Text

Annual 10 CFR 50.46 Report of Emergency Core Cooling System Evaluation Model Changes and Errors
	ML15097A126
Person / Time
Site:	Byron, Braidwood
Issue date:	04/07/2015
From:	Gullott D; Exelon Generation Co
To:	; Document Control Desk, Office of Nuclear Reactor Regulation
References
	RS-15-106
	Download: ML15097A126 (26)
	v • d • e

4300 Winfield Road 441.111, Warrenville. IL 60555 s'"Bw Exelon Generation 630 657 2000 Office RS-15-106 10 CFR 50.46 April 7, 2015 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 50-457 Byron Station, Units 1 and 2 Facility Operating License Nos. NPF-37 and NPF-66 NRC Docket Nos. STN 50-454 and 50-455

Subject:

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

Reference:

Letter from D. M. Gullott (Exelon Generation Company, LLC) to U.S. NRC, "Annual 10 CFR 50.46 Report of Emergency Core Cooling System Evaluation Model Changes and Errors," dated April 7, 2014 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 and Byron Stations, Units 1 and 2. The attachments describe the changes in accumulated peak cladding temperature (PCT) since the previous annual report submitted in the referenced letter.

There are no regulatory commitments contained in this submittal. Should you have any questions concerning this letter, please contact Jessica Krejcie at (630) 657-2816.

Respectfully, 442ifi:y David M. Gullott 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

April 7, 2015 U. S. Nuclear Regulatory Commission Page 2 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 Byron and Braidwood 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: 04/07/15 CURRENT OPERATING CYCLE: 18 ANALYSIS OF RECORD (AOR)

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-inch Break in the Bottom of the Cold Leg Reference Peak Cladding Temperature (PCT) PCT = 1624.0°F MARGIN ALLOCATION A. PRIOR LOSS OF COOLANT ACCIDENT (LOCA) MODEL ASSESSMENTS 10 CFR 50.46 report dated June 11, 2001 (Note 1) APCT = 0°F 10 CFR 50.46 report dated April 18, 2002 (Note 2) APCT = 0 °F 10 CFR 50.46 report dated April 14, 2003 (Note 3) APCT = 0 °F 10 CFR 50.46 report dated April 14, 2004 (Note 4) APCT = 35 °F 10 CFR 50.46 report dated April 14, 2005 (Note 5) APCT = 0 °F 10 CFR 50.46 report dated April 14, 2006 (Note 6) APCT = 0 °F 10 CFR 50.46 report dated April 13, 2007 (Note 7) APCT = 0 °F 10 CFR 50.46 report dated June 22, 2007 (Note 9) APCT = 0 °F 10 CFR 50.46 report dated November 19, 2007 (Note 10) APCT = 90 °F 10 CFR 50.46 report dated April 11, 2008 (Note 11) APCT = 0 °F 10 CFR 50.46 report dated April 9, 2009 (Note 12) APCT = 0 °F 10 CFR 50.46 report dated April 8, 2010 (Note 13) APCT = 0 °F 10 CFR 50.46 report dated April 6, 2011 (Note 15) APCT = 0 °F 10 CFR 50.46 report dated April 6, 2012 (Note 17) APCT = 0 °F 10 CFR 50.46 report dated April 5, 2013 (Note 19) APCT = 0 °F 10 CFR 50.46 report dated April 7, 2014 (Note 21) APCT = 0 °F NET PCT PCT = 1749.0°F Page 1 of 12

Attachment 1 Byron and Braidwood Units 1 and 2 10 CFR 50.46 Report B. CURRENT LOCA MODEL ASSESSMENTS General Code Maintenance (Note 22) APCT = 0 °F Fuel Rod Gap Conductance Error (Note 24) APCT = 0 °F Radiation Heat Transfer Model Error (Note 25) APCT = 0 °F SBLOCTA Pre-DNB Cladding Surface Heat Transfer Coefficient APCT = 0 °F Calculation (Note 26)

Evaluation of Change in Safety injection and Containment Spray APCT = 0 °F (Note 27)

Evaluation of an Increased Auxiliary Feedwater Switchover Delay APCT = 0 °F (Note 29)

Total PCT change from current assessments E APCT = 0 °F Cumulative PCT change from current assessments / I APCT I = 0 °F NET PCT PCT = 1749.0°F Page 2 of 12

