ML26013A009
| ML26013A009 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 01/21/2026 |
| From: | Michael Mahoney Plant Licensing Branch IV |
| To: | Gerfen P Pacific Gas & Electric Co |
| Lee S, 301-415-3158 | |
| References | |
| EPID L-2025-LLR-0064 | |
| Download: ML26013A009 (0) | |
Text
January 21, 2026 Ms. Paula Gerfen Senior Vice President. Generation and Chief Nuclear Officer Pacific Gas and Electric Company Diablo Canyon Nuclear Power Plant P.O. Box 56. Mail Code 104/6 Avila Beach. CA 93424
SUBJECT:
DIABLO CANYON NUCLEAR POWER PLANT. UNITS 1 AND 2 -
AUTHORIZATION OF PROPOSED ALTERNATIVE GEN-ISI-ALT-2024-01 TO USE ASME CODE CASE N-752-1. RISK-INFORMED CATEGORIZATION AND TREATMENT FOR REPAIR/REPLACEMENT ACTIVITIES IN CLASS 2 AND 3 SYSTEMS. SECTION XI. DIVISION 1 (EPID L-2025-LLR-0064)
Dear Ms. Gerfen:
By letter dated June 26. 2025 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML25177D083). Pacific Gas and Electric Company (the licensee) submitted a request to the U.S. Nuclear Regulatory Commission (NRC) for authorization to use proposed alternative. GEN-ISI-ALT-2024-01. to certain American Society of Mechanical Engineers (ASME). Boiler and Pressure Vessel Code (BPV Code).Section XI. requirements at Diablo Canyon Nuclear Power Plant. Units 1 and 2 (Diablo Canyon).
Specifically. the licensee requested to use ASME Code Case N-752-1. Risk-Informed Categorization and Treatment for Repair/Replacement Activities in Class 2 and 3 SystemsSection XI. Division 1. in lieu of certain requirements in ASME BPV Code Section XI.
articles IWA-1000. IWA-4000. and IWA-6000. as incorporated by reference in Title 10 of the Code of Federal Regulations (10 CFR) Section 50.55a. Codes and standards.
Pursuant to 10 CFR 50.55a(z)(1). the licensee requested to use the proposed alternative on the basis that the alternative provides an acceptable level of quality and safety. ASME Code Case N-752-1 has not been approved by the NRC staff or incorporated by reference for generic use. Therefore. the NRC staff reviewed the licensees submittal as a plant-specific request for Diablo Canyon.
The NRC staff has reviewed the proposed alternative and. as set forth in the enclosed safety evaluation. the staff determines that the proposed alternative provides an acceptable level of quality and safety. Accordingly. the NRC staff concludes that the licensee has adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a(z)(1). Therefore. the NRC staff authorizes the proposed alternative for the fourth and fifth inservice inspection intervals.
All other ASME BPV Code.Section XI. requirements for which an alternative was not specifically requested and authorized in this alternative remain applicable. including third party review by the Authorized Nuclear Inservice Inspector.
In its request. the licensee mentioned in several places that the risk-informed categorization process described in ASME Code Case N-752-1 is consistent with the risk-informed categorization process described in 10 CFR 50.69. Risk-informed categorization and treatment of structures. systems and components for nuclear power reactors. For the licensees facilities that have been approved to use a risk-informed categorization process under 10 CFR 50.69.
this authorization does not change any of the licensees obligations with its approved programs for implementing 10 CFR 50.69.
If you have any questions. please contact Samson Lee at 301-415-3168 or via email at Samson.Lee@nrc.gov.
Sincerely.
Michael Mahoney. Acting Chief Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-275 and 50-323
Enclosure:
Safety Evaluation cc: Listserv MICHAEL MAHONEY Digitally signed by MICHAEL MAHONEY Date: 2026.01.21 15:30:34 -05'00'
Enclosure SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION PROPOSED ALTERNATIVE TO USE ASME CODE CASE N-752-1. RISK-INFORMED CATEGORIZATION AND TREATMENT FOR REPAIR/REPLACEMENT ACTIVITIES IN CLASS 2 AND 3 SYSTEMS. SECTION XI. DIVISION 1 DIABLO CANYON NUCLEAR POWER PLANT. UNITS 1 AND 2 PACIFIC GAS AND ELECTRIC COMPANY DOCKET NOS. 50-275 AND 50-323
1.0 INTRODUCTION
By letter dated June 26. 2025 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML25177D083). Pacific Gas and Electric Company (PG&E. the licensee) requested an alternative to certain requirements of the American Society of Mechanical Engineers (ASME). Boiler and Pressure Vessel Code (BPV Code). to use ASME Code Case N-752-1. Risk-Informed Categorization and Treatment for Repair/Replacement Activities in Class 2 and 3 Systems.Section XI. Division 1. in lieu of certain requirements in ASME BPV Code.Section XI. articles IWA 1000. IWA-4000. and IWA-6000. as incorporated by reference in Title 10 of the Code of Federal Regulations (10 CFR) Section 50.55a. Codes and standards. at Diablo Canyon Nuclear Power Plant. Units 1 and 2 (Diablo Canyon. DCPP).
