RS-11-052, Units 1 and 2 - Annual 10 CFR 50.46 Report of the Emergency Core Cooling System Evaluation Model Changes and Errors

Units 1 and 2 - Annual 10 CFR 50.46 Report of the Emergency Core Cooling System Evaluation Model Changes and Errors

ML110970189
Person / Time
Site:	Byron, Braidwood
Issue date:	04/06/2011
From:	Hansen J Exelon Generation Co, Exelon Nuclear
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
RS-11-052
Download: ML110970189 (14)

Text

n Nuclear RS-11-0S2 10 CFR 50.46 April 6, 2011 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Braidwood Station, Units 1 and 2 Facility Operating License Nos. NPF-72 and NPF-77 NRC Docket Nos. STN 50-456 and STN 50-457 Byron Station, Units 1 and 2 Facility Operating License Nos. NPF-37 and NPF-66 NRC Docket Nos. STN 50-454 and STN 50-455

Subject:

Annual 10 CFR 50.46 Report of the Emergency Core Cooling System Evaluation Model Changes and Errors

Reference:

1. Letter from J. L. Hansen (Exelon Generation Company, LLC) to U. S. NRC, "ECCS Evaluation Model Error - 10 CFR 50.46 Reports,"

dated March 15,2011.

In accordance with 10 CFR 50.46, "Acceptance criteria for emergency core cooling systems for light-water nuclear power reactors," paragraph (a)(3)(ii), Exelon Generation Company, LLC, (EGC) is submitting the attached information to fulfill the annual reporting requirements for the Braidwood and Byron Stations, Units 1 and 2.

In Reference 1, EGC submitted a report to fulfill the 30-day reporting requirement in accordance with 10 CFR 50.46 for the new large break Best-Estimate LOCA (BELOCA) Automated Statistical Treatment of Uncertainty Method (ASTRUM) analysis in support of Braidwood and Byron Stations, Units 1 and 2. Updated assessment notes were provided with the PCT values for the limiting large break loss-of-coolant accident (LBLOCA) evaluations regarding the new BELOCA ASTRUM analysis. The small break loss-of-coolant accident (SBLOCA) analyses were not affected. provides peak cladding temperature (PCT) information for the limiting loss-of-coolant accident (LOCA) evaluations for the Braidwood and Byron Stations. Attachment 2 contains the assessment notes, which provides a detailed description for each change reported.

The Attachments indicate that there has been no net PCT change for the Braidwood and Byron Stations, Units 1 and 2.

April 6, 2010 U. S. Nuclear Regulatory Commission Page 2 There are no regulatory commitments contained in this letter. Should you have any questions concerning this letter, please contact Ms. Lisa A. Schofield at (630) 657-2815 .

. Hansen Manager - Licensing Exelon Generation Company, LLC Attachments:

1: Braidwood and Byron Stations, Units 1 and 2 - 10 CFR 50.46 Report 2: Braidwood and Byron Stations, Units 1 and 2 - 10 CFR 50.46 Report Assessment Notes cc:

NRC Regional Administrator, Region III NRC Senior Resident Inspector, Braidwood Station NRC Senior Resident Inspector, Byron Station NRR Project Manager, Braidwood and Byron Stations Illinois Emergency Management Agency - Division of Nuclear Safety

ATTACHMENT 1 Braidwood and Byron Stations, Units 1 and 2 10 CFR 50.46 Report PLANT NAME: Braidwood Station, Unit 1 ECCS EVALUATION MODEL: Small Break Loss-of-Coolant Accident (SBLOCA)