Attachment 1 Byron and Braidwood Units 1 and 2 10 CFR 50.46 Report PLANT NAME: Braidwood Station Unit 1 ECCS EVALUATION MODEL: Large Break Loss of Coolant Accident (LBLOCA)

REPORT REVISION DATE: 04/07/15 CURRENT OPERATING CYCLE: 18 AOR 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 POT = 1913.0°F MARGIN ALLOCATION A. PRIOR LOSS OF COOLANT ACCIDENT (LOCA) MODEL ASSESSMENTS 10 CFR 50.46 report dated March 15, 2011 (Note 14) APCT = 0°F 10 CFR 50.46 report dated April 6, 2011 (Note 15) APCT = 0 °F 10 CFR 50.46 report dated April 6, 2012 (Note 17) APCT = 0 °F 10 CFR 50.46 report dated May 21, 2012 (Note 18) APCT = 44 °F 10 CFR 50.46 report dated April 5, 2013 (Note 19) APCT = 0°F 10 CFR 50.46 report dated February 27, 2014 (Note 20) APCT = 66 °F 10 CFR 50.46 report dated April 7, 2014 (Note 21) APCT = 0 °F NET PCT PCT = 2023.0°F B. CURRENT LOCA MODEL ASSESSMENTS General Code Maintenance (Note 22) APCT = 0 °F Errors in Decay Group Uncertainty Factors (Note 23) APCT = 0 °F Evaluation of Change in Safety Injection and Containment Spray APCT = +2 °F Flow Rates (Note 28)

Total PCT change from current assessments E APCT = +2 °F Cumulative PCT change from current assessments I APCT I = 2 °F NET PCT PCT = 2025.0°F Page 3 of 12

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

REPORT REVISION DATE: 04/07/15 CURRENT OPERATING CYCLE: 18 AOR 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-inch Break in the Bottom of the Cold Leg Reference PCT PCT = 1627.0°F MARGIN ALLOCATION A. PRIOR LOCA MODEL ASSESSMENTS 10 CFR 50.46 report dated June 11, 2001 (Note 1) APCT = 3 °F 10 CFR 50.46 report dated April 18, 2002 (Note 2) APCT = 0°F 10 CFR 50.46 report dated April 14, 2003 (Note 3) APCT = 0 °F 10 CFR 50.46 report dated April 14, 2004 (Note 4) APCT = 35 °F 10 CFR 50.46 report dated April 14, 2005 (Note 5) APCT = 0 °F 10 CFR 50.46 report dated April 14, 2006 (Note 6) APCT = 0 °F 10 CFR 50.46 report dated April 13, 2007 (Note 7) APCT = 0 °F 10 CFR 50.46 report dated June 22, 2007 (Note 9) APCT = 0 °F 10 CFR 50.46 report dated April 11, 2008 (Note 11) APCT = 90 °F 10 CFR 50.46 report dated April 9, 2009 (Note 12) APCT = 0 °F 10 CFR 50.46 report dated April 8, 2010 (Note 13) APCT = 0 °F 10 CFR 50.46 report dated April 6, 2011 (Note 15) APCT = 0 °F 10 CFR 50.46 report dated April 6, 2012 (Note 17) APCT = 0 °F 10 CFR 50.46 report dated April 5, 2013 (Note 19) APCT = 0 °F 10 CFR 50.46 report dated April 7, 2014 (Note 21) APCT = 0 °F NET PCT PCT = 1755.0°F Page 4 of 12

Attachment 1 Byron and Braidwood Units 1 and 2 10 CFR 50.46 Report B. CURRENT LOCA MODEL ASSESSMENTS General Code Maintenance (Note 22) APCT = 0 °F Fuel Rod Gap Conductance Error (Note 24) APCT = 0 °F Radiation Heat Transfer Model Error (Note 25) APCT = 0 °F SBLOCTA Pre-DNB Cladding Surface Heat Transfer Coefficient APCT = 0 °F Calculation (Note 26)

Evaluation of Change in Safety Injection and Containment Spray APCT = 0 °F Flow Rates (Note 27)

Evaluation of an Increased Auxiliary Feedwater Switchover Delay APCT = 0 °F (Note 29)

Total PCT change from current assessments 1 APCT = 0 °F Cumulative PCT change from current assessments E 1APCT = 0 °F NET PCT PCT = 1755.0°F Page 5 of 12