Specifically. pursuant to 10 CFR 50.55a(z)(1). the licensee requested to use the proposed alternative on the basis that the alternative provides an acceptable level of quality and safety.
ASME Code Case N-752-1 has not been approved by the U.S. Nuclear Regulatory Commission (NRC) staff or incorporated by reference for generic use. Therefore. the NRC staff reviewed the licensees submittal as a plant-specific request for Diablo Canyon.
2.0 REGULATORY EVALUATION
2.1 Regulations The following requirement is applicable to this request:
10 CFR 50.55a(z)(1). Acceptable level of quality and safety.
2.2 Regulatory Guidance The NRC staff used the following guidance in the evaluation of this request:
Regulatory Guide (RG) 1.200. Revision 2. An Approach for Determining the Technical Adequacy of Probabilistic Risk Assessment Results for Risk Informed Activities.
March 2009 (ML090410014).
NRC Information Notice (IN) 2025-01. Lessons Learned When Implementing ASME Code Case N-752. dated February 10. 2025 (ML24323A057).
3.0 TECHNICAL EVALUATION
3.1 Licensees Proposed Alternative 3.1.1 Licensees Applicable ASME BPV Code Edition and Addenda The applicable ASME BPV Code editions and addenda for the specific inservice inspection (ISI) intervals are specified in the table below.
Plant ISI Interval ASME BPV Code Section XI.
Code of Record Edition/Addenda Interval Start Interval End Diablo Canyon. Unit 1 4th 2007 Edition with 2008 Addenda 5/7/2015 5/6/2025 Diablo Canyon. Unit 1 5th 2019 Edition 5/7/2025 5/6/2035 Diablo Canyon. Unit 2 4th 2007 Edition with 2008 Addenda 3/13/2016 3/12/2026 Diablo Canyon. Unit 2 5th 2019 Edition 3/13/2026 3/12/2036 3.1.2 ASME BPV Code Components Affected Section 1. American Society of Mechanical Engineers (ASME) Code Components Affected. of the enclosure to the licensees alternative request letter dated June 26. 2025. lists the affected Code components. which are ASME BPV Code Class 2 and 3 components and their supports except Class CC and MC items. greater than Nominal Pipe Size (NPS) 4 piping within the break exclusion region. and greater than NPS 4 feedwater system piping from the steam generator.
including the steam generator. to the outer containment isolation valve.
3.1.3 Applicable ASME BPV Code Requirements ASME BPV Code.Section XI. subsection IWA. provides the requirements for repair/replacement activities. Section 3. Applicable Code Requirement. of the enclosure to the licensees alternative request letter dated June 26. 2025. provides additional details of the Code requirements related to group classification. arrangement with an Authorized Inspection Agency.
written programs and plans. documentation of a Quality Assurance Program. specific requirements for pressure-retaining items or their supports. Owner reporting responsibilities.
and Owner retained records.
3.1.4 Proposed Alternative Section 5. Proposed Alternative and Basis for Use. of the enclosure to the licensees alternative request letter dated June 26. 2025. states:
Pursuant to 10 CFR 50.55a(z)(1). PG&E proposes to implement ASME Code Case N-752-1. without exception. as an alternative to the ASME Section XI requirements specified in Section 3 above. ASME Code Case N-752-1 provides a process for determining the risk-informed categorization and treatment requirements for Class 2 and 3 pressure-retaining items or their associated supports as delineated in Section 1. This requested implementation includes the categorization of passive SSCs [systems. structures. and components] (e.g..
piping) and implementation of alternative special treatment activities limited to the repair/replacement activities for Class 2 and 3 pressure-retaining items or their associated supports. For components that have both active and passive functions. only the passive function will be categorized. The alternative treatments associated with ASME Code Case N-752-1 will not be applied to the parts/components associated with the active function. Code Case N-752-1 may be applied on a system basis or on individual items within selected systems.
