RS-23-055, Annual 10 CFR 50.46 Report of Emergency Core Cooling System Evaluation Model Changes and Errors

From kanterella
Jump to navigation Jump to search
Annual 10 CFR 50.46 Report of Emergency Core Cooling System Evaluation Model Changes and Errors
ML23100A104
Person / Time
Site: Byron, Braidwood  Constellation icon.png
Issue date: 04/10/2023
From: Lueshen K
Constellation Energy Generation
To:
Office of Nuclear Reactor Regulation, Document Control Desk
References
RS-23-055
Download: ML23100A104 (1)
v • d • e


Text

4300 Winfield Road Warrenville, IL 60555 630 657 2000 Office RS-23-055 10 CFR 50.46 April 10, 2023 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Braidwood Station, Units 1 and 2 Renewed Facility Operating License Nos. NPF-72 and NPF-77 NRC Docket Nos. STN 50-456 and 50-457 Byron Station, Units 1 and 2 Renewed 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

References:

1) Letter from D. Murray (Exelon Generation Company, LLC) to U.S. Nuclear Regulatory Commission, "Annual 10 CFR 50.46 Report of Emergency Core Cooling System Evaluation Model Changes and Errors,"

dated April 9, 2021 (ADAMS Accession No. ML21099A106)

2) Letter from P. Simpson (Exelon Generation Company, LLC) to U.S. Nuclear Regulatory Commission, "Updated 10 CFR 50.46 Report of Emergency Core Cooling System Evaluation Model Changes and Errors,"

dated October 22, 2021 (ADAMS Accession No. ML21295A214)

3) Letter from K. Lueshen (Constellation Energy Company, LLC) to U.S. Nuclear Regulatory Commission, "Annual 10 CFR 50.46 Report of Emergency Core Cooling System Evaluation Model Changes and Errors,"

dated April 8, 2022 (ADAMS Accession No. ML22098A111)

In accordance with 10 CFR 50.46, "Acceptance criteria for emergency core cooling systems for light-water nuclear power reactors," paragraph (a)(3)(ii), Constellation Energy Generation, LLC, (CEG) is submitting the attached information to fulfill the annual reporting requirements for Braidwood and Byron Stations, Units 1 and 2. With this report, a new Full Spectrum LOCA (FSLOCA) analysis has been implemented at all four Braidwood and Byron units in place of both the Small Break and Large Break LOCA analyses.

This report includes the updated information, and a separate 30-day report will not be submitted.

Attachments 1 and 2 describe the changes in the evaluations associated with the accumulated peak cladding temperature (PCT) since the previous reports submitted in the referenced letters.

April 10, 2023 U.S. Nuclear Regulatory Commission Page 2 Attachments 3 and 4 provide the 10 CFR 50.46 Report Assessment Notes for Braidwood and Byron, respectively, which provide a detailed description for each change or error reported.

The previous year's report was submitted on April 8, 2022. As the due date for this year's annual report falls on a Saturday, in accordance with 10 CFR 50.4, "Written communications,"

the due date for this report will be the next Federal working day (i.e., Monday, April 10, 2023).

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

Respectfully, Digitally signed by Lueshen, Lueshen, Kevin Kevin Date: 2023.04.10 09:51:49

-05'00' Kevin Lueshen Sr. Manager - Licensing Constellation Energy Generation, LLC Attachments: 1) Braidwood Station, Units 1 and 2 - 10 CFR 50.46 Report

2) Byron Station, Units 1 and 2 - 10 CFR 50.46 Report
3) Braidwood Station, Units 1 and 2 - 10 CFR 50.46 Report Assessment Notes
4) Byron Station, 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 Station, Units 1 and 2 10 CFR 50.46 Report PLANT NAME: Braidwood Station Unit 1 ECCS EVALUATION MODEL: Full Spectrum LOCA EM Small Break REPORT REVISION DATE: 04/10/2023 CURRENT OPERATING CYCLE: 24 ANALYSIS OF RECORD (AOR)

