ML25317A784
| ML25317A784 | |
| Person / Time | |
|---|---|
| Site: | Catawba  |
| Issue date: | 01/16/2026 |
| From: | Geoffrey Miller Plant Licensing Branch II |
| To: | Huecker J Duke Energy Carolinas |
| Stone Z | |
| References | |
| EPID L-2025-LLR-0071 | |
| Download: ML25317A784 (0) | |
Text
January 16, 2025 Mr. Jonathan Huecker Site Vice President Catawba Nuclear Station Duke Energy Carolinas, LLC 4800 Concord Road York, SC 29745
SUBJECT:
CATAWBA NUCLEAR STATION, UNIT 2 - PROPOSED ALTERNATIVE TO USE REACTOR VESSEL HEAD PENETRATION EMBEDDED FLAW REPAIR METHOD (EPID L-2025-LLR-0071)
Dear Mr. Huecker:
By letter dated July 17, 2025, Duke Energy Carolinas, LLC (Duke Energy, the licensee) requested approval of an alternative to certain American Society of Mechanical Engineers (ASME) repair and replacement requirements at Catawba Nuclear Station, Unit 2.
Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(z)(1), the licensee requested to use an alternative on the basis that complying with the specified ASME Code Section XI, IWA-4000 and Section III, NB-4450 for an embedded flaw repair method provides an acceptable level of quality and safety.
The U.S Nuclear Regulatory Commission (NRC) staff has reviewed the subject request and concludes, as set forth in the enclosed safety evaluation, that Duke Energy has adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a(z)(1). Therefore, the NRC staff authorizes the alternative as requested in RA-24-0285 for the fifth inservice inspection (ISI) interval, scheduled to begin on March 29, 2026, and end on March 28, 2038.
All other ASME requirements for which an alternative was not specifically requested and authorized remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
If you have any questions, please contact Shawn Williams at Shawn.Williams@nrc.gov.
Sincerely, Michael T. Markley, Branch Chief Plant Licensing Branch II-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No.
50-414
Enclosure:
Safety Evaluation cc: Listserv GLENN MILLER Digitally signed by GLENN MILLER Date: 2026.01.16 08:36:37 -05'00'
Enclosure SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION PROPOSED ALTERNATIVE NO. RA-24-0285 TO USE REACTOR VESSEL HEAD PENETRATION EMBEDDED FLAW REPAIR METHOD DUKE ENERGY CAROLINAS, LLC CATAWBA NUCLEAR STATION, UNIT 2 DOCKET NO. 50-414
1.0 INTRODUCTION
By letter dated July 17, 2025 (Agencywide Documents and Access Management System (ADAMS) Accession No. ML25199A121), Duke Energy Carolinas, LLC (Duke Energy, the licensee) requested approval of an alternative to certain American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (BPV) repair and replacement requirements at Catawba Nuclear Station, Unit 2.
Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(z)(1), the licensee requested a proposed alternative to the ASME Code Section XI, IWA-4000 and Section III, NB-4450 for the continued use of the embedded flaw repair method for reactor vessel closure head penetration #74 for the fifth inservice inspection (ISI) interval. Per 10 CFR 50.55a(z)(1), the licensee states the proposed alternative provides an acceptable level of quality and safety.
2.0 REGULATORY EVALUATION
Pursuant to 10 CFR 50.55a(g)(4), ASME Code Class 1, 2, and 3 components (including supports) shall meet the requirements, except the design and access provisions and the preservice examination requirements set forth in the ASME Code,Section XI, to the extent practical within the limitations of design, geometry, and materials of construction of the components.
Regulations in 10 CFR 50.55a(g)(6)(ii)(D) state, in part, that holders of operating licenses or combined licenses for pressurized-water-reactors as of or after June 3, 2020, shall implement the requirements of ASME BPV Code Case N-729-6 instead of ASME BPV Code Case N-729-4, subject to the conditions specified in paragraphs (g)(6)(ii)(D)(2) through (8) of this section, by no later than one year after June 3, 2020. All previous NRC-approved alternatives from the requirements of paragraph (g)(6)(ii)(D) of this section remain valid.
