Text

Supplement to License Amendment Request to Adopt 10 CR 50.69
	ML26034C129
Person / Time
Site:	Wolf Creek
Issue date:	02/03/2026
From:	Bayer R; Wolf Creek
To:	; Office of Nuclear Reactor Regulation, Document Control Desk
References
	001182, EPID L-2024-LLA-0170, EPID L-2025-LLA-0017, EPID L-2023-NTR-0008
	Download: ML26034C129 (0)
	v • d • e

P.O. Box 411 l Burlington, KS 66839 l 620-364-8831 Robert J. Bayer Vice President Engineering February 3, 2026 001182 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001

References:

1)

Letter 000779, dated January 30, 2025, from M. T. Boyce, WCNOC, to USNRC, "License Amendment Request to Adopt 10 CFR 50.69, 'Risk-Informed Categorization and Treatment of Structures, Systems and Components for Nuclear Power Reactors',"

(NRC ADAMS ML25030A384)

2) Letter dated April 2, 2025, from S. Lee, USNRC, to C. Reasoner, WCNOC, Wolf Creek Generating Station, Unit 1 - Regulatory Audit Plan in Support of License Amendment Requests to Adopt TSTF-505, Revision 2, Provide Risk-Informed Extended Completion Times -

RITSTF Initiative 4B, and 10 CFR 50.69 Risk-Informed Categorization and Treatment of Structures, Systems and Components for Nuclear Power Reactors (EPID L-2024-LLA-0170 AND EPID L-2025-LLA-0017), (ADAMS ML25090A217)

3)

Email dated July 1, 2025, from S. Lee, USNRC, to N. Lee, WCNOC, Wolf Creek 10 CFR 50.69 audit questions (APLA) dated July 1, 2025, (ADAMS ML25183A016)

4)

NRC Safety Evaluation on EPRI Technical Report 3002025288, dated July 15, 2025, "Enhanced Risk-Informed Categorization Methodology for Pressure Boundary Components," (ADAMS ML25168A015)

5)

EPRI 2025 Technical Report 3002033536, dated August 2025, "Enhanced Risk-Informed Categorization Methodology for Pressure Boundary Components (Revision 1-A)" (ADAMS ML25241A331)

6)

Transmittal of NRC Form 896, dated September 9, 2025, "-A Topical Report Verification," for EPRI Report Entitled "Enhanced Risk-Informed Categorization Methodology for Pressure Boundary Components" (EPID L-2023-NTR-0008), (ADAMS ML25202A131)

001182 Page 2 of 3

Subject:

Docket No. 50-482: Supplement to License Amendment Request to Adopt 10 CFR 50.69 Commissioners and Staff:

By letter dated January 30, 2025 (Reference 1), Wolf Creek Nuclear Operating Corporation (WCNOC) submitted a license amendment request (LAR) for the Wolf Creek Generating Station (WCGS). The proposed amendment would modify the renewed facility operating license, NPF-42, to allow implementation of the provisions of 10 CFR 50.69, "Risk-Informed Categorization and Treatment of Structures, Systems, and Components for Nuclear Power Reactors."

The purpose of this supplement is to revise a portion of the LAR in Reference 1 by incorporating a recently approved methodology for categorizing pressure boundary components, consistent with Electric Power Research Institute (EPRI) Technical Report (TR) No. 3002033536.

As background information, on July 15, 2025 (Reference 4), the Nuclear Regulatory Commission (NRC) issued a Safety Evaluation for EPRI TR No. 3002025288, "Enhanced Risk-Informed Categorization Methodology for Pressure Boundary Components." The NRC staff concluded that the methodology outlined in Chapter 4 in that report was acceptable for use as part of a licensee's 10 CFR 50.69 categorization process.

Following issuance of the Safety Evaluation, EPRI published Revision 1-A as 3002033536, in August 2025. The revised report incorporates technical updates based on supplemental information EPRI submitted to the NRC during the review process. EPRI TR 3002033536 (Revision 1-A) is the approved version of the report, as documented on NRC Form 896, -A Topical Report Verification (Reference 6).

Attachment I to this letter provides the revisions to Reference 1 needed to integrate the enhanced passive categorization methodology described in Chapter 4 of EPRI TR 3002033536. WCNOC requests that the NRC apply this information in its ongoing review of Reference 1.

Attachment II contains a revised markup to the facility operating license, reflecting the proposed change from the Arkansas Nuclear One, Unit 2 passive categorization method to the new EPRI enhanced categorization method for passive components. Attachment II replaces the markup provided in Attachment VII of Reference 1.