Attachment 1 Byron and Braidwood Units 1 and 2 10 CFR 50.46 Report PLANT NAME: Braidwood Station Unit 2 ECCS EVALUATION MODEL: Large Break Loss of Coolant Accident (LBLOCA)

REPORT REVISION DATE: 04/07/15 CURRENT OPERATING CYCLE: 18 AOR 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 PCT = 2041.0°F MARGIN ALLOCATION A. PRIOR LOSS OF COOLANT ACCIDENT (LOCA) MODEL ASSESSMENTS 10 CFR 50.46 report dated March 15, 2011 (Note 14) APCT = 0 °F 10 CFR 50.46 report dated April 6,2011 (Note 15) APCT = 0°F 10 CFR 50.46 report dated March 19, 2012 (Note 16) APCT = -42 °F 10 CFR 50.46 report dated April 6, 2012 (Note 17) APCT = 0 °F 10 CFR 50.46 report dated April 5, 2013 (Note 19) APCT = 0 °F 10 CFR 50.46 report dated April 7, 2014 (Note 21) APCT = +46 °F NET PCT PCT = 2045.0°F B. CURRENT LOCA MODEL ASSESSMENTS General Code Maintenance (Note 22) APCT = 0 °F Errors in Decay Group Uncertainty Factors (Note 23) APCT = 0 °F Evaluation of Change in Safety Injection and Containment Spray APCT = +2 °F Flow Rates (Note 28)

Total PCT change from current assessments E APCT = +2 °F Cumulative PCT change from current assessments E I APCT = 2 °F NET PCT PCT = 2047.0°F Page 6 of 12

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

REPORT REVISION DATE: 04/07/15 CURRENT OPERATING CYCLE: 20 AOR 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-inch Break in the Bottom of the Cold Leg Reference PCT PCT = 1624.0°F MARGIN ALLOCATION A. PRIOR LOSS OF COOLANT ACCIDENT (LOCA) MODEL ASSESSMENTS 10 CFR 50.46 report dated June 11. 2001 (Note 1) APCT = 0 °F 10 CFR 50.46 report dated April 18, 2002 (Note 2) APCT = 0°F 10 CFR 50.46 report dated April 14, 2003 (Note 3) APCT = 0 °F 10 CFR 50.46 report dated April 14, 2004 (Note 4) APCT = 35 °F 10 CFR 50.46 report dated April 14, 2005 (Note 5) APCT = 0 °F 10 CFR 50.46 report dated April 14, 2006 (Note 6) APCT = 0 °F 10 CFR 50.46 report dated April 13, 2007 (Note 7) APCT = 0°F 10 CFR 50.46 report dated June 22, 2007 (Note 9) APCT = 0 °F 10 CFR 50.46 report dated April 11, 2008 (Note 11) APCT = 90 °F 10 CFR 50.46 report dated April 9, 2009 (Note 12) APCT = 0 °F 10 CFR 50.46 report dated April 8, 2010 (Note 13) APCT = 0 °F 10 CFR 50.46 report dated April 6, 2011 (Note 15) APCT = 0 °F 10 CFR 50.46 report dated April 6, 2012 (Note 17) APCT = 0 °F 10 CFR 50.46 report dated April 5, 2013 (Note 19) APCT = 0 °F 10 CFR 50.46 report dated April 7, 2014 (Note 21) APCT = 0 °F NET PCT PCT= 1749.0°F Page 7 of 12

Attachment 1 Byron and Braidwood Units 1 and 2 10 CFR 50.46 Report B. CURRENT LOCA MODEL ASSESSMENTS General Code Maintenance (Note 22) APCT = 0 °F Fuel Rod Gap Conductance Error (Note 24) APCT = 0 °F Radiation Heat Transfer Model Error (Note 25) APCT = 0 °F SBLOCTA Pre-DNB Cladding Surface Heat Transfer Coefficient APCT = 0 °F Calculation (Note 26)

Evaluation of Change in Safety Injection and Containment Spray APCT = 0 °F Flow Rates (Note 27)

Evaluation of an Increased Auxiliary Feedwater Switchover Delay APCT = 0 °F (Note 29)

Total PCT change from current assessments E APCT = 0 °F Cumulative PCT change from current assessments y I APCT I = 0 °F NET PCT PCT = 1749.0°F Page 8 of 12

Attachment 1 Byron and Braidwood Units 1 and 2 10 CFR 50.46 Report PLANT NAME: Byron Station Unit 1 ECCS EVALUATION MODEL: Larqe Break Loss of Coolant Accident (LBLOCA)

