RS-09-051, Annual 10 CFR 50 .46 Report of the Emergency Core Cooling System Evaluation Model Changes and Errors

Annual 10 CFR 50 .46 Report of the Emergency Core Cooling System Evaluation Model Changes and Errors

ML090990492
Person / Time
Site:	Byron, Braidwood
Issue date:	04/09/2009
From:	Simpson P Exelon Corp, Exelon Generation Co, Exelon Nuclear
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
RS-09-051
Download: ML090990492 (21)

Text

Exelon Nuclear wwwexeloncorp.com 4300 Wlnfield Road Warrenville, IL 60555 RS-09-051 10 CFR 50.46 April 9, 2009 U. S. Nuclear Regulatory Commission ATTN : Document Control Desk Washington, DC 20555-0001 Respectfully, Patrick R. Simpson Manager - Licensing 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 ioM Ck)

Nuclear Subject :

Annual 10 CFR 50.46 Report of the Emergency Core Cooling System Evaluation Model Changes and Errors 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 Braidwood Station, Units 1 and 2 and Byron Station, Units 1 and 2. provides updated information regarding the peak cladding temperature for the limiting small break and large break loss-of-coolant accident evaluations for the Braidwood and Byron Stations. Attachment 2 contains a detailed description and assessment for each change or error reported.

There are no regulatory commitments contained in this letter. If you have any questions concerning this letter, please contact Ms. Lisa A. Schofield at (630) 657-2815.

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

PLANT NAME :

ECCS EVALUATION MODEL:

REPORT REVISION DATE :

CURRENT OPERATING CYCLE :

• Cycle 15 to start April 2009 ANALYSIS OF RECORD Evaluation Model:

Calculation :

Fuel :

Limiting Fuel Type:

Limiting Single Failure:

Limiting Break Size and Location :

Reference Peak Cladding Temperature (PCT) :

MARGIN ALLOCATION Net PCT ATTACHMENT 1 Braidwood and Byron, Units 1 and 2 10 CFR 50.46 Report Braidwood Station, Unit 1 Small Break Loss-of-Coolant Accident (SBLOCA)

March 6, 2009 A1 C15*

NOTRUMP Westinghouse CN-LIS-00-208, December 2000 VANTAGE+ 17 x 17 VANTAGE+ 17 x 17 Loss of one train of ECCS flow 2" break in the bottom of the Cold Leg 1624.0° F A. PRIOR LOSS-OF-COOLANT ACCIDENT (LOCA) MODEL ASSESSMENTS Page 1 of 16 PCT = 1749.0°F 10 CFR 50.46 report dated June 11, 2001 (see note 1)

APCT = 0 °F 10 CFR 50.46 report dated April 18, 2002 (see note 2)

APCT = 0 °F 10 CFR 50.46 report dated April 14, 2003 (see note 3)

APCT = 0 °F 10 CFR 50.46 report dated April 14, 2004 (see note 4)

APCT = 35 °F 10 CFR 50.46 report dated April 14, 2005 (see note 5)

APCT = 0 °F 10 CFR 50.46 report dated April 14, 2006 (see note 6)

APCT = 0 °F 10 CFR 50.46 report dated April 13, 2007 (see note 7) 4PCT = 0 °F 10 CFR 50.46 report dated June 22, 2007 (see note 9)

APCT = 0 °F 10 CFR 50.46 report dated November 19, 2007 (see note 10)

APCT = 90 °F 10 CFR 50.46 report dated April 11, 2008 (see note 11)

APCT = 0 °F

B. CURRENT LOCA MODEL ASSESSMENTS ATTACHMENT 1 Braidwood and Byron, Units 1 and 2 10 CFR 50.46 Report Net PCT PCT = 1749.0°F Page 2 of 16 Errors in reactor vessel lower plenum surface area calculations see note 14 APCT = 0 °F Discrepancy in metal masses used from drawings see note 15 APCT = 0 °F General code maintenance (see note 16)

APCT = 0 °F AREVA Lead Use Assembly (see note 19)

APCT = 0 °F Total PCT change from current assessments APCT = 0 °F Cumulative PCT change from current assessments oPCT = O -F

PLANT NAME :

ECCS EVALUATION MODEL:

REPORT REVISION DATE :

CURRENT OPERATING CYCLE :

• Cycle 15 to start April 2009 ANALYSIS OF RECORD Evaluation Model :

