ML041130196

Emergency Core Cooling System (ECCS) Evaluation Model Changes - 30 Day Report and Revised Annual Notification and Reporting for 2003

ML041130196
Person / Time
Site:	Watts Bar
Issue date:	04/19/2004
From:	Pace P Tennessee Valley Authority
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
Download: ML041130196 (12)

Text

Tennessee Valley Authority, Post Office Box 2000, Spring City, Tennessee 37381-2000 April 19, 2004 U.S. Nuclear Regulatory Commission 10 CFR 50.46 ATTN: Document Control Desk Washington, D. C. 20555 Gentlemen:

In the Matter of ) Docket No. 50-390 Tennessee Valley Authority WATTS BAR NUCLEAR PLANT (WBN) UNIT 1 - EMERGENCY CORE COOLING SYSTEM (ECCS) EVALUATION MODEL CHANGES - 30 DAY REPORT AND REVISED ANNUAL NOTIFICATION AND REPORTING FOR 2003

References:

(1) TVA letter to NRC, December 18, 2003, "WBN Unit 1 - ECCS Evaluation Model Changes - 30 Day Report and Annual Report" (2) Westinghouse letter to TVA (WAT-D-11225), March 19, 2004, "Watts Bar Nuclear Plant Units 1 & 2, 10 CFR 50.46 Annual Notification and Reporting for 2003."

(3) TVA letter to NRC, April 3, 2002, "WBN Unit 1 - ECCS Evaluation Model Changes - Annual Notification and Reporting for 2001."

The purpose of this letter is notify the NRC of changes or errors discovered in the WBN ECCS evaluation models for peak cladding temperature (PCT) in accordance with 10 CFR 50.46, and actions TVA has taken to address a temporary change of more than 500 F in calculated PCT. This report includes model changes or errors since TVA's last report (Reference 1), and is intended to satisfy both the 30-day and annual reporting requirements of 10 CFR 50.46.

As reported by Westinghouse in Reference 2, the changes to WBN's ECCS evaluation model affect both the small break LOCA (SBLOCA) analysis and the best estimate large break LOCA (BELOCA) analysis, and are described in Enclosure 1. The PCT margin allocations resulting from these changes are summarized in Enclosure 2. TVA notes there were no additional PCT impacts reported in Reference 2 for SBLOCA from those previously reported in Reference 1. The updated PCT margin allocation sheet for SBLOCA reflects the removal of a temporary 120OF PCT assessment which expired in WBN Cycle 5 and was previously reported in Reference 1.

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U. S. Nuclear Regulatory Commission Page 2 APR 19 2004 As discussed in Enclosure 1, Westinghouse has identified an input value error which affects the BELOCA analysis for WBN. A plant specific calculation was performed for WBN to estimate the PCT effect of this error. It was confirmed that the fundamental LOCA transient characteristics (e.g., blowdown cooling and reflood turnaround timing and behaviors) were unchanged by the error correction. The effect was determined to be +600 F for the first reflood case (Reflood 1), 0F for the second reflood case, and 0F for the composite case. In addition, as discussed in Enclosure 1, a Tavg Bias Error of 80 F was assessed for each of these cases. As a result of these model assessments, the most significant change in PCT occurred with the Reflood 1 case (PCT increase of 680 F), with a resulting PCT of 1763 0 F. This PCT value is below the most recent BELOCA PCT value of 17770 F (Composite) reported in Reference 3. Due to the Tavg Bias Error of 8 0F, the resulting BELOCA Composite PCT is 17850 F and remains in compliance with 10 CFR 50.46(b).

The resulting Reflood 1 PCT assessment of 680 F for BELOCA exceeds the threshold defined in 10 CFR 50.46(a)(3)(i) for a change of more than 500 F in calculated PCT. Therefore, TVA is reporting this change within the 30-day time limit specified in 10 CFR 50.46. In accordance with 10 CFR 50.46(a)(3)(ii), TVA is required to provide a proposed schedule for providing a reanalysis or taking other actions needed to show compliance with 50.46 requirements for the changes or errors discussed above. However, this PCT value of 1763 0 F remains considerably below the 2200 0 F regulatory limit required by 10 CFR 50.46. Since the Reflood 1 case continues to be less limiting than the Reflood 2 case as reflected by the BELOCA Composite (Enclosure 2) and because the composite case has not changed by more than 500 F since the last BELOCA report (Reference 3), TVA does not propose to provide a best estimate reanalysis at this time. WBN remains in compliance with 10 CFR 50.46(b) requirements, will continue to monitor the periodic reports for significant changes, and will advise the NRC if a future reanalysis is warranted.

