positions at each temperature. Three thermocouples were placed centrally in each 43
44
LE. Pulentine / Calibration of irradiated SC re~pera~ure
Table 1 Irradiation temperatures from daily thermocouple
monitors
readings
Position of thermocouple in monobloc
Design temperature f”C)
Mean temperature over whole 31 days (and 2a spread)
Mean temperature over final 20 days (and 2a spread)
Upper Middle Lower
458 450 449
417+22 419 + 19 424 + 15
424 z+2.7 425 f 1.7 428 ?: 3.7
Upper Middle Lower
529 522 522
490 + 8 483 * 6 471 * 6
489 t 3.0 482 + 4.5 471 + 3.4
Upper Middle Lower
601 598 589
543 f 7 543 + 5 532 f 5
544 t 2.6 545 f 2.1 532 f 3.4
Upper Middle Lower
661 672 668
572 f 14 595 * 13 575 f 12
575 c 0.4 597 _+3.2 578 2 3.8
-
3. Analysis and results The specimens were measured using a Heidenhain digital length gauge (Heidenhain (GB) Ltd., Burgess Hill, Sussex) employing a vertical probe and measuring in units of 1O-3 mm. The support jig was as described in ref. [l] , allowing a fibre of diameter only 0.05-0.1 mm to be measured, and two sets of 12 measurements were made for each specimen. The length measurements were rationalised to 20°C to correct them for the known thermal expansions of the SiC and the measurement machine. The fractional change in length values due. to the irradiation are given in table 2, and plotted against irradiation temperature in fig. 1. A polynomial regression program was used on these data, but it was shown that a linear equation was adequate for relating length change to irradiation temperature, no statistically significant improvement being obtained from the use of higher order polynomials. The linear regression equation so obtained is: lo3 F= 8.1842 - 7.6355 X 10e3 Timd
3
Also plotted in fig. 1 are the 95% prediction bands for the irradiation temperature indicated by a single future monitor, and for three identically irradiated future monitors. The bands are at ?29 to 30°C for a
A
CACiBRAllObi LihrE
6
95%PREOlCTlON BANDS FUTURE MONITOR
C
95% PREDICTION BANDS FOR THREE IDENTICALLY IRRAOIATEC FUTURE MONITORS
6:
I
z ,p '
FORA
SINGLE
BCACB
FORSINGLE MONITOR
(1)
0
or
tRRADiATlON TEMPERATURE,"C
Fig. 1. The fractional length change of Sic as a function of irradiation temperature in DFR.
J.E. Palentine / Calibrationof irradiated Sic temperature monitors Table 2 Fractional length change and annealing intersection temperature
temperature
(with 95% confidence spread) as a function of DFR irradiation
Specimen number
Irradiation temperature (“C)
Fractional length change 103 @l/lo)
Annealing intersection temperature with 95% confidence spread (” C)
D3.53 F401 F411 F596 D393 F408 F410 F474 F471 F601 D392 F404 F405 F475 F592 F605 F354 D355 F406 D357 F400 F401 F412 F476 F594 D358 F402 F403 F604 D390 D391 F396 F391 F413 F603 D359 F398 F399 F606
425 425 425 425 428 428 428 428 428 428 471 471 471 471 471 471 482 482 482 532 532 532 532 532 532 545 545 545 545 578 578 578 578 578 578 597 597 597 597
4.9219 4.9964 4.9590
442.2 456.3 448.9 471.0 b) 438.3 452.1 457.8 440.9
+ 4.6 f 6.5 * 4.0 * 5.8
Y2 540.3 483.1 517.2 417.8 512.3 546.7 524.5 528.0 513.4 569.7 535.6 558.9 b) 566.1 572.6 554.3 538.1 560.5 583.3 578.6 648.8 561.2 b) 578.8 654.3 640.1 631.8 627.1
A 3.7 f 6.3 f 5.3 f 3.9 f 1.4 f 5.2 f 4.7 f 3.8 f 5.1 * 5.4 f 6.4 f 4.9 f 6.0
4.8357 5.0059 5.0414 4.8779 4.9916 4.9503 4.9497 4.3415 4.5051 4.4917 4.4435 4.6483 4.6039 4.4844 4.5472 4.4070 4.4196 4.2416 4.2194 3.9946 3.9979 4.1975 4.1599 3.9751 a) 4.0107 3.8306 3.7440 3.7296 3.8113 3.6698 3.6735 3.8056 3.5197 3.5758 3.6355
a) End chipped, but annealing intersection b, Annealing routine not performed. single future
future monitor, monitors.
and
at +I7
45
f 3.5 _+4.4 f 7.0 f 4.6
f 6.5 f 3.5 f 6.2 f 7.5 + 6.0 + 5.1 f 6.6 f 3.8 f 4.8 f 4.6 + 3.4 + 4.1 f 4.7 t 5.4
still valid.
