ML22327A141

10 CFR 50.46 Annual and 30-Day Report of Changes in Peak Cladding Temperatures (PCT)

ML22327A141
Person / Time
Site:	Sequoyah
Issue date:	11/22/2022
From:	Marshall T Tennessee Valley Authority
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
Download: ML22327A141 (1)

Text

Post Office Box 2000, Soddy Daisy, Tennessee 37384-2000 November 22, 2022 10 CFR 50.4 10 CFR 50.46 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Sequoyah Nuclear Plant, Units 1 and 2 Renewed Facility Operating License Nos. DPR-77 and DPR-79 NRC Docket Nos. 50-327 and 50-328

Subject:

10 CFR 50.46 Annual Report for Sequoyah Nuclear Plant, Units 1 and 2, and 30-Day for Sequoyah Nuclear Plant, Unit 1

References:

1. Letter from TVA to NRC, 10 CFR 50.46 Annual Report for Sequoyah Nuclear Plant Units 1 and 2, dated November 22, 2021

2. Letter from NRC to TVA, Sequoyah Nuclear Plant, Units 1 and 2 - Issuance of Amendment Nos. 356 and 349 Regarding the Transition to Westinghouse Robust Fuel Assembly-2 (RFA-2) Fuel (EPID L-2020-LLA-0216), dated October 26, 2021 The purpose of this letter is to provide the annual report of changes and errors in the emergency core cooling system (ECCS) evaluation model for Sequoyah Nuclear Plant (SQN) Units 1 and 2.

In accordance with Title 10 of the Code of Federal Regulations (10 CFR) 50.46, Acceptance Criteria for ECCS for Light-Water Nuclear Power Reactors, paragraph (a)(3)(ii), the Enclosure to this report describes the nature of the change or error and its estimated effect on the limiting ECCS analysis for SQN Units 1 and 2. This report also serves as the 30-day report of the Loss of Coolant Accident (LOCA) peak cladding temperature (PCT) impacts for SQN Unit 1 associated with the transition to Westinghouse RFA-2 fuel. As such, in addition to satisfying the annual reporting requirements of 10 CFR 50.46(a)(3)(ii) for SQN Units 1 and 2, this submittal also satisfies the 30-day reporting requirement for Unit 1.

The enclosed report provides a summary of the changes to the calculated PCTs for the limiting ECCS analyses applicable to SQN Unit 1. There have been no changes to the calculated PCT for SQN Unit 2 since the submittal of Reference 1.

U.S. Nuclear Regulatory Commission Page 2 November 22, 2022 The PCT for the Westinghouse RFA-2 fuel is calculated using the Full Spectrum LOCA (FSLOCA) evaluation model (EM) per Reference 2. The accumulated PCT changes for RFA-2 fuel have not yet exceeded the 50°F threshold for a significant change or error as identified in 10 CFR 50.46(a)(3)(i).

The identified PCT changes for the Framatome High Thermal Performance (HTP) fuel exceed the 50 degree Fahrenheit (°F) threshold for a significant change or error as defined in 10 CFR 50.46(a)(3)(i). Accordingly, any subsequently discovered change or error would be considered significant for the purposes of reporting until such time as a reanalysis of the ECCS evaluation model is completed. This report is the result of the loading of a transition core consisting of coresident Westinghouse RFA-2 and Framatome HTP fuel assemblies for SQN Unit 1 Cycle 26. When coresident with RFA-2 fuel, the calculated large-break Loss of Coolant Accident (LBLOCA) PCT for the HTP fuel is penalized by +23°F. Since the absolute magnitude of accumulated changes and errors in the LBLOCA PCT already exceeds 50°F, a 30-day report is required in accordance with 10 CFR 50.46(a)(3)(ii).

10 CFR 50.46(a)(3)(ii) also requires the licensee to provide a proposed schedule for providing a reanalysis or taking other action as may be needed to show compliance with 10 CFR 50.46 requirements. The Enclosure demonstrates that the HTP fuels updated net licensing basis PCT for the LBLOCA is below the 10 CFR 50.46(b)(1) PCT limit of 2200°F. Therefore, TVA has concluded that no proposed schedule for reanalysis or other action is required to show compliance with 10 CFR 50.46 requirements.

There are no new regulatory commitments associated with this submittal. If you have any questions regarding this information, please contact Jeffrey R. Sowa, SQN Site Licensing Manager, at (423) 843-8129.