The regulations in 10 CFR 50.55a(z) state that alternatives to the requirements of paragraph (g) of 10 CFR 50.55a may be used, when authorized by the NRC, if the licensee demonstrates (1) the proposed alternatives would provide an acceptable level of quality and safety or (2) compliance with a compensating increase in the level of quality and safety.
3.0 TECHNICAL EVALUATION
3.1 Licensees Proposed Alternative RA-24-0285 3.1.1 Applicable Code Edition and Addenda Unit ISI Interval ASME ISI Code Edition Interval Scheduled Start Date Interval Scheduled End Date CNS-2 Fifth 2019 Edition 3/29/2026 3/28/2038 Note-
- 1. These interval end dates are current estimates, with flexibilities due to transition in fuel cycle period or implementation of ASME Code Case N-921.
3.1.2 ASME Code RequirementsSection XI, IWA-4000, describes requirements for the removal of defects from and welded repairs performed on ASME Code components. Paragraph IWA 4421 states, in part, that defects be removed or mitigated in accordance with the requirements in IWA-4461 (by thermal methods), IWA-4462 (by mechanical processing) or IWA-4411 (by welding or brazing).
Specifically, paragraph IWA-4411 requires that welding, brazing, fabrication, and installation shall be performed in accordance with the Owners Requirements and the Construction Code of the item, with additional provisions allowing the use of later editions or addenda of the Construction Code.
Section III, paragraph NB-4451, provides the general requirements for removal and repair of weld metal defects. In addition, ASME Code,Section III, paragraph NB-4452 and subparagraph NB-4453.1 specify the requirements for eliminating weld surface defects and the requirements for excavating weld defects for repair activities, respectively.
3.1.3 Proposed Alternative Pursuant to 10 CFR 50.55a(z)(1), Duke Energy proposes continued use of the embedded flaw repair for Catawba, Unit 2, reactor vessel closure head (RVCH) penetration #74 for the fifth ISI interval.
3.1.4 Duration of Request The licensees proposed alternative is requested for the fifth inservice inspection interval at Catawba, Unit 2, which is scheduled to start on March 29, 2026, and end on March 28, 2038.
3.2
NRC Staff Evaluation
During the spring 2021 refueling outage at Catawba, Unit 2, the licensee detected an indication which required repair in the J-groove weld of RVCH penetration #74. The licensee used the embedded flaw repair process, in accordance with the NRC-approved WCAP-15987 P-A report, with some modifications, to repair the weld. On April 24, 2021 (ML21117A129), the NRC provided verbal authorization for the embedded flaw repair for one cycle of operation and by letter dated September 20, 2021 (ML21253A082), the NRC provided its follow up safety evaluation for the verbal relief request. By letter dated January 20, 2022 (ML22020A283), as supplemented by letter dated July 7, 2022 (ML22188A236), the licensee provided additional technical basis to support the continued use of the repair for the remaining life of the plant. By letter dated August 31, 2022 (ML22213A253), the NRC authorized the embedded flaw repair for RVCH penetration #74 for the fourth ISI interval at Catawba, Unit 2. The licensees current submittal dated July 17, 2025, requests authorization of the embedded flaw repair for the fifth ISI interval at Catawba, Unit 2.
The licensee made this request in accordance with 10 CFR 50.55a(z)(1) on the basis that the proposed alternative repair will provide an acceptable level of quality and safety. The NRC staff reviewed the following information: (1) the installed embedded flaw repair; (2) consistency of the repair, examination, and flaw evaluation methods with those described in the NRC-approved WCAP 15987-P-A report and current NRC regulations under 10 CFR 50.55a(g)(6)(ii)(D); (3) the stress corrosion cracking resistance of repair weld material (Alloy 52/52M); and (4) the flaw assessment for continued operation through the fifth ISI interval at Catawba, Unit 2.
The NRC-approved WCAP-15987-P, Revision 2 by letter dated July 3, 2003 (ML031840237), as a topical report to be used for referencing in licensing applications to request implementation of the embedded flaw repair process. The process embeds primary water stress corrosion cracking (PWSCC) flaws found in Alloy 600 RVCH penetration nozzles and J-groove welds under a non-structural seal weld which is more resistant to PWSCC. The licensee used Alloy 52/52M as the seal weld material. The NRC has performed extensive testing to verify the increased resistance to PWSCC of this material over the past 10 years at Argonne National Laboratory and Pacific Northwest National Laboratory and finds them acceptable for use in this application. Consistent with the original 2003 safety evaluation, NRC finds that seal weld repair technique of flaws of the type identified by the licensee in the J-groove weld of RVCH penetration #74 provides an acceptable level of safety and quality.
