ML25266A040

Relief Request (RA 23-0309) Fifth Ten-Year Inservice Inspection Limited Examinations

ML25266A040
Person / Time
Site:	Oconee
Issue date:	01/28/2026
From:	Markley M Plant Licensing Branch II
To:	Snider S Duke Energy Carolinas
Williams S
References
EPID L-2025-LLR-0070, RA-23-0309
Download: ML25266A040 (0)

Text

January 28, 2026 Mr. Steven M. Snider Vice President, Oconee Nuclear Station Duke Energy Carolinas, LLC 7800 Rochester Highway Seneca, SC 29672-0752

SUBJECT:

OCONEE NUCLEAR STATION, UNITS 1, 2, AND 3 - AUTHORIZATION OF RELIEF REQUEST (RA-23-0309) FIFTH TEN-YEAR INSERVICE INSPECTION LIMITED EXAMINATIONS (EPID L-2025-LLR-0070)

Dear Mr. Snider:

By letter dated July 14, 2025, Duke Energy Carolinas, LLC (Duke Energy, the licensee) submitted relief request RA-23-0309 to the U.S. Nuclear Regulatory Commission (NRC) requesting approval for relief from the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (B&PV) Code,Section XI, 2007 Edition through the 2008 Addenda at Oconee Nuclear Station, Units 1, 2, and 3 (ONS).

Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(g)(5)(iii),

the licensee requested relief from the ASME Code Section XI examination requirements on the basis that conformance with the code requirement is impractical.

The NRC staff has reviewed the subject request and concludes, as set forth in the enclosed safety evaluation, that granting relief pursuant to 10 CFR 50.55a(g)(6)(i) is authorized by law and will not endanger life or property, or the common defense and security, and is otherwise in the public interest, with due consideration to the burden on the licensee if the requirements were imposed on the facility. Furthermore, the NRC staff has concluded that the examinations performed to the extent practical provide reasonable assurance of structural integrity of the subject components. Accordingly, the NRC staff concludes that the licensee has adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a(g)(5)(iii).

Therefore, the NRC staff grants relief pursuant to 10 CFR 50.55a(g)(6)(i) for the subject limited examinations, as described in relief request RA-23-0309, for the fifth 10-year inservice inspection interval at ONS.

All other ASME BPV Code Section XI requirements for which relief was not specifically requested and approved, remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.

If you have any questions, please email Shawn.Williams@nrc.gov.

Sincerely, Michael T. Markley, Chief Plant Licensing Branch II-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-269, 50-270, and 50-287

Enclosure:

Safety Evaluation cc: Listserv MICHAEL MARKLEY Digitally signed by MICHAEL MARKLEY Date: 2026.01.28 07:54:27 -05'00'

Enclosure SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION AUTHORIZATION OF FIFTH TEN-YEAR INSERVICE INSPECTION LIMITED EXAMINATIONS DUKE ENERGY CAROLINAS, LLC (DUKE ENERGY)

OCONEE NUCLEAR STATION, UNIT NOS. 1, 2, AND 3 DOCKET NOS. 50-269, 50-270, AND 50-287

1.0 INTRODUCTION

By letter dated July 14, 2025 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML25195A322), Duke Energy Carolinas, LLC (Duke Energy, the licensee) submitted to the U.S. Nuclear Regulatory Commission (NRC, the Commission) relief request RA-23-0309 seeking approval of relief from the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (B&PV) Code,Section XI, 2007 Edition through the 2008 Addenda at Oconee Nuclear Station, Units 1, 2, and 3 (ONS).

Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) section 50.55a(g)(5)(iii), the licensee requested relief from the ASME Code Section XI examination requirements on the basis that conformance with the code requirement is impractical.

2.0 REGULATORY EVALUATION

Pursuant to 10 CFR 50.55a(g)(4), Inservice inspection standards requirement for operating plants, ASME Code Class 1, 2, and 3 components (including supports) must meet the requirements, except the design and access provisions and the preservice examination requirements, set forth in the ASME Code,Section XI, Rules for lnservice Inspection [lSI] of Nuclear Power Plant Components, to the extent practical within the limitations of design.

The regulations in 10 CFR 50.55a(g)(5)(iii) state that if the licensee has determined that conformance with a Code requirement is impractical for its facility, the licensee must notify the NRC and submit, as specified in § 50.4, information to support the determinations.

