ML26076A164
| ML26076A164 | |
| Person / Time | |
|---|---|
| Site: | Wolf Creek  (NPF-042) |
| Issue date: | 03/13/2026 |
| From: | Samson Lee Plant Licensing Branch IV |
| To: | Lee N Wolf Creek |
| Lee S, 301-415-3168 | |
| References | |
| EPID L-2024-LLA-0170 | |
| Download: ML26076A164 (0) | |
Text
From:
Samson Lee To:
Nathan Lee Cc:
Qiang Shi
Subject:
Wolf Creek TSTF-505 audit question APLC-08 through -13 dated March 13, 2026 (EPID: L-2024-LLA-0170)
Date:
Friday, March 13, 2026 8:35:00 AM By letters 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 additional audit discussion question below for seismic. If time allows, please prepare responses 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 may issue additional audit discussion questions.
PRA [Probabilistic Risk Assessment] Licensing Branch C (APLC)
Audit Questions APLC-08 Through -13 for Wolf Creek TSTF-505 on Updated Seismic Margin Assessment (SMA)
Special Request (Presentation)
Among the key updates to the original seismic margin assessment (SMA) in the Individual Plant Examination of External Events (IPEEE), the licensee identified refined fragility evaluations of the 60-cell batteries and racks and the engineered safety features actuation system (ESFAS)/ load shed emergency load sequencer (LSELS) cabinets, as well as a new assessment of a comprehensive set of relays. The NRC staff therefore seeks additional confidence in the technical adequacy of the licensees evaluation of these items.
The NRC staff requests that the licensee provide a presentation (e.g., PowerPoint or a similar format) during an upcoming audit meeting to demonstrate and discuss the following:
- a. The detailed steps used in the fragility evaluations of the 60-cell batteries/racks and the ESFAS/LSELS cabinets; and
- b. The detailed steps used in the relay assessment that supports the conclusion that the seismic capacities of the relays exceed the applicable screening level.
The NRC staff believes that such an interactive presentation may reduce the need for additional audit questions regarding evaluations of other similarly screened-in systems, structures, and components (SSCs) on the seismic equipment list (SEL). Providing the presentation materials in advance of the meeting would be helpful.
APLC-08 In the audit document, SAP-SMAN-TM-RA-00004, Rev. 1, 2025 Seismic Margin
Assessment Update for Wolf Creek (hereafter referred to as the 2025 SMA Update),
section 3.3.3.3, Relay Assessment (2025 SMA Update), non-safety-related relays were not addressed in the relay identification process.
Explain the basis for excluding non-safety-related relays from the relay chatter evaluation in the updated SMA. Specifically, describe how this approach aligns with the technical intent of NUREG-1407, Procedural and Submittal Guidance for the Individual Plant Examination of External Events (IPEEE) for Severe Accident Vulnerability, which calls for evaluating relays whose change-of-state could affect safe-shutdown success paths.
APLC-09 NUREG-1407 states that the development of the seismic equipment list (SEL) for an SMA should consider non-seismic failures and human actions.
In the 2025 SMA Update, section 3.3.2.5, Non-seismic Failures and Human Actions, is included in the description of the original SEL development process but does not appear to be addressed in the updated SEL development discussion for the 2025 SMA Update.
Describe how non-seismic failures and human actions were considered in the development of the updated SEL for the 2025 SMA Update. If they were not considered, provide the basis for why they were not required to be addressed in the SEL development for the 2025 SMA Update.
APLC-10 The licensee discusses upgraded high confidence of low probability of failure (HCLPF) values for two specific components, the 60-cell batteries/racks and the LSELS/ESFAS cabinets, in several locations in the 2025 SMA Update.
In section 3.8 of the original IPEEE SMA, the licensee states, the capacity of two components, the 60-cell batteries and racks and the LSELS/ESFAS cabinets, were considered to be indeterminate beyond the plant design basis without additional detailed evaluation.
In section 3.8 of the 2025 SMA Update, the licensee states, looking specifically at the limitations identified in the IPEEE, explicit fragility assessments have been performed for the 60-cell batteries and racks and for the ESFAS/LSELS cabinets, which were conservatively assessed to have an HCLPF of 0.20g [] in the IPEEE. The new calculations show a HCLPF of 0.47g for the batteries [] and a HCLPF of 0.53g for the ESFAS/LSELS cabinets.