Calculation :

Fuel :

Limiting Fuel Type:

Limiting Single Failure:

Limiting Break Size and Location :

Reference PCT:

MARGIN ALLOCATION A. PRIOR LOCA MODEL ASSESSMENTS Net PCT ATTACHMENT 1 Braidwood and Byron, Units 1 and 2 10 CFR 50.46 Report Braidwood Station, Unit 1 Large Break Loss-of-Coolant Accident (LBLOCA)

March 6, 2009 A1C15*

CQD (1996)

Westinghouse CN-LIS-00-7, September 2000 VANTAGE+ 17 x 17 VANTAGE+ 17 x 17 Loss of one train of ECCS flow Guillotine break in the Cold Leg 2044.0° F Page 3 of 16 PCT = 2081.0°F 10 CFR 50.46 report dated June 11, 2001 (see note 1)

APCT = 12 °F 10 CFR 50.46 report dated April 18, 2002 (see note 2)

APCT = 0 °F 10 CFR 50.46 report dated April 14, 2003 (see note 3)

APCT = 0 °F 10 CFR 50.46 report dated April 14, 2004 (see note 4)

APCT = 0 °F 10 CFR 50.46 report dated April 14, 2005 (see note 5)

APCT = 5 °F 10 CFR 50.46 report dated April 14, 2006 (see note 6)

APCT = 0 °F 10 CFR 50.46 report dated April 13, 2007 (see note 7)

APCT = 0 °F 10 CFR 50.46 report dated June 22, 2007 (see note 9)

APCT = 20 °F 10 CFR 50.46 report dated November 19, 2007 (see note 10)

APCT = 0 °F 10 CFR 50.46 report dated April 11, 2008 (see note 11)

APCT = 0 °F

B. CURRENT LOCA MODEL ASSESSMENTS ATTACHMENT 1 Braidwood and Byron, Units 1 and 2 10 CFR 50.46 Report Net PCT PCT = 2161.0°F Page 4 of 16 Axial power shape distribution envelope violation (see note 12)

APCT = 80 °F HOTSPOT burst temperature logic errors (see note 13) oPCT = 0 °F General code maintenance (see note 17) oPCT = 0 °F CCFL global volume error (see note 18) oPCT= 0 °F AREVA Lead Use Assembly (see note 19)

APCT = 0 °F Total PCT change from current assessments Y-APCT = 80 of Cumulative PCT change from current assessments APCT = 80 °F

PLANT NAME :

ECCS EVALUATION MODEL:

REPORT REVISION DATE :

CURRENT OPERATING CYCLE:

ANALYSIS OF RECORD Evaluation Model:

Calculation :

Fuel :

Limiting Fuel Type:

Limiting Single Failure :

Limiting Break Size and Location :

Reference PCT:

MARGIN ALLOCATION A. PRIOR LOCA MODEL ASSESSMENTS Net PCT ATTACHMENT 1 Braidwood and Byron, Units 1 and 2 10 CFR 50.46 Report Braidwood Station, Unit 2 SBLOCA March 6, 2009 A2C14 NOTRUMP Westinghouse CN-LIS-00-208, December 2000 VANTAGE+ 17 x 17 VANTAGE+ 17 x 17 Loss of one train of ECCS flow 2" break in the bottom of the Cold Leg 1627.0°F Page 5 of 16 PCT = 1755.0°F 10 CFR 50.46 report dated June 11, 2001 (see note 1)

APCT = 3 °F 10 CFR 50.46 report dated April 18, 2002 (see note 2)

APCT = 0 °F 10 CFR 50.46 report dated April 14, 2003 (see note 3)

APCT = 0 °F 10 CFR 50.46 report dated April 14, 2004 (see note 4)

APCT = 35 °F 10 CFR 50.46 report dated April 14, 2005 (see note 5)

APCT = 0 °F 10 CFR 50.46 report dated April 14, 2006 (see note 6)

APCT = 0 °F 10 CFR 50.46 report dated April 13, 2007 (see note 7)

APCT = 0 °F 1 0 CFR 50.46 report dated June 22, 2007 (see note 9)

APCT = 0 °F 10 CFR 50.46 report dated April 11, 2008 (see note-1 1) ---~ APCT = 90 °F

