ML20294A376
| ML20294A376 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 09/23/2020 |
| From: | Michael Wentzel NRC/NRR/DORL/LPL2-2 |
| To: | Orf T Tennessee Valley Authority |
| References | |
| L-2020-LLA-0058 | |
| Download: ML20294A376 (8) | |
Text
From:
Wentzel, Michael Sent:
Wednesday, September 23, 2020 7:59 AM To:
Orf, Tracy J
Subject:
Draft Request for Additional Information - Browns Ferry Nuclear Plant, Units 1, 2, and 3, Request to Adopt TSTF-425 (EPID L-2020-LLA-0058)
Attachments:
Browns Ferry Draft Request for Additional Information Regarding Request to Adopt TSTF-425 (L-2020-LLA-0058).docx
- Trace, By letter dated March 27, 2020, (Agencywide Documents Access and Management System Accession No. ML20087P262), the Tennessee Valley Authority (TVA), submitted a license amendment request for Browns Ferry Nuclear Plant, Units 1, 2, and 3, to relocate specific surveillance frequencies to a licensee-controlled program, consistent with Technical Specification Task Force Traveler, TSTF-425, Revision 3.
The U.S. Nuclear Regulatory Commissions (NRCs) Probabilistic Risk Assessment Branches B and C (APLB and APLC) staff are reviewing the application and have identified areas where they need additional information to support their review. The draft request for additional information (RAI) is provided in the attached.
Please let me know by September 30, 2020, if a clarification call is needed.
Sincerely, Michael Wentzel, Project Manager Plant Licensing Branch II-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation
Hearing Identifier:
NRR_DRMA Email Number:
842 Mail Envelope Properties (MN2PR09MB5867B17EC77EDB6CDB1C0F6FE7380)
Subject:
Draft Request for Additional Information - Browns Ferry Nuclear Plant, Units 1, 2, and 3, Request to Adopt TSTF-425 (EPID L-2020-LLA-0058)
Sent Date:
9/23/2020 7:59:03 AM Received Date:
9/23/2020 7:59:03 AM From:
Wentzel, Michael Created By:
Michael.Wentzel@nrc.gov Recipients:
"Orf, Tracy J" <tjorf@tva.gov>
Tracking Status: None Post Office:
MN2PR09MB5867.namprd09.prod.outlook.com Files Size Date & Time MESSAGE 978 9/23/2020 7:59:03 AM Browns Ferry Draft Request for Additional Information Regarding Request to Adopt TSTF-425 (L-2020-LLA-0058).docx 31625 Options Priority:
Normal Return Notification:
No Reply Requested:
No Sensitivity:
Normal Expiration Date:
REQUEST FOR ADDITIONAL INFORMATION REGARDING RISK-INFORMED JUSTIFICATION FOR THE RELOCATION OF SPECIFIC SURVEILLANCE FREQUENCY REQUIREMENTS TO A LICENSEE CONTROLLED PROGRAM TENNESSEE VALLEY AUTHORITY BROWNS FERRY NUCLEAR PLANT, UNITS 1, 2, AND 3 DOCKET NOS. 50-259, 50-260, AND 50-296 By letter dated March 27, 2020 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML20087P262), the Tennessee Valley Authority (TVA) submitted a license amendment request (LAR) regarding Browns Ferry Nuclear Plant, Units 1, 2, and 3 (Browns Ferry). The proposed amendments would modify the Browns Ferry Technical Specifications by relocating specific surveillance frequencies to a licensee-controlled program with the implementation of Nuclear Energy Industry (NEI) Topical Report 04-10, Revision 1, Risk-Informed Technical Specifications Initiative 5b - Risk-Informed Method for Control of Surveillance Frequencies (ADAMS Accession No. ML071360456). The licensee stated that the proposed changes are consistent with Nuclear Regulatory Commission (NRC)-approved
/Technical Specification Task Force (TSTF) Standard Technical Specification (STS) change TSTF-425, Revision 3, Relocate Surveillance Frequencies to Licensee Control - RITSTF Initiative 5b (ADAMS Accession No. ML090850642).