REPORT REVISION DATE: 04/07/15 CURRENT OPERATING CYCLE: 20 AOR 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 PCT = 1913.0°F MARGIN ALLOCATION A. PRIOR LOSS OF COOLANT ACCIDENT (LOCA) MODEL ASSESSMENTS 10 CFR 50.46 report dated March 15, 2011 (Note 14) APCT = 0 °F 10 CFR 50.46 report dated April 6, 2011 (Note 15) APCT = 0 °F 10 CFR 50.46 report dated April 6, 2012 (Note 17) APCT = 0 °F 10 CFR 50.46 report dated May 21, 2012 (Note 18) APCT = 44°F 10 CFR 50.46 report dated April 5, 2013 (Note 19) APCT = 0 °F 10 CFR 50.46 report dated February 27, 2014 (Note 20) APCT = 66 °F 10 CFR 50.46 report dated April 7, 2014 (Note 21) APCT = 0 °F NET PCT PCT = 2023.0°F B. CURRENT LOCA MODEL ASSESSMENTS General Code Maintenance (Note 22) APCT = 0 °F Errors in Decay Group Uncertainty Factors (Note 23) APCT = 0 °F Evaluation of Change in Safety Injection and Containment Spray APCT = +2 °F Flow Rates (Note 28)

Total PCT change from current assessments 1 APCT = +2 °F Cumulative PCT change from current assessments / 1 APCT 1 = 2 °F NET PCT PCT = 2025.0°F Page 9 of 12

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

REPORT REVISION DATE: 04/07/15 CURRENT OPERATING CYCLE: 19 AOR 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-inch Break in the Bottom of the Cold Leg Reference PCT PCT = 1627.0°F MARGIN ALLOCATION A. PRIOR LOCA MODEL ASSESSMENTS 10 CFR 50.46 report dated June 11, 2001 (Note 1) APCT = 3 °F 10 CFR 50.46 report dated April 18, 2002 (Note 2) APCT = 0 °F 10 CFR 50.46 report dated April 14, 2003 (Note 3) APCT = 0 °F 10 CFR 50.46 report dated April 14, 2004 (Note 4) APCT = 35 °F 10 CFR 50.46 report dated April 14, 2005 (Note 5) APCT = 0 °F 10 CFR 50.46 report dated April 14, 2006 (Note 6) APCT = 0 °F 10 CFR 50.46 report dated April 13, 2007 (Note 7) APCT = 0°F 10 CFR 50.46 report dated May 10, 2007 (Note 8) APCT = 90 °F 10 CFR 50.46 report dated June 22, 2007 (Note 9) APCT = 0 °F 10 CFR 50.46 report dated April 11, 2008 (Note 11) APCT = 0 °F 10 CFR 50.46 report dated April 9, 2009 (Note 12) APCT = 0 °F 10 CFR 50.46 report dated April 8, 2010 (Note 13) APCT = 0 °F 10 CFR 50.46 report dated April 6, 2011 (Note 15) APCT = 0 °F 10 CFR 50.46 report dated April 6, 2012 (Note 17) APCT = 0 °F 10 CFR 50.46 report dated April 5, 2013 (Note 19) APCT = 0 °F 10 CFR 50.46 report dated April 7, 2014 (Note 21) APCT = 0 °F NET PCT PCT = 1755.0°F Page 10 of 12

Attachment 1 Byron and Braidwood Units 1 and 2 10 CFR 50.46 Report B. CURRENT LOCA MODEL ASSESSMENTS General Code Maintenance (Note 22) APCT = 0 °F Fuel Rod Gap Conductance Error (Note 24) APCT = 0 °F Radiation heat Transfer Model Error (Note 25) APCT = 0 °F SBLOCTA Pre-DNB Cladding Surface Heater Transfer Coefficient APCT = 0 °F Calculation (Note 26)

Evaluation of Change in Safety Injection and Containment Spray APCT = 0 °F Flow Rates (Note 27)

Evaluation of an Increased Auxiliary Feedwater Switchover Delay APCT = 0 °F (Note 29)

Total PCT change from current assessments E APCT = 0 °F Cumulative PCT change from current assessments E I APCT I = 0 °F NET PCT PCT = 1755.0°F Page 11 of 12

