ML20066C392

Nonproprietary Supplemental Info on FATES3 Stored Energy Conservatism

ML20066C392
Person / Time
Site:	Calvert Cliffs
Issue date:	10/05/1982
From:	ABB COMBUSTION ENGINEERING NUCLEAR FUEL (FORMERLY
To:
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ML20066C384	List: ML20066C382 ML20066C392
References
CEN-220(B)-NP, NUDOCS 8211090488
Download: ML20066C392 (25)

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CEN-220(B)-NP j

SUPPLEMENTAL INFCAMATION ON FATES 3 STORED ENERGY CONSERVATISM October 5,1982 COMBUSTION ENGINEERING. INC.

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LEGAL NOTICE This report was prepared as an account of work sponsored by Combustion Engineering, Inc. Neither Combustion Engineering nor any person acting on its beh' Elf:

A. Makes any warranty or representation, express or implied including the warranties of fitness for a particular purpose or merchantability, with respect to accuracy, completeness, or usefulness of the information contained in this report, or that the use of any information, apparatus, method, or proces's disclosed in this report may not infringe privately owned rights; or B. Assumes any liabilities with respect to the use of, or for damages resulting from the use of, any information, apparatus, method or process disclosed in this report.

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- Supplemental Information on FATES 3 o

Stored Energy Conservatism OBJECTIVE The objective of providing supplementary infonnation is to assist the NRC staff in assessing the degree of conservatism in FATES 3 computed fuel temperatures at linear heat rates and burnups associated with the ECCS analysis. Although Calvert Cliffs 1 Cycle 6 is used as a reference, the information is generically applicable to FATES 3.

SulmARY AND CONCLUSIONS l An examination of FATES 3 bias and uncertainty in predicting fuel temperatures l and conservatisms introduced in the initial conditions for LOCA analysis has been made. It is quantitatively shown that sufficient conservatism has been included using the NRC suggested margin requirement of ensuring that 95% of the specified expel.imental data base would be overpredicted with a confidence level of 95%. _

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U Therefore, no additiona~1 conservatism is

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warranted beyond that already inc1Uted in the application of FATES 3 in ECCS analysis.

INTRODUCTION A new version of the C-E steady-state fuel performance code, FATES 3, was developed and submitted for review as .Ref.1. This new version is intended to be the fuel evaluation model for licensing applications and reflects significant, improvements in fission gas release modeling and in internal void volume and gas pressure modeling. It is intended to be applicable to extended I . burnup fuel. NRC questions related to the application of FATES 3 in licensing I

analyses were addressed in Ref. 2. However, NRC questions about the degree of conservatism in the stored energy for the Calvert Cliffs 1 Cycle 6 ECCS

. analysis remained, as summarized in Ref. 3, and further discussed in Ref. 5, where it has been noted to be an open issue. This was adequately addressed for Calvert Cliffs 1 Cycle 6 by the supplementary ECCS analysis of Ref. 4 as noted in the NRC's evaluation report, Ref. 5.

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TEWERATURE BIAS OF FATES 3 The FATES 3 code p'redicted fuel centerline temperatures were compared in Ref.

I with thermocouple data from well characterized fuel rods irradiated in the Halden test reactor. This centerline temperature compari4.0n was shown in Figure 9-4 gf Ref. I and is reproduced here as Figure 1. _. ..

__ Repfoducing the statistical galuation of-.RdY. 3 results in a

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mean and a standard deviation Therefore, the centarline tempet'hture margin required to atisfy the _NRC requirement of a one-sided probability of 955 at a confidence level of 955 . . _ . _ _

However, in lig of using this data to quantify conservatism required in the

! application of FATES 3, .it is reasonable *.o exclude certain data points which are shown as solid symbols in Figure 1. _

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Two of the rods in HPR 80 (IFA-11 Rod HBB' and IFA-21 Rod HCD) were initia]llTpower ramped at beginning of life, irradiated at high power .

levels to about 5,000 MWD /MTU, reduced in power, and then re-camped to about 12 kw/ft. FATES 3 predicts significant fission gas release for these two HPR 80 .

rods and, consequently, overpredicts fuel temperatures. The rods did not . -

-l cxperience significant fission ~ gas release as indicated by measured temperatures. Unpressurized fuel rod designs can, however, experience the fission gas release burst phenomenon, and these rods may, in reality, have been quite close to the release burst. These data points at 5,000 MWD /MTU b.prnup should be. excluded from the data base for determination of code bias. _

IFA-418 rods were prepressurized " ~ ~ 3and HPR 80 rods were unpressGPized.

Therefore, the data represent a godtr range in all important variables.

Detailed characterization of this data is provided in Table 1.

Reproducing the statistical eva luation of Ref. 3 for thi.s. modified da.fa set results in a mean and a standard deviation The centerline temperature margin 1 s computed, using the NRC7nethod, to 51!