REGULATORY BASES AND GUIDANCE Regulatory Guide (RG) 1.200, Revision 2, An Approach for Determining the Technical Adequacy of Probabilistic Risk Assessment Results for Risk-Informed Activities, Section 2.2, provides regulatory guidance regarding peer reviews and the staff regulatory position on NEI 00-02, Probabilistic Risk Assessment (PRA) Peer Review Process Guidance (ADAMS Accession No. ML061510619), NEI 05-04, Process for Performing Follow-On [Internal Events]
PRA Peer Reviews Using the American Society of Mechanical Engineers (ASME)/American Nuclear Society (ANS) PRA Standard (ADAMS Accession No. ML083430462), and NEI 07-12, Fire Probabilistic Risk Assessment (FPRA) Peer Review Process Guidelines (ADAMS Accession No. ML102230070).
The NEI guidance document NEI 04-10, Revision 1, provides guidance for relocating the surveillance frequencies from the Technical Specifications to a licensee-controlled program by providing an NRC-approved methodology for control of the surveillance frequencies. The guidance in NEI 04-10, Revision 1, is acceptable for referencing in licensing actions to the extent specified and under the limitations delineated in NEI 04-10, and the NRC safety evaluation providing the basis for NRC acceptance of NEI 04-10 (ADAMS Accession No. ML072570267).
REQUESTS FOR ADDITIONAL INFORMATION
, Section 3 of the LAR states that the PRA models have been developed in accordance with the requirements of RG 1.200, Revision 2, subjected to peer review and the Facts and Observations (F&O) independent assessment process.
The following requests for additional information (RAIs) are needed to enable the NRC staff to complete its review of the application:
APLB RAI 01: Peer Review History: Appendix X, Closure of Facts and Observations Section 3.4.2 of the LAR states, in part, that 95 Internals Events Finding F&Os identified in the peer review in May 2009 were subjected to an F&O Resolution Review FSPR [focused-scope peer review] in 2015, which followed the guidance from NEI 05-04. The LAR further states that
[a] subsequent F&O Closeout Assessment was completed in September 2018 at the TVA Chattanooga offices for the 48 Internals Events Findings that remained open. This assessment was completed in accordance with the process documented in Appendix X to NEI 05-04/07-12/12-13 (Appendix X), as well as the requirements published in the ASME/ANS PRA Standard (RA-Sa-2009) and RG 1.200 Revision 2 including NRC expectations. Section 3.5.1 of the LAR also states that [t]he focused scope peer review also assessed the closure of 68 F&Os resolved by TVA for the BFN FPRA The NRC staff acceptance of Appendix X for closure of F&Os, dated May 3, 2017 (ADAMS Accession No. ML17079A427) came after the resolution reviews that were conducted to address the internal events (including internal floods) PRA (IEPRA) and fire PRA (FPRA) F&Os that were performed in 2015. It is unclear to the NRC staff how these F&Os were determined to be closed as a result of the 2015 resolution reviews using the guidance from NEI 05-04, considering the Appendix X process for the closure of F&Os was incomplete and had not been accepted by the NRC staff at that time.
- a. Confirm that the closure of these F&Os represent the results of observations or suggestions as described in the ASME/ANS PRA standard and do not rise to the level of findings from previous peer reviews.
- b. Perform a subsequent Independent Assessment using Appendix X, as accepted, with conditions, by the NRC staff in the letter dated May 3, 2017 to include those finding-level F&Os. Provide any F&Os that remain open as a result of this review. For each F&O and/or item that remains open, provide its associated disposition to demonstrate that it has no adverse impact on the application.
- c. Propose a mechanism that assures all the open finding-level F&Os are addressed as applicable for the surveillance test interval (STI) at the time the evaluation is performed.
- d. Provide a table of all the findings (i.e., IEPRA and FPRA), for each finding-level F&O, provide the disposition and the impact of the F&O on the PRA as it pertains to the application.