Attachment 1 Byron and Braidwood Units 1 and 2 10 CFR 50.46 Report PLANT NAME: Byron Station Unit 2 ECCS EVALUATION MODEL: Large Break Loss of Coolant Accident (LBLOCA)

REPORT REVISION DATE: 04/07/15 CURRENT OPERATING CYCLE: 19 AOR 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 PCT = 2041.0°F MARGIN ALLOCATION A. PRIOR LOSS OF COOLANT ACCIDENT (LOCA) MODEL ASSESSMENTS 10 CFR 50.46 report dated March 15, 2011 (Note 14) APCT = 0 °F 10 CFR 50.46 report dated April 6, 2011 (Note 15) APCT = 0 °F 10 CFR 50.46 report dated March 19, 2012 (Note 16) APCT = -42 °F 10 CFR 50.46 report dated April 6, 2012 (Note 17) APCT = 0 °F 10 CFR 50.46 report dated April 5, 2013 (Note 19) APCT = 0 °F 10 CFR 50.46 report dated April 7, 2014 (Note 21) APCT = +46 °F NET PCT PCT = 2045.0°F B. CURRENT LOCA MODEL ASSESSMENTS General Code Maintenance (Note 22) APCT = 0 °F Errors in Decay Group Uncertainty Factors (Note 23) APCT = 0 °F Evaluation of Change in Safety Injection and Containment Spray APCT = +2 °F Flow Rates (Note 28)

Total PCT change from current assessments E APCT = +2 °F Cumulative PCT change from current assessments E APCT 1= 2 °F NET PCT PCT = 2047.0°F Page 12 of 12

Attachment 2 Byron and Braidwood Units 1 and 2 10 CFR 50.46 Report Assessment Notes

1. Prior LOCA Model Assessment The 10 CFR 50.46 report dated June 11, 2001 reported new small break loss of coolant accident (SBLOCA) analyses to support operations at uprated power conditions. The same report assessed the impact from annular axial blankets on SBLOCA analysis, which determined a 0°F PCT penalty for Units 1 and a 3°F PCT penalty for Units 2.

Evaluations for plant conditions and SBLOCA model changes which resulted in 0 °F 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 °F 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 °F PCT change.

4. Prior LOCA Model Assessment The 10 CFR 50.46 report dated April 14, 2004 reported evaluations for a SBLOCA assessment related to NOTRUMP bubble rise/drift flux model inconsistency corrections, which resulted in 35 °F 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 0 °F PCT change for Byron and Braidwood Unit 1 and Unit 2.

The Braidwood Station, Unit 1 assembly N1OS was reconstituted with two stainless steel filler rods during Braidwood Unit 1 Refueling Outage 11. This assembly is reloaded into the core and is in use during Braidwood Unit 1 Cycle 12 operation. The introduction of up to five stainless steel filler rods has been evaluated and shown to have no impact on SBLOCA analysis. The estimated PCT effect is 0°F for Braidwood Unit 1. 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 °F 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 6

Attachment 2 Byron and Braidwood 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 (AOR) was performed for the SBLOCA. 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.

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 Code 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°F penalty was assessed for Byron Units 1 and 2, and Braidwood Units 1 and 2, SBLOCA analysis.

10.Prior LOCA Model Assessment 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 GSM 91 related SI throttle valve replacements. The evaluation of recirculation phase ECCS flow changes relative to impact on the current Analysis of Record (AOR) was performed for the small break loss of coolant accident (SBLOCA). Based on the NOTRUMP and SBLOCTA calculations performed for Braidwood Unit 1, a conservative, bounding PCT assessment of +90°F was applied to the Braidwood Unit 1 SBLOCA 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 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.

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 Page 2 of 6

Attachment 2 Byron and Braidwood Units 1 and 2 10 CFR 50.46 Report Assessment Notes mass from drawings, and an evaluation of Areva LUAs. All of which have a 0 °F PCT penalty associated with them.

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 °F 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 Byron and Braidwood 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 had a 0 °F PCT impact with a net 0 °F PCT impact.

15. Prior LOCA Model Assessment The 10 CFR 50.46 report dated April 6, 2011 reported no evaluations for the LBLOCA model. For the SBLOCA model, the following errors, changes, corrections or enhancements were reported. Two errors relating to urania-gadolinia pellet thermal conductivity calculation, two errors relating to pellet crack and dish volume calculation, a discrepancy involving the treatment of vessel average temperature uncertainty, and general code maintenance were reported for the SBLOCA model. All of these issues were determined to have an estimated impact of 0°F.