B. CURRENT LOCA MODEL ASSESSMENTS ATTACHMENT 1 Braidwood and Byron, Units 1 and 2 10 CFR 50.46 Report Net PCT PCT = 1755.0°F Page 6 of 16 Errors in reactor vessel lower plenum surface area calculations see note 14 4PCT = 0 °F Discrepancy in metal masses used from drawings see note 15 4PCT = 0 °F General code maintenance (see note 16) 4PCT = 0 °F Total PCT change from current assessments Y. APCT = 0 °F Cumulative PCT change from current assessments E APCT 1=0 017

PLANT NAME :

ECCS EVALUATION MODEL:

REPORT REVISION DATE :

CURRENT OPERATING CYCLE:

ANALYSIS OF RECORD Evaluation Model:

Calculation:

Fuel :

Limiting Fuel Type:

Limiting Single Failure:

Limiting Break Size and Location :

Reference PCT:

MARGIN ALLOCATION A. PRIOR LOCA MODEL ASSESSMENTS Net PCT ATTACHMENT 1 Braidwood and Byron, Units 1 and 2 10 CFR 50.46 Report Braidwood Station, Unit 2 LBLOCA March 6, 2009 A2C 14 CQD (1996)

Westinghouse CN-LIS-00-7, September 2000 VANTAGE+ 17 x 17 VANTAGE+ 17 x 17 Loss of one train of ECCS flow Guillotine break in the Cold Leg 2088.0° F Page 7 of 16 PCT = 2168.0°F 10 CFR 50.46 report dated June 11, 2001 (see note 1)

APCT = 12 °F 10 CFR 50.46 report dated April 18, 2002 (see note 2)

APCT = 0 °F 10 CFR 50.46 report dated April 14, 2003 (see note 3)

APCT = 0 °F 10 CFR 50.46 report dated April 14, 2004 (see note 4)

APCT = 0 °F 10 CFR 50.46 report dated April 14, 2005 (see note 5)

APCT = 5 °F 10 CFR 50.46 report dated April 14, 2006 (see note 6)

APCT = 0 °F 10 CFR 50.46 report dated April 13, 2007 (see note 7)

APCT = 0 °F 10 CFR 50.46 report dated June 22, 2007 (see note 9)

APCT = 55 °F 10 CFR 50.46 report dated April 11, 2008 (see note 11)

APCT = 8 °F

B. CURRENT LOCA MODEL ASSESSMENTS ATTACHMENT 1 Braidwood and Byron, Units 1 and 2 10 CFR 50.46 Report Net PCT PCT = 2168.0°F Page 8 of 16 HOTSPOT burst temperature logic errors (see note 13)

OPCT = 0 °F General code maintenance (see note 17)

APCT = 0 °F CCFL global volume error (see note 18) 4PCT = 0 °F Total PCT change from current assessments Y-4PCT = 0 °F Cumulative PCT change from current assessments Y APCT = 0 °F

PLANT NAME :

ECCS EVALUATION MODEL:

REPORT REVISION DATE :

CURRENT OPERATING CYCLE:

ANALYSIS OF RECORD Evaluation Model:

Calculation:

Fuel :

Limiting Fuel Type:

Limiting Single Failure :

Limiting Break Size and Location :

Reference PCT:

MARGIN ALLOCATION A. PRIOR LOCA MODEL ASSESSMENTS Net PCT ATTACHMENT 1 Braidwood and Byron, Units 1 and 2 10 CFR 50.46 Report Byron Station, Unit 1 SBLOCA March 6, 2009 B1C16 NOTRUMP Westinghouse CN-LIS-00-208, December 2000 VANTAGE+ 17 x 17 VANTAGE+ 17 x 17 Loss of one train of ECCS flow 2" break in the bottom of the Cold Leg 1624.0° F Page 9 of 16 PCT =1749.0°F 10 CFR 50.46 report dated June 11, 2001 (see note 1)

APCT = 0 °F 10 CFR 50.46 report dated April 18, 2002 (see note 2)

APCT = 0 °F 10 CFR 50.46 report dated April 14, 2003 (see note 3)

APCT = 0 °F 10 CFR 50.46 report dated April 14, 2004 (see note 4)

APCT = 35 °F 10 CFR 50.46 report dated April 14, 2005 (see note 5)

APCT = 0 °F 10 CFR 50.46 report dated April 14, 2006 (see note 6)