to
19°C for 3
The monitors were then annealed for 2 h in 100 deg C steps from 100 to 1 lOO’C, length measurements being made on each occasion by the Heiden-
hain technique. All the length measurements, rationaked to 2O”C, were fitted by computer to give two intersecting lines (fig. 2), the points being allocated to the lines to minimise the total sum of squares of the residuals, and the 95% confidence in the intersection
46
J.E. Palentine f Calibration of irradiated WC temperature
monitors
temperature being computed. The resulting annealing intersection temperatures are given in table 2, and plotted in fig. 3 against irradiation temperature. It was again shown that a linear relationship was statistically most appropriate, this being:
12 561
Tsic = 43.36 + 0.9697 Tirrad ,
(3)
Or
Tirrad = 1.0312 Tsic - 44.71 .
ANNEALING
(4)
The 95% prediction bands for future monitors are also shown in fig. 4, these being at +45 to 48°C for a single monitor and at +27 to 31°C for three identically irradiated future monitors.
INTERSECTION
AT 546-12 47'C (95%
CONFIDENCE) a
12-53
4. Discussion \
t
w
0
ANNEALING
TEMPERATURE,'C
Fig. 2. A typical annealing curve (specimen D354).
The suggestion in the previous paper [l] that the thermal reactor calibration of Sic based on annealing intersection temperature could lead to a serious underestimate of irradiation temperature in a fast reactor has been borne out by these latest results. Fig. 4 shows the present calibration in DFR, the caliA LATEST DFR CALIBRATION B THERMAL REACTOR CALIBRATION
A CALIBRATION LINE B 95% PREDICTION BANDS FOR A SINGLE FUTURE MONITOR C 95% PREDICTION BANDS FOR THREE IDENTICALLY IRRADIATED FUTURE MONITORS
C AN EARLIER TENTATIVE RELATIONSHIF FOR FAS‘i REACTOR IRRAIIIATIONS"' 11000" 1000 t $
9ooI
E
8001
g
7001
/ 625°C
L
I
2ooi
I i
500 600 400 IRRADIATION TEMPERATURE,'C
annealing intersection temperature of irradiation temperature in DFR. Fig.3. SC
200
as a function
/ /'
,1__1--
B / 9'
/
/’
--I_
300 400 500 600 700 IRRADIATION TEMPERATURE,'C
__-
800
900
Fig. 4. Calibrations of SE in DFR, in a thermal reactor, and an earlier tentative relationship for fast reactors [ I].
J.E. Palentine / Calibrationof irradiated Sic temperature monitors
THEGMAL REACTOR CA~BRAT~O~
400
500
11)
600
IRRADIATION TEMPERATURE, 'C
Fig. 5. A comparison of the calibrations in thermal and fast reactors based on as-irradiated length change.
in a thermal reactor [ 11, and a tentative relationship for fast reactors [l] used to justify the need for the present calibration. It is apparent that the DFR c~bration (line A) lies remarkably close to the tentative curve (line C). It is clear, however, that the use of the thermal reactor calibration (line B) would lead to serious errors for fast reactor experiments, thus an annealing intersection temperature of 625*C would denote an irradiation temperature of 534*C according to the thermal reactor c~bration, but 600°C from the DFR calibration, an underestimate of 66 deg C. In addition, fig. 5 shows an appreciable discrepancy between the thermal and fast reactor calibrations based on as-irradiated length change. In this case, the thermal reactor calibration could cause the temperature in a fast reactor irradiation to be overestimated by up to 23 deg C at lower temperatures, or underestimated by up to 50 deg C at higher temperatures. The calibration produced by Sharpe [2] by the annealing techniques using lattice parameter measurements agrees well with that from length measurements. The calibration line obtained from lattice parameter measurements gave annealing intersection temperatures which were lower than given by the calibration line from the length measurements (by bration
41
13 deg C at an irradiation temperature of 400°C and by 4 deg C at 600°C). These differences might well be due to differences in annealing technique, a separate sample being used at each annealing temperature for lattic parameter measurements, whilst the same sample is used throughout the anneals for the length measurements. There were, however, no statistically si~i~c~t differences in the slopes or the intercepts of the two calibration lines. The as-irradiated lattice parameter changes observed by Sharpe [4] also fell within the scatter band of the length change measurements, and the two lines could not be said to be significantly different. It is, however, advisable that tempera~re assessments should only be made using the calibration line appropriate to the measurement technique (lattice parameter or length) used in determining the annealing intersection temperature . At first sight if would appear that irradiation temperature can be estimated from a single monitor with greater precision and with far less effort from the asirradiated length change (95% confidence +29 deg C) than by the annealing technique (*45 deg C). However, Bramman and Sharpe [S] observed a discrep ancy between lattice parameter change on irradiation to high doses and the expected change at the temperature concerned, and they concluded that this would set a limit to the dose at which the Sic would retain its saturation lattice expansion. The phenomenon was attributed to the aggregation of point defects into lattice planes, and it was hoped that length changes might be unaffected by such behaviour, Unfortunately, it now appears that this hope was ill-founded. Table 3 shows data from Sic specimens irradiated in DFR to total doses of 8.9 to 14.5 dpa (NRT) (Fe). Using the present calibration lines the apparent irradiation temperatures (column B) from the observed as-irradiated dilations (column A) can be compared with the irra~ation temperatures (column D) from the annealing intersection temperatures (column C). Clearly there are major discrepancies, the temperatures estimated from the dilations being 94 to 307 deg C higher than those estimated from the intersection temperatures. Column E shows the expected dilations based on the irradiation temperatures from the annealing intersections, and these are seen in all cases to be greater than the observed values (column A), Column F shows the ratios of the observed to
48
J.E. Palentine / Calibrationof irradiated Sic temperature monitors
Table 3 Data
from Sic specimensirradiatedin DFR
to doses of 8.6 to 16.1 dpa (NRT) --_-__.