16. Prior LOCA Model Assessment The 30-day 10 CFR 50.46 report dated March 19, 2012 applicable to Braidwood Unit 2 and Byron Unit 2 reported an assessment of Thermal Conductivity Degradation (TCD) with an associated peaking factor burndown and a design input change consisting of a reduction in upper bound steam generator tube plugging, a reduction in nominal upper bound nominal vessel average temperature, and an increase in the assumed containment pressure boundary condition. As a result, the estimated effect of the TCD with burndown was determined to be +148°F and the estimated effect of the design input changes was determined to be -190°F. These two assessments are coupled together via their evaluations of burnup effects which include thermal conductivity degradation, peaking factor burndown and design input changes. Therefore, the combined affect of these two changes results in a net change in the reported LBLOCA PCT for Braidwood Unit 2 and Byron Unit 2 of -42°F.

17. Prior LOCA Model Assessment The 10 CFR 50.46 report dated April 6, 2012 reported evaluations for LOCA model changes and errors. The report documents general code maintenance for both SBLOCA

& LBLOCA, errors in Radiation Heat Transfer Logic for SBLOCA, and an error in the Maximum Fuel Rod Time Step Logic for SBLOCA. All of which have a 0 °F PCT penalty associated with them.

Page 3 of 6

Attachment 2 Byron and Braidwood Units 1 and 2 10 CFR 50.46 Report Assessment Notes

18. Prior LOCA Model Assessment The 30-day 10 CFR 50.46 report dated May 21, 2012 applicable to Braidwood Unit 1 and Byron Unit 1 reported an assessment of Thermal Conductivity Degradation (TCD) with an associated peaking factor burndown an analysis input change consisting of a reduction in conservatism in analyzed FQ values and an increase in the assumed containment pressure boundary condition. As a result, the estimated effect of the TCD with burndown was determined to be +110°F and the estimated effect of the analysis input changes was determined to be -66°F. These two assessments are coupled together via their evaluations of burnup effects which include thermal conductivity degradation, peaking factor burndown and analysis input changes. Therefore, the combined affect of these two changes results in a net change in the reported LBLOCA PCT for Braidwood Unit 1 and Byron Unit 1 of +44°F.

19.Prior LOCA Model Assessment The 10 CFR 50.46 report dated April 5, 2013 reported evaluations for LBLOCA model changes, and HOTSPOT and WCOBRA/TRAC code corrections. For SBLOCA, thermal conductivity degradation (TCD) was evaluated with NOTRUMP to estimate the effect on the limiting cladding temperature model. All evaluations led to PCT impact of 0°F.

20. Prior LOCA Model Assessment The 30-day 10 CFR 50.46 report dated February 27, 2014 applicable to Braidwood Unit 1 and Byron Unit 1 reported evaluations for LBLOCA model changes and code corrections.

Revised heat transfer multiplier distributions, changes to grid blockage ratio and porosity and HOTSPOT burst strain error corrections were determined to have a 5°F, 24°F, and 37°F PCT impact, respectively for Braidwood Unit 1 and Byron Unit 1. Other model changes and code corrections sum to 0°F PCT impact. Therefore, the combined effect of the changes resulted in a net change of 66°F PCT impact for Braidwood Unit 1 and Byron Unit 1.

21. Prior LOCA Model Assessment The annual 10 CFR 50.46 report dated April 7, 2014 applicable to Byron and Braidwood Units 1 and 2 reported evaluations for LBLOCA and SBLOCA model changes and code corrections. Revised heat transfer multiplier distributions, changes to grid blockage ratio and porosity and HOTSPOT burst strain error corrections were determined to have a 7°F, 24°F, and 15°F PCT impact, respectively for Braidwood Unit 2 and Byron Unit 2. Other model changes and code corrections sum to 0°F PCT impact. Therefore, the combined effect of the changes resulted in a net change of 46°F PCT impact for Braidwood Unit 2 and Byron Unit 2 LBLOCA. For Braidwood and Byron Units 1 LBLOCA, other model changes and code corrections sum to 0°F PCT impact since the 30-day 10 CFR 50.46 report dated February 27, 2014 (see note 20). SBLOCTA cladding strain requirement for fuel rod burst resulted in a 0°F PCT impact to Byron and Braidwood Units 1 and 2 SBLOCA.