APCT = 0 °F 10 CFR 50.46 report dated April 13, 2007 (see note 7)

APCT = 0 °F 10 CFR 50.46 report dated June 22, 2007 (see note 9)

APCT = 0 °F 10 CFR 50.46 report dated April 11, 2008 (see note 11)

APCT = 90 °F

B. CURRENT LOCA MODEL ASSESSMENTS ATTACHMENT 1 Braidwood and Byron, Units 1 and 2 10 CFR 50.46 Report Net PCT PCT = 1749.0°F Page 10 of 16 Errors in reactor vessel lower plenum surface area calculations see note 14 OPCT = 0 °F Discrepancy in metal masses used from drawings see note 15 OPCT = 0 °F General code maintenance (see note 16)

APCT = 0 °F Total PCT change from current assessments I APCT = 0 °F Cumulative PCT change from current assessments Y-O PCT = 0 °F

PLANT NAME :

ECCS EVALUATION MODEL:

REPORT REVISION DATE :

CURRENT OPERATING CYCLE:

ANALYSIS OF RECORD Evaluation Model :

Calculation :

Fuel :

Limiting Fuel Type:

Limiting Single Failure:

Limiting Break Size and Location :

Reference PCT:

MARGIN ALLOCATION A. PRIOR LOCA MODEL ASSESSMENTS Net PCT ATTACHMENT 1 Braidwood and Byron, Units 1 and 2 10 CFR 50.46 Report Byron Station, Unit 1 LBLOCA March 6, 2009 B1 C16 CQD (1996)

Westinghouse CN-LIS-00-7, September 2000 VANTAGE+ 17 x 17 VANTAGE+ 17 x 17 Loss of one train of ECCS flow Guillotine break in the Cold Leg 2044.0°F Page 1 1 of 16 PCT = 2161.0°F 10 CFR 50.46 report dated June 11, 2001 (see note 1)

APCT = 12 °F 10 CFR 50.46 report dated April 18, 2002 (see note 2)

APCT = 0 °F 10 CFR 50.46 report dated April 14, 2003 (see note 3)

APCT = 0 °F 10 CFR 50.46 report dated April 14, 2004 (see note 4)

APCT = 0 °F 10 CFR 50.46 report dated April 14, 2005 (see note 5)

APCT = 5 °F 10 CFR 50.46 report dated April 14, 2006 (see note 6)

APCT = 0 °F 10 CFR 50.46 report dated April 13, 2007 (see note 7)

APCT = 0 °F 10 CFR 50.46 report dated June 22, 2007 (see note 9)

APCT = 20 °F 10 CFR 50.46 report dated April 11, 2008 (see note 11)

APCT = 80 °F

B. CURRENT LOCA MODEL ASSESSMENTS ATTACHMENT 1 Braidwood and Byron, Units 1 and 2 10 CFR 50.46 Report Net PCT PCT = 2161.0°F Page 12 of 16 HOTSPOT burst temperature logic errors (see note 13)

APCT = 0 °F General code maintenance (see note 17)

OPCT = 0 °F CCFL global volume error (see note 18)

APCT = 0 °F Total PCT change from current assessments Y-APCT = 0 °F Cumulative PCT change from current assessments Y OPCT = 0 °F

PLANT NAME :

ECCS EVALUATION MODEL:

REPORT REVISION DATE :

CURRENT OPERATING CYCLE:

ANALYSIS OF RECORD Evaluation Model:

Calculation:

Fuel :

Limiting Fuel Type:

Limiting Single Failure :

Limiting Break Size and Location :

Reference PCT:

MARGIN ALLOCATION A. PRIOR LOCA MODEL ASSESSMENTS Net PCT ATTACHMENT 1 Braidwood and Byron, Units 1 and 2 10 CFR 50.46 Report Byron Station, Unit 2 SBLOCA March 6, 2009 B2C 15 NOTRUMP Westinghouse CN-LIS-00-208, December 2000 VANTAGE+ 17 x 17 VANTAGE+ 17 x 17 Loss of one train of ECCS flow 2" break in the bottom of the Cold Leg 1627.0° F Page 1 3 of 16 PCT = 1755.0°F 10 CFR 50.46 report dated June 11, 2001 (see note 1)

APCT = 3 °F 10 CFR 50.46 report dated April 18, 2002 (see note 2)