Specimen number
Dose
A
B
C
D
E
[dpa (NRTI (Fe) 1
F -__-
Observed 103 x
Apparent
Observed anneahng intersection (“C)
Tirrad
Expected 103 x
Ratio of observed to expected lo3 X
(~~lkl)
T*wad from column A a)
co99 Cl08 co95 Cl01 CO82 Cl13 CO98 Cl02 co94 co97 Cl12
8.6 8.9 9.7 10.0 10.7 10.9 11.1 12.2 12.4 12.8 13.4
4.582 4.866 3.524 5.042 3.411 4.357 3.572 4.418 2.761 3.610 3.839
412 435 610 412 625 501 604 493 710 599 569
463.9 351.2 463.8 351.0 531.5 397.9 387.2
co93 CO96 co77
13.9 14.0 14.5
3.439 3.333 2.626
621 635 728
co92 Cl03 Cl10 Cl04
14.6 14.6 15.5 16.1
2.726 2.973 2.521 3.565
715 682 742 605
from column C b,
(Wo) from column D
468.1 511.6 465.8
378 288 456 286 434 317 434 317 503 366 355 438 483 436
5.298 5.985 4.702 6.000 4.870 5.764 4.870 5.764 4.344 5.390 5.474 4.840 4.496 4.855
457.3 406.8 388.2 361.6
427 375 356 328
4.924 5.321 5.466 5.680
409.6 322.5 485.3 320.7
_“___
(billow (column A/ column E) 0.865 0.813 0 749 0.840 0.700 0.756 0.733 0 766 0.636 0.670 0 701 0 711 0.741 0.541 0 554 0.559 0.461 0 628
a) Based on eq. (2). b, Based on eq. (4).
expected dilations, and these are plotted as a function of dose in fig. 6. It is seen that, as in the case of lattice parameter changes, the saturation length change is not retained, but progressively diminishes with increasing dose. A linear extrapolation of the
NEUTRON
DOSE
dpa iNRT)(Fel
Fig. 6. The ratio of observed to expected length dilation as a function of dose.
line in fig. 6 suggests that the saturation length change is retained for only ca. 4.5 dpa (NRT) (Fe) and, if the contraction were to continue linearly with dose, there might be no observable dilation after ca. 30 dpa (NRT) (Fe). Hence the use of as-irradiated length change as an indicator of irradiation temperature might well be of limited value, and care will be necessary to prevent the results being very mislead~g. A question of greater concern is whether or not, at high doses, there will be sufficient recoverable damage to give a satisfactory annealing curve. There is, fortunately, evidence to suggest that a contirmed linear extrapolation of the line in fig. 6 would be unduly pessimistic. Table 4 shows the annealing contraction obsexved in monitors annealed up to 1100°C after irradiation at up to 34 dpa (NRT) (Fe), and these data are plotted in fig. 7. The annealing contractions decrease as dose increases, but even at 34 dpa (NRT) there is still sufficient annealable
J.E. Palentine / CMbration of irradiated SC temperature monitors
49
Table 4 The contxaction on annealing to 1100°C as a function of dose Specimen
Dose
Annealing
number
Wa JNR’Q (Fell ._
~te~ction CC>
F410 F401 F474 F592 F405 F397 F401 F594 co95 CO82 CO98 co93 CO96 co77 CO92 0768 0777 0854 0772 0858 0662 0699 0716 0717 0860 0859 0664 0634 0633
1.0 1.0 1.0 1.2 1.2 1.2 1.3 1.3 9.7 10.7 11.1 13.9 14.0 14.5 14.6 25.6 28.8 30.4 30.4 30.4 30.4 30.4 30.4 30.4 30.4 30.4 30.4 33.6 33.6
452.1 456.3 457.8 477.8 483.1 567.2 535.6 566.1 485.3 463.9 463.8 468.1 511.6 465.8 457.3 470.9 465.0 473.7 479.5 483.5 483.4 489.2 487.2 498.0 523.2 528.8 601.9 442.9 481.0
Annealing contraction (mm)
0.0303 0.0314 0.0316 0.0276 0.0258 0.0206 0.0241 0.0247 0.0236 0.0238 0.0233 0.0205 0.0192 0.0200 0.0199 0.0177 0.0146 0.0150 0.0173 0.0154 0.0144 0.0157 0.0152 0.0162 0.0152 0.0160 0.0131 0.0154 0.0181
a) a) a) a) a) a) a) a)
a) Adjusted to be equivalent to a monitor of length 10.16 mm.
