ML13046A002
| ML13046A002 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 02/13/2013 |
| From: | James Shea Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| Download: ML13046A002 (6) | |
Text
Tennessee Valley Authority, 1101 Market Street, Chattanooga, Tennessee 37402 February 13, 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:
Supplement to 10 CFR 50.46 Day Special Report
Reference:
- 1. TVA Letter to NRC, "10 CFR 50.46 Day Special Report," dated October 18, 2012 [ML12296A254]
- 2. NRC Information Notice 2011-21, "Realistic Emergency Core Cooling System Evaluation Model Effects Resulting from Nuclear Fuel Thermal Conductivity Degradation," dated December 13, 2011 [ML113430785]
The purpose of this letter is to provide a supplement to the 30-day special report submitted on October 18, 2012 (Reference 1) for Watts Bar Nuclear Plant (WBN) Unit 1. This supplement revises the summary of changes and calculated peak cladding temperature (PCT) previously reported for the WBN Unit 1 Emergency Core Cooling System (ECCS) Large Break Loss of Coolant Accident (LBLOCA) evaluation model. This supplement was necessitated based on a letter received from the Westinghouse Electric Company (WEC) on January 17, 2013 informing the Tennessee Valley Authority (TVA) of an error in the 10 CFR 50.46 report provided by WEC to TVA on September 20, 2012. The error involved the inappropriate double crediting of the PCT benefit for the change from WEC Fuel Rod Performance and Design (PAD) computer model Version 3.4 to PAD Version 4.0.
The Reference 1 submittal provided a 30-day special report of the impact of fuel pellet thermal conductivity degradation (TCD) and peaking factor burndown on the calculated PCT for the WBN Unit 1 ECCS evaluation model as required by 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). United States Nuclear Regulatory Commission (NRC) Information Notice 2011-21 (Reference 2) notified addressees of the potential for this A D phenomenon to cause errors in realistic ECCS evaluation models. Fuel pellet TCD and peaking factor burndown had not been explicitly considered in the WBN Unit 1 ECCS LBLOCA evaluation analysis of record (AOR). As reported in Reference 1, the subsequent review by Printed onrecycled paper
U.S. Nuclear Regulatory Commission Page 2 February 13, 2013 WEC of the impact of the fuel pellet TCD and peaking factor burndown phenomenon resulted in an estimated 60 degree Fahrenheit (OF) reduction in the net licensing basis PCT for the LBLOCA. This change in net LBLOCA PCT included a 75°F beneficial reduction that was attributed to the upgrade to PAD Version 4.0 for the fuel rod design inputs into the WBN Unit 1 LBLOCA evaluation model AOR.
This supplement revises the Reference 1 submittal to delete the references to the 75 0 F reduction in LBLOCA PCT and the associated discussion in response to the discovery by WEC that the PAD 4.0 benefit had already been credited in the 1998 Best Estimate LBLOCA (BE LBLOCA) evaluation AOR. As described in the report provided in Reference 1, the 1998 BE LBLOCA AOR established the baseline PCT of 1892 0 F. The enclosed Revision 1 report provides an updated summary of the changes to the calculated PCT for the limiting ECCS analyses accounting for the deletion of the previously credited 75 0 F reduction in LBLOCA PCT.
Note that the 1998 BE LBLOCA evaluation continues to be the LBLOCA AOR for WBN Unit 1 as indicated in the enclosed Revision 1 report.
Furthermore, as presented in the enclosed Revision 1 report, there is an estimated 75 0 F increase in the net licensing basis PCT for the LBLOCA relative to the previous (Reference 1) report, resulting in an updated (net) licensing basis LBLOCA PCT of 1880 0 F. The updated (net) licensing basis Small Break Loss of Coolant Accident (SBLOCA) PCT remains at 11 32 0 F.
Accordingly, the LBLOCA and SBLOCA evaluation models for WBN Unit 1 continue to demonstrate compliance with the 10 CFR 50.46 requirements since the calculated PCTs for WBN Unit 1 remain below the 2200°F limit.
This issue was discussed with the NRC Project Manager for WBN on January 31, 2013 and it was agreed that this correction submittal would be provided by February 19, 2013.
There are no regulatory commitments in this letter. Please direct questions concerning this report to Clyde Mackaman at (423) 751-2834.