Determinations of impracticality in accordance with this section must be based on the demonstrated limitations experienced when attempting to comply with the Code requirements during the ISI interval for which the request is being submitted. Pursuant to 10 CFR 50.55a(g)(5)(iv), the basis for this determination must be submitted for NRC review and approval not later than 12 months after the expiration of the initial 120-month inspection interval or subsequent 120-month inspection interval for which relief is sought.

The regulations in 10 CFR 50.55a(g)(6)(i), Impractical ISI requirements: Granting of relief state, in part, that:

The Commission will evaluate determinations under paragraph (g)(5) of this section that code requirements are impractical. The Commission may grant such relief and may impose such alternative requirements as it determines are authorized by law, will not endanger life or property or the common defense and security, and are otherwise in the public interest giving due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility.

The licensee requested relief from the ASME Code,Section XI requirements pursuant to 10 CFR 50.55a(g)(5)(iii). The licensees request for relief is applicable to the fifth 10-year ISI interval program at ONS. The applicable Code of record for the fifth 10-year ISI interval program at ONS is the 2007 Edition of the ASME Code,Section XI, through the 2008 Addenda.

The proposed alternative is requested for the fifth ISI interval at ONS, which ran from July 15, 2014, to July 14, 2024.

The licensee submitted relief request RA-23-0309 within 12 months of the fifth 10-year ISI interval at ONS, satisfying 10 CFR 50.55a(g)(5)(iv), which requires relief requests to be submitted within 12 months of the intervals expiration.

Based on the above, and subject to the following technical evaluation, the NRC staff finds that regulatory authority exists for the licensee to request, and for the NRC to authorize, the proposed relief request.

3.0 TECHNICAL EVALUATION

3.1 Examination Category B-D ASME Code Requirement The examination requirements for ASME Code Class 1, Examination Category B-D, Item Number B3.110, Full Penetration Welded Nozzles in Vessels, require a volumetric examination of the pressurizer nozzle-to-vessel welds in accordance with Figure IWB-2500-7(a) through (d). The subject welds included surge nozzle-to-head welds, nozzle-to-shell welds, relief nozzle-to-shell welds, and spray nozzle-to-shell welds in the pressurizers of Units 1, 2, and 3.

The extent of examination is required to be essentially 100-percent of the required examination volume, as specified in IWA-2200(c).

Table 1 below provides a summary of the examinations for Examination Category B-D welds for which the licensee is seeking relief on the basis that conformance with the ASME Section XI requirements is impractical as it would require extensive structural modifications to the component or surrounding structure.

Component ID Weld Description Coverage Achieved

(%)