REPORT REVISION DATE: January 24, 2011 CURRENT OPERATING CYCLE: A1C16 ANALYSIS OF RECORD Evaluation Model: NOTRUMP Calculation: Westinghouse CN-US-00-208, December 2000 Fuel: VANTAGE+ 17 x 17 Limiting Fuel Type: VANTAGE+ 17 x 17 Limiting Single Failure: Loss of one train of ECCS flow Limiting Break Size and Location: 211 break in the bottom of the Cold Leg Reference Peak Cladding Temperature (PCT): 1624.0 of MARGIN ALLOCATION A. PRIOR LOSS..OF-COOlANT ACCIDENT (LOCA) MODEL ASSESSMENTS 10 CFR 50.46 report dated June 11, 2001 (see note 1) ~PCT = 0 of 10 CFR 50.46 report dated April 18, 2002 (see note 2) ~PCT= 0 of 10 CFR 50.46 report dated April 14, 2003 (see note 3) ~PCT= 0 of 10 CFR 50.46 report dated April 14, 2004 (see note 4) ~PCT = 35 of 10 CFR 50.46 report dated April 14, 2005 (see note 5) ~PCT= 0 of 10 CFR 50.46 report dated April 14, 2006 (see note 6) ~PCT = 0 of 10 CFR 50.46 report dated April 13, 2007 (see note 7) ~PCT= 0 of 10 CFR 50.46 report dated June 22, 2007 (see note 9) ~PCT = 0 of 10 CFR 50.46 report dated November 19, 2007 (see note 10) ~PCT = 90 of 10 CFR 50.46 report dated April 11 ,2008 (see note 11) ~PCT= 0 of 10 CFR 50.46 report dated April 9, 2009 (see note 12) ~PCT = 0 of 10 CFR 50.46 report dated April 8, 2010 (see note 13) ~PCT = 0 of Net PCT PCT = 1749.0 of B. CURRENT LOCA MODEL ASSESSMENTS Urania-Gadolinia Pellet Thermal Conductivity Calculation (see note 15) ~PCT = 0 of Pellet Crack and Dish Volume Calculation (see note 16) ~PCT = 0 of Treatment of Vessel Average Temperature Uncertainty (see note 17) ~PCT = 0 of General Code Maintenance (see note 18) ~PCT = 0 of Total PCT change from current assessments L ~PCT = 0 of Cumulative PCT change from current assessments L I~PCTI = 0 OF Net PCT PCT =1749.0 of Page 1 of 8

ATTACHMENT 1 Braidwood and Byron Stations, Units 1 and 2 10 CFR 50.46 Report PLANT NAME: Braidwood Station, Unit 1 ECCS EVALUATION MODEL: Large Break LossMof-Coolant Accident (LBLOCA)

REPORT REVISION DATE: January 24, 2011 CURRENT OPERATING CYCLE: A1C16 ANALYSIS OF RECORD Evaluation Model: ASTRUM (2004)

Calculation: Westinghouse WCAp M16841-P, November 2007 Fuel: VANTAGE+ 17 x 17 Limiting Fuel Type: VANTAGE+ 17 x 17 Limiting Single Failure: Loss of one train of ECCS flow Limiting Break Size and Location: Guillotine break in the Cold Leg Reference PCT: 1913.0 of MARGIN ALLOCATION A. PRIOR LOCA MODEL ASSESSMENTS I 10 CFR 50.46 report dated March 15, 2011 (see note 14)

Net PCT PCT = 1913.0 of B. CURRENT LOCA MODEL ASSESSMENTS No 2010 model changes, corrections, or enhancements ~PCT = 0 of Total PCT change from current assessments L ~PCT = 0 OF Cumulative peT change from current assessments L I,1PCT 1= 0 OF Net PCT PCT =1913.0 of Page 2 of 8

ATTACHMENT 1 Braidwood and Byron Stations, Units 1 and 2 10 CFR 50.46 Report PLANT NAME: Braidwood Station, Unit 2 ECCS EVALUATION MODEL: SBLOCA REPORT REVISION DATE: January 24,2011 CURRENT OPERATING CYCLE: A2C15 ANALYSIS OF RECORD Evaluation Model: NOTRUMP Calculation: Westinghouse CN-LiS-00-208, December 2000 Fuel: VANTAGE+ 17 x 17 Limiting Fuel Type: VANTAGE+ 17 x 17 Limiting Single Failure: Loss of one train of ECCS flow Limiting Break Size and Location: 2" break in the bottom of the Cold Leg Reference PCT: 1627.0 of MARGIN ALLOCATION A. PRIOR LOCA MODEL ASSESSMENTS 10 CFR 50.46 report dated June 11, 2001 (see note 1) ~PCT = 3 of 10 CFR 50.46 report dated April 18, 2002 (see note 2) ~PCT = 0 of 10 CFR 50.46 report dated April 14, 2003 (see note 3) ~PCT = 0 of 10 CFR 50.46 report dated April 14, 2004 (see note 4) ~PCT = 35 of 10 CFR 50.46 report dated April 14, 2005 (see note 5) ~PCT= 0 of 10 CFR 50.46 report dated April 14, 2006 (see note 6) ~PCT = 0 of 10 CFR 50.46 report dated April 13, 2007 (see note 7) ~PCT= 0 of 10 CFR 50.46 report dated June 22, 2007 (see note 9) ~PCT = 0 of 10 CFR 50.46 report dated April 11 ,2008 (see note 11) ~PCT = 90 of 10 CFR 50.46 report dated April 9, 2009 (see note 12) ~PCT = 0 of 10 CFR 50.46 report dated April 8, 2010 (see note 13) ~PCT = 0 OF Net PCT PCT =1755.0 OF B. CURRENT LOCA MODEL ASSESSMENTS Pellet Crack and Dish Volume Calculation (see note 16) ~PCT = 0 OF Treatment of Vessel Average Temperature Uncertainty ~PCT = 0 OF (see note 17)

