WBL-24-011, CFR 50.46 - Annual Report

CFR 50.46 - Annual Report

ML24081A014
Person / Time
Site:	Watts Bar
Issue date:	03/21/2024
From:	Anthony Williams Tennessee Valley Authority
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
WBL-24-011
Download: ML24081A014 (1)

Text

Post Office Box 2000, Spring City, Tennessee 37381 WBL-24-011 March 21, 2024 10 CFR 50.4 10 CFR 50.46 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Watts Bar Nuclear Plant, Units 1 and 2 Facility Operating License NPF-90 and NPF-96 NRC Docket Nos. 50-390 and 50-391

Subject:

10 CFR 50.46 - Annual Report for Watts Bar Nuclear Plant Units 1 and 2

Reference:

TVA Letter to NRC, WBL-23-013, 10 CFR 50.46 - Annual Report for Watts Bar Nuclear Plant Units 1 and 2, dated March 29, 2023 (ML23088A213)

The purpose of this letter is to provide the annual report of changes and errors to the calculated peak cladding temperature (PCT) for the Watts Bar Nuclear Plant (WBN) Units 1 and 2, Emergency Core Cooling System (ECCS) evaluation model. This report is required in accordance with Title 10 of the Code of Federal Regulations (10 CFR) 50.46, Acceptance Criteria for Emergency Core Cooling Systems for Light-Water Nuclear Power Reactors, paragraph (a)(3)(ii).

Tennessee Valley Authority (TVA) submitted the last 10 CFR 50.46 annual report for WBN Units 1 and 2 to the Nuclear Regulatory Commission (NRC) in the referenced letter. A Reactor Coolant System (RCS) Average Temperature (Tavg) Window has been incorporated into the Unit 1 Loss of Coolant Accident (LOCA) analysis, resulting in an 11°F impact to the updated (net) licensing basis Large Break LOCA (LBLOCA) peak cladding temperature (PCT) for Unit 1.

There are no changes to the updated (net) licensing basis LBLOCA PCT for Unit 2, or the Small Break LOCA (SBLOCA) PCT for either unit.

1\\14 TENNESSEE VALLEY AUTHORITY

U.S. Nuclear Regulatory Commission WBL-24-011 Page 2 March 21, 2024 As presented in this report, compliance with 10 CFR 50.46 requirements is demonstrated by the calculated PCT for both WBN units remaining below the 2200°F limit. Therefore, TVA has concluded that no proposed schedule for providing a reanalysis or other action is required. No further actions are needed to show compliance with 10 CFR 50.46 requirements.

There are no new regulatory commitments in this letter. Please address any questions regarding this response to Jonathan Johnson, Site Licensing Manager, at jtjohnson0@tva.gov.

Anthony L. Williams IV Site Vice President Watts Bar Nuclear Plant

Enclosure:

Watts Bar Nuclear Plant, 10 CFR 50.46 Annual Report for 2023 cc (Enclosure):

NRC Regional Administrator - Region II NRC Senior Resident Inspector - Watts Bar Nuclear Plant Division of Radiological Health - State of Tennessee

ENCLOSURE WBL-24-011 E1 of 7 Watts Bar Nuclear Plant, 10 CFR 50.46 Annual Report for 2023 In accordance with the reporting requirements of Title 10 of the Code of Federal Regulations (10 CFR) 50.46(a)(3)(ii), Tennessee Valley Authority (TVA) is providing the following summary of the limiting design basis loss of coolant accident (LOCA) analysis results established using the current Watts Bar Nuclear Plant (WBN) Emergency Core Cooling System (ECCS) evaluation models for WBN Units 1 and 2. This report describes the changes and errors affecting the calculated peak cladding temperatures (PCTs) since the last analysis of record was submitted to the Nuclear Regulatory Commission (NRC).

TVA submitted the last 10 CFR 50.46 annual report for WBN Units 1 and 2 to the NRC in Reference 1 of this Enclosure.

Tables 1 and 3 list the changes and errors in the Full-Spectrum LOCA (FSLOCA) large break LOCA (LBLOCA) Analysis of Record (AOR) and their associated effects on PCT for WBN Units 1 and 2, respectively. Tables 2 and 4 list the changes and errors in the FSLOCA small break LOCA (SBLOCA) AOR and their associated effect on PCT for WBN Units 1 and 2, respectively. The updated (net) licensing basis PCT for the LBLOCA and SBLOCA for WBN Unit 2, in addition to the SBLOCA for WBN Unit 1, remain unchanged since the last annual report. The updated (net) licensing basis PCT for the LBLOCA for WBN Unit 1 changed due to the incorporation of an analysis of operation with a Reactor Coolant System (RCS) Average Temperature (Tavg) Window.

As presented in this report, compliance with 10 CFR 50.46 requirements is demonstrated by the calculated PCT for both WBN units remaining below the 2200°F limit. Therefore, TVA has concluded that no proposed schedule for providing a reanalysis or other action is required.