In sections 3.5.6.15 and 3.5.6.21 of the 2025 SMA Update, the licensee explains how the new HCLPF values for the batteries/racks and ESFAS/LSELS cabinets were determined. In both cases, structural failure of the anchorage is identified as the controlling failure mode governing the equipments limiting HCLPF value.
However, the NRC staff notes that the report does not provide a level of detail for the fragility analysis of these two components comparable to that provided for other similar equipment evaluated in section 3.5.6 of the 2025 SMA Update.
To enhance the NRC staffs confidence in the updated HCLPF capacities of these components, provide additional details of the fragility analyses for the batteries/racks and the ESFAS/LSELS cabinets, including anchorage evaluations, with a level of detail comparable to that provided for similar equipment evaluated in section 3.5.6.
APLC-11 In section 3.4.2.4 of the 2025 SMA Update (page 212 of 363), the licensee states, a structural frequency shift of +/-15% is deemed appropriate for 84% non-exceedance
probability (NEP) demand to account for the additional uncertainty of the Control Building floor.
Explain how these parameter values (+/-15% structural frequency shift and 84% NEP demand) were selected. Also clarify whether these values were used in developing seismic demands for the fragility analyses of the batteries/racks and the ESFAS/LSELS cabinets discussed in audit question APLC-10.
APLC-12 In section 3.5.4.1 of the 2025 SMA Update (page 234 of 363), the licensee states, while the near-term task force (NTTF) Recommendation 2.3 effort verified adequacy of the current licensing basis seismic configuration, some walkdown observations may reflect potential limitations in beyond-design-basis seismic capacity.
The NRC staff recognizes that an SMA is intended primarily to evaluate a plants seismic capacity beyond the design basis. Identify the NTTF 2.3 seismic walkdown observations that reflect potential limitations in beyond-design-basis seismic capacity and discuss how these observations were considered in the determination of the plant-level HCLPF.
APLC-13 In section 3.1 of the 2025 SMA Update (page 25 of 363), the licensee indicates that the in-structure response spectra (ISRS) used in the updated SMA were developed using the 1E-5 uniform hazard response spectrum (UHRS) as the ground response spectrum (GRS).
The licensee further states, the selected 1E-5 UHRS is of similar spectral shape to the 1E-4 UHRS and GMRS and because the UHRS shapes are similar across a wide Annual Frequency of Exceedance range, fragility results are not sensitive to the choice of UHRS shape.
(a) It is generally understood that fragility results can be sensitive to the choice of GRS shape (or UHRS shape, in this case). However, since the 1E-5 UHRS, 1E-4 UHRS, and GMRS appear to have similar spectral shapes, the NRC staff understands that fragility results are relatively insensitive to the annual frequency of exceedance level associated with the UHRS rather than to the spectral shape itself. Clarify whether the quoted statement regarding insensitivity to UHRS shape is technically accurate and describe the basis for this conclusion.
(b) Table 3.1-1 of the 2025 SMA Update (page 30 of 363) states that 1E-4 UHRS was used to develop the new ISRS. Clarify whether this statement is correct, given that section 3.1 indicates that 1E-5 UHRS was used to develop the ISRS.
(c) In section 3.5.1 of the 2025 SMA Update (page 223 of 363), the licensee states, the ground response spectrum for this project was the 1E-5 UHRS developed in the site-specific probabilistic seismic hazard analysis (PSHA) in response to NTTF Recommendation 2.1. For 5% damping, the GMRS has a peak spectral acceleration of 1.50g and peak ground acceleration (PGA) of 0.60g, which for a 1.2g peak spectral acceleration screening level corresponds to a screened-out SSC nominal HCLPF of 0.48g as PGA. However, based on figure 3.21 of the 2025 SMA Update, it appears that the spectrum referenced in this statement may correspond to the 1E-5 UHRS rather than the GMRS. Clarify whether the reference to GMRS in the quoted statement is correct.
Docket No. 50-482