damage for the monitors to be readily measurable. witi a con~ued ~nution in annexable damage with increasing dose, it is still likely that measurement will be possible at doses well in excess of 40 dpa (NRT) (Fe). It has already been noted that the calibration of Sic against thermocouples in DFR differs from that obtained in a thermal reactor. It would seem reasonable to suggest that this is due to the different dose rates, these having been 3.8 to 4.6 X IO-’ dpa/s (NRT) (Fe) in the DFR breeder compared with 4.5 to 7.1 X 10q8 dpa/s in Pluto, a factor of ca. 7 increase. Whilst the effect of dose rate on the calibrations has already been discussed, as has the dose dependence of as-irra~ated length change, it has so far been tacitly assumed that, at a given irradiation temperaEven
I
A
450 ANNEALING
I
500 INTERSECTION
I
550
TEMPERATURE.?
I
600
Fig. 7. The effect of dose on the annealing contraction of SC monitors.
50
J.E. Palentine / Cl;rlibration of irradiated WC temperature
ture, annealing intersection temperature is independent of dose. In fact, there is no direct evidence either to support or to contradict this assumption, although indirect evidence from certain rigs irradiated at 14 to 26 dpa in DFR core show the SIC temperatures to agree well with those obtained from thermohydraulic calculations, suggesting that any dose effect is unlikely to be of major significance.
monitors
the 95% prediction bands being *29 to 30°C for a single monitor, and rtl7 to 19°C for three identically irradiated future monitors. However, there is uncertainty as to the dose range over which this latter technique is applicable, and it is recommended that it be used with considerable caution until more information becomes available from which to clarify the position. Finally, the lack of information of the effect of dose on annealing intersection temperature is noted.
5. Conclusions Silicon carbide temperature monitors have been calibrated against thermocouples at 425 to 6OO’C in a DFR irradiation. Using the annealing intersection technique and a specific annealing routine, the resulting calibration is:
Acknowledgements The author wishes to acknowledge the assistance afforded by many colleagues during the progress of this work.
T imad = 1.0312 Tsic - 44.7 1 , References the 95% prediction bands being +45 to 48°C for a single monitor, and +27 to 31°C for three identic~ly irradiated future monitors. Using the as-irradiated length change the calibration is: Tirrad = 1071.86 - 130.97
[I] J.E. Palentine, J. Nucl. Mater. 61 (1976) 243. [2] R.M. Sharpe, in: Proc. BNES Conf. on Post-irradiation Examination, Grangewer-Sands, 1980. [3] M.J. Norgett, M.T. Robinson and I.M. Torrens, Nucl. Eng. Design 33 (1975) 50. [4] R.M. Sharpe, DNPDE, private communication. IS] J.I. Bramman and R.M. Sharpe, UKAEA, DNPDE internal document.
THECALIBRATIONOFFASTREACTORIRRADIATEDSILICONCARBIDETEMPE~TU~ MONITORSUSINGALENGTHMEASUREMENTTECHNIQUE J.E. PALENTINE UKAEA, Springfields Nuclear Power Development Laboratories, Salwick, Preston PR4 ORR, UK Received 3 April 1980
Silicon carbide temperature monitors have been calibrated against thermocouples in the Dounreay Fast Reactor. Statistical confidence levels have been determined for future temperature estimates based on as-irradiated length change and on the post-irradiation annealing intersection temperature. Possible dose limitations are discussed.
monobloc, one at the mid-way position of each tier of specimens. The 12.7 mm long X 3.175 mm diameter monitors were made from ‘%rusilite” material ~orga~te Electroheat Ltd.) or from material manufactured internally at SNPDL. They were encapsulated in heliumfilled capsules of stainless steel, the Sic pellet being wrapped in molybdenum knit-mesh to prevent chemical interactions at higher temperatures. The silicon carbide pellets were prepared to the high standards of flatness and parellelism described in ref. [ 11, and had been accurately measured prior to encapsulation. In each monobloc, certain of the monitors were used for X-ray lattice parameter analysis at Dounreay [2], and the remainder, the analysis of which is reported herein, were examined at Springfields. The vehicle was irradiated in position 36/Ea5 during run 8 l/l for 31 days. During this period reactor power remained very steady at 60 MW, with no trips. The temperatures recorded throughout the period were as shown in table 1, and it is clear that these are appreciably lower than had been hoped. The dose attained by the monitors was 1.02 to 1.22 dpa (NRT) (Fe) [3] and the dose to damage saturation in the Sic, ca. 0.7 dpa (NRT) (Fe) was achieved in about 20 days. The temperature over the final 20 days is shown in table 1, and is seen to have been reasonably uniform over this period.
