CNL-21-065, Status Regarding the Improved Flood Mitigation System Project

Status Regarding the Improved Flood Mitigation System Project

ML21181A273
Person / Time
Site:	Watts Bar, Sequoyah
Issue date:	06/30/2021
From:	Polickoski J Tennessee Valley Authority
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
CNL-21-065
Download: ML21181A273 (4)

Text

1101 Market Street, Chattanooga, Tennessee 37402 CNL-21-065 June 30, 2021 10 CFR 50.4 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 Watts Bar Nuclear Plant, Units 1 and 2 Facility Operating License Nos. NPF-90 and NPF-96 NRC Docket Nos. 50-390 and 50-391

Subject:

Status Regarding the Improved Flood Mitigation System Project

References:

1. Letter from TVA to NRC, Status Regarding the Improved Flood Mitigation System Project, dated September 28, 2018 (ML18274A055)

2. Letter from TVA to NRC, Request for Review and Approval of Topical Report TVA-NPG-AWA16, TVA Overall Basin Probable Maximum Precipitation and Local Intense Precipitation Analysis, Calculation CDQ0000002016000041, Revision 1, dated June 22, 2018 (ML18192A510)

3. Letter from NRC to TVA, Final Safety Evaluation for Tennessee Valley Authority Topical Report TVA Overall Basin Probable Maximum Precipitation and Local Intense Precipitation Analysis Calculation CDQ0000002016000041, Rev. 1 (EPID L-2016-TOP-0011), dated March 18, 2019 (ML19010A212)

4. Letter from TVA to NRC, Application to Revise Sequoyah Nuclear Plant Units 1 and 2 Updated Final Safety Analysis Report Regarding Changes to Hydrologic Analysis, (SQN-TS-19-02), dated January 14, 2020 (ML20016A396)

5. Letter from TVA to NRC, Supplement to Application to Revise Sequoyah Nuclear Plant Units 1 and 2 Updated Final Safety Analysis Report Regarding Changes to Hydrologic Analysis, (TS-19-02) (EPID L-2020-LLA-0004), dated February 18, 2020 (ML20048H184)

6. Letter from TVA to NRC, Status Regarding the Improved Flood Mitigation System Project, dated December 17, 2020 (ML20352A141)

U.S. Nuclear Regulator Commission CNL-21-065 Page 2 June 30, 2021 By letter dated September 28, 2018, Tennessee Valley Authority (TVA) informed the Nuclear Regulatory Commission (NRC) of a change in the specified field implementation completion schedule to install improved flood mode mitigation systems (FMMS) at the Sequoyah Nuclear Plant (SQN), Units 1 and 2, and the Watts Bar Nuclear Plant (WBN), Units 1 and 2 (Reference 1). The change in the implementation schedule was based on the ongoing TVA project to upgrade precipitation models and rerun hydraulic models to determine new probable maximum flood levels for both design basis and beyond-design-basis purposes.

In a letter dated December 17, 2020 (Reference 6), TVA committed to provide a written update regarding the reevaluated SQN and WBN flood levels using updated precipitation data. The purpose of this letter is to provide that update.

TVA completed an updated precipitation calculation that includes updated data (storm and dew point), meteorological science, technology, weather radar, Geographic Information System (GIS) tools, and treatment of topography. TVA submitted this precipitation calculation for NRC review by letter dated June 22, 2018 (Reference 2). The NRC completed the review of the revised precipitation calculation. The review and conclusions drawn from the review are documented in a Safety Evaluation that was provided by NRC by letter dated March 18, 2019 (Reference 3).

The revised precipitation data has been used as input into TVAs hydraulic models to determine the resulting flood levels at the SQN and WBN sites. The preliminary results from the hydraulic models used to establish resulting changes in flood levels at the SQN and WBN sites reflect decreases in analyzed flood levels at both sites. Analysis work is currently ongoing to address a potentially nonconservative assumption that was discussed with NRC on October 13, 2020 (ML20293A080).

TVA has submitted a License Amendment Request (LAR) to update its licensing basis for SQN with the analyzed flood levels by letter dated January 14, 2020 (Reference 4), and supplemented by letter dated February 18, 2020 (Reference 5). A similar LAR for WBN is planned to be submitted in the future.

Consequently, as described in Reference 6, TVA has concluded it is prudent to defer the final decision regarding the field implementation of FMMS until resolution of the potentially nonconservative assumption and the submittal of LAR documentation associated with the update to the SQN and WBN licensing bases. This will allow TVA to demonstrate what appropriate margin, if any, should be designed into additional flood mitigating systems at SQN and WBN.

TVA will provide a written update regarding the reevaluated SQN and WBN flood levels using the revised precipitation data by December 31, 2021.

U.S. Nuclear Regulator Commission CNL-21-065 Page 3 June 30, 2021 The enclosure to this letter provides one new regulatory commitment contained in this letter. If additional information is needed regarding this update, please contact Russell Thompson at (423) 751-2567.

Respectfully, James T. Polickoski Director, Nuclear Regulatory Affairs Enclosure cc (Enclosure):

NRC Regional Administrator - Region II NRC Senior Resident Inspector - Sequoyah Nuclear Plant NRC Senior Resident Inspector - Watts Bar Nuclear Plant NRR Director - NRC Headquarters NRR Project Manager - Sequoyah Nuclear Plant NRR Project Manager - Watts Bar Nuclear Plant

ENCLOSURE COMMITMENT

1. TVA will provide a written update regarding the reevaluated SQN and WBN flood levels using the revised precipitation data by December 31, 2021.

CNL-21-065 E-1