General Code Maintenance (see note 18) ~PCT = 0 OF Total PCT change from current assessments L ~PCT = 0 OF Cumulative PCT change from current assessments L I~PCT 1= 0 OF Net PCT PCT = 1755.0 OF Page 3 of 8

ATIACHMENT1 Braidwood and Byron Stations, Units 1 and 2 10 CFR 50.46 Report PLANT NAME: Braidwood Station, Unit 2 ECCS EVALUATION MODEL: LBLOCA REPORT REVISION DATE: January 24,2011 CURRENT OPERATING CYCLE: A2C15 ANALYSIS OF RECORD Evaluation Model: ASTRUM (2004)

Calcu lation: Westinghouse WCAP 16841 P, November 2007 M M Fuel: VANTAGE+ 17 x 17 Limiting Fuel Type: VANTAGE+ 17 x 17 Limiting Single Failure: Loss of one train of ECCS flow Limiting Break Size and Location: Guillotine break in the Cold Leg Reference PCT: 2041.0 of MARGIN ALLOCATION A. PRIOR LOCA MODEL ASSESSMENTS I 10 CFR 50.46 report dated March 15, 2011 (see note 14)

Net PCT PCT = 2041.0 of B. CURRENT LOCA MODEL ASSESSMENTS No 2010 model changes, corrections, or enhancements ~PCT = 0 of Total PCT change from current assessments L 6PCT = 0 OF Cumulative PCT change from current assessments L I~PCT 1= 0 OF Net peT PCT = 2041.0 of Page 4 of 8

ATTACHMENT 1 Braidwood and Byron Stations, Units 1 and 2 10 CFR 50.46 Report PLANT NAME: Byron Station, Unit 1 ECCS EVALUATION MODEL: SBLOCA REPORT REVISION DATE: January 24,2011 CURRENT OPERATING CYCLE: B1C18*

• Cycle 18 scheduled to start April 2011 ANAL VSIS OF RECORD Evaluation Model: NOTRUMP Calculation: Westinghouse CN-L\S-00-208, December 2000 Fuel: VANTAGE+ 17 x 17 Limiting Fuel Type: VANTAGE+ 17 x 17 Limiting Single Failure: Loss of one train of ECCS flow Limiting Break Size and Location: 2" break in the bottom of the Cold Leg Reference PCT: 1624.0 of MARGIN ALLOCATION A. PRIOR LOCA MODEL ASSESSMENTS 10 CFR 50.46 report dated June 11, 2001 (see note 1) ~PCT= O°F 10 CFR 50.46 report dated April 18, 2002 (see note 2) ~PCT = 0 of 10 CFR 50.46 report dated April 14, 2003 (see note 3) ~PCT = 0 of 10 CFR 50.46 report dated April 14, 2004 (see note 4) ~PCT = 35 of 10 CFR 50.46 report dated April 14, 2005 (see note 5) ~PCT = 0 of 10 CFR 50.46 report dated April 14, 2006 (see note 6) ~PCT = 0 of 10 CFR 50.46 report dated April 13, 2007 (see note 7) ~PCT= O°F 10 CFR 50.46 report dated June 22, 2007 (see note 9) ~PCT = 0 of 10 CFR 50.46 report dated April 11, 2008 (see note 11) ~PCT = 90 OF 10 CFR 50.46 report dated April 9, 2009 (see note 12) ~PCT = 0 OF 10 CFR 50.46 report dated April 8, 2010 (see note 13) ~PCT = 0 OF Net PCT PCT =1749.0 OF B. CURRENT LOCA MODEL ASSESSMENTS Pellet Crack and Dish Volume Calculation (see note 16) ~PCT = 0 OF Treatment of Vessel Average Temperature Uncertainty ~PCT = 0 OF (see note 17)

General Code Maintenance (see note 18) ~PCT = 0 OF Total PCT change from current assessments L ~PCT = 0 OF Cumulative PCT change from current assessments L I~PCT 1= 0 OF Net PCT PCT = 1749.0 OF Page 5 of 8