WCNOC acknowledges that this supplement may affect the review timeline; however, WCNOC anticipates any impact to be minor based on the NRCs recent approval of the EPRI methodology (References 4 and 6).

In addition to the above, Attachment III provides responses to NRC audit questions (Reference 3). These were identified during the ongoing audit (Reference 2) as requiring docketed information.

Since the new EPRI enhanced risk-informed categorization methodology for pressure boundary components has already been reviewed and approved by the NRC through the Safety Evaluation in Reference 4, this supplement does not impact the conclusions of the No Significant Hazards Consideration provided in Reference 1. In accordance with 10 CFR 50.91, "Notice for public comment; State consultation," a copy of this supplement is being provided to the designated Kansas State official.

001182 Page 3 of 3 This letter contains no regulatory commitments. If you have any questions regarding this matter, please contact me at (620) 364-4015, or Dustin Hamman at (620) 364-4204.

I declare under penalty of perjury that the foregoing is true and correct.

Executed on the 3rd day of February 2026.

Sincerely, Robert J. Bayer RJB/nwl Attachments:

I: Supplement to License Amendment Request to Adopt 10 CFR 50.69 II: Revised Proposed Markup to Appendix D of Facility Operating License (FOL) for Method Change III: Responses to NRC APLA Audit Questions Requiring Docketed Information cc:

A. N. Agrawal (NRC), w/a S. S. Lee (NRC), w/a J. Meinholdt (KDHE), w/a J. D. Monninger (NRC), w/a Senior Resident Inspector (NRC), w/a WCNOC Licensing Correspondence ET 26-001182, w/a

Attachment I to 001182 Page 1 of 10 Supplement to License Amendment Request to Adopt 10 CFR 50.69

Attachment I to 001182 Page 2 of 10 Summary Wolf Creek Nuclear Operating Corporation (WCNOC) submitted a license amendment request (LAR) for the Wolf Creek Generating Station (WCGS), seeking approval from the Nuclear Regulatory Commission (NRC) to adopt 10 CFR 50.69 (Reference 1).

On July 15, 2025, the NRC staff issued a Safety Evaluation (Reference 2) for Electric Power Research Institute (EPRI) Technical Report (TR) No. 3002025288, "Enhanced Risk-Informed Categorization Methodology for Pressure Boundary Components." The NRC staff concluded that the methodology detailed in Chapter 4 of the approved version of EPRI TR 3002025288 was acceptable for use as part of a licensee's 10 CFR 50.69 categorization process. EPRI 3002033536 (Revision 1-A), issued in August 2025 (Reference 3), incorporates technical updates based on supplemental information provided to the NRC during audits and in response to requests for additional information (RAIs). Therefore, since the methodology in EPRI 3002033536 is NRC-approved, WCNOC proposes its use in performing 10 CFR 50.69 risk-informed categorization at WCGS.

The purpose of this supplement is to revise WCNOC's LAR to adopt 10 CFR 50.69 (Reference 1) by incorporating the approved methodology for categorizing pressure boundary components in accordance with EPRI 3002033536. This supplement identifies the necessary changes to WCNOC's existing request (Reference 1).

Specific sections being revised by this supplement include the following:

LAR Section 2.3.. Description of the Proposed Change LAR Section 3.1.2.. Passive Categorization Process LAR Section 3.2.8.. PRA Uncertainty Evaluations LAR Section 3.5.. Feedback and Adjustment Process

Attachment I to 001182 Page 3 of 10 LAR Section 2.3 - Description of the Proposed Change In Section 2.3 of the LAR, WCNOC proposed adding a license condition to Appendix D of the renewed facility operating license (FOL), NPF-42, for the WCGS. The new license condition would document the NRC's approval for the use of 10 CFR 50.69. Below is the original text from Reference 1, along with markups that highlight the proposed revisions. These updates are necessary to incorporate the enhanced passive methodology from EPRI 3002033536. Text proposed for deletion is highlighted with red strikethroughs, while new text is presented with blue, underlined font. This revised wording also replaces INSERT 1 in Attachment 7 of Reference 1.

WCNOC is approved to implement 10 CFR 50.69 using the processes for categorization of Risk-Informed Safety Class (RISC) RISC-1, RISC-2, RISC-3, and RISC-4 structures, systems, and components (SSCs) using: probabilistic risk assessment (PRA) models to evaluate risk associated with internal events, including internal flooding, and internal fire; the shutdown safety assessment process to assess shutdown risk; the Arkansas Nuclear One, Unit 2 (ANO-2) passive categorization method Enhanced Risk-Informed Categorization Methodology for Pressure Boundary Componentsto assess passive component risk for Class 2, Class 3, and non-class SSCs and their associated supports; the results of non-PRA evaluations that are based on the Individual Plant Examination of External Events (IPEEE)

Screening Assessment for External Hazards updated using the external hazard screening significance process identified in the ASME/ANS PRA Standard RA-Sa-2009 for other external hazards except seismic and high winds; and the alternative seismic and high winds approaches described in WCNOCs submittal letter ET 25-000779 dated January 30, 2025, as supplemented by letter 001182 dated February 3, 2026, as specified in License Amendment No. [XXX] dated [DATE].