Code Case N-752-1 does not apply to Class 1 items.
The use of this proposed alternative is requested on the basis that requirements in Code Case N-752-1 will provide an acceptable level of quality and safety.
3.2
NRC Staff Evaluation
The NRC evaluated the licensees request to determine if the proposed alternative meets the requirements of 10 CFR 50.55a(z)(1) for an acceptable level of quality and safety in lieu of the ISI requirements in the ASME BPV Code.Section XI. as incorporated by reference in 10 CFR 50.55a. The NRC staff verified that the precedents cited by the licensee are applicable. The NRC staff also reviewed deviations from the licensee precedents.
3.2.1 Applicability of Precedents The licensee provided a list of precedents in section 7 of the enclosure to the licensees alternative request letter dated June 26. 2025. The precedents are Arkansas Nuclear One.
Units 1 and 2 (ANO). alternative EN-20-RR-001. approved May 19. 2021 (ML21118B039); ANO changes to the Quality Assurance Program Manual. approved May 19. 2021 (ML21132A279);
and NextEra Energy alternative FRR 23-01. approved June 12. 2024 (ML24149A286). The NRC staff did not re-review these precedents. but verified that they are applicable to this licensee request.
Section 5.2.B. Categorization Process. of the enclosure to the licensees alternative request letter. indicates that the licensees categorization process is technically equivalent to the process approved by the NRC staff on April 22. 2009. for ANO2-R&R-004. Revision 1 (ML090930246). Alternative ANO2-R&R-004 was the basis for ASME Code Case N-752-1. The NRC staff reviewed the proposed alternative as a risk-informed request because the proposed alternative includes the use of a risk-informed process described in Appendix I of Code Case N-752-1. This process requires technical acceptability of the probabilistic risk assessment (PRA) used to support the ASME Code Case N-752-1 required evaluations as described in section 3.2.3 of this safety evaluation. Section 5.2.B of the enclosure to the licensees alternative request letter. indicates that the licensees risk-informed categorization evaluation is performed by an Owner-defined team that includes members with expertise in PRA. plant operations. system design. and safety or accident analysis. Section 5.2.D. Feedback and Process Adjustment. indicates that the licensee will continue to review and assess the existing PRAs to demonstrate adequate technical capability and to maintain a feedback and adjustment process consistent with that of 10 CFR 50.69(e). to update the PRA. categorization. and treatment processes based on review of new insights resulting from available risk information changes (i.e.. PRA model or other analysis used in the categorization). plant design changes.
operational changes. and SSC performance. The NRC staff finds this approach for categorization. feedback. and process adjustment to be acceptable. Therefore. the NRC staff verified that the approved ANO2-R&R-004. Revision 1. categorization methodology is applicable to Diablo Canyon.
Section 5.2.E. Treatment Requirements for LSS [Low Safety Significant] Items. of the enclosure to the licensees alternative request letter. states. in part:
DCPP will define alternative treatment requirements that confirm with reasonable confidence that each Class 2 and 3 LSS SSC will remain capable of performing its safety-related function under design-basis conditions.
Section 5.2.E of the enclosure to the licensees alternative request letter. indicates that the licensees alternative treatment requirements include specific provisions. The NRC staff found that the ANO alternative EN-20-RR-001. and NextEra Energy alternative FRR 23-01.
precedents have similar provisions for alternative treatment. Therefore. the Diablo Canyon provisions for alternative treatment are acceptable.
Section 5.2.E of the enclosure to the licensees alternative request letter. also indicates that the licensee plans to amend the Diablo Canyon Quality Assurance Program Description for safety-related Class 2 and 3 SSCs identified as LSS in accordance with ASME Code Case N-752-1.
The NRC staff finds that this is consistent with the ANO changes to Quality Assurance Program Manual precedent and is acceptable.
The NRC staff notes that the ANO licensee followed 10 CFR 50.54. Conditions of licenses.
paragraph (a)(4) to establish supplemental processes and procedures that the NRC staff accepted as satisfying the requirements of 10 CFR Part 50. Appendix B. Quality Assurance Criteria for Nuclear Power Plants and Fuel Reprocessing Plants. given the low safety significance of the components within the scope of Code Case N-752. The Diablo Canyon licensee proposes to follow 10 CFR 50.54(a)(3) to apply quality assurance (QA) treatment of components within the scope of ASME Code Case N-752. The NRC regulations in 10 CFR 50.54(a)(3) allow licensees to adjust their QA activities as accepted by the NRC in response to prior licensee requests under 10 CFR 50.54(a)(4). Therefore. the Diablo Canyon licensee must satisfy the QA treatment allowed by the NRC staff for the ANO licensee request under 10 CFR 50.54(a)(4) for components within the scope of ASME Code Case N-752 to provide an acceptable level of quality and safety under 10 CFR 50.55a(z)(1).