ATTACHMENT 1 Braidwood and Byron Stations, Units 1 and 2 10 CFR 50.46 Report PLANT NAME: Byron Station, Unit 1 ECCS EVALUATION MODEL: LBLOCA REPORT REVISION DATE: January 24,2011 CURRENT OPERATING CYCLE: B1C18*

• Cycle 18 scheduled to start April 2011 ANALYSIS OF RECORD Evaluation Model: ASTRUM (2004)

Calculation: Westinghouse WCAP-16841, November 2007 Fuel: VANTAGE+ 17 x 17 Limiting Fuel Type: VANTAGE+ 17 x 17 Limiting Single Failure: Loss of one train of ECCS flow Limiting Break Size and Location: Guillotine break in the Cold Leg Reference PCT: 1913.0 of MARGIN ALLOCATION A. PRIOR LOCA MODEL ASSESSMENTS

\10 CFR 50.46 report dated March 15, 2011 (see note 14)

Net PCT PCT = 1913.0 of B. CURRENT LOCA MODEL ASSESSMENTS No 2010 model changes, corrections, or enhancements LlPCT = 0 of Total PCT change from current assessments L LlPCT = 0 of Cumulative peT change from current assessments L ILlPCT 1= 0 OF Net PCT PCT =1913.0 of Page 6 of 8

ATIACHMENT1 Braidwood and Byron Stations, Units 1 and 2 10 CFR 50.46 Report PLANT NAME: Byron Station, Unit 2 ECCS EVALUATION MODEL: SBLOCA REPORT REVISION DATE: January 24,2011 CURRENT OPERATING CYCLE: B2C16 ANALYSIS OF RECORD Evaluation Model: NOTRUMP Calculation: Westinghouse CN-US-00-208, December 2000 Fuel: VANTAGE+ 17 x 17 Limiting Fuel Type: VANTAGE+ 17 x 17 Limiting Single Failure: Loss of one train of ECCS flow Limiting Break Size and Location: 211 break in the bottom of the Cold Leg Reference PCT:

MARGIN ALLOCATION A. PRIOR LOCA MODEL ASSESSMENTS 10 CFR 50.46 report dated June 11, 2001 (see note 1) ~PCT = 3 of 10 CFR 50.46 report dated April 18, 2002 (see note 2) ~PCT = 0 of 10 CFR 50.46 report dated April 14, 2003 (see note 3) ~PCT = 0 of 10 CFR 50.46 report dated April 14, 2004 (see note 4) ~PCT = 35 of 10 CFR 50.46 report dated April 14, 2005 (see note 5) ~PCT= 0 of 10 CFR 50.46 report dated April 14,2006 (see note 6) ~PCT = 0 of 10 CFR 50.46 report dated April 13, 2007 (see note 7) ~PCT = 0 of 10 CFR 50.46 report dated May 10, 2007 (see note 8) ~PCT = 90 of 10 CFR 50.46 report dated June 22, 2007 (see note 9) ~PCT = 0 of 10 CFR 50.46 report dated April 11 ,2008 (see note 11) ~PCT = 0 of 10 CFR 50.46 report dated April 9, 2009 (see note 12) ~PCT = 0 of 10 CFR 50.46 report dated April 8, 2010 (see note 13) ~PCT = 0 of Net PCT PCT =1755.0 of B. CURRENT LOCA MODEL ASSESSMENTS Pellet Crack and Dish Volume Calculation (see note 16) ~PCT= O°F Treatment of Vessel Average Temperature Uncertainty ~PCT = 0 of (see note 17)

General Code Maintenance (see note 18) ~PCT = 0 of Total PCT change from current assessments L ~PCT = 0 OF Cumulative PCT change from current assessments L I~PCT 1= 0 of Net PCT PCT = 1755.0 of Page 7 of 8

ATTACHMENT 1 Braidwood and Byron Stations, Units 1 and 2 10 CFR 50.46 Report PLANT NAME: Byron Station, Unit 2 ECCS EVALUATION MODEL: LBLOCA REPORT REVISION DATE: January 24,2011 CURRENT OPERATING CYCLE: B2C16 ANALYSIS OF RECORD Evaluation Model: ASTRUM (2004)