Prior NRC approval, under 10 CFR 50.90, is required for a change to the categorization process specified above.

Attachment I to 001182 Page 4 of 10 LAR Section 3.1.2 - Passive Categorization Process WCNOC proposes a complete replacement of Section 3.1.2 of Reference 1 with the following information.

For the purposes of 10 CFR 50.69 categorization, passive components are those components that have a pressure retaining function. Passive components and the passive function of active components will be evaluated in accordance with EPRI 3002033536, "Enhanced Risk-Informed Categorization Methodology for Pressure Boundary Components (Revision 1-A)" (Reference 3).

This enhanced passive methodology was initially submitted to the NRC as EPRI Technical Report (TR) No. 3002025288 (Reference 4). After conducting an audit and reviewing supplements that addressed requests for additional information (RAIs), the NRC approved the enhanced passive categorization methodology, as documented in the Safety Evaluation (SE) issued on July 15, 2025 (Reference 2). The NRC's review and approval were specifically focused on the enhanced passive categorization methodology contained in Chapter 4 of EPRI 3002025288, as supplemented.

EPRI 3002033536 (Reference 3) includes responses to NRC RAIs, some of which were needed to support a regulatory finding on the enhanced passive methodology. The NRC's SE details the review and approval of EPRI TR 3002025288, as supplemented. EPRI 3002033536 is the final version of the enhanced passive methodology for pressure boundary components, incorporating the supplemental information referenced in the NRC's SE. Therefore, EPRI 3002033536 is the approved version that will be utilized for assessing pressure boundary components during 10 CFR 50.69 risk-informed categorization.

This enhanced methodology for passive categorization requires an evaluation of the pressure retention function of all systems. In this enhanced approach the pressure boundary function is treated as a system for 10 CFR 50.69 categorization and alternative treatment purposes. Treating the pressure boundary function as a system is consistent with 10 CFR 50.69 rule language and the final rules Statement of Considerations (the boundaries for the pressure boundary system are limited to pressure retention) in that there will be no other important functions that would escape categorization and appropriate assignment of safety significance. As documented in the SE (Reference 2), the NRC staff found that the approach to define the pressure boundary function as a new system for 10 CFR 50.69 categorization complies with the requirements in 10 CFR 50.69(c)(1)(v).

When categorizing a system that contains active and passive (pressure boundary) components, active components (non-pressure-retaining functions) must follow the existing process for categorization in NEI 00-04 which ensures that all safety functions are properly identified and categorized regarding their safety significance. In some cases, a component may have both active and passive functions. For example, the internals of a safety-related valve may be categorized as HSS for active functions, while the valve body is categorized as LSS for passive functions, resulting in the overall SSC being classified as RISC-1. In such cases, alternative treatments (e.g., alternative repair/replacement activities) may be applied to the LSS pressureretaining function, since the pressure boundary is categorized RISC-3, while special treatments are maintained for the active HSS functions categorized as RISC-1. Alternative treatments can be applied to the RISC-3 valve body and other pressure boundary piece parts regardless of whether the SSCs performing active functions are categorized. This approach to alternative treatment requirements is consistent with 10 CFR 50.69(d).

Attachment I to 001182 Page 5 of 10 While a pressure boundary component may be categorized as HSS or LSS under the enhanced methodology, no change to the special treatment of the active function is permitted from its current safety-related treatment. Alternate treatment of an active function would only be allowed if the guidance in NEI 00-04 for active functions were applied and the safety-related active function were categorized as LSS (i.e., RISC-3) in accordance with the current NEI 00-04 approach.

Passive categorization will continue to follow the applicable guidance in NEI 00-04, supplemented by the steps outlined in Chapter 4 of EPRI 3002033536. The enhanced passive methodology contains a set of prerequisites and a predetermined set of HSS systems/subsystems, along with a plant-specific search for pressure boundary components to be added to the predetermined HSS scope. The process consists of the following five phases:

Phase 1 - Prerequisites Phase 2 - Predetermined HSS passive SSCs Phase 3 - Design and plant specific search for HSS passive SSCs Phase 4 - Sensitivity study and IDP review and concurrence Phase 5 - Performance monitoring Phase 1 - Prerequisites

1. PRA Technical Adequacy WCGS maintains a robust internal events PRA, including internal flooding, that addresses the failure of all pressure boundary components. Section 3.3 of the LAR describes the PRA review process, confirming that the WCGS PRA models are of sufficient quality and level of detail to support the categorization process.

