ML13080A405

Day Report Changes to the Calculated Peak Cladding Temperature Emergency Core Cooling System Evaluation Model

ML13080A405
Person / Time
Site:	Watts Bar
Issue date:	03/19/2013
From:	James Shea Tennessee Valley Authority
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
Download: ML13080A405 (6)

Text

Tennessee Valley Authority, 1101 Market Street, Chattanooga, Tennessee 37402 March 19, 2013 10 CFR 50.46 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Watts Bar Nuclear Plant, Unit 1 Facility Operating License No. NPF-90 NRC Docket No. 50-390

Subject:

10 CFR 50.46 Day Report for Watts Bar, Unit 1

Reference:

TVA Letter to NRC, "Supplement to 10 CFR 50.46 Day Special Report,"

dated February 13, 2013 [ML13046A002]

The purpose of this letter is to provide a 30-day report of changes to the calculated peak cladding temperature (PCT) for the Watts Bar Nuclear Plant (WBN) Unit 1 Emergency Core Cooling System (ECCS) evaluation model. This submittal satisfies the reporting requirements for a significant change or error in accordance with Title 10 of the Code of Federal Regulations (10 CFR) 50.46, "Acceptance Criteria for Emergency Core Cooling Systems for Light-Water Nuclear Power Reactors," paragraph (a)(3)(ii). The enclosed report provides a summary of the changes to the calculated PCT for the limiting ECCS analyses.

The PCT changes identified for WBN Unit 1 in the. referenced supplemental report submitted on February 13, 2013, when expressed as the cumulative sums of the absolute magnitudes, exceed the 50 degrees Fahrenheit (OF) threshold for a significant change or error as defined in 10 CFR 50.46(a)(3)(i). Accordingly, any subsequently discovered change or error is considered significant for the purposes of reporting until such time as a re-analysis of the ECCS evaluation model is completed.

By letter dated February 22, 2013, the Westinghouse Electric Company notified Tennessee Valley Authority (TVA) of a change to the ECCS Large Break Loss of Coolant Accident (LBLOCA) evaluation model to correct the dimension of the thermal-hydraulic history file for the WCOBRA/TRACTM computer code used in the HSDRIVERTM computer code. As indicated in the enclosed report, there is a 0°F effect on the updated (net) licensing basis PCT for the WBN Unit 1 LBLOCA analysis of record (AOR). Note that this issue is not applicable to the Printedon recycledpaper

U.S. Nuclear Regulatory Commission Page 2 March 19, 2013 WBN Unit 1 Small Break LOCA (SBLOCA) AOR because it does not use the WCOBRA/TRACTM or HSDRIVERTM computer code. Accounting for the change, the updated (net) licensing basis LBLOCA PCT remains at 1880°F and the updated (net) licensing basis SBLOCA PCT remains at 1132 0 F, which are below the 2200°F limit. However, the cumulative sum of the absolute magnitudes of the LBLOCA PCT changes for WBN Unit 1 remains above the 50°F threshold defined for a significant change or error, thus necessitating this 30-day report. The due date for compliance with the 30-day reporting requirement is March 24, 2013. Considering that this date falls on a Sunday, the official date for reporting is the next business day, which is March 25, 2013.

In addition, when the cumulative sum of the absolute magnitudes of the resulting PCT changes exceeds 50 0 F, 10 CFR 50.46(a)(3)(ii) requires the licensee to include with the 30-day report a proposed schedule for providing a re-analysis or taking other action as may be needed to show compliance with the 10 CFR 50.46 requirements. As presented in this report, compliance with the 10 CFR 50.46 requirements is demonstrated by the calculated LBLOCA and SBLOCA PCTs for WBN Unit 1 remaining below the 2200°F limit. Therefore, TVA has concluded that no proposed schedule for providing a re-analysis or other action is required.

There are no regulatory commitments in this letter. Please direct questions concerning this report to Clyde Mackaman at (423) 751-2834.