Calculation: Westinghouse WCAP-16841-P, November 2007 Fuel: VANTAGE+ 17 x 17 Limiting Fuel Type: VANTAGE+ 17 x 17 Limiting Single Failure: Loss of one train of ECCS flow Limiting Break Size and Location: Guillotine break in the Cold Leg Reference PCT: 2041.0 of MARGIN ALLOCATION A. PRIOR LOCA MODEL ASSESSMENTS 110 CFR 50.46 report dated March 15, 2011 (see note 14)

Net PCT PCT =2041.0 of B. CURRENT LOCA MODEL ASSESSMENTS No 2010 model changes, corrections, or enhancements APCT= 0 OF Total PCT change from current assessments L APCT = 0 of Cumulative PCT change from current assessments L IAPCT 1= 0 OF Net PCT PCT =2041.0 of Page 8 of 8

ATTACHMENT 2 Braidwood and Byron Stations, Units 1 and 2 10 CFR 50.46 Report Assessment Notes

1. Prior Loss-of-Coolant Accident (LOCA) Model Assessment The 10 CFR 50.46 report dated June 11, 2001, reported a new small break loss-of-coolant accident (SBLOCA) analysis to support operations at uprated power conditions. The same report assessed the impact from annular axial blankets on SBLOCA analysis, which determined a 0 OF PCT penalty each for Braidwood Unit 1 and Byron Unit 1 and resulted in a 3 of PCT penalty each for Braidwood Unit 2 and Byron Unit 2. Evaluations for plant conditions and SBLOCA model changes that resulted in 0 OF PCT change were reported.

2. Prior LOCA Model Assessment The 10 CFR 50.46 report dated April 18, 2002, reported evaluations for SBLOCA model changes, which resulted in 0 of PCT change.

3. Prior LOCA Model Assessment The 10 CFR 50.46 report dated April 14, 2003, reported evaluations for SBLOCA model changes, which resulted in 0 OF PCT change.

4. Prior LOCA Model Assessment The 10 CFR 50.46 report dated April 14, 2004, reported evaluations for an SBLOCA assessment related to NOTRUMP bubble rise/drift flux model inconsistency corrections, which resulted in 35 of PCT assessment.

5. Prior LOCA Model Assessment The 10 CFR 50.46 report dated April 14, 2005, reported evaluations for SBLOCA model changes, which resulted in a 0 OF PCT change. Assembly N10S was reconstituted with two stainless steel filler rods during Braidwood Unit 1 Refueling Outage 11. This assembly was reloaded into the core and was used during Braidwood Unit 1 Cycle 12 operation. The introduction of up to five stainless steel filler rods was evaluated and shown to have no impact on SBLOCA analysis. The estimated PCT effect was 0 of. This assembly was discharged during Reload 12.

6. Prior LOCA Model Assessment The 10 CFR 50.46 report dated April 14, 2006, reported evaluations for SBLOCA NOTRUMP General Code Maintenance, which resulted in 0 of PCT change.

7. Prior LOCA Model Assessment The 10 CFR 50.46 report dated April 13, 2007, reported evaluations for SBLOCA model changes and errors. The report documented general code maintenance for NOTRUMP, AXIOM lead test assembly evaluation and NOTRUMP refined break spectrum, which resulted in 0° F PCT impact.

Page 1 of 4

ATTACHMENT 2 Braidwood and Byron Stations, Units 1 and 2 10 CFR 50.46 Report Assessment Notes

8. Prior LOCA Model Assessment The 30-day 10 CFR 50.46 report dated May 10, 2007, applicable to Byron Unit 2 reported an assessment of the Emergency Core Cooling System (ECCS), which evaluated changes in ECCS flow during the recirculation phase due to Generic Safety Issue (GSI) 191 related safety injection (SI) throttle valve replacements. The evaluation of recirculation phase ECCS flow changes relative to impact on the current Analysis of Record was performed for the SBLOCA. Based on the NOTRUMP and SBLOCA calculations performed for Byron Unit 2, a conservative, bounding PCT assessment of +90 of was applied to the current Byron Unit 2 SBLOCA PCT.

9. Prior LOCA Model Assessment A 30-day report was submitted to the NRC dated June 22,2007, to report an error in the HOT SPOT Gode, which did not impact the SBLOCA analysis. The 30-day report also reported minor errors with the reactor vessel data collections that potentially affected the vessel inlet and outlet fluid volume, metal mass, and surface area. The corrected values were evaluated for impact, and a 0 of penalty was assessed for the SBLOGA analysis for the Braidwood and Byron Stations, Units 1 and 2.

