ML25163A010
| ML25163A010 | |
| Person / Time | |
|---|---|
| Site: | Wolf Creek  |
| Issue date: | 06/12/2025 |
| From: | Samson Lee Plant Licensing Branch IV |
| To: | Lee N Wolf Creek |
| Lee S, 301-415-3168 | |
| References | |
| EPID L-2024-LLA-0170 | |
| Download: ML25163A010 (1) | |
Text
From:
Samson Lee To:
Nathan Lee
Subject:
Wolf Creek TSTF-505 audit questions (APLB, EEEB, EICB) dated June 12, 2025 (EPID: L-2024-LLA-0170)
Date:
Thursday, June 12, 2025 5:36:00 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 initial audit discussion questions below for certain technical areas. If time allows, please prepare responses to these questions 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 to support breakout audit meetings for efficiency.
Wolf Creek TSTF-505 Audit Questions (APLB, EEEB, EICB, June 12, 2025)
PRA [Probabilistic Risk Assessment] Licensing Branch B (APLB)
APLB-01 Frequently asked question (FAQ) 13-0004, "Clarifications on Treatment of Sensitive Electronics," (Agencywide Documents Access and Management System (ADAMS)
Accession No.: ML13322A085) provides supplemental guidance for application of the damage criteria provided in Sections 8.5.1.2 and H.2 of NUREG/CR-6850, Volume 2, for solid-state and sensitive electronics.
a) Describe the treatment of sensitive electronics for fire probabilistic risk assessment (FPRA) and explain whether it is consistent with the guidance in FAQ 13-0004, including the caveats about configurations that can invalidate the approach (i.e.,
sensitive electronics mounted on the surface of cabinets and the presence of louver or vents).
b) If the approach cannot be justified to be consistent with FAQ 13-0004, then justify that the treatment of sensitive electronics has no impact on the risk-informed completion time (RICT) calculations.
c) As an alternative to item b above, consider adding an implementation item to replace the current approach with an acceptable approach prior to the implementation of the RICT program. Include a description of the replacement method along with justification that it is consistent with NRC-accepted guidance.
APLB-02 The key factors used to justify using transient fire reduced heat release rates (HRRs) below those prescribed in NUREG/CR-6850 are discussed in the June 21, 2012, letter from
Joseph Giitter, U.S. Nuclear Regulatory Commission, to Biff Bradley, Nuclear Energy Institute (NEI), Recent Fire PRA Methods Review Panel Decisions and Electrical Power Research Institute (EPRI) 1022993, Evaluation of Peak Heat Release Rates in Electrical Cabinet Fires. (ML12172A406).
Clarify whether any reduced transient HRRs below the bounding 98% HRR of 317kW from NUREG/CR-6850 were used, and if so, discuss the key factors used to justify the reduced HRRs. Include the following in this discussion:
a) Identification of the fire areas where a reduced transient fire HRR is credited and what reduced HRR value was applied.
b) A description for each location where a reduced HRR is credited, and a description of the administrative controls that justify the reduced HRR including how location-specific attributes and considerations are addressed.
Include a discussion of the required controls for ignition sources in these locations and the types and quantities of combustible materials needed to perform maintenance. Also, include discussion of the personnel traffic that would be expected through each location.
c) The results of a review of records related to compliance with the transient combustible and hot work controls.
APLB-03 NUREG-1792, Good Practices for Implementing Human Reliability Analysis (HRA)
(ML051160213), recommends that joint human error probability (HEP) values should not be below 1E-5. The licensee stated that the configuration risk management (CRM) probabilistic risk assessment (PRA) model that will be used to support the RICT calculations will apply a 1E-06 minimum joint human failure event probability (MJHEP), and a sensitivity study was performed to characterize the risk impact from applying this MJHEP value.
a) Please provide additional discussion and justification such as the RICT sensitivity study results, to support the conclusion that the MJHEP value has no impact on the remaining technical specification limiting conditions for operation (LCOs) proposed for the RICT application.
b) If, in response to part (a), it cannot be justified that the MJHEP value has no impact on the application, then provide the following:
- i. Confirm that each joint HEP value below 1E-5 includes its own justification that demonstrates the inapplicability of the NUREG-1792 lower value guideline (i.e.,
using such criteria as the dependency factors identified in NUREG-1921 to assess level of dependence). Provide an estimate of the number of these joint HEP values below 1.0E-5, discuss the range of values, and provide at least two different examples where this justification is applied.
ii. If joint HEP values used is below 1E-5 and cannot be justified, consider adding an implementation item to set these joint HEPs to 1E-5 in the PRA model prior to the implementation of the RICT program.