Respectfully, Digitally signed by Marshall, Thomas Marshall, Thomas B. B.Date: 2022.11.22 14:26:27 -05'00' Thomas B. Marshall Site Vice President Sequoyah Nuclear Plant

Enclosure:

10 CFR 50.46 Annual and 30-Day Report of Changes in PCT cc:

NRC Regional Administrator - Region II NRC Senior Resident Inspector - Sequoyah Nuclear Plant NRC Project Manager - Sequoyah Nuclear Plant

ENCLOSURE TENNESSEE VALLEY AUTHORITY SEQUOYAH NUCLEAR PLANT (SQN)

UNIT 1 10 CFR 50.46 ANNUAL AND 30-DAY REPORT OF CHANGES IN PCT 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 (LOCA) analysis results established using the emergency core cooling system (ECCS) evaluation models for Sequoyah Nuclear Plant (SQN)

Unit 1. 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 SQN Unit 1 in Reference 1 of this Enclosure. The last PCT change was tabulated in the Summary of Changes for the 2019 reporting year, or Reference 2 of this Enclosure.

SQN Unit 1 is transitioning from Framatome High Thermal Performance (HTP) fuel to Westinghouse Robust Fuel Assembly-2 (RFA-2) fuel. Each vendor calculates a PCT for its respective fuel type using its own LOCA analysis methodologies, resulting in two distinct PCTs until a full core of RFA-2 fuel is loaded. The LOCA Analysis of Record (AOR) for RFA-2 fuel at SQN uses the Full-Spectrum Loss of Coolant Accident (FSLOCA) evaluation model (EM). The application of FSLOCA to SQN was described as part of the SQN Technical Specification (TS)

Change SQN-TS-20-09 to modify the TSs to allow the use of Westinghouse RFA-2 fuel. This TS amendment was approved by the NRC as documented in the Safety Evaluation dated October 26, 2021 (Reference 3 of this Enclosure).

The baseline PCTs for RFA-2 fuel in SQN Unit 1 result from the implementation of this analysis.

Table 1 lists the subsequent changes in the large break LOCA (LBLOCA) PCT for the RFA-2 fuel since the baseline analysis, for both offsite power available (OPA) and loss-of-offsite power (LOOP) scenarios. Table 2 lists the changes in the small break LOCA (SBLOCA) PCT for the RFA-2 fuel since the baseline analysis. PCT impacts incurred since the adoption of the baseline AOR are described in the notes to the tables.

The LOCA AORs for the HTP fuel at SQN are detailed in Topical Reports ANP-2970(P) and ANP-2970Q1(P), Sequoyah Units 1 and 2 HTP Fuel Realistic Large Break LOCA Analysis, and ANP-2971(P), Sequoyah Units 1 and 2 HTP Fuel S-RELAP5 Small Break LOCA Analysis.

These reports were submitted to the Nuclear Regulatory Commission (NRC) as part of SQN Technical Specifications (TS) Change TS-SQN-2011-07 to modify the TS to authorize the use of AREVA HTP fuel assemblies. The TS change associated with the HTP fuel design and E1 of E7

supporting documentation were approved by the NRC as documented in the associated Safety Evaluation dated September 26, 2012 (Reference 4).

Table 3 details the changes in the LBLOCA and SBLOCA PCTs AOR PCTs for the HTP fuel since the baseline analysis. PCT impacts incurred against this analysis since the last submitted Summary of Changes (Reference 2 of this Enclosure) are described in the notes to the tables.

The changes in PCTs since the previous report, for SQN Unit 1, are summarized as follows:

The calculated PCT in the LBLOCA analysis for RFA-2 fuel remains unchanged, with a current licensing basis PCT of 1878°F.

The calculated PCT in the SBLOCA analysis for RFA-2 fuel remains unchanged, with a current licensing basis PCT of 1213°F.

The calculated PCT in the LBLOCA analysis for HTP fuel has increased 23°F, with a current licensing basis PCT of 2024°F.

The calculated PCT in the SBLOCA analysis for HTP fuel remains unchanged, with a current licensing basis PCT of 1543°F.

