ML20086K336
| ML20086K336 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 07/13/1995 |
| From: | Marsh W SOUTHERN CALIFORNIA EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9507200103 | |
| Download: ML20086K336 (5) | |
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f[5 Southem Califomia Edison Company P. O DOX 128 SAN CLEMENTE. CALFORNIA02674 4128 BA%4AGER OP NG 4 Nf JL Y APFAm&
(79 368 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D. C. 20555 Gentlemen:
Subject:
Docket Nos 50-361 and 50-362 Emergency Core Cooling System Annual l') CFR 50.46 Report San Onofre Nuclear Generating Station Units 2 and 3 This letter transmits the San Onofre Units 2 and 3 annual report for 1994 required by paragraph (a)(3)(ii) of 10 CFR 50.46, " Acceptance criteria for emergency core cooling systems for light water nuclear power reactors." (CENPD-279, Supplement 6) describes the changes and errors in the ABB/ Combustion Engineering (ABB/CE) codes and methodology for Emergency Core Cooling Systems (ECCS) analysis'in'1994.
For the 1994 reporting period, one error in the PARCH Peak Cladding Temperature (PCT) code for small break Loss of Coolant Accident (LOCA) analysis and two errors in the PARCH steam cooling heat transfer coefficient code for Large Break LOCA (LBLOCA) analysis were found and corrected. There were no changes in the evaluation models or methods for the large break, small break, or post-LOCA long term cooling calculations.
The correction of the errors in PARCH had no effect on the PCT for LBLOCA. The sum of'the absolute magnitudes of the temperature changes for LBLOCA from all repcits to date continues to be less than laF. No change occurred in the PCT due to the correction of the error in PARCH for small break LOCA, nor was there any change due to post-LOCA long term cooling.
l As recuested by Southern California Edison (Edison), ABB/CE completed and i
issuec on August 31, 1994, a new limiting LBLOCA PCT analysis'for San Onofre l'
Units 2 and 3.
The above errors in the PARCH codes were corrected prior to the new analysis. The new analysis was based on the latest NRC approved (1985) i ECCS evaluation model and incerporated all changes to plant design and operating conditions made throagh August 1994, including a new Peak Linear Heat Generation Rate (PLHGR) of 13 kw/ft. The new PLHGR was requested by Edison in License Amendment Application Nos. 145 and 129 to the San Onofre Units 2 and 3 Technical Specifications. The results of the new analysis indicated a limiting LBLOCA PCT of 2160af.
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9507200103 950713 A08l PDR ADOCK 05000361 R
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fCf Document Control Desk There were no additional changes made to the plant specific input assumptions for the limiting LBLOCA evaluated under 10 CFR 50.59 during the period August through December 1994.
Therefore, the limiting LBLOCA PCT as of the end of 1994 is 2160oF, which is below the 10 CFR 50.46 acceptance criterion of 2200cf. provides a summary of the effect on PCT of the errors or changes to the ECCS evaluation model reported under 10 CFR 50.46 for 1994 and the changes in 1994 to plant specific input assumptions for the limiting LBLOCA evaluated under 10 CFR 50.59. The arithmetic sum of the PCT effects of both the 10 CFR 50.46 and 10 CFR 50.59 changes is a 0.0*F effect on the new 2160af LBLOCA analysis PCT.
If you have any questions or need additional information on this report, please let me know.
Sincerely, Enclosures cc:
L. J. Callan, Regional Administrator, NRC Region IV J. Dyer, Director, Division of Reactor Projects, Region IV K. E. Perkins, Jr., Director, Walnut Creek Field Office, Region IV J. A. Sloan, NRC Senior Resident Inspector, San Onofre Units 1, 2, and 3 M. B. Fields, NRC Project Manager, San Onofre Units 2 and 3
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10 CFR 50.46 Report l
ENCLOSURE 1 CENPD-279, SUPPLEMENT 6
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h COMBUSTION ENGINEERING OWNERS GROUP l
3 CENPD-279 SUPPLEMENT 6 7
3 ANNUAL REPORT ON
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3 EVALUATION MODELS
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FINAL REPORT 3
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CEOG TASK 865 1
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prepared for the C-E OWNERS GROUP
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1' February 1995 3
h _h 0 Copyright 1995 Combustion Engineering, Inc. All rights reserved
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-L LEGAL NOTICE This report was prepared as an account of work sponsored by the Combustion Engineering Owners Group and ABB Combustion Engineering.
.J Neither Combustion Engineering, Inc. nor any person acting on its behalf:
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makes any warranty or representation, express or implied including the warranties of fitness for a particular purpose or merchantability, with respect to the accuracy, completeness, or usefulness of the
..J information contained in this report, or that the use of any information, apparatus, method, or process disclosed in this report
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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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l 3.0 EVALUATION MODEL CHANGES AND ERROR CORRECTIONS This section discusses all error corrections and model changes to the ABB CE ECCS perfomance evaluation models which may affect the calculated PCT.