The WCGS PRA model key assumptions and sources of uncertainty have been reviewed in the context of this application.

2. Integrity Management WCGS implements a robust program to address localized corrosion, such as pitting and microbiologically influenced corrosion, following guidance from References 5, 6, 7, 8, and 9.

The station has a robust flow-accelerated corrosion (FAC) program aligned with the recommendations in Reference 10.

Erosion management at WCGS aligns with the recommendations in Reference 11.

3. Protection Measures for Internal Flooding Events Prerequisite 3 addresses protective measures for internal flooding events, such as floor drains, flood alarm equipment, and flood barriers. This prerequisite provides that such protective measures should not be categorized as LSS unless additional evaluations have been conducted to show that loss of these measures, or a subset of them, does not invalidate the HSS determination provided in Section 4.2 of EPRI TR 3002033536. For example, if a submarine door has been credited to prevent a flood from propagating from one flood zone to another, it will be considered HSS unless an evaluation shows that loss of the door will

Attachment I to 001182 Page 6 of 10 not significantly increase plant risk (i.e., exceed the risk criteria in Criterion 11 of Section 4.2).

4. Reflect the As-Built As-Operated Plant WCGS ensures that the PRA model accurately reflects the as-built, as-operated plant by following a process outlined in approved station procedures. PRA maintenance and updates are addressed in Section 3.2.7 of the LAR, while the feedback and adjustment process is addressed in Section 3.5. The process includes periodic requirements for reviewing PRA inputs and updating information, such as PRA data updates.

Phase 2 - Predetermined HSS passive SSCs (Criteria 1 through 10)

Section 4.2 of EPRI 3002033536 outlines the scope of systems, subsystems, and piping segments that are to be categorized as HSS. Twelve criteria are used to categorize passive components and their associated supports. If an SSC meets any of these criteria, it is categorized as preliminary HSS. Conversely, all other SSCs that do not meet any of these criteria are categorized as preliminary LSS. Criteria 1 through 10, along with the HSS criteria considerations in EPRI 3002033536, are used to identify the predetermined HSS passive SSCs.

Phase 3 - Design and plant specific search for HSS passive SSCs (Criteria 11 and 12)

Criterion 11 is uniquely plant-specific and based on the quantitative results (risk metrics) from the internal events and internal flooding PRA models. Regardless of initial determinations using Criteria 1 through 10, each pipe segment must still be evaluated against Criterion 11. This involves assessing Core Damage Frequency (CDF), Large Early Release Frequency (LERF), Conditional Core Damage Probability (CCDP), and Conditional Large Early Release Probability (CLERP) metrics. HSS components will include those whose contributions exceed the risk metrics in Criterion

11. The use of CDF/LERF and CCDP/CLERP metrics ensure that plant-specific outliers are identified, considering both risk and consequence.

Criterion 12 provides three options for addressing piping and component supports, including hangers and snubbers: (1) supports may remain uncategorized, (2) if categorized, supports are assigned the same categorization as the highest-ranked piping segment within the piping analytical model in which the support is included, or (3) a combination of restraints or supports such that the LSS piping and associated SSCs attached to the HSS piping are included in the scope up to a boundary point that encompasses at least two supports in each of the three orthogonal directions.

External events are evaluated in accordance with Section 4.3 of EPRI 3002033536. The preliminary HSS/LSS assignments shall be reviewed and adjusted to reflect the pressure boundary failure's impact on the mitigation of external events. The purpose of this review is to confirm and adjust as necessary, that the assignment of HSS/LSS criteria is valid in the context of other hazards (fire, seismic, other hazards).

Phase 4 - Sensitivity study and IDP review and concurrence The sensitivity study that is conducted as part of the enhanced passive methodology is addressed in Section 3.2.8 of the LAR.

Attachment I to 001182 Page 7 of 10 In addition to the IDP review and approval process outlined in Section 9 of NEI 00-04, the IDP is tasked with confirming that all steps of the enhanced passive categorization methodology have been followed:

The IDP shall ensure that the prerequisites cited in Section 4.1 are met.

The IDP shall confirm the assignment of HSS components (from the results of using Criteria 1 through 11) is appropriate.