Examination Results ONS Unit 1 1-PZR-WP15 Pressurizer Surge Nozzle-to-Head 41.2 No Recordable Indications 1-PZR-WP26-1 Pressurizer Nozzle-to-Shell 66.0 No Recordable Indications 1-PZR-WP26-2 Pressurizer Nozzle-to-Shell 66.0 No Recordable Indications 1-PZR-WP26-3 Pressurizer Nozzle-to-Shell 64.9 No Recordable Indications 1-PZR-WP26-4 Pressurizer Nozzle-to-Shell 64.9 No Recordable Indications 1-PZR-WP26-5 Pressurizer Nozzle-to-Shell 64.9 No Recordable Indications 1-PZR-WP26-6 Pressurizer Nozzle-to-Shell 64.9 No Recordable Indications 1-PZR-WP26-7 Pressurizer Nozzle-to-Shell 64.9 No Recordable Indications 1-PZR-WP33-1 Pressurizer Relief Nozzle-to-Shell 28.8 No Recordable Indications 1-PZR-WP33-2 Pressurizer Relief Nozzle-to-Shell 25.8 No Recordable Indications 1-PZR-WP33-3 Pressurizer Relief Nozzle-to-Shell 28.7 No Recordable Indications 1-PZR-WP34 Pressurizer Spray Nozzle-to-Shell/Head 45.6 No Recordable Indications ONS, Unit 2 2-PZR-WP15 Pressurizer Surge Nozzle-to-Head 68.25 No Recordable Indications 2-PZR-WP26-4 Pressurizer Sampling Nozzle-to-Shell 66.0 No Recordable Indications 2-PZR-WP26-5 Pressurizer Sampling Nozzle-to-Shell 66.0 No Recordable Indications 2-PZR-WP26-6 Pressurizer Sampling Nozzle-to-Shell 66.0 No Recordable Indications 2-PZR-WP26-7 Pressurizer Sampling Nozzle-to-Vessel 70.3 No Recordable Indications 2-PZR-WP33-1 Pressurizer Safety Relief Nozzle-to-Vessel 71.4 No Recordable Indications 2-PZR-WP33-2 Pressurizer Safety Relief Nozzle-to-Vessel 71.4 No Recordable Indications 2-PZR-WP33-3 Pressurizer Safety Relief Nozzle-to-Vessel 71.4 No Recordable Indications 2-PZR-WP34 Pressurizer Spray Nozzle-to-Vessel 78.98 No Recordable Indications ONS, Unit 3 3-PZR-WP15 Pressurizer Surge Nozzle-to-Vessel 67.3 No Recordable Indications 3-PZR-WP26-1 Pressurizer Sampling Nozzle-to-Shell 45.69 No Recordable Indications 3-PZR-WP26-2 Pressurizer Sampling Nozzle-to-Shell 45.69 No Recordable Indications 3-PZR-WP26-3 Pressurizer Sampling Nozzle-to-Shell 64.9 No Recordable Indications 3-PZR-WP26-4 Pressurizer Sampling Nozzle-to-Shell 64.9 No Recordable Indications 3-PZR-WP26-5 Pressurizer Sampling Nozzle-to-Shell 64.9 No Recordable Indications 3-PZR-WP26-6 Pressurizer Sampling Nozzle-to-Shell 64.9 No Recordable Indications 3-PZR-WP26-7 Pressurizer Sampling Nozzle-to-Shell 64.9 No Recordable Indications 3-PZR-WP33-1 Pressurizer Safety Relief Nozzle-to-Head 61.0 No Recordable Indications 3-PZR-WP33-2 Pressurizer Safety Relief Nozzle-to-Head 70.4 No Recordable Indications 3-PZR-WP33-3 Pressurizer Safety Relief Nozzle-to-Head 68.94 No Recordable Indications 3-PZR-WP34 Pressurizer Spray Nozzle-to-Head 75.4 No Recordable Indications Impracticality of Compliance In its submittal dated July 14, 2025, the licensee stated, in part, that:

Pursuant to 10 CFR 50.55a(g)(5)(iii), relief is requested on the basis that conformance with these ASME Section XI Code requirements is impractical as conformance would require extensive structural modifications to the component or surrounding structure.

10 CFR 50.55a recognizes the limitations to Inservice Inspection of components in accordance with the ASME Section XI Code that are imposed due to a plants early design and construction. A design modification would be required to obtain ASME Code required coverage. Therefore, it is impractical for ONS Units 1, 2, and 3 to satisfy the ASME Section XI code requirements to perform a volumetric examination of the components listed in Tables 1, 2, and 3 due to the physical component configuration and interference from permanent plant equipment.

Licensees Reason for Request Due to component design configuration limitations, the licensee was unable to obtain the ASME Code-required examination coverage for the components identified in its submittal. The licensee indicated that the subject welds were examined to the maximum extent practical and the design and nozzle geometry of the pressurizer restricted the scanning area, resulting in limited coverage. The licensee clarified that further coverage would require extensive structural modifications to the component or surrounding structure. The licensee explained that radiography is not a desired option because it is limited in its ability to detect service-induced flaws and use of other manual or automated ultrasonic testing (UT) techniques, whether conventional or phased array, were considered, but would not increase coverage due to limitations created by the component configuration.

The licensee also explained that Examination Category B-D Welds, Item B3.110, are Class 1 pressure retaining welds and that the examinations were limited due to the design and nozzle geometry of the pressurizer which restricted the scanning area and limited coverage.

Proposed Alternative The licensee described that obtaining the required examination coverage is impractical due to physical obstructions and limitations imposed by original plant design and fabrication (i.e., pressurizers design and nozzle geometry restricted the scanning area); therefore, no alternative examination for additional UT examination coverage is proposed.

The licensee determined that based on the volumetric coverage obtained, along with the ASME Code required System Pressure Tests, it is reasonable that if significant service induced degradation were occurring, it would have been evident by the examinations and testing that were performed.

