ML25234A100

TSTF-505 Audit Question (APLC-01 Follow Up)

ML25234A100
Person / Time
Site:	Wolf Creek
Issue date:	08/22/2025
From:	Samson Lee Plant Licensing Branch IV
To:	Lee N Wolf Creek
Lee S, 301-415-3168
References
EPID L-2024-LLA-0170 TSTF-505
Download: ML25234A100 (1)

Text

From:

Samson Lee To:

Nathan Lee

Subject:

Wolf Creek TSTF-505 audit question (APLC-01 follow up) dated August 22, 2025 (EPID: L-2024-LLA-0170)

Date:

Friday, August 22, 2025 8:57:00 AM By letter dated December 17, 2024, (Agencywide Documents Access and Management System (ADAMS) Accession No. ML24352A438), Wolf Creek Nuclear Operating Corporation (the licensee) submitted license amendment request (LAR) to amend the license for Wolf Creek Generating Station (WCGS, Wolf Creek), Renewed Facility Operating License No. NPF-42. The LAR would adopt Technical Specifications Task Force (TSTF) Traveler TSTF-505, Revision 2, Provide Risk-informed Extended Completion Times - RITSTF [Risk-Informed TSTF] Initiative 4b. The U.S. Nuclear Regulatory Commission (NRC) staff has identified the need for a regulatory audit to examine the licensees non-docketed information with the intent to gain understanding, to verify information, or to identify information that will require docketing to support the basis of the licensing or regulatory decision. The NRC staff issued an audit plan dated April 2, 2025 (ML25090A217).

The NRC staff has formulated the below follow-up audit discussion question for PRA

[Probabilistic Risk Assessment] Licensing Branch C (APLC) APLC-01 to provide additional context and clarify NRC staff expectations regarding the licensees seismic margin assessment (SMA) upgrade to support the proposed enhanced high confidence low probability of failure (HCLPF) value. If time allows, please prepare responses to the question in advance. It would facilitate the audit discussions, especially if responses can be posted in the online portal as they become available. The NRC staff plans to issue additional audit discussion questions for other technical areas as available to support breakout audit meetings for efficiency.

Wolf Creek TSTF505, Audit Question APLC01 FollowUp (8-22-2025)

The Wolf Creek TSTF-505 license amendment request (LAR) incorporates seismic risk into the risk-informed completion time (RICT) calculations through penalty factors derived from the plant-level high confidence low probability of failure (HCLPF) value. Generic Issue 199 (GI-199) reports a current HCLPF value of 0.2g peak ground acceleration (PGA) for Wolf Creek. In response to TSTF-505 Audit Question APLC-01, the licensee elected option b, which relies on an increased HCLPF value of 0.3g PGA.

In APLC-01, the NRC staff requested that the licensee provide a completed seismic probabilistic risk assessment (SPRA) fragility evaluation notebook, including the detailed steps used to derive the plant-level HCLPF, along with documentation of independent peer review results. Following further assessment, the NRC staff determined that the approach used to establish a plant-level HCLPF does not follow established guidance, such as the seismic margin assessment (SMA) performed under the NRCs Individual Plant Examination of External Events (IPEEE) program.

Wolf Creeks current HCLPF value of 0.2g PGA, which equals its designbasis safe shutdown earthquake (SSE), was derived from a reducedscope SMA performed under its IPEEE analysis. The licensee now seeks to increase this value to 0.3g PGA. To support this enhancement, the licensee may follow applicable IPEEE guidance in NUREG1407, Procedural and Submittal Guidance for the Individual Plant Examination of External Events

(IPEEE) for Severe Accident Vulnerabilities, (ML063550238) June 1991, and EPRI NP-6041-SL, A Methodology for Assessment of Nuclear Plant Seismic Margin, Revision 1, Electric Power Research Institute, August 1991. NUREG1407 (appendix B, section B.2.2),

does not support establishing a plantlevel HCLPF from a reducedscope SMA. Therefore, a possible path forward is to upgrade the existing reducedscope SMA to a focusedscope SMA.

Although the existing Wolf Creek SMA is categorized as reducedscope, it appears to include certain elements consistent with a focusedscope SMA. These elements may be credited toward meeting the focusedscope guidance. However, the licensee should consider addressing all remaining gaps between the existing reduced-scope SMA and the criteria for a focusedscope SMA. If a post-IPEEE seismic walkdown was conducted as part of the post-Fukushima actions (NRC Near Term Task Force (NTTF) Recommendation 2.3 (ML12053A340)), the licensee may leverage that effort to validate more recent plant conditions.

Upon completion, the upgraded focusedscope SMA should be submitted for NRC staff review to support the proposed 0.3g HCLPF value. Per section 7 of NUREG-1407, an independent peer review is desirable but not required. However, if peer review is conducted, the licensee should ensure that the peer reviewer was not associated with the initial evaluation and is able to provide an independent, objective, and critical review.

Docket No. 50-482