The IDP shall confirm that the assignment of HSS criteria is valid in the context of other hazards (fire, seismic, other hazards).

Phase 5 - Performance Monitoring Performance monitoring is addressed in Section 3.5 of the LAR.

Attachment I to 001182 Page 8 of 10 LAR Section 3.2.8 - PRA Uncertainty Evaluations WCNOC proposes a revision to Section 3.2.8 of Reference 1 as follows.

After this paragraph:

In the overall risk sensitivity studies, WCNOC will utilize a factor of three (3) to increase the unavailability or unreliability of LSS components consistent with NEI 00-04. The performance monitoring process monitors the component performance to ensure that potential increases in failure rates of categorized components are detected and addressed, through WCNOCs [CAP], before reaching the rate assumed in the sensitivity study.

Insert the following paragraph:

Sensitivity studies conducted as part of the enhanced passive categorization methodology will follow Section 4.4 of EPRI 3002033536. For pressure boundary components modeled in the internal events or internal flooding PRA and determined to be LSS, their failure rates, such as pipe break frequency, are increased by a factor of 3. The CDF and LERF are then recalculated, and the results are compared against the quantitative acceptance guidelines in RG 1.174. Pressure boundary components modeled in the FPIE PRA that exceed the CDF/LERF guidelines will be candidate HSS, subject to IDP concurrence. Conversely, all pressure boundary components determined to be LSS per Section 4.2 of EPRI 3002033536 and whose sensitivity study results remain below the RG 1.174 acceptance guidelines will continue to be categorized as LSS.

Attachment I to 001182 Page 9 of 10 LAR Section 3.5 - Feedback and Adjustment Process WCNOC proposes a revision to Section 3.5 of Reference 1 as follows.

After this paragraph:

To more specifically address the feedback and adjustment (i.e., performance monitoring) process as it pertains to the proposed alternative seismic method for Tier 2 sites discussed in Section 3.2.3 of this submittal, implementation of the WCNOC design control and corrective action programs provide assurance that the inputs for the qualitative determinations for seismic continue to remain valid to maintain compliance with the requirements of 10 CFR 50.69(e).

Insert the following paragraph:

The operational programs required by the enhanced passive risk-informed categorization methodology for pressure boundary components provide robust performance monitoring of passive SSCs susceptible to localized corrosion, including FAC and erosion. The plants performance monitoring process is intended to monitor component performance, ensuring that potential increases in failure rates of categorized components are identified and addressed before they exceed the rates assumed in the sensitivity study. Given that passive components have historically lower failure rates, even a single failure event can significantly alter the failure frequency for a specific type of piping, potentially exceeding acceptable guidelines for that subset of components. This underscores the importance of maintaining robust integrity management programs, as required by Prerequisite 2 of EPRI 3002033536 and 10 CFR 50.69(e). If any of these integrity management programs are discontinued or modified in such a way that Prerequisite 2 is no longer satisfied, the application of the categorization process using the enhanced passive methodology would no longer be permitted. Future alterations to the integrity management programs would require evaluation under 10 CFR 50.69(e), consequently ensuring alterations are appropriately evaluated relative to the methodology.

Attachment I to 001182 Page 10 of 10 References for Attachment I:

1. WCNOC Letter ET 25-00079 to NRC, "License Amendment Request to Adopt 10 CFR 50.69,

'Risk-Informed Categorization and Treatment of Structures, Systems and Components for Nuclear Power Reactors'," January 30, 2025 (ML25030A384).

2. Safety Evaluation on EPRI Technical Report 3002025288, "Enhanced Risk-Informed Categorization Methodology for Pressure Boundary Components'," July 15, 2025 (ML25168A015).

3. EPRI 2025 Technical Report 3002033536, "Enhanced Risk-Informed Categorization Methodology for Pressure Boundary Components (Revision 1-A)", August 2025.

4. EPRI 2023 Technical Report 3002025288, "Enhanced Risk-Informed Categorization Methodology for Pressure Boundary Components," June 2023 (ML23234A268); submitted to the NRC for review and approval on August 17, 2023 (ML23234A267); see ML23234A266 for the combined package in ADAMS.

5. Service Water System Corrosion and Deposition Sourcebook. EPRI, Palo Alto, CA: 1994.

TR-103403.

6. Engineering and Design Considerations for Service Water Chemical Addition Systems.

EPRI, Palo Alto, CA: 2014. 3002003190.

7. Guide for the Examination of Service Water System Piping. EPRI, Palo Alto, CA: 1994. TR-102063.

8. Service Water Piping Guideline. EPRI, Palo Alto, CA: 2005. 1010059.

9. Recommendations for an Effective Program to Control the Degradation of Buried and Underground Piping and Tanks (1016456, Revision 2), EPRI, Palo Alto, CA: 2020, 3002018352.