10. Prior LOGA Model Assessment The 30-day 10 CFR 50.46 report dated November 19, 2007, applicable to Braidwood Unit 1 reported an assessment of the EGGS, which evaluated changes in EGGS flow during the recirculation phase due to GSI-191 related SI throttle valve replacements. The evaluation of recirculation phase EGGS flow changes relative to impact on the current Analysis of Record was performed for the SBLOGA. Based on the NOTRUMP and SBLOCA calculations performed for Braidwood Unit 1, a conservative, bounding PCT assessment of +90 of was applied to the Braidwood Unit 1 SBLOGA PCT.

11 . Prior LOCA Model Assessment The 10 CFR 50.46 report dated April 11, 2008, reported evaluations for LOCA model changes and errors. Applicable to Braidwood Unit 2 and Byron Unit 1, the ECCS assessment evaluated changes in ECCS flow during the recirculation phase due to GSI-191 related SI throttle valve replacements. A conservative, bounding PCT assessment of +90 of was applied to the Braidwood Unit 2 and Byron Unit 1 SBLOCA PCTs. The report also documented general code maintenance for SBLOCA and evaluation for pump weir resistance modeling for SBLOCA analysis, which resulted in 0 of PCT impact.

12. Prior LOCA Model Assessment The 10 CFR 50.46 report dated April 9, 2009, reported evaluations for LOCA model changes and errors. The report documents general code maintenance for SBLOCA, errors in reactor vessel lower plenum surface area calculations, discrepancies in metal mass from drawings, and an evaluation of Areva Lead Use Assemblies (LUA). All have a 0 of PGT penalty associated with them.

Page 2 of 4

ATTACHMENT 2 Braidwood and Byron Stations, Units 1 and 2 10 CFR 50.46 Report Assessment Notes

13. Prior LOCA Model Assessment The 10 CFR 50.46 report dated April 8, 2010, reported no evaluations for SBLOCA model changes, which resulted in 0 of PCT change.

14. Prior LOCA Model Assessment The 30-day 10 CFR 50.46 report dated March 15, 2011, reported a new large break BELOCA (ASTRUM) analysis to support operations for the Braidwood and Byron Stations, Units 1 and 2. The same report assessed the impact from several errors, issues, and code enhancements. Each of these errors / issues / code enhancements resulted in 0 of PCT impact with a net 0 of PCT impact.

15. Urania-Gadolinia Pellet Thermal Conductivity Calculation (SBLOCA)

Two errors were discovered in the pellet thermal conductivity calculation for urania-gadolinia pellets in the SBLOCA code. First, the calculation did not include the terms required to adjust for pellet densities other than 95% of the theoretical density. Second, the conversion from Fahrenheit to Rankine used an adder of 459 instead of 459.67. These errors have been corrected and were evaluated for impact on SBLOCA analysis for Braidwood Station, Unit 1; a PCT assessment of 0 OF was applied to the Braidwood Station, Unit 1.

16. Pellet Crack and Dish Volume Calculation (SBLOCA)

Two errors were discovered in the calculation of the normalized peJlet crack and dish volumes in the SBLOCA code. First, an incorrect operator was used to select between two tables of normalized volume vs. linear heat generation rate. Second, the normalized volume at 18 kW/ft was incorrectly programmed in one of the tables as 1.58 instead of 1.59. These errors were evaluated for impact on existing SBLOCA analysis; based on a combination of SBLOCA sensitivity calculations and engineering judgment, a 0 of PCT penalty was assessed for the Braidwood and Byron Stations, Units 1 and 2.

17. Treatment of Vessel Average Temperature Uncertainty (SBLOCA)

Historically, the overall vessel average temperature uncertainty calculated by Westinghouse considered only II_II instrument uncertainties, corresponding to the indicated temperature being lower than the actual temperature. This uncertainty was then applied as a "+1-"

uncertainty in some LOCA analyses, rather than using specific "+11 and "_" uncertainties.

This discrepancy was evaluated for impact on the SBLOCA analysis results, and a 0 of PCT penalty was assessed for the Braidwood and Byron Stations, Units 1 and 2.

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ATTACHMENT 2 Braidwood and Byron Stations, Units 1 and 2 10 CFR 50.46 Report Assessment Notes

18. General Code Maintenance (SBLOCA)

Various changes have been made to enhance the usability of the codes and to help preclude errors in analyses. This includes items such as modifying input variable definitions, units, and defaults; improving the input diagnostic checks; enhancing the code output; optimizing active coding; and eliminating inactive coding. These changes resulted in 0 of PCT impact with a net 0 OF PCT impact.

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