1. introduction In a previous paper [l] the present author described the development of improved techniques for the preparation and measurement of silicon carbide temperature monitors, and for the objective analysis of the measurement data. Calibration data from a thermal reactor irradiation were presented, but evidence was put forward to suggest that the use of such a calibration could seriously underestimate irradiation temperatures if applied to monitors from a fast reactor. A fast flux calibration experiment was recommended. This report describes just such an experiment performed in the Dounreay Fast Reactor (DFR) to calibrate SE temperature monitors against thermocouples in a f&t flux.
2. The calibration experiment The irradiation was carried out in an instrumented gamma-heated rig in the DFR breeder. The rig consisted of 4 stainless steel monoblocs mounted one on top of the other and designed to operate at temperatures of 450, 520, 590 and 660°C. Each monobloc had six lon~tud~~ holes for the specimen capsules, there being three tiers of specimens per monobloc, and hence 18 specimen positions at each temperature. Three thermocouples were placed centrally in each 43
44
LE. Pulentine / Calibration of irradiated SC re~pera~ure
Table 1 Irradiation temperatures from daily thermocouple
monitors
readings
Position of thermocouple in monobloc
Design temperature f”C)
Mean temperature over whole 31 days (and 2a spread)
Mean temperature over final 20 days (and 2a spread)
Upper Middle Lower
458 450 449
417+22 419 + 19 424 + 15
424 z+2.7 425 f 1.7 428 ?: 3.7
Upper Middle Lower
529 522 522
490 + 8 483 * 6 471 * 6
489 t 3.0 482 + 4.5 471 + 3.4
Upper Middle Lower
601 598 589
543 f 7 543 + 5 532 f 5
544 t 2.6 545 f 2.1 532 f 3.4
Upper Middle Lower
661 672 668
572 f 14 595 * 13 575 f 12
575 c 0.4 597 _+3.2 578 2 3.8
-
3. Analysis and results The specimens were measured using a Heidenhain digital length gauge (Heidenhain (GB) Ltd., Burgess Hill, Sussex) employing a vertical probe and measuring in units of 1O-3 mm. The support jig was as described in ref. [l] , allowing a fibre of diameter only 0.05-0.1 mm to be measured, and two sets of 12 measurements were made for each specimen. The length measurements were rationalised to 20°C to correct them for the known thermal expansions of the SiC and the measurement machine. The fractional change in length values due. to the irradiation are given in table 2, and plotted against irradiation temperature in fig. 1. A polynomial regression program was used on these data, but it was shown that a linear equation was adequate for relating length change to irradiation temperature, no statistically significant improvement being obtained from the use of higher order polynomials. The linear regression equation so obtained is: lo3 F= 8.1842 - 7.6355 X 10e3 Timd
3
Also plotted in fig. 1 are the 95% prediction bands for the irradiation temperature indicated by a single future monitor, and for three identically irradiated future monitors. The bands are at ?29 to 30°C for a
A
CACiBRAllObi LihrE
6
95%PREOlCTlON BANDS FUTURE MONITOR
C
95% PREDICTION BANDS FOR THREE IDENTICALLY IRRAOIATEC FUTURE MONITORS
6:
I
z ,p '
FORA
SINGLE
BCACB
FORSINGLE MONITOR
(1)
0
or
tRRADiATlON TEMPERATURE,"C
Fig. 1. The fractional length change of Sic as a function of irradiation temperature in DFR.