R esp ully, J. . SheaA Vi'e resident, Nuclear Licensing
Enclosure:
10 CFR 50.46 30-Day Report, Revision 1, 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 30-DAY REPORT, REVISION 1, FOR WATTS BAR NUCLEAR PLANT, UNIT I 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 30-Day Report Removal of PAD 4.0 Benefit I
The most recent 10 CFR 50.46 Annual Report for WBN Unit 1 (Reference 1) was submitted to the United States Nuclear Regulatory Commission (NRC) on April 25, 2012. The previous 10 CFR 50.46 Day Special Report for WBN Unit 1 (Reference 2) was submitted to the NRC on October 18, 2012. As indicated in this report, WEC WCAP-14839, Revision 1, "Best Estimate Analysis of the Large Break Loss of Coolant Accident for the Unit 1 Watts Bar Nuclear Plant" (Reference 3), is the current analysis of record (AOR) for the Best Estimate Large Break Loss of Coolant Analysis (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 4), with a baseline PCT of 1132°F.
On January 17, 2013, WEC notified the Tennessee Valley Authority (TVA) of a revision to the Unit 1 Cycle 12 ECCS PCT report. Specifically, WEC notified TVA that during an evaluation of fuel pellet thermal conductivity degradation (TCD) completed for WBN Unit 1, a benefit in ECCS PCT associated with an upgrade to the Westinghouse Improved Performance Analysis and Design (PAD) computer model from Version 3.4 to Version 4.0 had been doubly accounted.
This ECCS PCT benefit had been previously credited in the evaluation for the use of WEC RFA-2 fuel assemblies at WBN Unit 1. As a result, WEC revised the ECCS PCT report to remove the credit. Accordingly, this report revises the PCT value previously reported in the most recent 30-day report for WBN Unit 1 (Reference 1) consistent with WEC's revised ECCS PCT report.
The following Table details the accumulated PCT impact resulting from the changes or errors in the LBLOCA and SBLOCA analyses since each of the respective AORs (References 3 and 4) was established. The composite values are provided for the effects on the LBLOCA analysis because they represent the worst case PCT impact from either the Reflood 1 or the Reflood 2 accident scenario sequence. As indicated in the Table, the change to the LBLOCA limiting composite PCT has decreased by 12°F relative to the BE LBLOCA AOR Baseline PCT. This represents a 75 0 F increase over the most recent estimated net ECCS PCT value (Reference 2).
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 3) was performed exceeds 50'F.
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ENCLOSURE 10 CFR 50.46 30-DAY REPORT, REVISION 1, 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 IAPCT! APCT IAPCTI (OF) (OF) (F) (OF) 1998 BE LBLOCA AOR Baseline PCT 1892 3 3--
2006 SBLOCA AOR Baseline PCT --- --- 1132 --- 4 1999 Vessel Channel DX Error -4 4 .... 5 2000 Increased Accumulator Room 4 4 -- - - -- 5 Temperature Evaluation 2000 1.4% Uprate Evaluation 12 12 --- --- 5 2000 Accumulator Line/Pressurizer -131 131 --- --- 5 Surge Line Data Evaluation 2000 MONTECF Decay Heat 4 4 --- --- 6 Uncertainty Error 2001 WBN Specific LBLOCA Vessel 0 0 --- --- 7 Geometry Input Errors 2003 Input Error Resulting in 0 0 -- 8 Incomplete Solution Matrix 2003 Tavg Bias Error 8 8 ...... 8 2004 Increased Stroke Time for ECCS 0 0 --- --- 9 Valves 2004 Revised Blowdown Heatup 5 5 --- --- 9 Uncertainty Distribution 2006 Replacement Steam Generators -10 10 0 0 10 (D3 to 68AXP) 2006 HOTSPOT Fuel Relocation Error 65 65 0 0 10 E-2 of 4
ENCLOSURE 10 CFR 50.46 30-DAY REPORT, REVISION 1, 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 (OF) °(F) (OF) (OF) 2012 PMID/ PBOT Violation Evaluation 20 20 0 0 2 2012 TCD and Peaking Factor 15 15 --- 2 Burndown Updated (net) licensing basis PCT 1880 --- 1132 --- ---
AOR PCT + ) APCT Cumulative sum of PCT --- 278 --- 0 changes
- I I APCTI E-3 of 4
ENCLOSURE 10 CFR 50.46 30-DAY REPORT, REVISION 1, FOR WATTS BAR NUCLEAR PLANT, UNIT I REFERENCES
- 1. Letter from TVA to NRC, "10 CFR 50.46 Annual Report for Model Year 2011," dated April 25, 2012 [ML12117A261]
- 2. Letter from TVA to NRC, "10 CFR 50.46 - 30 Day Special Report," dated October 18, 2012 [ML12296A254]
3: WCAP-14839, Revision 1, "Best Estimate Analysis of the Large Break Loss of Coolant Accident for the Watts Bar Nuclear Plant," September 1998
- 4. WTV-RSG-06-015, "LOCA & Non-LOCA Analysis Summary for Replacement Steam Generator," February 2006
- 5. 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]
- 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 Revised Annual Notification Report for 2000," dated September 7, 2001 [ML012570290]
- 7. 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]
- 8. 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]
- 9. 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]
- 10. 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]
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