APCT = 0 °F 10 CFR 50.46 report dated April 14, 2003 (see note 3)

APCT = 0 °F 10 CFR 50.46 report dated April 14, 2004 (see note 4)

APCT = 35 °F 10 CFR 50.46 report dated April 14, 2005 (see note 5)

APCT = 0 °F 10 CFR 50.46 report dated April 14, 2006 (see note 6)

APCT = 0 °F 10 CFR 50.46 report dated April 13, 2007 (see note 7)

APCT = 0 °F 10 CFR 50.46 report dated May 10, 2007 (see note 8)

APCT = 90 °F 10 CFR 50.46 report dated June 22, 2007 (see note 9)

APCT = 0 °F 10 CFR 50.46 report dated April 11, 2008 (see note 11)

APCT = 0 °F

B. CURRENT LOCA MODEL ASSESSMENTS ATTACHMENT 1 Braidwood and Byron, Units 1 and 2 10 CFR 50.46 Report Net PCT PCT = 1755.0°F Page 14 of 16 Errors in reactor vessel lower plenum surface area calculations see note 14 APCT = 0 °F Discrepancy in metal masses used from drawings see note 15 APCT = 0 °F General code maintenance (see note 16)

APCT = 0 °F Total PCT change from current assessments Y-APCT = 0 °F Cumulative PCT change from current assessments Y-OPCT = 0 °F

PLANT NAME :

ECCS EVALUATION MODEL:

REPORT REVISION DATE :

CURRENT OPERATING CYCLE:

ANALYSIS OF RECORD Evaluation Model:

Calculation :

Fuel :

Limiting Fuel Type:

Limiting Single Failure:

Limiting Break Size and Location :

Reference PCT:

MARGIN ALLOCATION A. PRIOR LOCA MODEL ASSESSMENTS Net PCT ATTACHMENT 1 Braidwood and Byron, Units 1 and 2 10 CFR 50.46 Report Byron Station, Unit 2 LBLOCA March 6, 2009 B2C15 CQD (1996)

Westinghouse CN-LIS-00-7, September 2000 VANTAGE+ 17 x 17 VANTAGE+ 17 x 17 Loss of one train of ECCS flow Guillotine break in the Cold Leg 2088.0° F Page 1 5 of 16 PCT = 2168.0°F 10 CFR 50.46 report dated June 11, 2001 (see note 1)

APCT = 12 °F 10 CFR 50.46 report dated April 18, 2002 (see note 2)

APCT = 0 °F 10 CFR 50.46 report dated April 14, 2003 (see note 3)

PCT = 0 °F 10 CFR 50.46 report dated April 14, 2004 (see note 4)

APCT = 0 °F 10 CFR 50.46 report dated April 14, 2005 (see note 5)

PCT = 5 °F 10 CFR 50.46 report dated April 14, 2006 (see note 6)

APCT = 0 °F 10 CFR 50.46 report dated April 13, 2007 (see note 7)

APCT = 8 °F 10 CFR 50.46 report dated May 10, 2007 (see note 8)

APCT = 0 °F 10 CFR 50.46 report dated June 22, 2007 (see note 9)

APCT = 55 °F 10 CFR 50.46 report dated April 11, 2008 (see note-1 1)

APCT = 0 °F

B. CURRENT LOCA MODEL ASSESSMENTS ATTACHMENT 1 Braidwood and Byron, Units 1 and 2 10 CFR 50.46 Report Net PCT PCT = 2168.0°F Page 1 6 of 16 HOTSPOT burst temperature logic errors (see note 13)

APCT = 0 °F General code maintenance (see note 17)

APCT = 0 °F CCFL global volume error (see note 18)

APCT = 0 °F Total PCT change from current assessments I APCT = O 'F Cumulative PCT change from current assessments PCT = 0 °F

2.

Prior LOCA Model Assessment

3.

Prior LOCA Model Assessment

4. Prior LOCA Model Assessment 5.

Prior LOCA Model Assessment ATTACHMENT 2 Braidwood and Byron, 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 new large break loss-of-coolant accident (LBLOCA) and small break loss-of-coolant accident (SBLOCA) analyses to support operations at uprated power conditions. The same report assessed the impact from decay heat uncertainty error in Monte Carlo calculations on LBLOCA analysis and the impact from annular axial blankets on SBLOCA analysis. Evaluations for plant conditions and LBLOCA and SBLOCA model changes that resulted in 0°F PCT change were reported. Cycle specific evaluations related to axial power shape distribution envelope violation were reported for the applicable operating cycles.