NRC Staff Evaluation

The NRC staff evaluated Relief Request RA-23-0309 pursuant to 10 CFR 50.55a(g)(6)(i). The NRC staffs evaluation focused on whether: (1) sufficient technical justification exists to support the determination that the ASME Code requirements are impractical; (2) imposition of the Code-required examinations would result in a burden to the licensee; and (3) the licensees proposed alternative (i.e., acceptance of the reduced inspection coverage, periodic system pressure tests, and VT-2 visual examinations performed during each refueling outage associated with the Class 1 leakage test) provides reasonable assurance of structural integrity and leak tightness of the subject welds. The NRC staff determined that if these three criteria are met, then the requirements of 10 CFR 50.55a(g)(6)(i), will also be met.

Impracticality of Compliance The design of ONS Units 1, 2, and 3 provides access for examinations. However, component design configurations with conditions resulting in examination limitations (for example, those from surface configuration and surrounding plant components) did not allow for the full required examination volume coverage. The licensee explained that when examined, the welds listed in its submittal did not receive the required ASME Code volume coverage due to physical component configuration and interference from permanent plant equipment. These conditions resulted in scanning access limitations that prohibited essentially 100-percent examination coverage (i.e., greater than 90-percent) of the required examination volumes. Given these constraints, ONS performed the required examinations to the maximum extent practical. The licensee provided a summary of the examination limitations for each component for which they requested relief.

The NRC confirmed that all the B-D weld configurations in the request prevented the licensee from scanning the welds from the nozzle side. Additionally, as shown in the sketches and technical descriptions included in the licensees submittal, the subject components have access limitations which resulted in reduced volumetric examination coverage.

Based on its review of the submittal, including the diagrams provided, the NRC staff finds that due to geometric limitations associated with the aforementioned welds, it was impractical to meet the ASME Code-required essentially 100-percent volumetric examination coverage for the subject welds during the fifth 10-year ISI interval for ONS, Units 1, 2, and 3.

Burden of Compliance The licensee noted that for each weld in the scope of this request, conformance with the requirements is impractical as it would require extensive structural modifications to the component or surrounding structure. The licensee explained that using radiography as an alternative would not be able to detect service-induced flaws. Additionally, use of other manual or automated UT techniques, whether conventional or phased array, were considered, but would not increase coverage due to limitations created by the component configuration.

The NRC staff finds that replacing, reconfiguring, or modifying the components of the subject welds, or the use of radiography in order to increase the examination coverage, are the only reasonable means to achieve greater than 90-percent of the required ASME BPV Code examination volume, and that replacement or reconfiguration, or use of radiography of the subject components constitutes a burden on the licensee.

Structural Integrity and Leak Tightness The NRC staffs review considered whether the licensees achieved examination coverage for the subject welds in Examination Category B-D, Item Number B3.110, provides reasonable assurance of structural integrity and leak tightness of the subject welds. This was based on:

(1) the examination coverage achieved and (2) the safety significance of unexamined volumes and unachievable coverages (e.g., the presence or absence of known active degradation mechanisms and essentially 100-percent coverage achieved for similar welds in similar environments subject to similar degradation mechanisms).

In evaluating the licensees achieved examination coverage, the NRC staff assessed whether the licensee obtained as much coverage as reasonably possible and the way the licensee reported the coverage achieved. From review of the submittal, the NRC staff determined that:

The welds were examined using the appropriate equipment, UT modes of propagation, probe angles, frequencies, and scanning directions to obtain maximum coverage.

The coverage was calculated in a reasonable manner.

The personnel and procedures utilized for the examination were qualified as required by the ASME Code,Section XI.

The coverage was limited due to physical limitations or access.

No unacceptable indications were identified.

The NRC staff reviewed the licensees non-destructive examination data for the surge nozzle-to-head welds, nozzle-to-shell welds, relief nozzle-to-shell welds, and spray nozzle-to-shell welds in the pressurizer identified above in Table 1. The staff noted that the range of examination coverage achieved varied between 25.8-percent and 78.89-percent of the examination volume as listed in Tables 1, 2 and 3 for ONS Units 1, 2 and 3, respectively, within Enclosure 1 of the submittal. Based on its review of the configuration diagrams of the associated components in of the submittal, the staff finds that the licensee has demonstrated that physical limitations exist to obtain essentially 100 percent of the ASME Code-required examination coverage for the respective components addressed by Examination Category B-D, Item No. B3.110. Additionally, the staff finds the licensee performed the ASME Code Section XI required examination to the maximum extent practical as documented by Enclosure 2 of the submittal.