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Details of the modified data set arer provided in Table 2. <

Sources of discrepancy between predicted and measured centerline temperatures are generally unknown. The ratio of the temperature difference (predicted cinus mea'sured) for volumetric average temperature to centerline temperature

. can vary from less than 0.5 to greater than 0.5, depending on the individual sources. Therefc.'e, C-E concludes that a reasonable overall conversion factor.

l for volumetric average temperature for the experimental centerline data is

- approximately 0.5 as used in Ref. 3. Using this ratio gives a margin requirement on volumetric average fuel temperature, enveloping 957, of the data at 957, confidence level, of '

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FIGURE 1 Comparison of Predicted and Measured Fuel

. Centerline Temperature Using FATES 3 with Best Estimata Input W

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l MEASURED FUEL CENTERLINE TEMPERATURE, OF

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TABLE 1 Tsst Rod Identification Range in -

Fuel-Clad ' .

Data LHGR , Rod Burnup, . Diametral Fill Gas Composition Enrichment, Set Rod kw/ft ' W O/MTUx10-3 Gap, mils and Pressure, psi 5

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HBC 6+15 O 6.5 5 j 21 HCA 6+14 0 1.9 5 HCC 0 6.6 5 6+14 5 5 i HCD2 , 2.3 .

-2 Data from second ramp at 5,000 WO/MTU excluded in Table 2. -

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1 TABLE 2 Test Rod Temperature Data i

Thermo- Local Local Measured FATES 3 Temperature .

Data Data Couple Burnup. LHGR. Temperature. Overprediction.

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TABLE 2. continued Thermo. Local Local Measured FATES 3 Temperature Data Data Couple Burnup. LHGR, Temperature. Overprediction, '

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TABLE 2, continued 1

i Thermo- Local Local Measured FATES 3 Temperature Data Data -

Couple- Burnup, LHGR, Temperature. Overprediction, I

Point Source Rod Location MWT/MTU F.w/ft *F *F O

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Thermo- Local Local Measured FATES 3 Temperature i Data Data Couple Burnup. LHGR, Temperature. Overprediction.

Point Source Rod Location MWT/MTU kw/ft *F *F i  !

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! 3 15.48 2530 HB8 0 6.10 1160 ,

1 9.14 1600 l 2 12.19 2120 l 3 15.24 2640 .

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- TABLE 2, continued Thermo- Local Local Measured FATES 3 Temperature Data Data Couple Burnup. LHGR, Tempera.ture. Overprediction, Point Source Rod Location MWT/MTU kw/ft *F 'F .

IFA-11 HBC 0 6.10 1330 1 9.14 1880 2 12.19 2390 3 15.00 2750 IFA-21 HCA 0 6.10 1130 1 9.14 1580 2 12.19 2050 3 14.54 2370 HCC 0 6.10 1340 1 9.14 1870 i i 2 12.19 2390 i L 3 14.11 2610 }

j' HCD 0 6.10 1180 1 9.14 1630 i 2 12.19 2160 l 3 14.32 2550 l

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BIAS AND SCATTER' TRENDS WITH GAP SIZE, LINEAR HEAT RATE, AND BURNUP

._ .. . _ _ . . . . _ .. . _.- in the data with respect to gap size, as

_hown s in Figure 2. For example, -

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Also, the 6_.IFA~11 and -21 rods ~ Fange~ in gap size from 1.9 to 6.6 mils _

The data (less the excluded points) have been plotted as a function of linear

. heat rate and burnup in Figures 3_ and 4, respectively.

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If only the data points at.high linear heat rates as suggested by the NRC,Ta7

>14 kw/ft, are considered in order to evaluate bias and scatter near the

.Talyert Clif's 1 LOCA limit, one calculates for., centerline temperature a mean a standard deviation,- and a margin requirement Tusing the NkC sthod of Ref. 3)

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In terms of vo _umetric average temperature,

.s A summary is provided in the following table.

All Data _ _ Data >14 kw/ft _

Centerline Temperature, F Average Temperature, F w.-.... .

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FIGURE 2 Temperature Difference vs. As-Fabricated Diametral Gap 9

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r CONSERVATISM ADDITIONALLY INTRODUCED INTO THE STORED ENERGY FOR ECCS ANALYSIS ,

The procedure for introducing conservatisra into the stored energy for ECCS analysis is described in detail in ReL 2. A summary of these sources of conservatism is provided in Table 3.

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Many of the sources listed in Table 3 accumulate significant conservatism with burnup and will not be evaluated here since limiting conditions for LOCA occur near beginning of life. At or near beginning of life sources of conservatism include <

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_ f .~ ~ Effst _.._ __. [ and treatment'o' these paramitters

.is given in Tabi r 4. As ndYtd, the combinTd total of these on volumetrE average fdel temperature. .A plot of the absolute value of De fuel average temperature as a unction of burnup toJ4,000 MWD /MTU) is given in Figure 5. A nominal value of was used in the generation of this figure. The overall tored energy conservir; ism is significantly greater than that r'equired when considering the margin requirement as a whole or the margin requirement near the LOCA limit as demonstrated in the following table:

Overall At LOCA Limit Therefore, it is concluded that no additional conservatism is warranted beyond that already included in the application of FATES 3 in the ECCS analysis.