Evaluation Model: FSLOCA Calculation: Westinghouse WCAP-18448-P, August 2019 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: 3.8-inch Break in the Cold Leg Reference Peak Cladding Temperature (PCT) PCT = 1181.0°F MARGIN ALLOCATION A. PRIOR LOSS OF COOLANT ACCIDENT (LOCA) MODEL ASSESSMENTS 10 CFR 50.46 Report Dated April 9, 2021 (Att. 3, Note 1) PCT = +20 F 10 CFR 50.46 Report Dated April 8, 2022 (Att. 3, Note 3) PCT = 0 F NET PCT PCT = 1201.0°F B. CURRENT LOCA MODEL ASSESSMENTS Error in Hoop Stress Used in Cladding Rupture Model (Att. 3, Note 4) PCT = 0 F Non-Conservation of Energy in the Generalized Energy Deposition PCT = 0 F Model (Att. 3, Note 4)

General Code Maintenance (Att. 3, Note 4) PCT = 0 F Total PCT change from current assessments PCT = 0 F Cumulative PCT change from current assessments PCT = 0 F NET PCT PCT = 1201.0°F Page 1 of 4

Attachment 1 Braidwood Station, Units 1 and 2 10 CFR 50.46 Report PLANT NAME: Braidwood Station Unit 1 ECCS EVALUATION MODEL: Full Spectrum LOCA EM Large Break REPORT REVISION DATE: 04/10/2023 CURRENT OPERATING CYCLE: 24 AOR Evaluation Model: FSLOCA Calculation: Westinghouse WCAP-18448-P, August 2019 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 = 1643.0°F MARGIN ALLOCATION A. PRIOR LOCA MODEL ASSESSMENTS 10 CFR 50.46 Report Dated April 9, 2021 (Att. 3, Note 1) PCT = 0 F 10 CFR 50.46 Report Dated April 8, 2022 (Att. 3, Note 3) PCT = 0 F NET PCT PCT = 1643.0°F B. CURRENT LOCA MODEL ASSESSMENTS Error in Hoop Stress Used in Cladding Rupture Model (Att. 3, Note 4) PCT = 0 F Non-Conservation of Energy in the Generalized Energy Deposition PCT = 0 F Model (Att. 3, Note 4)

General Code Maintenance (Att. 3, Note 4) PCT = 0 F Total PCT change from current assessments PCT = 0 F Cumulative PCT change from current assessments PCT = 0 F NET PCT PCT = 1643.0°F Page 2 of 4

Attachment 1 Braidwood Station, Units 1 and 2 10 CFR 50.46 Report PLANT NAME: Braidwood Station Unit 2 ECCS EVALUATION MODEL: Full Spectrum LOCA EM Small Break REPORT REVISION DATE: 04/10/2023 CURRENT OPERATING CYCLE: 23 ANALYSIS OF RECORD (AOR)

Evaluation Model: FSLOCA Calculation: Westinghouse WCAP-18449-P, August 2019 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: 3.7-inch Break in the Cold Leg Reference Peak Cladding Temperature (PCT) PCT = 1169.0°F MARGIN ALLOCATION A. PRIOR LOSS OF COOLANT ACCIDENT (LOCA) MODEL ASSESSMENTS 30-Day 10 CFR 50.46 report dated October 22, 2021 (Att. 3, Note 2) PCT = +20 F 10 CFR 50.46 report dated April 8, 2022 (Att. 3, Note 3) PCT = 0 F NET PCT PCT = 1189.0°F B. CURRENT LOCA MODEL ASSESSMENTS Error in Hoop Stress Used in Cladding Rupture Model (Att. 3, Note 4) PCT = 0 F Non-Conservation of Energy in the Generalized Energy Deposition PCT = 0 F Model (Att. 3, Note 4)