The licensee modified the original embedded flaw repair process to address changes in non-destructive examination (NDE) requirements since the 2003 approval of the WCAP. The licensee provided updated examination requirements to be consistent with the NRC regulations in 10 CFR 50.55a(g)(6)(ii)(D), which mandates the use of ASME Code Case N-729-6, with conditions, for the examination of RVCH penetration nozzles and welds. The NRC staff verified that the examination types and frequencies were consistent with the current regulatory requirement and latest approvals of use of the embedded flaw repair process for other licensees. The NRC staff find these examinations will provide reasonable assurance of the structural integrity of the RVCH through the fifth ISI interval at Catawba, Unit 2.
The licensee previously provided and referenced the Westinghouse Report WCAP-18708, Revision 1 (ML22188A236), Technical Basis for Westinghouse Embedded Flaw Repair of Catawba, Unit 2, Reactor Vessel Head Penetration Nozzles and Attachment Welds. This report provides a technical basis for the design life of the embedded flaw repair for head penetration
- 74 for the remainder of the current plant license at Catawba, Unit 2. The report meets the criteria for application of the embedded flaw repair process stated in Appendix C of WCAP-15987-P-A. Given that the flaw remains in the structural material of the head penetration, WCAP-18708 provides an analysis of the flaw in the possible growth mechanisms to ensure structural integrity of the component of the embedded flaw repair. Due to the inability of NDE to size the flaw in the J-groove weld, the licensee assumed a hypothetical flaw that covers the entire attachment J-groove weld. The NRC staff finds this to be a conservative flaw assessment. The NRC staff finds the licensees methodology of assessment of structural integrity to be in compliance per the ASME Code, Regulatory Guide 1.161, Evaluation of Reactor Pressure Vessels With Charpy Upper-Shelf Energy Less Than 50 ft-lb, (ML003740038) and NUREG/CR-5729, Multivariable Modeling of Pressure Vessel and Piping J-R Data, (ML20077F133) and, therefore, find it acceptable. WCAP-18708, Revision 1, states the limiting flaw path is fatigue growth through the embedded flaw repair thickness itself, but that structural integrity of the repaired weld layer would be maintained for 47 years of service life.
The NRC staff finds this result is consistent with previous reviews of head penetration flaw repairs.
Given the proposed alternative NDE is performed in accordance with 10 CFR 50.55a(g)(6)(ii)(D) and the conservative flaw assessment, the NRC staff continues to find reasonable assurance of structural integrity of the embedded flaw repaired RVCH penetration #74 for the licensees calculated 47 years of service life. Therefore, the NRC staff concludes the licensees proposed alternative provides an acceptable level of quality and safety for the remainder of the current fifth ISI interval.
4.0 CONCLUSION
The NRC staff has determined that the proposed alternative in the licensees request referenced above would provide an acceptable level of quality and safety.
The NRC staff concludes that the licensee has adequately addressed the regulatory requirements set forth in 10 CFR 50.55a(z)(1).
The NRC staff authorizes the use of proposed alternative under RA-24-0285 at Catawba Nuclear Station, Unit 2, for the fifth ISI interval which is scheduled to begin on March 29, 2026, and end on March 28, 2038.
All other ASME BPV Code,Section XI, requirements for which an alternative was not specifically requested and authorized remain applicable, including third party review by the Authorized Nuclear Inservice Inspector.
Principal Contributor: JCollins, NRR Date: January 16, 2026
ML25317A784 OFFICE NRR/DORL/LPL2-1/PM NRR/DORL/LPL2-1/LA NRR/DNRL/NPHP/BC NAME SWilliams KZeleznock MMitchell DATE 1/15/2026 01/15/2026 01/14/2026 OFFICE NRR/DORL/LPL2-1/BC NAME MMarkley (EMiller for)
DATE 1/16/2026