Page 4 of 6

Attachment 2 Byron and Braidwood Units 1 and 2 10 CFR 50.46 Report Assessment Notes

22. Current LOCA Model Assessment General Code Maintenance (LBLOCA and SBLOCA)

Various changes have been made to enhance the usability of codes and to streamline future analyses. Examples of these changes include 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 an estimated PCT impact of 0°F.

23. Current LOCA Model Assessment Errors in Decay Group Uncertainty Factors (LB LOCA)

An error was discovered in the calculation of decay heat in WCOBRA/TRAC. The uncertainty factors for 239Pu were applied to 238U, and those for 238U were applied to 239Pu.

This error causes an over-prediction of the uncertainty in decay power from 239PU and an under-prediction of the uncertainty in decay power from 238U. Further, the decay group uncertainty factor for Decay Group 6 of 235U was erroneously coded as 2.5% instead of 2.25%. Correction of the decay heat calculation resulted in an estimated PCT impact of 0°F.

24. Current LOCA Model Assessment Fuel Rod Gap Conductance Error (SBLOCA)

An error was identified in the fuel rod gap conductance model in the NOTRUMP computer code. This error is associated with the use of an incorrect temperature in the calculation of the cladding emissivity term. The correction of this error led to an estimated PCT impact of 0°F.

25. Current LOCA Model Assessment Radiation Heat Transfer Model Error (SBLOCA)

Two errors were discovered in the calculation of the radiation heat transfer coefficient within the fuel rod model of the NOTRUMP computer code. First, existing logic did not preclude non-physical negative or large (negative or positive) radiation heat transfer coefficients from being calculated. These erroneous calculations occurred when the vapor temperature exceeded the cladding surface temperature or when the predicted temperature difference was less than 1°F. Second, a temperature term incorrectly used degrees Fahrenheit instead of Rankine. The effect of these errors was estimated to be 0°F.

26. Current LOCA Model Assessment SBLOCTA Pre-DNB Cladding Surface Heat Transfer Coefficient Calculation (SBLOCA)

Two errors were discovered in the pre-departure from nucleate boiling (pre-DNB) cladding surface heat transfer coefficient calculation in the SBLOCTA code. The first error is a result of inconsistent time units (hours vs. seconds) in the parameters used for the calculation of the Reynolds and Prandtl numbers, and the second error relates to an incorrect diameter used to develop the area term in the cladding surface heat flux calculation. This correction of these errors led to an estimated PCT impact of 0°F.

Pages of 6

Attachment 2 Byron and Braidwood Units 1 and 2 10 CFR 50.46 Report Assessment Notes

27. Current LOCA Model Assessment Evaluation of Change in Safety Injection and Containment Spray Flow Rates (SBLOCA)

Changes to the emergency core cooling system (ECCS) and containment spray (CS) flow rates were evaluated to determine the impact on the Byron and Braidwood Units 1 and 2.

A qualitative evaluation and engineering judgment were used to conclude that the changes to the ECCS flow rates and containment spray flow rates assumed in the SBLOCA analysis would have a negligible impact on the SBLOCA transient results. The evaluation and engineering judgment concluded changes to the ECCS flow rates and containment spray flow rates resulted in an estimated PCT impact of 0°F.

28. Current LOCA Model Assessment Evaluation of Change in Safety Injection and Containment Spray Flow Rates (LBLOCA)

Changes to the emergency core cooling system (ECCS) and containment spray (CS) flow rates were evaluated to determine the impact on the Bryon and Braidwood Units 1 and 2.

A quantitative evaluation was performed to estimate an overall PCT change due to the change in safety injection and containment spray flow rates for the thermal conductivity degradation (TCD) re-evaluation for Byron and Braidwood Units 2. Engineering judgment was then used to conclude that those results applied equally to the current licensing bases for Byron and Braidwood Units 1 and 2. The evaluation concluded that the estimated PCT impact is +2°F.

29. Current LOCA Model Assessment Evaluation of an Increased Auxiliary Feedwater Switchover Delay (SBLOCA)

A circuit modification caused an increase in the Auxiliary Feedwater (AFW) switchover delay due to a 12 second circuitry delay present in the switchover from the Condensate Storage Tank (CST) to Essential Service Water (ESW), resulting in a total delay of 102 seconds in the SBLOCA. The increased switchover delay resulted in PCT impact of 0°F.

Page 6 of 6