Accordingly, TVA has completed the analysis required of 10 CFR 50.46 for changes or errors in the BELOCA ECCS model and no further action is currently required. TVA's commitment to perform an SBLOCA reanalysis as reported in Reference 1 remains valid.

There are no regulatory commitments associated with this submittal.

U. S. Nuclear Regulatory Commission Page 3 APR 19 2004 If you have any questions about this change, please contact me at (423) 365-1824.

Sincerely, P. L. e Manager, Site Licensing and Industry Affairs Enclosures cc (Enclosures):

NRC Resident Inspector Watts Bar Nuclear Plant 1260 Nuclear Plant Road Spring City, Tennessee 37381 Ms. Margaret H. Chernoff, Project Manager U.S. Nuclear Regulatory Commission MS 08G9 One White Flint North 11555 Rockville Pike Rockville, Maryland 20852-2738 U.S. Nuclear Regulatory Commission Region II Sam Nunn Atlanta Federal Center 61 Forsyth St., SW, Suite 23T85 Atlanta, Georgia 30303

ENCLOSURE 1 DESCRIPTION OF CHANGES WHICH AFFECT WBN'S EMERGENCY CORE COOLING SYSTEM EVALUATION MODEL(S) AND ITS CALCULATION OF PEAK CLADDING TEMPERATURE

1. Input Error Resulting in Incomplete Solution Matrix

Background

Input parameter MSIM identifies the last cell number in each simultaneous solution group for the 3-D vessel component. A survey of WCOBRA/TRAC input decks identified two plant models and one test simulation model in which the MSIM input value was less than the total number of cells in the vessel. This resulted in an incomplete solution matrix. An input diagnostic check has been added to prevent future occurrences. This input correction was determined to be a Non-Discretionary change in accordance with Section 4.1.2 of WCAP-13451.

Affected Evaluation Models 1996 Westinghouse Best Estimate Large Break LOCA Evaluation Model Estimated Effect A plant specific calculation was performed for Watts Bar to estimate the PCT effect of this error. It was confirmed that the fundamental LOCA transient characteristics (e.g., blowdown cooling and reflood turnaround timing and behaviors) were unchanged by the error correction. The reference double-ended guillotine break was used to develop the PCT assessments. The effect is +600 F for the first reflood case and 0F for the second reflood case.

2. T.,, BIAS ERROR

Background

An error has been identified in the Watts Bar Best-Estimate Large Break LOCA (BELOCA) analysis. The Analysis-of-Record for Watts Bar Unit 1 is documented in WCAP-14839 Revision 1. The treatment of the uncertainties for the vessel average temperature (Ta.) do not account for a -1.00 F bias that has been established. The

-1.0F bias means that an indicated Tag value could actually be 1.00 F lower than the actual value. Because the actual value could be higher than indicated, and because a higher Ta,. is more limiting for the calculation of the PCT for the Watts Bar BELOCA, an evaluation was required.

Affected Evaluation Models 1996 Westinghouse BELOCA Evaluation Model El-l

Estimated Effect In the application of the 1996 BELOCA Evaluation Model, a Monte Carlo simulation is used to calculate the PCT at the 9 5 th percentile. This simulation was re-performed to establish an estimated effect on the PCT. To estimate the change, the nominal value for Tar was increased by 1.00 F. The effect is +8.0F for both the reflood 1 and reflood 2 time periods. It is judged that the sensitivities calculated with WCOBRA/TRAC for a +1.00 F change would prove sufficiently linear so that the initial condition results (Tavg sensitivity) will remain applicable and the estimated effects are therefore appropriate.