ENCLOSURE WBL-24-011 E2 of 7 Table 1 Watts Bar Unit 1 LBLOCA Year Description PCT (°F)

PCT (°F)

Notes Reference 2020 FSLOCA AOR Baseline 1477 1

3 2020 General Code Maintenance 0

0 1

2021 General Code Maintenance 0

0 1

2022 Hoop Stress Error 0

0 1

2022 Generalized Energy Deposition Model (GEDM) Energy Non-Conservation 0

0 1

2022 General Code Maintenance 0

0 1

2023 Tavg Window 11 11 2

2023 Thimble Components Flow Error 0

0 3

2023 General Code Maintenance 0

0 4

2023 Vapor/Continuous Liquid Interfacial Drag Coefficient 0

0 5

Updated (net) licensing basis PCT (AOR PCT + PCT) 1488 Cumulative sum of PCT changes PCT 11

ENCLOSURE WBL-24-011 E3 of 7 Table 2 Watts Bar Unit 1 SBLOCA Year Description PCT (°F)

PCT (°F)

Note Reference 2020 FSLOCA AOR Baseline 978 1

3 2020 General Code Maintenance 0

0 1

2021 General Code Maintenance 0

0 1

2022 Hoop Stress Error 0

0 1

2022 GEDM Energy Non-Conservation 0

0 1

2022 General Code Maintenance 0

0 1

2023 Tavg Window 0

0 2

2023 Thimble Components Flow Error 0

0 3

2023 General Code Maintenance 0

0 4

2023 Vapor/Continuous Liquid Interfacial Drag Coefficient 0

0 5

Updated (net) licensing basis PCT (AOR PCT + PCT) 978 Cumulative sum of PCT changes PCT 0

ENCLOSURE WBL-24-011 E4 of 7 Table 3 Watts Bar Unit 2 LBLOCA Year Description PCT (°F)

PCT (°F)

Notes Reference 2020 FSLOCA AOR Baseline 1477 1

3 2020 General Code Maintenance 0

0 2021 General Code Maintenance 0

0 2022 Tavg Window 11 11 2022 Hoop Stress Error 0

0 2022 GEDM Energy Non-Conservation 0

0 2022 General Code Maintenance 0

0 2023 Thimble Components Flow Error 0

0 3

2023 General Code Maintenance 0

0 4

2023 Vapor/Continuous Liquid Interfacial Drag Coefficient 0

0 5

Updated (net) licensing basis PCT (AOR PCT + PCT) 1488 Cumulative sum of PCT changes PCT 11

ENCLOSURE WBL-24-011 E5 of 7 Table 4 Watts Bar Unit 2 SBLOCA Year Description PCT (°F)

PCT (°F)

Note Reference 2020 FSLOCA AOR Baseline 978 1

3 2020 General Code Maintenance 0

0 1

2021 General Code Maintenance 0

0 1

2022 Tavg Window 0

0 1

2022 Hoop Stress Error 0

0 1

2022 GEDM Energy Non-Conservation 0

0 1

2022 General Code Maintenance 0

0 1

2023 Thimble Components Flow Error 0

0 3

2023 General Code Maintenance 0

0 4

2023 Vapor/Continuous Liquid Interfacial Drag Coefficient 0

0 5

Updated (net) licensing basis PCT (AOR PCT + PCT) 978 Cumulative sum of PCT changes PCT 0

ENCLOSURE WBL-24-011 E6 of 7 Notes for Tables 1 through 4:

1. The analysis of record PCT reflects correction of a gamma energy redistribution error as it was included in the original submittal to adopt FSLOCA for WBN Units 1 and 2.

2. A quantitative evaluation was performed to demonstrate that FSLOCA analyses contain sufficient margin to the 50.46 acceptance criteria to accommodate implementation of the Tavg window. The Region I (SBLOCA) uncertainty analysis and Region II (LBLOCA) uncertainty analysis using Loss of Offsite Power (LOOP) were re-executed mapping the sampled Tavg values from the original Tavg sampling range to the expanded Tavg window implementation range. The estimated effect of Tavg window implementation on Region I analysis is 0°F. The estimated effect for the Region II analyses is 11°F.

3. The number of assemblies modeled in the LOCA analysis was inconsistent with the number of assemblies represented by one or more thimble components, leading to an incorrect flow area and volume for the affected thimble components. The error was evaluated to have a negligible impact on the calculated results, leading to an estimated PCT impact of 0°F.

4. 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. The nature of these changes leads to an estimated peak cladding temperature impact of 0°F.

5. Two deficiencies were identified in the calculation of the churn-turbulent vapor / continuous liquid interfacial drag coefficient calculation within WCOBRA/TRAC-TF2 due to the potential calculation of a negative critical liquid fraction. The negative critical liquid fraction results in an over-prediction of the vapor / continuous liquid interfacial area and a negative vapor /

continuous liquid interfacial drag coefficient which leads to a significantly large interfacial drag coefficient (i.e., no slip). The closely-related group of deficiencies was qualitatively evaluated, and the nature of the deficiencies leads to an estimated peak cladding temperature impact of 0°F.

ENCLOSURE WBL-24-011 E7 of 7

References:

1. TVA Letter to NRC, 10 CFR 50.46 - Annual Report for Watts Bar Nuclear Plant Units 1 and 2, dated March 29, 2023 (ML23088A213)

2. WCAP-18437-P, Engineering Summary Report of the Watts Bar Units 1 and 2 Loss-of-Coolant Accident (LOCA) Analysis with the FULL SPECTRUM LOCA (FSLOCA) Methodology, dated April 3, 2019.

3. NRC Letter to TVA, Watts Bar Nuclear Plant, Units 1 and 2 - Issuance of Amendment Nos. 143 and 50 Regarding Implementation of Full Spectrum' Loss-of-Coolant Accident Analysis (LOCA) and New LOCA-Specific Tritium Producing Burnable Absorber Rod Stress Analysis Methodology (EPID L-2020-LLA-0005), dated February 26, 2021 (ML21034A169)