In addition to the coverage analysis described above, the NRC staff evaluated the conditions affecting the unexamined volumes of welds and unachievable coverage. Based on its review of the submittal, the NRC staff determined that the licensees volumetric examinations have covered, to the extent possible, the regions that are typically susceptible to higher stresses and, therefore, more susceptible to potential degradation. The licensee did not detect any recordable indications in the volumes examined. Therefore, based on the coverage achieved by the qualified inspection method and the examination of the subject welds, to the extent possible, the NRC staff finds it reasonable that if significant service-induced degradation had occurred, evidence of it would have been detected by the examinations that the licensee performed.

Based on the aggregate coverage obtained for the subject components, the extent of the examinations, and considering the licensees performance of essentially 100-percent coverage for the accessible portions of these welds, the NRC staff determined that if generic degradation mechanisms were present in the inaccessible areas, some evidence would likely have been detected in the accessible areas. The licensee utilized multiple weld scans, including radial and circumferential scans, utilizing skews to maximize coverage and determined that there were no recordable indications identified in the subject B-D welds for ONS, Units 1, 2, or 3. Based on the above, the NRC staff finds that the examinations performed provide reasonable assurance of the structural integrity and leak tightness of the subject welds and that full compliance with the ASME Code requirements for these welds would be an undue burden on the licensee.

The NRC staff also determined that, in addition to the required examinations, the subject welds have received and will continue to receive the system leakage test required by ASME Code Section XI, Table IWB-2500-1, Examination Category B-P, for all pressure-retaining components. Despite reduced coverage of the required examination volume of the subject welds, the NRC staff finds that this system leakage test will provide additional assurance that any pattern of degradation, if it were to occur, would be detected and that the licensee will be able to take appropriate corrective actions prior to returning the plant to power operation. This leakage test provides a defense-in-depth measure to monitor the structural integrity of these components. Additionally, the NRC staff noted that there is continuous monitoring instrumentation, required to be operable by ONS Technical Specification (TS) 3.4.15, RCS

[reactor coolant system] Leakage Detection Instrumentation, ensures early detection of any RCS pressure boundary leakage and compliance with ONS TS 3.4.13, RCS Operational Leakage.

The NRC staff determined that the examinations performed, despite the limited coverage obtained by the licensee, provide reasonable assurance of the structural integrity for the subject component welds in Examination Category B-D, Item Number B3.110. Furthermore, the continued performance of the periodic required VT-2 visual examinations during the system pressure tests provides additional assurance of structural integrity and leak tightness of the subject welds and that any generic degradation mechanisms that may be occurring in these components will be identified and dispositioned via the corrective action program. Full compliance with the ASME Code requirements for these welds would be impractical and constitute a burden on the licensee without a commensurate increase in level of quality and safety. Based on the above, the NRC staff finds that there is reasonable assurance of structural integrity and the risk associated with authorizing the requested relief would be acceptably low.

Therefore, the NRC concludes that the licensees request concerning Examination Category B-D items is acceptable.

3.2 Examination Category C-A ASME Code Requirement The examination requirements for ASME Code Class 2, Examination Category C-A, Item Number C1.20, Head Circumferential Welds, as delineated in ASME Code,Section XI, Table IWC-2500-1, require the volumetric examination coverage of all head-to-shell welds. The examination volumes shall conform to the applicable Figures IWC-2500-1 (a) through (c). The subject weld is a letdown storage tank head-to-shell weld in Unit 1.

ASME Code Class 2, Examination Category C-A, Item Number C1.30, Tubesheet-to-Shell Weld, as delineated in ASME Code,Section XI, Table IWC-2500-1, requires volumetric examination of all tubesheet-to-shell welds. The examination volumes shall conform to the applicable Figure IWC-2500-2. The subject welds include steam generator upper tubesheet-to-shell welds in Units 1 and 3.

Table 2 below provides a summary of the examinations for Examination Category C-A welds for which the licensee is seeking relief on the basis that conformance with the ASME Section XI requirements is impractical as it would require extensive structural modifications to the component or surrounding structure.