Respec J7 ea V ce resident, Nuclear Licensing

Enclosure:

10 CFR 50.46 Day Report for Watts Bar Nuclear Plant Unit 1 cc (Enclosure):

NRC Regional Administrator - Region II NRC Senior Resident Inspector - Watts Bar Nuclear Plant

ENCLOSURE 10 CFR 50.46 DAY REPORT FOR WATTS BAR NUCLEAR PLANT UNIT 1 The Watts Bar Nuclear Plant (WBN) Unit 1 reactor core currently contains only the Westinghouse Electric Company (WEC) Robust Fuel Assembly (RFA-2TM) fuel design.

Description of Changes or Errors Relative to the Previous 10 CFR 50.46 Report WCOBRATRACTM Thermal-Hydraulic History File Dimension Used in HSDRIVERTM The most recent Title 10 of the Code of Federal Regulations (10 CFR) 50.46 Annual Report for WBN Unit 1 (Reference 3) was submitted to the United States Nuclear Regulatory Commission (NRC) on April 25, 2012. A 10 CFR 50.46 Day Special Report for WBN Unit 1 (Reference 2) was submitted to the NRC on October 18, 2012, and supplemented (Reference 1) on February 13. 2013. As indicated in the these reports, WEC WCAP-14839, Revision 1, "Best Estimate Analysis of the Large Break Loss of Coolant Accident for the Watts Bar Nuclear Plant" (Reference 4), is the current analysis of record (AOR) for the Best Estimate Large Break Loss of Coolant Accident (BE LBLOCA), with a baseline Peak Cladding Temperature (PCT) of 1892 degrees Fahrenheit (OF). The indicated AOR for the Small Break Loss of Coolant Accident (SBLOCA) is WTV-RSG-06-015, "LOCA & Non-LOCA Analysis Summary for Replacement Steam Generator for WBN Unit 1" (Reference 5), with a baseline PCT of 11 32°F.

By letter dated February 22, 2013, WEC notified the Tennessee Valley Authority (TVA) of a discrepancy in the HSDRIVERTM computer code related to the dimension of the thermal-hydraulic history file for the WCOBRA/TRACTM computer code. The array that is used to identify and locate component response curves in the WCOBRAITRAC TM thermal-hydraulic history file is dimensioned to 3000 in HSDRIVERTM. It is possible for this file to contain more than 3000 curves. If that were the case, the curves may not be used correctly in the downstream HOTSPOTTM software execution for LBLOCA evaluation modeling. An extent of condition review performed by WEC indicated that resolution of this issue results in a 00 F effect on the PCT calculation for the existing WBN Unit 1 BE LBLOCA AOR. This issue is not applicable to the WBN Unit 1 SBLOCA AOR because it does not use the WCOBRAITRACTM or HSDRIVERTM computer code.

The following Table details the accumulated effects on PCT resulting from the changes or errors in the LBLOCA and SBLOCA evaluation models since each of the respective AORs (References 4 and 5) was established. The composite values are provided for the effects on the LBLOCA analysis because they represent the worst case effects on PCT from either the Reflood 1 or the Reflood 2 accident scenario sequence. As indicated in the Table, the LBLOCA limiting composite PCT has decreased by 120 F relative to the BE LBLOCA AOR Baseline PCT and remains unchanged from the most recent 10 CFR 50.46 Report (Reference 1).

In accordance with 10 CFR 50.46(a)(3)(i), this change is considered significant for reporting purposes because the absolute magnitudes of the accumulated changes and errors to the calculated PCT since the baseline BE LBLOCA AOR analysis (Reference 4) was performed exceeds 50'F.

E-1 of 4

ENCLOSURE 10 CFR 50.46 DAY REPORT FOR WATTS BAR NUCLEAR PLANT UNIT I TABLE (Sheet I of 2)

Summary of Changes to WBN Unit I PCT for LBLOCA and SBLOCA Year Description LBLOCA LBLOCA SBLOCA SBLOCA Reference APCT jIAPCTI APCT IAPCTI (F) (OF)