J.E. Palentine / Calibrationof irradiated Sic temperature monitors Table 2 Fractional length change and annealing intersection temperature
temperature
(with 95% confidence spread) as a function of DFR irradiation
Specimen number
Irradiation temperature (“C)
Fractional length change 103 @l/lo)
Annealing intersection temperature with 95% confidence spread (” C)
D3.53 F401 F411 F596 D393 F408 F410 F474 F471 F601 D392 F404 F405 F475 F592 F605 F354 D355 F406 D357 F400 F401 F412 F476 F594 D358 F402 F403 F604 D390 D391 F396 F391 F413 F603 D359 F398 F399 F606
425 425 425 425 428 428 428 428 428 428 471 471 471 471 471 471 482 482 482 532 532 532 532 532 532 545 545 545 545 578 578 578 578 578 578 597 597 597 597
4.9219 4.9964 4.9590
442.2 456.3 448.9 471.0 b) 438.3 452.1 457.8 440.9
+ 4.6 f 6.5 * 4.0 * 5.8
Y2 540.3 483.1 517.2 417.8 512.3 546.7 524.5 528.0 513.4 569.7 535.6 558.9 b) 566.1 572.6 554.3 538.1 560.5 583.3 578.6 648.8 561.2 b) 578.8 654.3 640.1 631.8 627.1
A 3.7 f 6.3 f 5.3 f 3.9 f 1.4 f 5.2 f 4.7 f 3.8 f 5.1 * 5.4 f 6.4 f 4.9 f 6.0
4.8357 5.0059 5.0414 4.8779 4.9916 4.9503 4.9497 4.3415 4.5051 4.4917 4.4435 4.6483 4.6039 4.4844 4.5472 4.4070 4.4196 4.2416 4.2194 3.9946 3.9979 4.1975 4.1599 3.9751 a) 4.0107 3.8306 3.7440 3.7296 3.8113 3.6698 3.6735 3.8056 3.5197 3.5758 3.6355
a) End chipped, but annealing intersection b, Annealing routine not performed. single future
future monitor, monitors.
and
at +I7
45
f 3.5 _+4.4 f 7.0 f 4.6
f 6.5 f 3.5 f 6.2 f 7.5 + 6.0 + 5.1 f 6.6 f 3.8 f 4.8 f 4.6 + 3.4 + 4.1 f 4.7 t 5.4
still valid.
to
19°C for 3
The monitors were then annealed for 2 h in 100 deg C steps from 100 to 1 lOO’C, length measurements being made on each occasion by the Heiden-
hain technique. All the length measurements, rationaked to 2O”C, were fitted by computer to give two intersecting lines (fig. 2), the points being allocated to the lines to minimise the total sum of squares of the residuals, and the 95% confidence in the intersection
46
J.E. Palentine f Calibration of irradiated WC temperature
monitors
temperature being computed. The resulting annealing intersection temperatures are given in table 2, and plotted in fig. 3 against irradiation temperature. It was again shown that a linear relationship was statistically most appropriate, this being:
12 561
Tsic = 43.36 + 0.9697 Tirrad ,
(3)
Or
Tirrad = 1.0312 Tsic - 44.71 .
ANNEALING
(4)
The 95% prediction bands for future monitors are also shown in fig. 4, these being at +45 to 48°C for a single monitor and at +27 to 31°C for three identically irradiated future monitors.
INTERSECTION
AT 546-12 47'C (95%
CONFIDENCE) a
12-53
4. Discussion \
t
w
0
ANNEALING
TEMPERATURE,'C
Fig. 2. A typical annealing curve (specimen D354).
The suggestion in the previous paper [l] that the thermal reactor calibration of Sic based on annealing intersection temperature could lead to a serious underestimate of irradiation temperature in a fast reactor has been borne out by these latest results. Fig. 4 shows the present calibration in DFR, the caliA LATEST DFR CALIBRATION B THERMAL REACTOR CALIBRATION
A CALIBRATION LINE B 95% PREDICTION BANDS FOR A SINGLE FUTURE MONITOR C 95% PREDICTION BANDS FOR THREE IDENTICALLY IRRADIATED FUTURE MONITORS
C AN EARLIER TENTATIVE RELATIONSHIF FOR FAS‘i REACTOR IRRAIIIATIONS"' 11000" 1000 t $
9ooI
E
8001
g
7001
/ 625°C
L
I
2ooi
I i
500 600 400 IRRADIATION TEMPERATURE,'C
annealing intersection temperature of irradiation temperature in DFR. Fig.3. SC
200
as a function
/ /'
,1__1--
B / 9'
/
/’
--I_
300 400 500 600 700 IRRADIATION TEMPERATURE,'C
__-
800
900
Fig. 4. Calibrations of SE in DFR, in a thermal reactor, and an earlier tentative relationship for fast reactors [ I].
J.E. Palentine / Calibrationof irradiated Sic temperature monitors
THEGMAL REACTOR CA~BRAT~O~
400
500
11)
600
IRRADIATION TEMPERATURE, 'C
Fig. 5. A comparison of the calibrations in thermal and fast reactors based on as-irradiated length change.