General Code Maintenance (Att. 3, Note 4) PCT = 0 F Total PCT change from current assessments PCT = 0 F Cumulative PCT change from current assessments PCT = 0 F NET PCT PCT = 1189.0°F Page 3 of 4

Attachment 1 Braidwood Station, Units 1 and 2 10 CFR 50.46 Report PLANT NAME: Braidwood Station Unit 2 ECCS EVALUATION MODEL: Full Spectrum LOCA EM Large Break REPORT REVISION DATE: 04/10/2023 CURRENT OPERATING CYCLE: 23 AOR Evaluation Model: FSLOCA Calculation: Westinghouse WCAP-18449-P, August 2019 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 = 1752.0°F MARGIN ALLOCATION A. PRIOR LOCA MODEL ASSESSMENTS 30-Day 10 CFR 50.46 report dated October 22, 2021 (Att. 3, Note 2) PCT = 0 F 10 CFR 50.46 report dated April 8, 2022 (Att. 3, Note 3) PCT = 0 F NET PCT PCT = 1752.0°F B. CURRENT LOCA MODEL ASSESSMENTS Error in Hoop Stress Used in Cladding Rupture Model (Att. 3, Note 4) PCT = 0 F Non-Conservation of Energy in the Generalized Energy Deposition PCT = 0 F Model (Att. 3, Note 4)

General Code Maintenance (Att. 3, Note 4) PCT = 0 F Total PCT change from current assessments PCT = 0 F Cumulative PCT change from current assessments PCT = 0 F NET PCT PCT = 1752.0°F Page 4 of 4

Attachment 2 Byron Station, Units 1 and 2 10 CFR 50.46 Report PLANT NAME: Byron Station Unit 1 ECCS EVALUATION MODEL: Full Spectrum LOCA EM Small Break REPORT REVISION DATE: 04/10/2023 CURRENT OPERATING CYCLE: 26 ANALYSIS OF RECORD (AOR)

Evaluation Model: FSLOCA Calculation: Westinghouse WCAP-18448-P, August 2019 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: 3.8-inch Break in the Cold Leg Reference Peak Cladding Temperature (PCT) PCT = 1181.0°F MARGIN ALLOCATION A. PRIOR LOSS OF COOLANT ACCIDENT (LOCA) MODEL ASSESSMENTS 30-Day 10 CFR 50.46 report dated October 22, 2021 (Att. 4, Note 1) PCT = +20 F 10 CFR 50.46 report dated April 8, 2022 (Att. 4, Note 3) PCT = 0 F NET PCT PCT = 1201.0°F B. CURRENT LOCA MODEL ASSESSMENTS Error in Hoop Stress Used in Cladding Rupture Model (Att. 4, Note 4) PCT = 0 F Non-Conservation of Energy in the Generalized Energy Deposition PCT = 0 F Model (Att. 4, Note 4)

General Code Maintenance (Att. 4, Note 4) PCT = 0 F Total PCT change from current assessments PCT = 0 F Cumulative PCT change from current assessments PCT = 0 F NET PCT PCT = 1201.0°F Page 1 of 4

Attachment 2 Byron Station, Units 1 and 2 10 CFR 50.46 Report PLANT NAME: Byron Station Unit 1 ECCS EVALUATION MODEL: Full Spectrum LOCA EM Large Break REPORT REVISION DATE: 04/10/2023 CURRENT OPERATING CYCLE: 26 AOR Evaluation Model: FSLOCA Calculation: Westinghouse WCAP-18448-P, August 2019 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 = 1643.0°F MARGIN ALLOCATION A. PRIOR LOCA MODEL ASSESSMENTS 30-Day 10 CFR 50.46 report dated October 22, 2021 (Att. 4, Note 1) PCT = 0 F 10 CFR 50.46 report dated April 8, 2022 (Att. 4, Note 3) PCT = 0 F NET PCT PCT = 1643.0°F B. CURRENT LOCA MODEL ASSESSMENTS Error in Hoop Stress Used in Cladding Rupture Model (Att. 4, Note 4) PCT = 0 F Non-Conservation of Energy in the Generalized Energy Deposition PCT = 0 F Model (Att. 4, Note 4)