E2 of E7

TABLE 1 Summary of Changes in SQN Unit 1 LBLOCA PCT for RFA-2 Fuel OPA LOOP PCT PCT PCT PCT Year Description (°F) (°F) (°F) (°F) Note 2020 FSLOCA AOR Baseline 1,878 --- 1,878 ---

2020 General Code Maintenance 0 0 0 0 1 2021 General Code Maintenance 0 0 0 0 1 Updated (net) licensing basis PCT 1,878 --- 1,878 ---

AOR PCT + PCT Cumulative sum of PCT changes

--- 0 --- 0 PCT E3 of E7

TABLE 2 Summary of Changes in SQN Unit 1 SBLOCA PCT for RFA-2 Fuel PCT PCT Year Description (°F) (°F) Note 2020 FSLOCA AOR Baseline 1,213 ---

2020 General Code Maintenance 0 0 1 2021 General Code Maintenance 0 0 1 Updated (net) licensing basis PCT 1,213 ---

AOR PCT + PCT Cumulative sum of PCT changes

--- 0 PCT E4 of E7

TABLE 3 Summary of Changes in SQN Unit 1 LBLOCA and SBLOCA PCT for HTP Fuel LBLOCA LBLOCA SBLOCA SBLOCA Year Description PCT (°F) PCT (°F) PCT (°F) PCT (°F) Note 2013 AOR PCT associated with 1,950 --- 1,470 ---

AREVA HTP fuel 2012 Sleicher-Rouse heat Included in transfer correlation 0 -89 89 AOR PCT equation error 2013 Cathcart-Pawel Uncertainty 0 0 --- ---

Correlation in RLBLOCA 2013 RODEX3a error in treatment of trapped stack -10 10 --- ---

condition 2014 S-RELAP5 vapor 0 0 +11 11 absorptivity correlation 2014 Axial power shape mapping 0 0 --- ---

by modal decomposition 2015 Operator action time allowance for restarting the high head ECCS pumps

--- --- +151 151 when transferring the pump suctions from the RWST to the containment sump 2017 M5 LOCA Swelling and Rupture Model (SRM) 0 0 0 0 Update 2017 Higher metal water reaction 61 61 0 0 rate 2019 Cathcart-Pawel correlation 0 0 --- ---

implementation 2022 RFA-2 Fuel Transition Core

+23 23 0 0 2 Effects Updated (net) licensing

--- basis PCT 2,024 --- ---

1,543 AOR PCT + PCT Cumulative sum of PCT

--- changes: +74 94 +73 251 PCT and PCT E5 of E7

Notes for Tables 1, 2, and 3:

1) 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.

2) Westinghouse evaluated HTP/RFA-2 mixed cores with respect to the LOCA analyses assuming homogenous cores of each fuel type. Because the loss coefficient of Westinghouse RFA-2 fuel is slightly lower than the Framatome HTP fuel, the RFA-2 fuel would receive a flow benefit in the presence of the HTP fuel, which would experience a flow reduction. For SBLOCA, the core-wide collapsed liquid levels correspond closely to a 1-dimensional flow pattern and the effects of differing grid loss coefficients are relatively insignificant in regard to PCT. For LBLOCA, the hydraulic mismatch effects are more substantial. A PCT increase was calculated based on these effects on a transient with the reflood time and cladding heatup rate consistent with the Framatome RLBLOCA case that yielded the PCT for homogenous HTP cores.

The effect of this change for SBLOCA is 0°F since the existing AOR supports HTP/RFA-2 transition cores. For LBLOCA, the PCT increase was estimated to be 23°F.

E6 of E7

REFERENCES

1) Letter from TVA to NRC, 10 CFR 50.46 Annual Report for Sequoyah Nuclear Plant Units 1 and 2, dated November 22, 2021

2) Letter from TVA to NRC, 10 CFR 50.46 Annual and 30 Day Report for Sequoyah Nuclear Plant, Units 1 and 2, dated October 22, 2019

3) Letter from NRC to TVA, Sequoyah Nuclear Plant, Units 1 and 2 - Issuance of Amendment Nos. 356 and 349 Regarding the Transition to Westinghouse Robust Fuel Assembly-2 (RFA-2) Fuel (EPID L-2020-LLA-0216), dated October 26, 2021

4) Letter from NRC to TVA, Sequoyah Nuclear Plant, Units 1 and 2 - Issuance of Amendments to Revise the Technical Specification to Allow Use of AREVA Advanced W17 High Thermal Performance Fuel (TS-SQN-2011-07) (TAC Nos. ME6538 and ME6539), dated September 26, 2012 E7 of E7