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ENCLOSURE 2

SUMMARY

OF PEAK CLADDING TEMPERATURE MARGIN ALLOCATIONS RESULTING FROM CHANGES TO THE EMERGENCY CORE COOLING SYSTEM EVALUATION MODEL

Attachment 3 - PCT Sheets Page 2 of 7

- Our ref: WAT-D-1 1225 March 19, 2004 Westinghouse LOCA Peak Clad Temperature Summary for Best Estimate Large Break Plant Name: Watts Bar Unit I Utility Name: Tennessee Valley Authority Revision Date: 3 /4104 Analysis Information EMI: WCOBRAITRAC Analysis Date: 8/1/98 Litniting Break Size: Guillotine FQ: 25 Fdll: 1.65 Fuel: Vantage + SGTP (%): 10 Composite Notes: Mixed Core - Vantage + / Performance +

Clad Temp (OJF) Ref. Notes LICENSING BASIS Analysis-Of-Record PCT 1892 1,2 MARGIN ALLOCATIONS (Delta PCT)

A. PRIOR PERMNIANE;NT ECCS MODEL ASSESSMENTS I . Vessel Channel DX Error -4 3 2 . IONTECFDecayHeatUnicertainityError 4 6

13. I'LANNE'ED PLANT CHANGE EVALUATIONS I . Accumulator Line/Prcssurizer Surge Line Data Evaluation -131 4 2 . IncreasedAccunulatorTecperaturcRangeEvaluationi 4 5 3 . 1.4% Uprate Evaluation 12 5 C. 2003 PERMANEN'T ECCS MODEL ASSESSMENTS I . Ioput Error Resulting in IncompIete Solution Matrix 0 7 2 .TavgBiasError 8 7 D. TEMPORARY EGCS MODEL ISSUES*

I . None 0 E'. OTIIER I . None 0 LICENSING BASIS PCT + MARGIN ALLOCATIONS PCT= 1785

• It is reconuncnded that these temporary PCT1 allocations which address current LOCA nodel issues not be considered with respect to 10 CFR 50.46 reporting requirements.

References:

I . WCAP.14839. Rev. 1.lBest Estirnate Analysis of the Large Break Loss of Coolant Accident for the WVatts Bar Nuclear Plant." August 1998.

2 .WAT.D-10499. "Tennessee Valley Authority Watts Bar Nuclear Plant Units 1 and 2, 10 CFR 50.46 Annual Notification and Reporting for 1997." February 27. 1998.

3 .VAT.D-10618."Tennessec Valley Authority. Watts Bar Nuclear Plant Units I and 2, 10 CFR 50.46 Annual Notificationl and Reporting for 1998," Marchi 5. 1999.

4 .WAT-D-10725."Tennessce Valley Authority.Watts Bar Nuclear Plant Unit 1, 10 CFR 50.46 Annual Notification and Reporting for 1999," February 23.2000.

5 . WAT-D-10840. Tennesse Valley Authority. Watts Bar Nuclear Plant Unit 1 Final Deliverables for 1A% Uprate Prograrm" August 31,2000.

6 .WAT-D-109W, "10 CFR 50.46 Annual Notification and Reporting for 2000." Fcbruary 2001.

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Attachment 3 - PCT Sheets Page 3 of 7 Our ref: WAT-D-1 1225 March 19,2004 Westinghouse LO CA Peak Clad Temperature Summary for Best Estimate Large Break Plant Name: Watts Bar Unit 1 Utility Name: Tennessee Valley Authority Revision Date: 3 /4 /04 7 WAT.D-t 1225. 10 CFR 50.46 Annual Notification and Reporting for 2003." March 2004.

Notes:

None E2 -2 A BNFL Group company

Attachment 3 - PCT Sheets Page 4 of 7 Our ref: WVAT-D-1 1225 March 19, 2004 Westingliousc LO CA Peak Clad Temperature Summary for Best Estimate Large Break Plant Namc: Watts Bar Unit 1 Utility Name: Tennessee Valley Authority Revision Date: 3 /4 /04 Analysis Inrormation ENM: WCOBRAfFRAC Analysis Date: 8/1/98 Limiting Break Size: Guillotine FQ: 2.5 FdII: 1.65 Fuel: Vantage+ SGTP (%): 10 Reflood 1 Notes: Mixed Core -Vantage + / Performance +