APLB RAI 02 Disposition for Open F&Os Tables 11 and 13 of the LAR, Open Internal Events With Internal Flooding PRA Open F&Os, and Fire PRA Open F&Os, respectively, provide the licensees disposition for each of the PRA F&Os. Address the following:
- a. For several of the findings (i.e., 4-18, 4-25, 6-30, and IFQU A6-01) TVA concludes for impact on the surveillance frequency control program (SFCP) that STI [surveillance test interval] changes are not affected by human error probabilities (HEPs) as the calculation determines the change in risk due to changes in reliability, and goes on to further state that minimal or no impact on the PRA results is expected. A PRA model uses the as-built, as-operated plant, which includes operational practices that can influence the results of the PRA. For the SFCP, the results of the PRA assess changes in the core damage frequency (CDF) and large early release frequency (LERF) to determine the extension for an STI. For the above F&Os (i.e., 4-18, 4-25, 6-30, and IFQU A6-01), it is unclear to the NRC staff why the operator responses and HEPs will not impact potential STI changes.
- i.
Provide sufficient justification for these F&Os that supports how it was determined that future STI extensions are not adversely impacted (e.g., results of a sensitivity) or identify how NEI 04-10 (generic sensitivities) addresses future STI extensions within the established process for each of the F&Os. If any F&Os are determined to need to be addressed on a case-by-case basis for future STI evaluations, include that in the justification.
- b. The finding (F&O 1-33) pertaining to supporting requirement LE-F2 observes that TVA did not review LERF contributors for reasonableness. TVA stated that its documentation provides a listing of addressed phenomena and failures postulated to lead to LERF and explained that the Browns Ferry model provides mapping to these postulated events in the QU notebook and includes a comparison of absolute frequency to similar designs.
TVA further states that this is a documentation issue and that a reasonableness check of results ensures the actual results obtained align with expected results and, therefore, no impact is expected on the STI change evaluations performed in accordance with the SFCP. Although no impact is expected on the STI change evaluations, it is unclear to the NRC staff how TVA assured that conservatisms have not skewed the results (level of plant-specificity is appropriate for significant contributors, etc.). Either:
- i.
Provide sufficient justification that confirms the expectation that the F&O will have no impact on the STI change evaluations.
OR ii. Perform and document a review of the reasonableness of the contributors to LERF consistent with SR LE-F2 at capability category (CC)-II of the ASME/ANS RA-Sa-2009 PRA standard and provide a summary of those results to the NRC staff.
- c. For several of the findings (i.e., IFSN-A10-01, IFSN-A10-02, IFEV-A1-01, and IFQU A9-
- 01) TVA concludes for impact on the SFCP that [the] issues impact potential initiating events, but the scenario response would be characterized by scenarios already modeled [and] STI changes are not affected by flood initiating events It is unclear to the NRC staff how the potential impact of the initiating events has been appropriately
characterized to ensure that the scenario responses are adequate to ensure that future STI changes are not affected.
- i. For the finding-level F&Os (i.e., IFSN-A10-01, IFSN-A10-02, IFEV-A1-01, and IFQU A9-01), provide sufficient justification that determines that future STI changes are not adversely impacted (e.g., results of a sensitivity) or identify how NEI 04-10 (generic sensitivities) addresses future STI changes within the established process for each of the F&Os. If any F&Os are determined to need to be addressed on a case-by-case basis for future STI evaluations, include in the justification.
- d. For several of the findings related to the fire PRA (FPRA) (i.e., 2-38, 2-39, 2-50, AS-A5, 4-21, 4-12 for SR AS-A5), and 9-4,) the analysis does not reflect the as-built, as-operated plant (e.g., existing Browns Ferry procedures cannot be updated until the NFPA 805 modifications and completion of the post-transition safe shutdown procedures have been completed). For impact on SFCP the licensee concludes the STI changes are not affected by either HEPs or spurious operations events, etc. Furthermore, in Section 7.1 of the LAR the licensee provides a table that includes the FPRA results for Units 1, 2, and 3. It is unclear to the NRC staff why the operator responses, HEPs, spurious operations events, etc. will not impact future STI evaluations. Also, it is not clear to the NRC staff if the results for the FPRA provided in Table 16 of the LAR reflect the current as-built, as-operated plant or the future state after the NFPA-805 transition has been completed.
- i.
Provide sufficient justification for these F&Os that supports how it was determined that future STI extensions are not adversely impacted (e.g., results of a sensitivity) or identify how NEI 04-10 addresses future STI extensions (within the established process) for each of the F&Os.