3.2.2 Deviations from Precedents The NRC staff identified a deviation from the licensee cited precedents. Section 5.2.E of the enclosure to the licensees alternative request letter dated June 26. 2025. states. in part:
DCPP has reviewed the guidance provided in the recent NRC Information Notice (IN) 2025-01 (Reference 8.17 [ML24323A057]). As discussed in the Information Notice. the alternative supplemental processes and procedures for safety-related Class 2 and Class 3 LSS items within the scope of the Code Case N-752-1 will satisfy the requirements of Appendix B to 10 CFR Part 50. given the low safety significance of individual safety-related Class 2 and Class 3 LSS items within the scope of ASME Code Case N-752-1.
The NRC staff noted that IN 2025-01 was issued after approval of the licensee cited precedents.
However. the NRC staff finds that IN 2025-01 provides important clarification regarding Appendix B to 10 CFR Part 50 requirements. and is appropriate and acceptable for the licensee to include the information in its alternative treatment.
3.2.3 PRA Technical Acceptability The NRC staff verified the technical acceptability/adequacy of the Diablo Canyon PRA model for its risk-informed inservice inspection (RI-ISI) program. The NRC staffs review of the Diablo Canyon PRA was based. in part. on the NRC staffs previous determinations that the PRA model was acceptable to support adoption of Technical Specifications Task Force (TSTF)
Traveler TSTF-505. Revision 2. Provide Risk-Informed Extended Completion Times - RITSTF
[Risk-Informed TSTF] Initiative 4b. dated May 29. 2024 (ML24099A219) and Diablo Canyon license amendment for adoption of 10 CFR 50.69. Risk-Informed Categorization and Treatment of Structures. Systems and Components for Nuclear Power Reactors. dated December 11.
2024 (ML24269A083). The licensee stated that all applicable PRA technical requirements are met at Capability Category (CC) II or higher in PRA Standard ASME/ANS Ra-Sa-2009. as endorsed by RG 1.200. Revision 2. and that there are no remaining open finding-level facts and observations for the PRA models relevant to this application (i.e.. internal events and internal flooding). Based on the above. the NRC staff finds the Diablo Canyon PRA acceptable to use for the purpose of this proposed alternative to use ASME Code Case N-752-1.
3.3 NRC Staff Conclusion
The NRC staff finds the licensee cited precedents that are applicable to Diablo Canyon regarding the use of ASME Code Case N-752-1. The proposed use of N-752 in this application is consistent with previous alternatives to ASME BPV Code.Section XI. requirements that NRC staff has previously concluded that did meet the five key principles of risk-informed decision-making. The NRC staff also identified a deviation from the cited precedents. but finds it appropriate and acceptable. The NRC staff finds that the licensees PRA is of sufficient quality and is acceptable for this application. The feedback and process adjustment will allow a timely update of the elements of this program. Therefore. the NRC staff finds that the proposed alternative will provide an acceptable level of quality and safety.
4.0 CONCLUSION
Based on the above. the NRC staff determined that the proposed alternative provides an acceptable level of quality and safety. Accordingly. the NRC staff concludes that the licensee has adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a(z)(1).
Therefore. the NRC staff authorizes the proposed alternative for the fourth and fifth ISI intervals at Diablo Canyon.
All other ASME BPV Code.Section XI. requirements for which an alternative was not specifically requested and authorized in this alternative remain applicable. including third party review by the Authorized Nuclear Inservice Inspector.
Principal Contributors: Todd Hilsmeier. NRR Thomas Scarbrough. NRR Drew Childs. NRR Tiffany Lee. NRR Date: January 21, 2026
- by eConcurrence NRR-028 OFFICE NRR/DORL/LPL4/PM*
NRR/DORL/LPL4/LA*
NRR/DRA/APLA/BC NRR/DRO/IQVB/BC NAME SLee PBlechman MGonzalez KKavanagh DATE 1/13/2026 1/15/2026 12/5/2025 12/10/2025 OFFICE NRR/DNRL/NPHP/BC NRR/DEX/EMIB/BC NRR/DORL/LPL4/BC(A)*
NAME MMitchell SBailey (KHsu for)
MMahoney DATE 12/9/2025 12/8/2025 1/21/2026