APLB-04 The licensee stated that the Wolf Creek FPRA credited obstructed plumes during the fire modeling task using the guidance in NUREG-2178, Volume 1, Refining and Characterizing Heat Release Rates from Electrical Enclosures During Fire (RACHELLE-FIRE), Volume 1:
Peak Heat Release Rates and Effect of Obstructed Plume. NUREG-2178
(ML16110A14016) contains refined peak HRRs, compared to those presented in NUREG/CR-6850, and guidance on modeling the effect of plume obstruction. Additionally, NUREG-2178 provides guidance that indicates the obstructed plume model is not applicable to cabinets in which the fire is assumed to be located at elevations of less than one-half of the cabinet. Please clarify:
a) Whether the base of the fire was assumed to be located at an elevation of less than one-half of the cabinet.
b) Justify any modelling in which the base of an obstructed plume is located at less than one half of the cabinet's height.
c) As an alternative to item b above, consider adding an implementation item to remove credit for the obstructed plume model in the FPRA prior to the implementation of the RICT program.
Electrical Engineering Branch (EEEB)
EEEB-01 License amendment request (LAR) Section2.3.2, Technical Variations, Item7 states, in part WCGS RAs [Required Actions] C.3 and C.4 refer to restoring the SBO DGs
[station backout diesel generators] to available status. While the TSTF505A
[Technical Specification Task Force traveler] acceptance criteria does not specifically address availability versus operability, availability is the premise of PRA modeling. Therefore, it is technically justified to apply RICT to these Completion Times for SBO DG unavailability.
However, the proposed RICT for TS3.8.1, Required ActionsC.3 andC.4 appears inconsistent with the requirements of TSTF505, Revision2.
As stated in the exclusion criteria listed in TSTF505, the traveler will only modify Required Actions that specify that a system be restored to OPERABLE status, that require an instrument channel to be placed in trip, or that require isolating an inoperable isolation valve. Accordingly, TSTF505 does not authorize applying a RICT to a Required Action that specifies that a system be restored to a status other than OPERABLE (e.g.,
available).
The proposed changes, as currently structured, would apply RICT to Required ActionsC.3 andC.4, which specify, in part, that a system (in this case, station blackout diesel generators) be restored to available status. Therefore, it does not meet the criteria of TSTF505. Please address this variation from the traveler, including the corresponding technical specification Bases and Action Item in Table E11.
EEEB-02 LAR Enclosure1, Table E11 (page 19 of 33), the design success criteria (DSC) for TS 3.8.1, Condition D - Two offsite circuits inoperable states, One qualified circuit between the offsite transmission network and the onsite 1E AC Electrical Power Distribution System.
With both offsite circuits inoperable, please explain how one inoperable offsite circuit satisfies the DSC.
EEEB-03 In the LAR Enclosure1, Table E11, the PRA success criteria for TS 3.8.1.A and 3.8.4.A
states, As needed to supply AC [alternating current] power to supported functions and As needed to supply AC power to supported functions, respectively. However, there is no description of what the PRA success criteria are. Please explain.
EEEB-04 LAR Attachment1, Section2.3.1, Administrative Variations, and Section 2.3.2, Technical Variations, describe the variations from TSTF505. However, these sections do not identify and provide the variation descriptions of the following Wolf Creek technical specifications:
TS3.8.1, Condition B, Required Action B.2 TS3.8.1, Condition G, Required Action G.1 TS3.8.1, Condition H TS3.8.4 does not include technical specification Conditions and associated Required Actions for battery chargers and batteries TS3.8.9, Conditions A, E, and F and associated Required Actions Please explain.
EEEB-05 The LAR markup for TS3.8.9, ConditionE, states, Required Action and associated Completion Time not met. It is not clear what technical specification condition(s) associated with the Required Action this condition (i.e., ConditionE) refers to (e.g.,
Condition A, B, C, and/or D). Please explain.
Instrumentation & Controls Branch (EICB)
EICB-01
TSTF-505 Rev. 2 (ML18183A493) PDF page 113 of 850 states:
The description of proposed changes to the protective instrumentation and control features in TS Section 3.3, "Instrumentation," should confirm that at least one redundant or diverse means (other automatic features or manual action) to accomplish the safety functions (for example, reactor trip, SI
[safety injection], containment isolation, etc.) remains available during use of the RICT, consistent with the defense-in-depth philosophy as specified in RG 1.174. (Note that for each application, the staff may selectively audit the licensing basis of the most risk-significant functions with proposed RICTs to verify that such diverse means exist.)
The LAR (ML24352A438) - See LAR PDF page 194 of 264 (a.k.a. LAR Enclosure 1 page 20 of 33) Section 3. Evaluation of Instrumentation and Control - includes an evaluation to address the above; however, this evaluation is missing the table (typically supplied in TSTF-505 applications), which systematically demonstrates, for each event in Chapter 15 (that is mitigated by instrumentation and control (I&C) subject to RICT), the credited means and the diverse means to initiate the protective function. Please provide this table for discussion during the audit.
Docket No. 50-482