Clad Temp (°I) Ref. Notes LICENSING BASIS Analysis-Or-Record PCT 1656 1,2 MARGIN ALLOCATIONS (Delta PCT)

A. PRIOR PERMANENT ECCS MODEL ASSESSMENTS I Vessel Chnannel DX Error 56 3 2 . 2ONTECF Decay leat Unccrtainty Error 4 5

13. PLANNED PLANT CHANGE EVALUATIONS I . Accumulator LIne/Pressurizcr Surge Linc Data Evaluation .37 4 2 . Increased Accumiulator Temperature Range Evaluation 4 4 3 .1.4% UprateEvaluatiorn 12 4 C. 2003 PERMANTENT ECCS MODEL ASSESSMENTS I Input Error Rcsulting in IncoipIlete Solution Matrix 60 6 2 .Tavg Dias Error 8 6 D. TEMPORARY ECCS MODEL ISSUES*

I . None 0 E. OTHER I . None 0 LICENSING BASIS PCT + MARGIN ALLOCATIONS PCT - 1763

• It is reconunendcd that these terporary PCT allocations which address current LOCA n adel issues not be considered with respect to 10 CfrR 50.46 reporting requiremtnts.

Rererences:

1 . VCAP-14839,Rev. 1, est Estimate AnalysisortheLargeBreakLoss of Coolant Accident for thetWatts BarNuclear Plant," August 1998.

2 . WAT-D.10499, "Tennessee Valley Authority Watts Bar Nuclear Plant Units I and 2, 10 CFR 50.46 Annual Notification and Reporting for 1997," February 27. 1998.

3 . WAT-D-10618."Tennesse ValleyAuthority. NattsBarNuclearPlant Unitsl and2.10CFR50.46 Annual Notification and Reporting for 1998," March 5. 1999.

4 . WAT-D-10840. "Tennesse Valley Authority lVatts Bar Nuclear Plant Unit .Final Deliverables for IA% Uprate Programn." August 31. 2000.

5 . WAT-D-10904. "10 CFR 50.46 Annual Notification and Reporting for 2000." February2001.

6 . tVAT-D-I 1225. "10 CFR 50.46 Annual Notification and Reporting for 2003," March 2004.

Notes:

None

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Attachment 3 - PCT Sheets Page 5 of 7 Our ref: WNAT-D-1 1225 March 19, 2004 Westinghouse LO CA Peak Clad Temperature Summary for Best Estimiate Large Break Plant Name: Watts Bar Unit 1 Utility Name: Tennessee Valley Authority Revision Date: 3 /4/04 Analysk Information ENI: WCOBRA/TRAC Analysis Date: 8/1/98 Limiting Break Size: Guillotine FQ: 2.5 Fdll: 1.65 Fucl: Vantage + SGTI'(%): 10 Reflood 2 Notes: Mixed Core - Vantage + / Performtnce +

Clad Temp (°F) Ref. Notes LICENSING BASIS Analysis-Of-Record PCT 1892 1,2 MIARGIN ALLOCATIONS (Delta PCI')

A. PRIOR PERMANENT ECCS MODEL ASSESSMENTS I Vessel Channel DX Error -4 3 2 . IONTECF Decay Heat Uncertainty Error 4 6 B3. PLANNED PLANT CHANGE EVALUATIONS I Accuniulator Line/Pressurizer Surge Liie Data Evaluation -131 4 2 . Increased Accunailator Tcmipcraturc Rangc Evaluation 4 5 3 . 1.4% Uprate Evaluation 12 5 C. 2003 PERMANENT ECCS MODEL ASSESSMENTS I Input Error Resulting in lacomilete Solution NMatrix 0 7 2 . Tavg Bias Error 8 7 D. TEMPORARY ECCS MODEL ISSUES*

I . None 0 E. OTIIER I . None 0 LICENSING BASIS P'CT + NIARGIN ALLOCATIONS PCT 1785 It is reconuicnidcd that these tenlrorary PCT allocations which address current LOCA nodcl issues not be considered with respect to 10 CFR 50.46 reporting requirements.

References:

I . WCAP-14839, Rev. 1. 'Best Estimate Analysis of the Large Break Loss of Coolant Accident for the Watts Bar Nuclear Plant." August 1998.