in a thermal reactor [ 11, and a tentative relationship for fast reactors [l] used to justify the need for the present calibration. It is apparent that the DFR c~bration (line A) lies remarkably close to the tentative curve (line C). It is clear, however, that the use of the thermal reactor calibration (line B) would lead to serious errors for fast reactor experiments, thus an annealing intersection temperature of 625*C would denote an irradiation temperature of 534*C according to the thermal reactor c~bration, but 600°C from the DFR calibration, an underestimate of 66 deg C. In addition, fig. 5 shows an appreciable discrepancy between the thermal and fast reactor calibrations based on as-irradiated length change. In this case, the thermal reactor calibration could cause the temperature in a fast reactor irradiation to be overestimated by up to 23 deg C at lower temperatures, or underestimated by up to 50 deg C at higher temperatures. The calibration produced by Sharpe [2] by the annealing techniques using lattice parameter measurements agrees well with that from length measurements. The calibration line obtained from lattice parameter measurements gave annealing intersection temperatures which were lower than given by the calibration line from the length measurements (by bration
41
13 deg C at an irradiation temperature of 400°C and by 4 deg C at 600°C). These differences might well be due to differences in annealing technique, a separate sample being used at each annealing temperature for lattic parameter measurements, whilst the same sample is used throughout the anneals for the length measurements. There were, however, no statistically si~i~c~t differences in the slopes or the intercepts of the two calibration lines. The as-irradiated lattice parameter changes observed by Sharpe [4] also fell within the scatter band of the length change measurements, and the two lines could not be said to be significantly different. It is, however, advisable that tempera~re assessments should only be made using the calibration line appropriate to the measurement technique (lattice parameter or length) used in determining the annealing intersection temperature . At first sight if would appear that irradiation temperature can be estimated from a single monitor with greater precision and with far less effort from the asirradiated length change (95% confidence +29 deg C) than by the annealing technique (*45 deg C). However, Bramman and Sharpe [S] observed a discrep ancy between lattice parameter change on irradiation to high doses and the expected change at the temperature concerned, and they concluded that this would set a limit to the dose at which the Sic would retain its saturation lattice expansion. The phenomenon was attributed to the aggregation of point defects into lattice planes, and it was hoped that length changes might be unaffected by such behaviour, Unfortunately, it now appears that this hope was ill-founded. Table 3 shows data from Sic specimens irradiated in DFR to total doses of 8.9 to 14.5 dpa (NRT) (Fe). Using the present calibration lines the apparent irradiation temperatures (column B) from the observed as-irradiated dilations (column A) can be compared with the irra~ation temperatures (column D) from the annealing intersection temperatures (column C). Clearly there are major discrepancies, the temperatures estimated from the dilations being 94 to 307 deg C higher than those estimated from the intersection temperatures. Column E shows the expected dilations based on the irradiation temperatures from the annealing intersections, and these are seen in all cases to be greater than the observed values (column A), Column F shows the ratios of the observed to
48
J.E. Palentine / Calibrationof irradiated Sic temperature monitors
Table 3 Data
from Sic specimensirradiatedin DFR
to doses of 8.6 to 16.1 dpa (NRT) --_-__.
Specimen number
Dose
A
B
C
D
E
[dpa (NRTI (Fe) 1
F -__-
Observed 103 x
Apparent
Observed anneahng intersection (“C)
Tirrad
Expected 103 x
Ratio of observed to expected lo3 X
(~~lkl)
T*wad from column A a)
co99 Cl08 co95 Cl01 CO82 Cl13 CO98 Cl02 co94 co97 Cl12
8.6 8.9 9.7 10.0 10.7 10.9 11.1 12.2 12.4 12.8 13.4
4.582 4.866 3.524 5.042 3.411 4.357 3.572 4.418 2.761 3.610 3.839
412 435 610 412 625 501 604 493 710 599 569
463.9 351.2 463.8 351.0 531.5 397.9 387.2
co93 CO96 co77
13.9 14.0 14.5
3.439 3.333 2.626
621 635 728
co92 Cl03 Cl10 Cl04
14.6 14.6 15.5 16.1
2.726 2.973 2.521 3.565
715 682 742 605
from column C b,
(Wo) from column D
468.1 511.6 465.8
378 288 456 286 434 317 434 317 503 366 355 438 483 436
5.298 5.985 4.702 6.000 4.870 5.764 4.870 5.764 4.344 5.390 5.474 4.840 4.496 4.855
457.3 406.8 388.2 361.6
427 375 356 328
4.924 5.321 5.466 5.680
409.6 322.5 485.3 320.7
_“___
(billow (column A/ column E) 0.865 0.813 0 749 0.840 0.700 0.756 0.733 0 766 0.636 0.670 0 701 0 711 0.741 0.541 0 554 0.559 0.461 0 628
a) Based on eq. (2). b, Based on eq. (4).
expected dilations, and these are plotted as a function of dose in fig. 6. It is seen that, as in the case of lattice parameter changes, the saturation length change is not retained, but progressively diminishes with increasing dose. A linear extrapolation of the
NEUTRON
DOSE
dpa iNRT)(Fel
Fig. 6. The ratio of observed to expected length dilation as a function of dose.