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4 TA8LE 3 CONSERVATISMS IN LOCA STORED ENERGY O

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FATES 3 AND GAPCON-THERMAL 2 COMPARISON MRC audit cciculations of fuel average tempera'ture for Calvert Cliffs 1 Cycle 6 using GAPCON-TMERMAL-2 (G-T-2) is provided by Ref. 3 and is reproduced here as Figure 6. As nra yd in Ref. 3, the peak temperature predicted by G-T-2 is

, approximately 214*l higher than FATES 3. . A detailed comparison of code submodels and results has been made which lead to the conclusion that G-T-2 calculation is more conservative than the FATES 3 calculation near 0 MWD /MTU

. burnup, but that the FATES 3 calculation is still conservative by the amounts -

quantified in previous sections of this report. Discussion of the comparison is prosided below, and a summary of the components of the G-T-2 and FATES 3 temperature differences is offered in Table 5 for NRC consideration.

Flux depression - Flux depression used in FATES 3 resulted in a greater local power density shift toward the pellet surface than in G-T-2. This gives higher fuel centerline and fuel average temperature _ _

ir. G-T-2.

Clad conductivity - A small difference in clad conductivity results in a higher clad temperature gradient in G-T-2 than in FATES 3. The e,levated temperature on the clad inner diameter is amplified somewhat by the f,gedback effects of '1 decreasing fuel conductivity to a total difference of .

Fuel pellet relocation - Fuel pellet relocation does not occur in the G-T-2 calculation until after 50 MWD /MTU burnup. This is the point where emperatures start to decrease as shown in Figure 6. Relocation in FATES 3 is u _ _ .

The absence of any relocation in G-T-2 resul.ts irl. a major difference in fuel 4verage temperature. G-T-2 i s approximately -

higher than FATES 3 due to this parameter alone. Due to the fact that the Hiaxim-um temperature occurs in FATES 3 at about 3,000 MWD /MTU, some hurn.y dependent relocation has occurred and is, of course, a component of the

- '. di fference. .

Fuel densification -[ _ _

However, because

, the maximum temperature occurs in FATES 3 at about 3,000 ME/MTU burnup, l significantly more densification has occur d ttun in G-T-2. FATES 3 l

temperstures are, therefore, approximately higher than G-T-2. The t

.gombited effect of densification and reloc fon is shown in Table 5 and is (G-T-2 is higher than FATES 3 overall). -

Clad creepdown - It appeared that the major difference in clad creep is due to the elasped time to accumulate 3,00Q, MWD /1TU in FATES 3. As shown in Table 5 this is equivalent to approximately G-T-2 is higher because essentially

- no creepdown has occurred.,

Thermal expansion - Differences in fuel pellet thermal expansion exist.

Although both codes utilize a partially cracked fuel pellet, the thermal expansion of the uncracked portion is treated differently, the assumed location of the crack radius is slightly different, and the coefficient of expansion

_ _ _ _ _ _ _ - _ _ _ _ _ _ _ _ _ - _ - - - - - -e- - -

slightly different. A minor difference in thermal exp1DsioI of the clad also cxists. A net repult is estimated to be approximately - . -', higher average fuel temperature in G-T-2 than in FATES 3.

Energy deposition - Energy deposition in the clad in FATES 3 is 1% of the linear heat rate as defined in Ref. 2. The G-T-2 calculation neglected this energy deposition. Lhis_cifference is estimated to increase the FATES 3 temperature by

, approximately _

over that of G-T-2.

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TABLE 5

SUMMARY

OF GAPCON VS. FATES 3 TEWERATURE DIFFERENCES NRC REPORTED DIFFERENCE + 214* F SOURCE

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o FLUX DEPRESSION IN PELLET o CLAD CONDUCTIVITY ,

o RELOCATION ._

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o DENSIFICATION _

TOTAL o CLAD CREEPDOWN l

o THERMAL EXPANSION o NRC AUDIT LHGR DIFFERENCE NOTE: TEW ERATURE DIFFERENCES ARE APPROXIMATE AND NEGLECT FEEDBACK 0F COLLECTIVE APPLICATION l '

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REFERENCES .

1. CEN-161-(B)-P', " Improvements to Fuel Evaluation Model", Combustion Engineering, Inc., July,1981. 1 l

= 2. CEN-193-(B)-P, Supplement 2-P, " Partial Response to NRC Questions

= on CEN-161-(B)-P, Improvements to Fuel Evaluation Model", i Combustion Engineering, Inc., March 21, 1982.

3. NRC Memorandum, John C. Voglewede to Carl H. Berlinger, "Viewgraphs for Meeting on FATES-3 Code", May 14, 1982.

C-E Letter BG&E-9676-703, P. W. Kruse to W. J. Lippold, "Calvert

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Cliffs 1 Cycle 6 Supplement ECCS Calculatin", May 19, 1982.

5. Safety Evaluation by the Office of Nuclear Reactor Regulation Supporting Amendment No.71 to Facility Operating License No. DPR-53 Calvert Cliffs Nuclear Power Plant Unit No.1 Docket No. 50-317.

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