ML20261H417

NRR E-mail Capture - Sequoyah Nuclear Plant, Units 1 and 2 - Request for Additional Information Regarding Hydrologic UFSAR Update

ML20261H417
Person / Time
Site:	Sequoyah
Issue date:	09/14/2020
From:	Michael Wentzel NRC/NRR/DORL/LPL2-2
To:	Taylor A Tennessee Valley Authority
References
L-2020-LLA-0004
Download: ML20261H417 (5)

Text

From: Wentzel, Michael Sent: Monday, September 14, 2020 11:04 AM To: Taylor, Andrew Charles Cc: Wells, Russell Douglas

Subject:

Sequoyah Nuclear Plant, Units 1 and 2 - Request for Additional Information Regarding Hydrologic UFSAR Update (EPID L-2020-LLA-0004)

Attachments: Final Request for Additional Information Regarding License Amendment Request to Revise UFSAR Hydrologic Analysis (EPID L-2020-LLA-0004).pdf

Dear Mr. Taylor:

By application dated January 14, 2020, (Agencywide Documents Access and Management System (ADAMS) Accession No. ML20016A396); as supplemented by letters dated February 18, May 14, and August 12, 2020 (ADAMS Accession Nos. ML20049H184, ML20135H067, and ML20225A170, respectively); the Tennessee Valley Authority (TVA), submitted a license amendment request to revise the Sequoyah Nuclear Plant, Units 1 and 2, Updated Final Safety Analysis Report hydrologic analysis.

The NRCs External Hazards Branch (EXHB) staff is reviewing the application and identified areas where it needs additional information to support its review. By e-mail dated September 2, 2020, the NRC staff transmitted a draft request for additional information (RAI). Based on a clarification call held on September 10, 2020, the NRC staff has revised the RAI to clarify the information being requested and to consolidate overlapping requests. In addition, the NRC staff deleted Items 1a and 1b from RAI 2.4-2 because that information was previously submitted and is available for the NRC staffs review. The revised, final RAI is attached. As discussed with you on the clarification call, the NRC staff requests your response to the RAI within 30 days of the date of this email.

If you have any questions, please contact me at (301) 415-6459 or michael.wentzel@nrc.gov.

Sincerely, Michael Wentzel, Project Manager Plant Licensing Branch II-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-327 and 50-328

Hearing Identifier: NRR_DRMA Email Number: 782 Mail Envelope Properties (MN2PR09MB5867E923B91C3D59CE0875D2E7230)

Subject:

Sequoyah Nuclear Plant, Units 1 and 2 - Request for Additional Information Regarding Hydrologic UFSAR Update (EPID L-2020-LLA-0004)

Sent Date: 9/14/2020 11:04:28 AM Received Date: 9/14/2020 11:04:28 AM From: Wentzel, Michael Created By: Michael.Wentzel@nrc.gov Recipients:

"Wells, Russell Douglas" <rdwells0@tva.gov>

Tracking Status: None "Taylor, Andrew Charles" <actaylor@tva.gov>

Tracking Status: None Post Office: MN2PR09MB5867.namprd09.prod.outlook.com Files Size Date & Time MESSAGE 1597 9/14/2020 11:04:28 AM Final Request for Additional Information Regarding License Amendment Request to Revise UFSAR Hydrologic Analysis (EPID L-2020-LLA-0004).pdf 55222 Options Priority: Normal Return Notification: No Reply Requested: No Sensitivity: Normal Expiration Date:

REQUEST FOR ADDITIONAL INFORMATION REGARDING LICENSE AMENDMENT REQUEST TO REVISE UPDATED FINAL SAFETY ANALYSIS REPORT HYDROLOGIC ANALYSIS TENNESSEE VALLEY AUTHORITY SEQUOYAH NUCLEAR PLANT, UNITS 1 AND 2 DOCKET NOS. 50-327 AND 50-328 RAI 2.4-2: PMP Input/Output Files Section 2.4.3, PMP [Probable Maximum Precipitation] on Streams and Rivers of the proposed Updated Final Safety Analysis Report (UFSAR) revision present the revised flood hazard estimations at the plant site due to riverine flooding. NUREG-0800, Standard Review Plan

[SRP] for the Review of Safety Analysis Reports for Nuclear Power Plants: LWR [Light-water Reactor] Edition, Revision 4, Section 2.4.3, Probable Maximum Flood (PMF) on Streams and Rivers (Agencywide Documents Access and Management System (ADAMS) Accession No. ML070730405), and Regulatory Guide (RG) 1.59, Design Basis Floods for Nuclear Power Plants (ADAMS Accession No. ML003740388), provide guidelines for estimating this flood causing mechanism. After reviewing the license amendment request (LAR) and enclosed documents, the NRC staff has determined that it needs additional information related to estimating this flood causing mechanism to independently verify the licensees proposed change. Therefore, the NRC staff requests all PMP input/output files be provided, as summarized in Figure No. 1 of Response to NRC IQVB Request for Additional Information (ADAMS Accession No. ML20135H067), including:

1. Input Information

a. User input (including storm types, durations, basins of interest)

b. ArcGIS base Python script

c. Tennessee Valley Authority (TVA) Project sub-basins shapefile

d. Sub-basin geographic information system (GIS) encapsulating shapefile of TVA sub-basins, shapes, area, and positions

2. Gridded PMP Point Data Development - Dedicated Software

a. Sub-basin text file of user input

b. Event specific Python script

c. Modified PMP Evaluation Tool scripts and associated documentation

d. Gridded PMP Point Data used for local intense precipitation (LIP) and PMF

3. Non-QA GIS Software Tools - Alternate ArcGIS Calculations

a. Python scripts for creating Triangular Irregular Network (TIN) and utilizing Polygon Volume Tool b ArcGIS sub-basin weighted average PMP depths for controlling PMF scenario RAI 2.4-3: LIP Modeling Input/Output Files Section 2.4.2, Floods of the proposed UFSAR revision presents the revised flood hazard estimations at the plant site due to LIP flooding. SRP Section 2.4.2, Floods (ADAMS Accession No. ML070100647), provides guidelines for estimating this flood causing mechanism.

After reviewing the submitted LAR and enclosed documents, the NRC staff has determined that it needs additional information related to estimating this flood causing mechanism to independently verify the licensees proposed change. Therefore, the NRC staff requests all LIP modeling input/output files be provided, including:

x LIP hydrodynamic model input/output files for simulating local intense precipitation surface runoff, routing, and flooding.

RAI 2.4-4: PMF Modeling Input/Output Files Section 2.4.3, PMF Flood in Rivers and Streams of the proposed UFSAR revision presents the revised flood hazard estimations at the plant site due to LIP flooding. SRP Section 2.4.3 provides guidelines for estimating this flood causing mechanism. After reviewing the license amendment request (LAR) and enclosed documents, the NRC staff determined that it needs additional information related to estimating this flood causing mechanism to independently verify the licensees proposed change. Therefore, the NRC staff requests all modeling input/output data files be provided for controlling PMF (with hydrologic dam failures) scenario, including:

1. Tabular data associated with the controlling primary and secondary area nesting sequence and the controlling PMP rainfall depth spatial distribution over the watershed (LAR Enclosure, Section 2.4.3.1) as well as executable version of the tools (if any) used to distribute the gridded PMP values into subbasin space and time:

a. LAR Enclosure 3, Figure 2.4.3-1

b. LAR Enclosure 3, Figure 2.4.3-5a (as provided in LAR Enclosure 4, Table 2.4.3-1)

2. Executable version of sub-basin unit hydrograph calculations (as referenced in LAR Enclosure 4, Section 2.4.3.3), as well as electronic version of data shown in LAR Enclosure 3, Figure 2.4.3-6.

3. Executable version of calculation files (if applicable) for estimating precipitation excess (as referenced in LAR Enclosure 4, Section 2.4.3.2).

4. Shapefiles (or similar locational data) for HEC-RAS model limits, river gage, Sequoyah plant site and dam locations, as shown in LAR Enclosure 3, Figure 2.4.3-4 and Figure 2.4.3-5 (as referenced in LAR Enclosure 4, Section 2.4.3.3)

5. Executable version of the runoff and HEC-RAS model files, including HEC-RAS inputs such as calibrated geometry, unsteady flow rules and inflows (as referenced in LAR Enclosure 4, Section 2.4.3.3).

RAI 2.4-5: Seismic Dam Failure Modeling Input/Output Files Section 2.4.4, Potential Dam Failures, Seismically Induced of the proposed UFSAR revision in the application presents the revised flood hazard estimations at the plant site due to seismic dam failure flooding. SRP Section 2.4.3 provides guidelines for estimating this flood causing mechanism. After reviewing the license amendment request (LAR) and enclosed documents, the NRC staff determined that it needs additional information related to estimating this flood causing mechanism to independently verify the licensees proposed change. Therefore, the NRC staff requests all modeling input/output data files be provided for controlling seismic dam failure scenario, including:

1. Hydrologic Engineering Center River Analysis System simulation setup, input and output files for four potentially critical seismic-flood event combinations (as referenced in LAR Enclosure 4, Section 2.4.4.2).

2. Calculations for 25-year and 500-year flood inflows (as referenced in LAR Enclosure 4, Section 2.4.4.1)