Table 2 ASME Code,Section XI, Examination Category C-A ASME Code Item Component ID Weld Description Coverage Achieved

(%)

Examination Results ONS, Unit 1 C1.20 1-LST-HD-SH-2 Letdown Storage Tank Head to Shell 80.24 No Recordable Indications C1.30 1-SGB-W69 Steam Generator Upper Tubesheet to Shell 86.0 No Recordable Indications ONS, Unit 3 C1.30 3-SGA-W69 Steam Generator Upper Tubesheet to Shell 86.0 No Recordable Indications Licensees Reason for Request Due to component design configuration limitations, the licensee was unable to obtain the ASME Code-required examination coverage for the components identified in its submittal. The licensee noted that the subject welds were examined to the maximum extent practical and the design and geometry of the letdown storage tank and the steam generator restricted the scanning area, resulting in limited coverage. The licensee clarified that further coverage would require extensive structural modifications to the component or surrounding structure to be examined.

The licensee also explained that Examination Category C-A Welds, Items C1.20 and C1.30, are Class 2 pressure retaining welds and that the examinations were limited due to the design and geometry of the letdown storage tank and steam generator which restricted the scanning area and limited coverage.

Proposed Alternative The licensee described that obtaining the required examination coverage is impractical due to physical obstructions and limitations imposed by original plant design and fabrication (i.e., the location of permanent Steam Generator supports and welded pads for support legs of the Letdown Storage Tank, consistent with previous exams); therefore, no alternative examination for additional ultrasonic testing (UT) examination coverage is proposed. The licensee explained that radiography is not a desired option because it is limited in its ability to detect service-induced flaws and use of other manual or automated UT techniques, whether conventional or phased array, were considered, but would not increase coverage due to limitations created by the component configuration.

The licensee determined that, based on the volumetric coverage obtained and the ASME Code-required system pressure tests, if significant service-induced degradation were occurring, it would have been evident by the examinations and testing performed on accessible areas.

NRC Staff Evaluation

The NRC staffs evaluation focused on whether: (1) sufficient technical justification exists to support the determination that the ASME Code requirements are impractical; (2) imposition of the Code-required examinations would result in a burden to the licensee; and (3) the licensees proposed alternative (i.e., acceptance of the reduced inspection coverage, periodic system pressure tests, and VT-2 visual examinations performed during each refueling outage associated with the Class 2 leakage test) provides reasonable assurance of structural integrity and leak tightness of the subject welds. The NRC staff determined that if these three criteria are met, then the requirements of 10 CFR 50.55a(g)(6)(i) will also be met.

Impracticality of Compliance The design of ONS Units 1, 2, and 3 provides access for examinations. However, component design configurations with conditions resulting in examination limitations (for example, those from surface configuration and surrounding plant components) did not allow for the full required examination volume coverage. The licensee explained that when examined, the welds listed in its submittal did not receive the required ASME Code volume coverage due to physical component configuration and interference from permanent plant equipment. These conditions resulted in scanning access limitations that prohibited essentially 100-percent examination coverage (i.e., greater than 90 percent) of the required examination volumes. Given these constraints, the licensee performed the required examinations to the maximum extent practical.

The licensee provided a summary of the examination limitations for each component for which they requested relief.

The NRC confirmed that all the C-A weld configurations in the request prevented the licensee from scanning the welds from the nozzle side. Additionally, as shown in the sketches and technical descriptions included in the submittal, the subject components have access limitations which resulted in reduced volumetric examination coverage, including proximity to weld pads, lifting trunnions, and lateral restraint configurations.

Based on its review of the submittal, including the provided diagrams, the NRC staff finds that due to geometric limitations associated with the aforementioned welds, it was impractical to meet the ASME Code-required essentially 100-percent volumetric examination coverage for the subject welds during the fifth 10-year ISI interval for ONS, Units 1, 2, and 3.

Burden of Compliance The licensee noted that for each weld in the scope of this request, conformance with the requirements is impractical as it would require extensive structural modifications to the component or surrounding structure. The licensee explained that using radiography as an alternative would not be able to detect service-induced flaws. Additionally, use of other manual or automated UT techniques, whether conventional or phased array, were considered, but would not increase coverage due to limitations created by the component configuration.