General Code Maintenance (Att. 4, Note 4) PCT = 0 F Total PCT change from current assessments PCT = 0 F Cumulative PCT change from current assessments PCT = 0 F NET PCT PCT = 1643.0°F Page 2 of 4

Attachment 2 Byron Station, Units 1 and 2 10 CFR 50.46 Report PLANT NAME: Byron Station Unit 2 ECCS EVALUATION MODEL: Full Spectrum LOCA EM Small Break REPORT REVISION DATE: 04/10/2023 CURRENT OPERATING CYCLE: 24 ANALYSIS OF RECORD (AOR)

Evaluation Model: FSLOCA Calculation: Westinghouse WCAP-18449-P, August 2019 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: 3.7-inch Break in the Cold Leg Reference Peak Cladding Temperature (PCT) PCT = 1169.0°F MARGIN ALLOCATION A. PRIOR LOSS OF COOLANT ACCIDENT (LOCA) MODEL ASSESSMENTS 10 CFR 50.46 report dated April 8, 2022 (Att. 4, Notes 2 and 3) PCT = +20 F NET PCT PCT = 1189.0°F B. CURRENT LOCA MODEL ASSESSMENTS Error in Hoop Stress Used in Cladding Rupture Model (Att. 4, Note 4) PCT = 0 F Non-Conservation of Energy in the Generalized Energy Deposition PCT = 0 F Model (Att. 4, Note 4)

General Code Maintenance (Att. 4, Note 4) PCT = 0 F Total PCT change from current assessments PCT = 0 F Cumulative PCT change from current assessments PCT = 0 F NET PCT PCT = 1189.0°F Page 3 of 4

Attachment 2 Byron Station, Units 1 and 2 10 CFR 50.46 Report PLANT NAME: Byron Station Unit 2 ECCS EVALUATION MODEL: Full Spectrum LOCA EM Large Break REPORT REVISION DATE: 04/10/2023 CURRENT OPERATING CYCLE: 24 AOR Evaluation Model: FSLOCA Calculation: Westinghouse WCAP-18449-P, August 2019 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 = 1752.0°F MARGIN ALLOCATION A. PRIOR LOCA MODEL ASSESSMENTS 10 CFR 50.46 report dated April 8, 2022 (Att. 4, Notes 2 and 3) PCT = 0 F NET PCT PCT = 1752.0°F B. CURRENT LOCA MODEL ASSESSMENTS Error in Hoop Stress Used in Cladding Rupture Model (Att. 4, Note 4) PCT = 0 F Non-Conservation of Energy in the Generalized Energy Deposition PCT = 0 F Model (Att. 4, Note 4)

General Code Maintenance (Att. 4, Note 4) PCT = 0 F Total PCT change from current assessments PCT = 0 F Cumulative PCT change from current assessments PCT = 0 F NET PCT PCT = 1752.0°F Page 4 of 4

Attachment 3 Braidwood Station, Units 1 and 2 10 CFR 50.46 Report Assessment Notes

1. Prior LOCA Model Assessment The 10 CFR 50.46 report dated April 9, 2021, reported a new Full Spectrum LOCA (FSLOCA) analysis was to be implemented for Braidwood Unit 1 in place of both the Small Break and Large Break LOCA analyses at the start of Cycle 23. This analysis creates new analyses of record Peak Clad Temperature (PCT) of 1181°F for the small break region and 1643°F for the large break region. With these new analyses were one assessment to the small break region and two changes to the large break region along with their impacts.

The assessment to the small break region was an ECCS Line Void Evaluation that was included in the licensing amendment request for FSLOCA approval at Braidwood Unit 1.

That evaluation had a limit PCT impact of +20°F.

The first change to the large break region involved General Code Maintenance. Various changes have been made to enhance the usability of codes and to streamline future analyses, which represent Discretionary Changes and had an estimated peak cladding temperature impact of 0°F.