10. Recommendations for an Effective Flow-Accelerated Corrosion Program (NSAC-202L-R4).

EPRI, Palo Alto, CA: 2013, 3002000563.

11. Recommendations for an Effective Program Against Erosive Attack: Revision 1, EPRI, Palo Alto, CA: 2023. 3002023786.

Attachment II to 001182 Page 1 of 3 Revised Proposed Markup to Appendix D of Facility Operating License for Method Change Additional Condition Implementation

_____Date____

179 (Contd)

(b)

The first performance of the periodic assessment of CRE habitability, Specification 5.5.18c.(ii), shall be within 3 years, plus the 9-month allowance of SR 3.0.2, as measured from August 16, 2004, the date of the most recent successful tracer gas test, as stated in the November 16, 2004, letter response to Generic Letter 2003-01, or within the next 9 months if the time period since the most recent successful tracer gas test is greater than 3 years.

(c)

The first performance of the periodic measurement of control room pressure, Specification 5.5.18.d, shall be within 18 months, plus the 138 days allowed by SR 3.0.2, as measured from February 2, 2007, the date of the most recent successful pressure measurement test.

213 Automated Statistical Treatment of Uncertainty Method (ASTRUM), as corrected for thermal conductivity degradation (TCD) including the use of PAD 4.0 + TCD, has specifically been approved for use in the WCGS licensing basis analyses.

Upon NRC approval of a revised generic best-estimate loss-of-coolant accident (LOCA) analysis methodology and fuel performance analysis methodology that accounts for TCD and is applicable to the fuel in use at WCGS, WCNOC will within 6 months, either:

(a)

Demonstrate that the WCGS safety analyses remain conservatively bounded in licensing basis analyses when compared to the new generically approved version of the LOCA analysis methodology and fuel performance analysis methodology that accounts for TCD, or (b)

Provide a schedule for re-analysis of any of the affected licensing basis analyses using the new generically approved version of the LOCA analysis methodology and fuel performance analysis methodology that accounts for TCD.

Within 6 months of NRC approval of a revised methodology that accounts for TCD Amendment No. 179, 213 Attachment II to 001182 Page 2 of 3 Amendment Number Insert 1

Attachment II to 001182 Page 3 of 3 INSERT 1:

XXX WCNOC is approved to implement 10 CFR 50.69 using the processes for categorization of Risk-Informed Safety Class (RISC) RISC-1, RISC-2, RISC-3, and RISC-4 structures, systems, and components (SSCs) using: probabilistic risk assessment (PRA) models to evaluate risk associated with internal events, including internal flooding, and internal fire; the shutdown safety assessment process to assess shutdown risk; the Enhanced Risk-Informed Categorization Methodology for Pressure Boundary Components; the results of non-PRA evaluations that are based on the Individual Plant Examination of External Events (IPEEE)

Screening Assessment for External Hazards updated using the external hazard screening significance process identified in the ASME/ANS PRA Standard RA-Sa-2009 for other external hazards except seismic and high winds; and the alternative seismic and high winds approaches described in WCNOCs submittal letter 000779 dated January 30, 2025, as supplemented by letter 001182 dated February 3, 2026, as specified in License Amendment No. [XXX] dated

[DATE].

Prior NRC approval, under 10 CFR 50.90, is required for a change to the categorization process specified above.

The amendment shall be implemented within 90 days from the date of issuance.

Attachment III to 001182 Page 1 of 10 Responses to NRC APLA Audit Questions Requiring Docketed Information

Attachment III to 001182 Page 2 of 10 NRC Question APLA-01 Interfacing System Categorization Section 7.1 of Nuclear Energy Institute (NEI) 00-04 states, "[d]ue to the overlap of functions and components, a significant number of components support multiple functions. In this case, the system, structure, and component (SSC), or part thereof, should be assigned the highest risk significance for any function that the SSC or part thereof supports." Section 4 of NEI 00-04 states that a candidate low safety-significant (LSS) SSC that supports an interfacing system should remain uncategorized until all interfacing systems are categorized. The license amendment request (LAR) does not discuss consideration or implementation of the guidance in Section 7.1 of NEI 00-04.

Explain how the categorization process will be implemented to ensure that the cited guidance in NEI 00-04 will be followed and that any functions/SSCs that serve as an interface between two or more systems will not be categorized until the categorization for all of the systems that they support is completed and that SSCs that support multiple functions will be assigned the highest risk significance for any of the functions they support.