2 . WAT-D-10499. "Tennessee Valley Authority Watts Bar Nuclear Plant Units I and 2. 10 CFR 50.46 Annual Notification and Reporting for 1997." February 27, 1993.

3 . WAT-D.10618."Teniessee Valley Authority. NVatts Bar Nuclear Plant Units I and 2. 10 CFR 50.46 Annual Notification and Reporting for 1998." Mardc 5. 1999.

4 . WAT-D-10725,"Tecnessce Valley Authority.lNVattsBarNuclear PlantUnit 1.10 CFR5OA6 Annual Notificationand Reporting for 1999." February 23, 2000.

5 . WAT-D-IOS40. "Tennessee Valley Authority, Watts Bar Nuclear Plant Unit lFinal Deliverables for 1A% Uprate Programn." August 31. 2000.

6 . WAT-D-10904, "10 CFR 50.46 Annual Notificationand Reporting for 2000." February 2001.

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Attachment 3 - PCT Sheets Page 6 of 7 Our ref: WAT-D-I 1225 March 19, 2004 Westinghouse LOCA Peak Clad Temperature Summary for Best Estimate Large Break Plant Name: Watts Bar Unit I Utility Name: Tennessee Valley Authority Revision Date: 3 /4 /04 7 WAT-D-1 1225. "1 oCFR 50.46 Annual Notification and Reporting for 2003. Mlarcl 2004.

Notes:

None E2 -5 A BNFL Group company

Attachment 3 - PCT Sheets Page 7 of 7 Our ref: WAT-D-1 1225 March 19, 2004 Westinghouse LO CA Peak Clad Temperature Summary for Small Break Plant Name: Watts Bar Unit 1 Utility Narnc: Tennessee Valley Authority Revision Date: 3 A4/04 Analvsis Information ENM: NOTRINP Analysis Date: 11/1/96 Limtiting 3reak Size: 4 inch FQ: 2.5 Fdll: 1.65 Fuel: Vantagc + SGTP(%): 10 Notes: Mixed Core - Vantage + / Pcrformance +

Clad Temp (of) Ref. Notes LICENSING BASIS Analysis-Of-Record PCT 1126 1,2 MARGIN ALLOCATIONS (Delta PCI)

A. PRIOR PERMANE NT ECCS MODEL ASSESSMENTS I . NOTRUhlPblattureLevelTracking/RegionDcpletionErrors 13 4

13. PLANNED PLANT CHANGE EVALUATION'S I . Atunular Blankets 10 3 C. 2003 PERMANE NT ECCS MODEL ASSESSMENTS I . NOTRUMIP Bubblc Rise / Drift Flus Modcl Inconsistency Corrections 35 5 D. TEMPlORARY ECCS MODEL ISSUES*

I . None 0 E. OTIIER I . Tavg Uncertainty of 6 IF I LICENSING BASIS PCI + MARGIN ALLOCATIONS PCT = 1185 It is recommuicindcl thlat tiesc tetorary PCT allocations whiicl address current LOCA nmdcl issues not bc considered with respect to 10 CFR 50.46 reporting requirements.

References:

I WAT.D-10337. "Teinessee Valley Authority, Watts Bar Nuclear Plant, Final Safety Evaluation to Support Tecinical Specification, Changes." Ntarch 5, 1997.

2 . WAT-D-I 0356. "Tennessee Valley Authority, Watts Bar Nuclear Plant Units I & 2, Final Report and Safety Evaluation for the 10% SGTP Program," June 2. 1997.

3 . WAT-D.10618, "Tennessee Valley Authority. Watts Bar Nuclear Plant Unit 1, 10 CFR 50.46 Annual Notification and Reporting for 1998," Mlarch 5, 1999.

4 WAT-D.-10S10. 1Tennessee Valley Authority, Watts Bar Nuclear Plant Unit 1, 10 CFR 50.46 Appendix K (BART/BASIUNOTRUMP) Evaluation Model lid-Year Notification and Reporting for 2000," June 30,2000.

5 . WAT-D-1 1195. "10 CFR 50.46 Mid-Year Notifcation and Reporting for 2003," Novcmabr 2003.

Notes:

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