The second change to the large break region involved an impact to the lucifer kinetics and decay heat model. The WCOBRA/TRAC-TF2 code is the thermal-hydraulic system code licensed as part of the FULL SPECTRUM LOCA evaluation model. The kinetics and decay heat models in the code are described in Section 9 of WCAP-16996-P-A, Revision 1. The nuclear physics data supporting the code models was generated using the ARK depletion program, which evolved from the LEOPARD and CINDER codes as described in the response to Request for Additional Information (RAI) #25 on the FSLOCA EM. Since the approval of the FSLOCA EM, the kinetics and decay heat model in the WCOBRA/TRAC-TF2 code was updated to support the analysis of higher burnup fuel as described in Section 4.6 of WCAP-18446-P. The updated nuclear physics data is based on the NRC-approved PARAGON code (WCAP-16045-P-A). While the primary purpose of this update is for the analysis of higher burnup fuel, the change will impact licensing basis analysis calculations with the FSLOCA EM even under the existing burnup limits imposed via Limitation and Condition (L&C) #5 on the FSLOCA EM. This change to the WCOBRA/TRAC-TF2 code represents a Discretionary Change and will be implemented on a forward-fit basis.

Therefore, this effort has no impact on the current FSLOCA evaluation model.

2. Prior LOCA Model Assessment The 30-day 10 CFR 50.46 report dated October 22, 2021, reported that a new FSLOCA analysis was implemented for Braidwood Unit 2 in place of both the Small Break and Large Break LOCA analyses at the start of Cycle 23. This analysis creates new analyses of record PCT of 1169°F for the small break region and 1752°F for the large break region. With these new analyses were one assessment to the small break region and two changes to the large break region along with their impacts.

The assessment to the small break region was an ECCS Line Void Evaluation that was included in the licensing amendment request for FSLOCA approval at Braidwood Unit 2.

That evaluation had a limit PCT impact of +20°F.

Page 1 of 3

Attachment 3 Braidwood Station, Units 1 and 2 10 CFR 50.46 Report Assessment Notes The first change to the large break region involved General Code Maintenance. Various changes have been made to enhance the usability of codes and to streamline future analyses, which represent Discretionary Changes and had an estimated peak cladding temperature impact of 0°F.

The second change to the large break region involved an impact to the lucifer kinetics and decay heat model. The WCOBRA/TRAC-TF2 code is the thermal-hydraulic system code licensed as part of the FULL SPECTRUM LOCA evaluation model (EM). The kinetics and decay heat models in the code are described in Section 9 of WCAP-16996-P-A, Revision 1.

The nuclear physics data supporting the code models was generated using the ARK depletion program, which evolved from the LEOPARD and CINDER codes as described in the response to Request for Additional Information (RAI) #25 on the FSLOCA EM. Since the approval of the FSLOCA EM, the kinetics and decay heat model in the WCOBRA/TRAC-TF2 code was updated to support the analysis of higher burnup fuel as described in Section 4.6 of WCAP-18446-P. The updated nuclear physics data is based on the NRC-approved PARAGON code (WCAP-16045-P-A). While the primary purpose of this update is for the analysis of higher burnup fuel, the change will impact licensing basis analysis calculations with the FSLOCA EM even under the existing burnup limits imposed via Limitation and Condition (L&C) #5 on the FSLOCA EM. This change to the WCOBRA/TRAC-TF2 code represents a Discretionary Change and will be implemented on a forward-fit basis.

Therefore, this effort has no impact on the current FSLOCA EM.