I

_(OF) 1998 BE LBLOCA AOR Baseline PCT 1892 --- - -- -- 4 2006 SBLOCA AOR Baseline PCT --- --- 1132 --- 5 1999 Vessel Channel DX Error -4 4 -.-.-. 6 2000 Increased Accumulator Room 4 4 ... ... 6 Temperature Evaluation 2000 1.4% Uprate Evaluation 12 12 --- --- 6 2000 Accumulator Line/Pressurizer -131 131 --- --- 6 Surge Line Data Evaluation 2000 MONTECF Decay Heat 4 4 7 Uncertainty Error 2001 WBN Specific LBLOCA Vessel 0 0 8 Geometry Input Errors 2003 Input Error Resulting in 0 0 9 Incomplete Solution Matrix 2003 Tavg Bias Error 8 8 .... 9 2004 Increased Stroke Time for ECCS 0 0 -- --- 10 Valves 2004 Revised Blowdown Heatup 5 5 --- --- 10 Uncertainty Distribution 2006 Replacement Steam Generators -10 10 0 0 11 (D3 to 68AXP) 2006 HOTSPOT Fuel Relocation Error 65 65 0 0 11 E-2 of 4

ENCLOSURE 10 CFR 50.46 DAY REPORT FOR WATTS BAR NUCLEAR PLANT UNIT I TABLE (Sheet 2 of 2)

Summary of Changes to WBN Unit I PCT for LBLOCA and SBLOCA Year Description LBLOCA LBLOCA SBLOCA SBLOCA Reference APCT IAPCTI APCT IAPCTI (F (_F)_(_F_ _ _ _F) 2012 PMID/ PBOT Violation Evaluation 20 20 0 0 1,2 2012 TCD and Peaking Factor 15 15 --- --- 1,2 Burndown 2013 WCOBRA/TRAC History File 0 0 --- ---

Dimension Error Updated (net) licensing basis PCT 1880 --- 1132 --- ---

AOR PCT + I APCT Cumulative sum of PCT --- 278 --- 0 ---

changes

I APCTI

• Discussed in the text of this enclosure.

E-3 of 4

ENCLOSURE 10 CFR 50.46 DAY REPORT FOR WATTS BAR NUCLEAR PLANT UNIT I REFERENCES

1. Letter from TVA to NRC, "Supplement to 10 CFR 50.46 - 30 Day Special Report," dated February 13, 2013 [ML13046A002]

2. Letter from TVA to NRC, "10 CFR 50.46 - 30 Day Special Report," dated October 18, 2012 [ML12296A254]

3. Letter from TVA to NRC, "10 CFR 50.46 Annual Report for Model Year 2011," dated April 25, 2012 [ML12117A261]

4. WCAP-14839, Revision 1, "Best Estimate Analysis of the Large Break Loss of Coolant Accident for the Watts Bar Nuclear Plant," September 1998

5. WTV-RSG-06-015, "LOCA & Non-LOCA Analysis Summary for Replacement Steam Generator," February 2006

6. Letter from TVA to NRC, "Watts Bar Nuclear Plant (WBN) Unit 1 - Emergency Core Cooling System (ECCS) Evaluation Model Changes - 30 Day Report and Annual Notification and Reporting for 2000," dated October 26, 2000 [ML003764646]

7. Letter from TVA to NRC, "Watts Bar Nuclear Plant (WBN) Unit 1 - Emergency Core Cooling System (ECCS) Evaluation Model Changes - 30 Day Report and Revised Annual Notification Report for 2000," dated September 7, 2001 [ML012570290]

8. Letter from TVA to NRC, "Watts Bar Nuclear Plant (WBN) Unit 1 - Emergency Core Cooling System (ECCS) Evaluation Model Changes - Annual Notification and Reporting for 2001," dated April 3, 2002 [ML021070404]

9. Letter from TVA to NRC, "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," dated April 19, 2004 [ML041130196]

10. Letter from TVA to NRC, "Watts Bar Nuclear Plant (WBN) Unit 1 - Emergency Core Cooling System (ECCS) Evaluation Model Changes - 30 Day Annual Notification and Reporting for 2004," dated April 19, 2005 [ML051120164]

11. Letter from TVA to NRC, "Watts Bar Nuclear Plant (WBN) Unit 1 - Emergency Core Cooling System (ECCS) Evaluation Model Changes - 30 Day Report and Annual Notification and Reporting for 2006," dated July 3, 2007 [ML071860388]

E-4 of 4