WCNOC Response Components that support more than one system function will be assigned the highest risk of any supported function. It is noted that, per NEI 00-04, Section 10.2, detailed categorization may be subsequently performed which can result in some components mapped to HSS functions being treated as LSS.

Interfacing components, such as heat exchangers, will remain uncategorized and thus, continue to receive their current level of treatment requirements, until the interfacing system is categorized.

Attachment III to 001182 Page 3 of 10 NRC Question APLA-02 Determination of Key Sources of Uncertainty for the 10 CFR 50.69 Categorization Process and Sensitivity Results Sections 50.69(c)(1)(i) and 50.69(c)(1)(ii) of Title 10 of the Code of Federal Regulations (10 CFR)

Section 50.69 require that a licensees probabilistic risk assessment (PRA) be of sufficient quality and level of detail to support the SSC categorization process, and that all aspects of the integrated, systematic process used to characterize SSC importance must reasonably reflect the current plant configuration and operating practices, and applicable plant and industry operational experience. The guidance in NEI 00-04 specifies that sensitivity studies be conducted for each PRA model to address uncertainty. The sensitivity studies are performed to ensure that assumptions and sources of uncertainty (e.g., human error, common cause failure, and maintenance probabilities) do not mask the importance of components. The guidance in NEI 00-04 states that additional applicable sensitivity studies from characterization of PRA adequacy should be considered.

of the LAR describes the process used for reviewing the PRA assumptions and sources of uncertainty. The submittal states: The Internal Events and Fire PRAs identify assumptions and determine if those assumptions are related to sources of model uncertainty and characterize that uncertainty, as necessary. The NRC staff reviewed the uncertainty documents provided on this audits electronic portal for the internal events, internal flooding, and fire PRA and found that further clarification is necessary regarding the review of assumptions and sources of uncertainty for this application. It is unclear if additional analysis was performed and documented to determine if any source of uncertainty could adversely impact any SSC categorization. In light of these observations, provide the following information:

a. Provide details of how the Wolf Creek PRA sources of uncertainty were evaluated as a potential key source of uncertainty for this application. In this response provide any documentation of this process.

b. Provide the results of sensitivity studies that determined the impact on risk for each associated source of uncertainty. Include in this discussion justification that the sensitivity results demonstrate that the associated source of uncertainty does not adversely impact any SSC categorization.

WCNOC Response WCNOC has performed uncertainty analyses on the internal events, internal flood, and internal fire PRA models used for the categorization of systems described in submitted license amendment dated January 30, 2025. These uncertainty analyses demonstrate technical adequacy of the models consistent with ASME/ANS RA-Sa-2009 in alignment with Regulatory Guides 1.200, Revision 2. The uncertainty analyses were developed in accordance with industry guidance including NEI 00-04, EPRI TR-1016737, NUREG-1855, and EPRI-1026511. These analyses cover both generic and plant specific sources of uncertainty.

of the WCGS 10 CFR 50.69 License Amendment Request (LAR) briefly discusses the disposition of key assumptions and sources of uncertainty and includes the following conclusion:

The evaluation of uncertainty for internal events and fire addressed generic sources of uncertainty and assessed other uncertainty sources specific to the PRA modeling of the WCGS design and

Attachment III to 001182 Page 4 of 10 operation. The degree to which uncertainties impact a specific accident progression varies but was determined to not be significant overall. The impact of uncertainty could be greater on accident sequence specific components or human actions but would not have a significant impact to the overall PRA results.

WCNOC performed detailed uncertainty analyses to evaluate the impact of assumptions and sources of uncertainty using industry and regulatory guidance. Each sensitivity study performed has been reviewed for impact to the 10 CFR 50.69 categorization process for the internal events, internal flood, and internal fire models. Key aspects of the results and conclusions are summarized for information below.

Assumptions/Uncertainties related to WCNOC Internal Events, Internal Flood, and Internal Fire Generic Sources of Uncertainty The uncertainty analyses associated with generic sources of uncertainty identified three areas where uncertainties could have a potential impact on core damage frequency (CDF) and large early release frequency (LERF). These areas are:

Basis for HEP values Treatment of human failure event dependencies, and Intra-system common cause events.