AND ii. Clarify, if the FPRA results provided in Table 16 of the LAR represent the current as-built, as-operated Browns Ferry plant or the future state after the NFPA-805 transition has been completed. If the FPRA results represent the future state of the plant, propose a mechanism that ensures that any open F&Os will be addressed as applicable for the STI at the time the evaluation is performed (e.g., PRA model used will represent the as-built, as-operated plant).
APLB/C RAI 03: Key Assumptions and Sources of Uncertainties NEI 04-10, Revision 1, Step 5 discusses how Regulatory Guide RG 1.200, Revision 2, provides attributes of importance for risk determinations relative to external events, seismic, internal fires, and shutdown. This RG specifically addresses the need to evaluate important assumptions that relate to key modeling uncertainties and the need to evaluate parameter uncertainties and demonstrate that calculated risk metrics (e.g., CDF and LERF) represent mean values.
Sections 3.4.4, 3.5.3, and 3.6.3 of Attachment 2 to the LAR describes the approach for the licensee used for the identification of Internal Events (includes internal floods), fire, and seismic key assumptions and sources of uncertainty. For seismic, the licensee states that the seismic PRA (SPRA) was built off of the full-power IEPRA; therefore, any assumptions that are key in the full-power IEPRA are also key assumptions for the SPRA. However, the licensee did not provide a complete list identifying the key assumptions and sources of uncertainty, and how impacts for this application were assessed.
- a. Provide a brief description of how the key assumptions and sources of uncertainties for the IEPRA (includes internal floods), FPRA, and SPRA were identified from the initial comprehensive list of PRA model(s) (i.e., base model) source of uncertainties and assumptions, including those associated with plant-specific features, modeling choices, and generic industry concerns. Include a disposition for each of the assumptions and/or uncertainties addressing their impact on the risk-informed application. For any key source of uncertainty or key assumption judged not to be key to the application, provide discussion for why it is not pertinent to the application and therefore does not need to be further addressed. Identify appropriate sensitivity cases that will be used to support the disposition for this application or use a qualitative discussion to justify that the identified key assumption would not affect this application.
APLC RAI 04: Considerations of Tornado Missiles NEI 04-10, Revision 1, states that external events risk impact may be considered quantitatively or qualitatively. The NRC staffs safety evaluation on NEI 04-10, Revision 1, states that a qualitative screening analysis may be used when the surveillance frequency impact on plant risk can be shown to be negligible or zero.
Section 4.1 of Attachment 2 to the LAR provides the considerations of extreme wind and tornado. The licensee screened extreme wind and tornado based on the current plant design.
However, the licensee did not provide any discussion on tornado missile impacts on the systems, structures, and components that are considered in this LAR. Therefore, it is unclear to the NRC staff whether and how the tornado missile impact has been considered for this application.
Explain how the risk from tornado generated missiles on systems, structures, and components, including, but not limited to, the non-conformances identified in the licensees LAR to use the Tornado Missile Risk Evaluator (TMRE) methodology (ADAMS Accession No. ML20127H904), is considered for this application. The explanation should include either a description of the approach that will be followed for considering such risks and its consistency with the endorsed guidance in NEI 04-10, Revision 1, or justification for screening the risk from tornado generated missiles for this application.
APLC RAI 05: Considerations of External Flooding NEI 04-10, Revision 1, states that external events risk impact may be considered quantitatively or qualitatively. The NRC staffs safety evaluation on NEI 04-10, Revision 1, states that a qualitative screening analysis may be used when the surveillance frequency impact on plant risk can be shown to be negligible or zero.
Section 4.1 of Attachment 2 to the LAR provides the considerations of external flooding, including the probable maximum flood (PMF). The licensee screened external flooding based on the current plant design. However, the licensee did not discuss other external flooding mechanism, such as the local intense precipitation (LIP) event. The licensees flood hazard re-evaluation report (FHRR; ADAMS Accession No. ML15072A130) and its corresponding NRC staff assessment (ADAMS Accession No. ML16196A088) identified LIP as an external flooding hazard that exceeds the plants design basis. Therefore, it is unclear to the NRC staff whether and how the risk from LIP has been considered for this application.
Explain how the risk from LIP, is considered for this application. The explanation should include either a description of the approach that will be followed for considering the risk and its consistency with the endorsed guidance in NEI 04-10, Revision 1, or justification for screening the risk for this application.