The 10 CFR 50.46 report dated April 18, 2002, reported evaluations for LBLOCA and SBLOCA model changes, which resulted in 0°F PCT change. Cycle specific evaluations related to axial power shape distribution envelope violation were reported for the applicable operating cycles.

The 10 CFR 50.46 report dated April 14, 2003, reported evaluations for LBLOCA and SBLOCA model changes which resulted in 0°F PCT change. Cycle specific evaluations related to axial power shape distribution envelope violation were reported for the applicable operating cycles.

The 10 CFR 50.46 report dated April 14, 2004, reported evaluations for LBLOCA model changes, which resulted in 0°F PCT change. A SBLOCA assessment related to NOTRUMP bubble rise/drift flux model inconsistency corrections, which resulted in 35°F PCT assessment, was reported. Cycle specific evaluations related to axial power shape distribution envelope violation were reported for the applicable operating cycles.

The 10 CFR 50.46 report dated April 14, 2005, reported evaluations for LBLOCA model changes, which resulted in a 5°F PCT change due to the Revised Blowdown Heatup Uncertainty Calculation. 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 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 LBLOCA and SBLOCA analyses. The estimated PCT effect was 0°F. This assembly was discharged during Reload 12. Cycle-specific evaluations related to axial power shape distribution envelope violation were reported for the applicable operating cycles.

6. Prior LOCH Model Assessment

7. Prior LOCA Model Assessment

8.

Prior LOCA Model Assessment

9.

Prior LOCA Model Assessment

10. Prior LOCA Model Assessment ATTACHMENT 2 Braidwood and Byron, Units 1 and 2 10 CFR 50.46 Report Assessment Notes The 10 CFR 50.46 report dated April 14, 2006, reported evaluations for LBLOCA model changes, which resulted in a 0°F PCT change due to the Revised Iteration Algorithm for Calculating the Average Fuel Temperature, Pellet Radial Profile, Improved Automation of End of Blowdown Time, Thermodynamic Properties from THERMO, Vessel Unheated Conductor Noding and Containment Relative Humidity Assumption. NOTRUMP General Code Maintenance resulted in 0°F change for SBLOCA. Cycle specific evaluations related to axial power shape distribution envelope violation were reported for the applicable operating cycles.

The 10 CFR 50.46 report dated April 13, 2007, reported evaluations for LOCA model changes and errors. The report documented general code maintenance for NOTRUMP, containment heat sink addition evaluation, AXIOM lead test assembly evaluation and NOTRUMP refined break spectrum, which resulted in 0°F PCT impact. Cycle specific evaluations related to axial power shape distribution envelope violation were reported for the applicable operating cycles.

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 and LBLOCA. The LBLOCA analysis was unaffected and a 0°F penalty was assessed. Based on the NOTRUMP and SBLOCTA calculations performed for Byron Unit 2, a conservative, bounding PCT assessment of +90°F was applied to the current Byron Unit 2 SBLOCA PCT.

A 30-day report was submitted to the NRC dated June 22, 2007, to report an error in the HOTSPOT code, which resulted in an increase of 55°F in the LBLOCA PCT for Braidwood Unit 2 and Byron Unit 2 and a 20°F LBLOCA PCT increase for Braidwood Unit 1 and Byron Unit 1. In addition, the 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°F penalty was assessed for Byron Units 1 and 2, and Braidwood Units 1 and 2, SBLOCA analysis. The LBLOCA analyses were not affected by these minor errors.

The 30-day 10 CFR 50.46 report dated November 19, 2007, applicable to Braidwood Unit 1 reported an assessment of the Emergency Core Cooling System (ECCS), which evaluated changes in ECCS flow during the recirculation phase due to GSI-191 related SI throttle Page 2 of 4

11. Prior LOCA Model Assessment ATTACHMENT 2 Braidwood and Byron, Units 1 and 2 10 CFR 50.46 Report Assessment Notes valve replacements. The evaluation of recirculation phase ECCS flow changes relative to impact on the current Analysis of Record was performed for the SBLOCA and LBLOCA.