Industry guidance from EPRI report TR-1016737 recommends developing a standard set of sensitivity cases at a relatively high level in lieu of trying to identify and characterize all potential sources of uncertainty associated with these issues. This has the benefit of highlighting the potential impact of these specific issues prior to performing applications. Therefore, a standard set of four sensitivity cases is recommended as follows:

All human error probabilities (HEP) (including pre-initiators, post-initiators, and dependent HEP values) set to their 5th percentile value (the use of zero value HEP probabilities is also deemed acceptable)

All HEP probabilities (including pre-initiators, post-initiators, and dependent HEP values) set to their 95th percentile value All common cause failure (CCF) probabilities set to their 5th percentile value (the use of zero value CCF probabilities is also deemed acceptable)

All CCF probabilities set to their 95th percentile value These specific four sensitivity cases related to Human Reliability Analysis (HRA) and CCF are included in the 10 CFR 50.69 categorization process as required sensitivity cases for each categorized system in accordance with NEI 00-04. Therefore, the 10 CFR 50.69 categorization process directly addresses these generic sources of uncertainty.

Although there is not a specific sensitivity case for postulated intra-system common cause events, the required sensitivity study of all low safety significant (LSS) components for all categorized equipment have their failure rates increased by a factor of 3 (i.e., cumulative risk assessment sensitivity study). The cumulative sensitivity study assumes the lack of special treatments is essentially a surrogate common cause source for increased LSS component failure rates for all LSS components regardless of their system assignments (i.e., across all categorized systems). This includes the intent of intra-system common cause concerns since LSS components cross system

Attachment III to 001182 Page 5 of 10 boundaries, vary by component type, and have varied and different failure modes. High safety significant (HSS) components retain their respective special treatments and, therefore, are not included in the scope of this sensitivity.

Thus, generic sources of uncertainty are adequately addressed in the WCNOC 10 CFR 50.69 categorization process and do not represent a constraint or require special sensitivity studies in addition to the sensitivity studies already required for 10 CFR 50.69 implementation.

Plant Specific Sources of Uncertainty Assumptions and uncertainties associated with the internal events, internal flood, and internal fire models were evaluated based on the industry and regulatory guidance documents. Peer review and subsequent Facts and Observations closure conclude the impact of uncertainties on the quantitative results is appropriately assessed and sufficient detail is documented for assessing impact to risk informed applications. A wide range of areas were evaluated with specific sensitivity studies. Both assumptions and conservatisms were evaluated from equipment failure to human action. The sensitivity studies do not result in any recommended PRA model changes for 10 CFR 50.69 implementation and do not result in any recommendations or limitation in performing component categorizations per 10 CFR 50.69.

The sensitivity studies required by the 10 CFR 50.69 categorization process are sufficient for categorization purposes. Additional sensitivity studies will not provide further risk insights that may alter conclusions of the WCNOC 50.69 categorization process.

Summary:

Each sensitivity study performed by WCNOC as part of the detailed uncertainty analysis was reviewed with respect to impacts to the 10 CFR 50.69 application. Key aspects of this review are as follows:

The sensitivity studies performed by WCNOC address both generic and plant specific sources of uncertainty with appropriate sensitivity analyses which include testing assumptions and conservatisms related to the severity of phenomena, equipment performance, equipment availability, human performance, and component dependencies.

Many of the sensitivity results indicated negligible or very small percentage changes in CDF or LERF. In these cases, the PRA models are not sensitive to the sensitivity study assumptions or conservatisms (i.e., less than 10% change from base case) and thus there is no impact to 10 CFR 50.69 processes.

Some sensitivity studies evaluated parametric limits (i.e., 5th and 95th percentile assumptions). In these cases, there were some non-negligible changes to CDF and LERF.

However, these sensitivity studies are reflective of the required sensitivity studies for 10 CFR 50.69 that are performed for each categorized system.

Non-negligible changes were seen in some of the sensitivity studies related to the unavailability of installed equipment (refer to table below). These sensitivity studies, as intended, evaluate uncertainties but do not require additional studies for 10 CFR 50.69 purposes since those components are explicitly modeled and will undergo all the requirements (sensitivity studies included) of the 10 CFR 50.69 categorization process.

The following table summarizes the WCNOC uncertainty analysis review relative to 10 CFR 50.69 implementation for internal events, internal flood, and internal fire only. WCNOC has elected to perform the 10 CFR 50.69 seismic evaluation using the NRC approved EPRI alternative approach

Attachment III to 001182 Page 6 of 10 for addressing seismic risk (EPRI Technical Report 3002022453), therefore seismic uncertainty is not evaluated.

PRA Sources of Assumption/Uncertainty PRA 10 CFR 50.69 Impact PRA Model Sensitivity and Disposition Credit for the Fire Protection System for RWST Refill Components or functions related to ECCS operation in the injection phase of LOCA Response Insignificant change to results; no impact with respect to the 10 CFR 50.69 application. This sensitivity study examines the use of fire protection water as a backup for RWST refill.