3. Prior LOCA Model Assessment The 10 CFR 50.46 report dated April 8, 2022, reported General Code Maintenance that represents Discretionary Changes and resulted in a 0°F PCT change.
4. Current LOCA Model Assessment An error was noted in the hoop stress used in the cladding rupture model. For two instances within the cladding rupture logic, the incorrect hoop stress variable was used. In both instances, the hoop stress variable for the cladding elastic deformation model was used when the hoop stress variable for the cladding creep deformation and cladding rupture models should have been used. The correction of this error represents a Non-Discretionary Change in accordance with Section 4.1.2 of WCAP-13451. The error was evaluated to have a negligible impact on the calculated results for the FSLOCA EM analysis, resulting in an estimated PCT impact of 0°F.

Another error was also noted. Non-conservation of deposited energy was discovered to exist that resulted in a very small fraction of the redistributed energy not being included in the core balance rods. The energy deposited in the hot rod and hot assembly was confirmed to be conserved and correct. This item represents a Non-Discretionary Change in accordance with Section 4.1.2 of WCAP-13451. The error was qualitatively evaluated, and the nature of the error leads to an estimated PCT impact of 0°F.

Page 2 of 3

Attachment 3 Braidwood Station, Units 1 and 2 10 CFR 50.46 Report Assessment Notes The current report noted the following areas of General Code Maintenance. Various changes have been made to enhance the usability of codes and to streamline future analyses. Examples of these changes include improving the input diagnostic checks; enhancing the code output; optimizing active coding; and eliminating inactive coding. These changes represent Discretionary Changes that will be implemented on a forward-fit basis in accordance with Section 4.1.1 of WCAP-13451. The nature of these changes leads to an estimated PCT impact of 0°F.

Page 3 of 3

Attachment 4 Byron Station, Units 1 and 2 10 CFR 50.46 Report Assessment Notes

1. Prior LOCA Model Assessment The 10 CFR 50.46 report dated October 22, 2021, reported that a new Full Spectrum LOCA (FSLOCA) analysis was implemented for Byron Unit 1 in place of both the Small Break and Large Break LOCA analyses at the start of Cycle 25. This analysis creates new analyses of record Peak Clad Temperature (PCT) of 1181°F for the small break region and 1643°F for the large break region. With these new analyses were one assessment to the small break region and two changes to the large break region along with their impacts.

The assessment to the small break region was an ECCS Line Void Evaluation that was included in the licensing amendment request for FSLOCA approval at Byron Unit 1. That evaluation had a limit PCT impact of +20°F.

The first change to the large break region involved General Code Maintenance. Various changes have been made to enhance the usability of codes and to streamline future analyses, which represent Discretionary Changes and had an estimated peak cladding temperature impact of 0°F.

The second change to the large break region involved an impact to the lucifer kinetics and decay heat model. The WCOBRA/TRAC-TF2 code is the thermal-hydraulic system code licensed as part of the FULL SPECTRUM LOCA evaluation model. The kinetics and decay heat models in the code are described in Section 9 of WCAP-16996-P-A, Revision 1. The nuclear physics data supporting the code models was generated using the ARK depletion program, which evolved from the LEOPARD and CINDER codes as described in the response to Request for Additional Information (RAI) #25 on the FSLOCA EM. Since the approval of the FSLOCA EM, the kinetics and decay heat model in the WCOBRA/TRAC-TF2 code was updated to support the analysis of higher burnup fuel as described in Section 4.6 of WCAP-18446-P. The updated nuclear physics data is based on the NRC-approved PARAGON code (WCAP-16045-P-A). While the primary purpose of this update is for the analysis of higher burnup fuel, the change will impact licensing basis analysis calculations with the FSLOCA EM even under the existing burnup limits imposed via Limitation and Condition (L&C) #5 on the FSLOCA EM. This change to the WCOBRA/TRAC-TF2 code represents a Discretionary Change and will be implemented on a forward-fit basis.

Therefore, this effort has no impact on the current FSLOCA evaluation model.

2. Prior LOCA Model Assessment The 10 CFR 50.46 report dated April 8, 2022, reported a new FSLOCA analysis was being implemented for Byron Unit 2 in place of both the Small Break and Large Break LOCA analyses at the start of Cycle 24. This analysis creates new analyses of record PCT of 1169°F for the small break region and 1752°F for the large break region. With these new analyses were one assessment to the small break region and two changes to the large break region along with their impacts.