In 1994 one error in the PARCH computer code used in the small break LOCA evaluation model (EM) was corrected. Two errors in the PARCH computer code used in the large break LOCA evaluation model were corrected. The nature of these errors and the steps taken to resolve them are described below. No other changes were made to the ABB CE evaluation model for ECCS analysis.
3.1 PARCH for Small Break LOCA 3.1.1 Code Description PARCH calculates the fuel rod heatup and the resulting cladding surface temperature and zirconium oxidation for a small break LOCA transient. Models are provided in the code for pool boiling heat transfer, fuel rod temperature,
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fuel-cladding gap conductivity, coolant heatup and steam release, cladding
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swelling and rupture, and zirconium-water reaction.
3.1.2 Error in Code The error identified and corrected is in the model used to calculate Young's
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modulus for the zirconium cladding. The original model implemented in the code, Reference 8, finds Young's modulus, E, from a linear fit as E - X(186) - X(187)*T, where T, is the cladding temperature in *F.
This is correct for temperatures f
up to about 1760'F. At higher cladding temperatures, this expression predicts too small a value for Young's modulus. As temperature increases, it falls to
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2ero and becomes negative. The resulting temperature dependence of Young's L-modulus is shown by the solid line in Figure 1.
This is incorrect for higher 3
temperatures.
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The drror in Young's modulus can affect the temperature history of the
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cladding by its effect on the cladding thennal expansion, consequently, on the fuel-cladding gap conductivity. The inside diameter of the cladding increases
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as the pressure difference between the gas gap and the coolant increases and as the cladding temperature increases. Young's modulus determines the elastic deformation component of the cladding dimension change. An increase in the fuel-cladding gap decreases the gap conductivity which reduces heat transfer 4
across the gap. During the approach to maximum cladding temperature, more energy is stored in the fuel when the gap is large and less is stored when the 7
gap is small. Consequently, the maximum cladding temperature and zirconium oxidation can be affected.
3 Two conditions must be satisfied for the error in Young's modulus to affect 7
cladding temperature. First, cladding temperature must exceed about 1760*F 4
f where the error in Young's modulus becomes significant, Figure 1.
Second, the cladding must not rupture until temperatures above this threshold are exceeded.
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3.1.3 Correction of Code Error
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The error is corrected by revising the correlation for Young's modulus of zirconium in PARCH to follow the representation used in STRIKIN-II, Reference
- 10. The STRIKIN-II model uses the same linear fit for Young's modulus as PARCH does until it deviates from a straight line fit.
Linear interpolation from a table is used above this temperature with a minimum value of Young's
,j) modulus at higher temperatures. The corrected representation Young's modulus is shown by the broken line in Figure 1.
3.1.4 Impact of Error on Cladding Temperature d
The effect of the erroneous model for Young's modulus is shown in Figure 2.
q In order to observe the potential impact of the error, the cladding rupture
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The solid line in Figure 2 shows that the monotonic cladding temperature 5
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heatup is interupted before the maximum temperature is reached. The interuption occurs at the temperature where Young's modulus approaches zero and the width of the fuel-cladding gap increases. This is followed by an abrupt rise in cladding temperature after Young's modulus becomes negative and the fuel-cladding gap closes. The corrected model for Young's modulus, broken line in Figure 2, produces a monotonic rise in cladding temperature like that produced by the erroneous Young's modulus model except that there is no interuption in the temperature rise before the maximum value is reached.
The PARCH code error for Young's modulus has little effect on the maximum j
cladding temperature for small break LOCA.
For several plants, the maximum cladding temperature for small break LOCA is below the temperature at which the error in Young's modulus has any effect on the transient.
For most other plants, cladding rupture occurs for a cladding temperature below that at which a significant error is made in the value of Young's modulus.
In such cases, the error in Young's modulus has no effect on the maximum cladding temperature.
Finally, one plant has been reanalyzed with the corrected version of PARCH.
3.2 PARCH for Larae Break LOCA 3.2.1 Code Description PARCH calculates the steam cooling heat transfer coeffients for large break LOCA at and above the rupture node when the reflood rate is less than one inch per second. The code contains the models described in Section 3.1.1 for small break LOCA analysis with the additional models described in Reference 9.
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3.2.2 Errors in Code A,
The two errors found and corrected are in Young's modulus for zirconium and in default values for several input parameters to the code.
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r The error in Young's modulus described in Section 3.1.2 also existed in PARCH
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for large break LOCA analysis.
It does not affect large break LOCA results as
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f discussed in Section 3.2.4.
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The second error affects default values of nine input parameters for the code.
3 The code used a value of zero instead of the intended default values if no
>w data was entered for these input parameters. This would prevent the code from
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h ranning if all nine values were omitted from the input.
It might affect the
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steam cooling heat transfer coefficients calculated by the code if some of the iI variables were omitted from the input.
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3.2.3 Correction of Code Errors
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'T The error in Young's modulus is corrected as described in Section 3.1.3.