line in fig. 6 suggests that the saturation length change is retained for only ca. 4.5 dpa (NRT) (Fe) and, if the contraction were to continue linearly with dose, there might be no observable dilation after ca. 30 dpa (NRT) (Fe). Hence the use of as-irradiated length change as an indicator of irradiation temperature might well be of limited value, and care will be necessary to prevent the results being very mislead~g. A question of greater concern is whether or not, at high doses, there will be sufficient recoverable damage to give a satisfactory annealing curve. There is, fortunately, evidence to suggest that a contirmed linear extrapolation of the line in fig. 6 would be unduly pessimistic. Table 4 shows the annealing contraction obsexved in monitors annealed up to 1100°C after irradiation at up to 34 dpa (NRT) (Fe), and these data are plotted in fig. 7. The annealing contractions decrease as dose increases, but even at 34 dpa (NRT) there is still sufficient annealable
J.E. Palentine / CMbration of irradiated SC temperature monitors
49
Table 4 The contxaction on annealing to 1100°C as a function of dose Specimen
Dose
Annealing
number
Wa JNR’Q (Fell ._
~te~ction CC>
F410 F401 F474 F592 F405 F397 F401 F594 co95 CO82 CO98 co93 CO96 co77 CO92 0768 0777 0854 0772 0858 0662 0699 0716 0717 0860 0859 0664 0634 0633
1.0 1.0 1.0 1.2 1.2 1.2 1.3 1.3 9.7 10.7 11.1 13.9 14.0 14.5 14.6 25.6 28.8 30.4 30.4 30.4 30.4 30.4 30.4 30.4 30.4 30.4 30.4 33.6 33.6
452.1 456.3 457.8 477.8 483.1 567.2 535.6 566.1 485.3 463.9 463.8 468.1 511.6 465.8 457.3 470.9 465.0 473.7 479.5 483.5 483.4 489.2 487.2 498.0 523.2 528.8 601.9 442.9 481.0
Annealing contraction (mm)
0.0303 0.0314 0.0316 0.0276 0.0258 0.0206 0.0241 0.0247 0.0236 0.0238 0.0233 0.0205 0.0192 0.0200 0.0199 0.0177 0.0146 0.0150 0.0173 0.0154 0.0144 0.0157 0.0152 0.0162 0.0152 0.0160 0.0131 0.0154 0.0181
a) a) a) a) a) a) a) a)
a) Adjusted to be equivalent to a monitor of length 10.16 mm.
damage for the monitors to be readily measurable. witi a con~ued ~nution in annexable damage with increasing dose, it is still likely that measurement will be possible at doses well in excess of 40 dpa (NRT) (Fe). It has already been noted that the calibration of Sic against thermocouples in DFR differs from that obtained in a thermal reactor. It would seem reasonable to suggest that this is due to the different dose rates, these having been 3.8 to 4.6 X IO-’ dpa/s (NRT) (Fe) in the DFR breeder compared with 4.5 to 7.1 X 10q8 dpa/s in Pluto, a factor of ca. 7 increase. Whilst the effect of dose rate on the calibrations has already been discussed, as has the dose dependence of as-irra~ated length change, it has so far been tacitly assumed that, at a given irradiation temperaEven
I
A
450 ANNEALING
I
500 INTERSECTION
I
550
TEMPERATURE.?
I
600
Fig. 7. The effect of dose on the annealing contraction of SC monitors.
50
J.E. Palentine / Cl;rlibration of irradiated WC temperature
ture, annealing intersection temperature is independent of dose. In fact, there is no direct evidence either to support or to contradict this assumption, although indirect evidence from certain rigs irradiated at 14 to 26 dpa in DFR core show the SIC temperatures to agree well with those obtained from thermohydraulic calculations, suggesting that any dose effect is unlikely to be of major significance.
monitors
the 95% prediction bands being *29 to 30°C for a single monitor, and rtl7 to 19°C for three identically irradiated future monitors. However, there is uncertainty as to the dose range over which this latter technique is applicable, and it is recommended that it be used with considerable caution until more information becomes available from which to clarify the position. Finally, the lack of information of the effect of dose on annealing intersection temperature is noted.
5. Conclusions Silicon carbide temperature monitors have been calibrated against thermocouples at 425 to 6OO’C in a DFR irradiation. Using the annealing intersection technique and a specific annealing routine, the resulting calibration is:
Acknowledgements The author wishes to acknowledge the assistance afforded by many colleagues during the progress of this work.
T imad = 1.0312 Tsic - 44.7 1 , References the 95% prediction bands being +45 to 48°C for a single monitor, and +27 to 31°C for three identic~ly irradiated future monitors. Using the as-irradiated length change the calibration is: Tirrad = 1071.86 - 130.97
[I] J.E. Palentine, J. Nucl. Mater. 61 (1976) 243. [2] R.M. Sharpe, in: Proc. BNES Conf. on Post-irradiation Examination, Grangewer-Sands, 1980. [3] M.J. Norgett, M.T. Robinson and I.M. Torrens, Nucl. Eng. Design 33 (1975) 50. [4] R.M. Sharpe, DNPDE, private communication. IS] J.I. Bramman and R.M. Sharpe, UKAEA, DNPDE internal document.