The assessment to the small break region was an ECCS Line Void Evaluation that was included in the licensing amendment request for FSLOCA approval at Byron Unit 2. That evaluation had a limit PCT impact of +20°F.

Page 1 of 3

Attachment 4 Byron Station, Units 1 and 2 10 CFR 50.46 Report Assessment Notes The first change to the large break region involved General Code Maintenance. Various changes have been made to enhance the usability of codes and to streamline future analyses, which represent Discretionary Changes and had an estimated peak cladding temperature impact of 0°F.

The second change to the large break region involved an impact to the lucifer kinetics and decay heat model. The WCOBRA/TRAC-TF2 code is the thermal-hydraulic system code licensed as part of the FULL SPECTRUM LOCA evaluation model (EM). The kinetics and decay heat models in the code are described in Section 9 of WCAP-16996-P-A, Revision 1.

The nuclear physics data supporting the code models was generated using the ARK depletion program, which evolved from the LEOPARD and CINDER codes as described in the response to Request for Additional Information (RAI) #25 on the FSLOCA EM. Since the approval of the FSLOCA EM, the kinetics and decay heat model in the WCOBRA/TRAC-TF2 code was updated to support the analysis of higher burnup fuel as described in Section 4.6 of WCAP-18446-P. The updated nuclear physics data is based on the NRC-approved PARAGON code (WCAP-16045-P-A). While the primary purpose of this update is for the analysis of higher burnup fuel, the change will impact licensing basis analysis calculations with the FSLOCA EM even under the existing burnup limits imposed via Limitation and Condition (L&C) #5 on the FSLOCA EM. This change to the WCOBRA/TRAC-TF2 code represents a Discretionary Change and will be implemented on a forward-fit basis.

Therefore, this effort has no impact on the current FSLOCA EM.

3. Prior LOCA Model Assessment The 10 CFR 50.46 report dated April 8, 2022, reported General Code Maintenance that represents Discretionary Changes and resulted in a 0°F PCT change.
4. Current LOCA Model Assessment An error was noted in the hoop stress used in the cladding rupture model. For two instances within the cladding rupture logic, the incorrect hoop stress variable was used. In both instances, the hoop stress variable for the cladding elastic deformation model was used when the hoop stress variable for the cladding creep deformation and cladding rupture models should have been used. The correction of this error represents a Non-Discretionary Change in accordance with Section 4.1.2 of WCAP-13451. The error was evaluated to have a negligible impact on the calculated results for the FSLOCA EM analysis, resulting in an estimated PCT impact of 0°F.

Another error was also noted. Non-conservation of deposited energy was discovered to exist that resulted in a very small fraction of the redistributed energy not being included in the core balance rods. The energy deposited in the hot rod and hot assembly was confirmed to be conserved and correct. This item represents a Non-Discretionary Change in accordance with Section 4.1.2 of WCAP-13451. The error was qualitatively evaluated, and the nature of the error leads to an estimated PCT impact of 0°F.

Page 2 of 3

Attachment 4 Byron Station, Units 1 and 2 10 CFR 50.46 Report Assessment Notes The current report noted the following areas of General Code Maintenance. Various changes have been made to enhance the usability of codes and to streamline future analyses. Examples of these changes include improving the input diagnostic checks; enhancing the code output; optimizing active coding; and eliminating inactive coding. These changes represent Discretionary Changes that will be implemented on a forward-fit basis in accordance with Section 4.1.1 of WCAP-13451. The nature of these changes leads to an estimated PCT impact of 0°F.

Page 3 of 3

Retrieved from "https://kanterella.com/w/index.php?title=RS-23-055,_Annual_10_CFR_50.46_Report_of_Emergency_Core_Cooling_System_Evaluation_Model_Changes_and_Errors&oldid=3535812"