The LBLOCA analysis was unaffected and a 0°F penalty was assessed. Based on the NOTRUMP and SBLOCTA calculations performed for Braidwood Unit 1, a conservative, bounding PCT assessment of +90°F was applied to the current Braidwood Unit 1 SBLOCA PCT.

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 safety injection SI throttle valve replacements. A conservative, bounding PCT assessment of +90°F 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 analyses, which resulted in 0 °F PCT impact.

Cycle specific evaluations related to axial power shape distribution envelope violation were reported for the applicable operating cycles.

12. Axial Power Shape Distribution Envelope Violation (PMID, PBOT)

The LBLOCA analysis is performed based on assuming an axial power shape distribution envelope (PMID, PBOT), where PMID is the power in the middle one-third of the core ; and PBOT is the power in the lower one-third of the core. The envelope is pertinent to the BELOCA analysis and is presented as Figure 11-1 of WCAP-15585, "Best Estimate Analysis of the Large Break Loss of Coolant Accident for the Byron /Braidwood Units 1 and 2 Nuclear Plant," November 2000. For every reload cycle Westinghouse verifies that the envelope remains limiting.

If there is a violation then a PCT penalty is calculated.

For Braidwood Unit 1 Cycle 15, there was a violation and a PCT penalty of 80°F was calculated, which was first reported for Braidwood Unit 1 Cycle 11 in the 10 CFR 50.46 notification to the NRC, dated April 14, 2003. The assessment for the Braidwood Unit 1 Cycle 15 does not affect the net PCT.

13. HOTSPOT Burst Temperature Logic Errors (LBLOCA)

The HOTSPOT code has been updated to incorporate the following corrections to the burst temperature logic:

(1) change the rod internal pressure used to calculate the cladding engineering hoop stress from the value in the previous time step to the value in the current time step ;

(2) revise the average cladding heatup rate calculation to reset selected variables to zero at the beginning of each trial and use the instantaneous heat-up rate when fewer than five values are available; and (3) reflect the assumed saturation of ramp rate effects above 28°C/s for Zircaloy-4 cladding.

Sample calculations for each change showed no effect on PCT, leading to an estimated impact of 0°F.

Page 3 of 4

16. General Code Maintenance (SBLOCA) 17. General Code Maintenance (LBLOCA) 18. CCFL Global Volume Error (LBLOCA)

ATTACHMENT 2 Braidwood and Byron, Units 1 and 2 10 CFR 50.46 Report Assessment Notes 14. Errors in Reactor Vessel Lower Plenum Surface Area Calculations (SBLOCA)

Two errors were discovered in the calculations of reactor vessel lower plenum surface area.

The differences are relatively minor and are expected to have a negligible effect on small break LOCA analysis results, leading to an estimated PCT impact of 0°F.

15. Discrepancy in Metal Masses Used from Drawings (SBLOCA)

Discrepancies were discovered in the use of metal masses from drawings. The updated reactor vessel metal masses and fluid volumes have been evaluated. The differences in reactor vessel metal mass and fluid volume are relatively minor and would be expected to produce a negligible effect on small break LOCA analysis results, leading to an estimated PCT impact of 0°F.

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. The nature of these changes leads to an estimated PCT impact of 0°F.

A number of coding changes were made as a part of normal code maintenance. Examples include additional information in code outputs, improved automation and diagnostics in the codes, increased code dimensions, and general code cleanup. The nature of these changes leads to an estimated PCT impact of 0°F.

An error was identified during the course of a recent Best Estimate LBLOCA analysis in which the volume between the core barrel and the baffle plates in the counter-current flow limiting (CCFL) region above the active fuel length was modeled incorrectly. The corrected values have been evaluated for impact on the current licensing-basis analysis results. The CCFL global volume modeling error has been evaluated to have a negligible impact on PCT for affected analyses and a penalty of 0°F is assigned.

19. AREVA Lead Use Assembly (LBLOCA and SBLOCA)

Eight AREVA Lead Use Assemblies (LUA) will be loaded into the Braidwood Unit 1 Cycle 15 core. AREVA has determined that an eight percent radial peaking penalty in the AREVA fuel assemblies relative to the.co-resident Westinghouse fuel assures that the PCT of the LUAs will be less than that of the Westinghouse fuel. Westinghouse concluded that the LUAs have a negligible impact on the Westinghouse resident fuel and no Peak Cladding Temperature penalty is required. A penalty of 0°F is assigned.

Page 4 of 4