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The second error is corrected by removal of coding that produces duplicate declarations of default values for the nine input parameters. The corrected 7"l coding ensures that the desired default values are used if no input values are j
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entered for these parameters.
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3.2.4 Impact of Errors on PCT
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Correction of the errors in Young's modulus and,the default input parameters has no effect on PCT for large break LOCA. The error in Young's modulus does
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not affect the cladding dimension or the fuel-cladding gap since PARCH is d
initialized with the cladding ruptured. Hence, it has no effect on the steam cooling heat transfer coefficients. The erroneous default values for input
,J parameters had no effect on any large break LOCA transient results since values have been input for all of these parameters in all plant analyses.
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4.0 CQNCLUSIONS One error was found and corrected in the PARCH computer code used for small break LOCA analysis during 1994. Two errors were found and corrected in the PARCH computer code used for large break LOCA analysis. There was no change in the PCT as a result of correcting these errors. No other changes to the ABB CE ECCS performance evaluation models or corrections of errors were made in 1994. The sum of the absolute magnitudes of the changes in PCT calculated using the ABB CE ECCS performance evaluation models, including those from
]l previous annual reports, References 2-7, remains less than l'F.
- l Based on the results reported here, the errors found and corrected during this reporting period were determined to not be significant as defined in Section 10CFR50.46 (a)(3)(1) of Reference 1.
Therefore, in accordance with Section 10CFR50.46 (a)(3)(ii) of Reference 1, no action beyond the submission of this report is needed.
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5.0 REFERENCES
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" Emergency Core Cooling System; Revisions to Acceptance Criteria, "10CFR50, Federal Register, Vol. 53, No.180, September 16, 1988.
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2.
" Annual Report on C-E ECCS Codes and Methods for 10CFR50.46," CENPD-279, April, 1989.
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3.
" Annual Report on C-E ECCS Codes and Methods for 10CFR50.46," CENPD-279, Supplement 1, February,1990.
9 4.
" Annual Report on C-E ECCS Codes and Methods for 10CFR50.46," CENPD-279, Supplement 2, April, 1991.
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5.
" Annual Report on C-E ECCS Codes and Methods for.10CFR50.46," CENPD-279, Supplement 3, April,1992.
n 6.
" Annual Report on C-E ECCS Codes and Methods for 10CFR50.46," CENPD-279,-
Q Supplement 4, April, 1993.
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7.
" Annual Report on C-E ECCS Codes and Methods for 10CFR50.46," CENPD-279, Supplement 5, February,1994.
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" PARCH, A FORTRAN-IV Digital Computer Program to Evaluate Pool Boiling, Axial Rod and Coolant Heatup," CENPD-138 P, August 1974.
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" PARCH, A FORTRAN-IV Digital Computer Program to Evaluate Pool Boiling,
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Axial Rod and Coolant Heatup (Modifications)," CENPD-138 P, Supplement 1, February 1975.
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" PARCH, A FORTRAN-IV Digital Computer Program to Evaluate Pool Boiling, l
q Axial Rod and Coolant Heatup," CENPD-138, Supplement 2-P, January 1977.
9.
"C-E ECCS Evaluation Model, Flow Blockage Analysis," Enclosure 1-P to
%d LD-81-095, December 1981.
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"STRIKIN-II, A Cylindrical Geometry Fuel Rod Heat Transfer Progras,"
CENPD-135 P, August 1974.
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TEMPERATURE (DEGREES F) l 11 a
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Fioure 2 Effect of PARCH Error on Small Break LOCA Claddina Surface Temperature 4
ORIGINAL MODEL CORRECTED MODEL h
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TIME (SECONDS) 12 m
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10 CFR 50.46 Report ENCLOSURE 2 LOS'.' 0F COOLANT ACCIDENT MARGIN
SUMMARY
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LOSS OF COOLANT. ACCIDENT (LOCA) MARGIN
SUMMARY
SAN ONOFRE NUCLEAR GENERATING STATION UNITS 2 AND 3 1
A.
Limiting LBLOCA PCT APCT PCT San Onofre Units 2 and 3 LBLOCA ECCS Performance 2160*F Analysis with the 1985 Evaluation Model (ABB/CE S-94-091 - August 31,1994)
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B.
10 CFR Su.46 Changes / Errors Discovered (1994) 0.0aF C.
Limiting LBLOCA 10 CFR 50.59 Changes (1994) 0.0aF
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D.
Current Limiting LBLOCA PCT (1994) 2160af (Arithmetic Sum of the 10 CFR 50.46 changes and errors and the 10 CFR 50.59 changes for 1994) l l
1 ABB/CE 3erformed a new limiting LBLOCA analysis for San Onofre Units 2 and 3 using tie 1985 Evaluation Model and accommodating all changes to plant design and operating conditions made through August 1994. The analysis result demonstrates conformance to the ECCS performance criteria of 10 CFR 50.46 at a peak linear heat generation rate (PLHGR) of 13 kw/ft.
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