The NRC staff finds that replacing, reconfiguring, or modifying the components of the subject welds, or the use of radiography in order to increase the examination coverage, are the only reasonable means to achieve greater than 90-percent of the required ASME Code examination volume, and that replacement or reconfiguration, or use of radiography of the subject components constitutes a burden on the licensee.

Structural Integrity and Leak Tightness The NRC staffs review considered whether the licensees achieved examination coverage for the subject welds in Examination Category C-A, Item Numbers C1.20 and C1.30, provides reasonable assurance of structural integrity and leak tightness of the subject welds. This was based on: (1) the examination coverage achieved and (2) the safety significance of unexamined volumes and unachievable coverages (e.g., the presence or absence of known active degradation mechanisms and essentially 100-percent coverage achieved for similar welds in similar environments subject to similar degradation mechanisms).

In evaluating the licensees achieved examination coverage, the NRC staff assessed whether the licensee obtained as much coverage as reasonably possible and the way the licensee reported the coverage achieved. From review of the submittal, the NRC staff determined that:

The welds were examined using the appropriate equipment, UT modes of propagation, probe angles, frequencies, and scanning directions to obtain maximum coverage.

The coverage was calculated in a reasonable manner.

The personnel and procedures utilized for the examination were qualified as required by the ASME Code,Section XI.

The coverage was limited due to physical limitations or access.

No unacceptable indications were identified.

The NRC staff reviewed the licensees non-destructive examination data for the head circumferential weld in the letdown storage tank and the tubesheet-to-shell welds in the steam generators identified above in Table 2. The staff noted that the range of examination coverage achieved varied between 80.24-percent and 86-percent coverage of the examination volume, as listed in Tables 1 and 3 for ONS, Units 1 and 3, respectively, within Enclosure 1 of the submittal.

Based on its review of the configuration diagrams of the associated components in Enclosure 2 of the submittal, the staff finds that the licensee has demonstrated that physical limitations exist to obtain essentially 100 percent of the ASME Code-required examination coverage for the respective components addressed by Examination Category C-A, Items Nos. C1.20 and C1.30 for Unit 1, and Examination Category C-A, Item No. C1.30 for Unit 3. Additionally, the staff finds the licensee performed the ASME Code Section XI required examination to the maximum extent practical as documented by Enclosure 2 of the submittal.

In addition to the coverage analysis described above, the NRC staff evaluated the conditions affecting the unexamined volumes of welds and unachievable coverage. Based on its review of the submittal, the NRC staff determined that the licensees volumetric examinations have covered, to the extent possible, the regions that are typically susceptible to higher stresses and, therefore, more susceptible to potential degradation. The licensee did not detect any recordable indications in the volumes examined. Therefore, based on the coverage achieved by the qualified inspection method and the examination of the subject welds to the extent possible, the NRC staff finds it reasonable that if significant service-induced degradation had occurred, evidence of it would have been detected by the examinations that the licensee performed.

Based on the aggregate coverage obtained for the subject components, the extent of the examinations and considering the licensees performance of essentially 100-percent coverage for the accessible portions of these welds, the NRC staff determined that if generic degradation mechanisms were present in the inaccessible areas, some evidence would likely have been detected in the accessible areas. The licensee utilized multiple weld scans, including radial and circumferential scans, utilizing skews to maximize coverage and determined that there were no recordable indications identified in the subject C-A welds for ONS, Units 1 or 3. Therefore, the NRC staff finds that the examinations performed provide reasonable assurance of the structural integrity and leak tightness of the subject welds and that full compliance with the ASME Code requirements for these welds would be an undue burden on the licensee.

The NRC staff also determined that, in addition to the required examinations, the subject welds have received and will continue to receive the system leakage test required by ASME Code Section XI, Table IWC-2500-1, Examination Category C-H, for all pressure-retaining components. Despite reduced coverage of the required examination volume of the subject welds, the NRC staff finds that this system leakage test will provide additional assurance that any pattern of degradation, if it were to occur, would be detected and that the licensee will be able to take appropriate corrective actions prior to returning the plant to power operation. The NRC finds that this leakage test provides a defense-in-depth measure to monitor the structural integrity of these components. Additionally, the NRC staff noted that continuous monitoring instrumentation, required to be operable by ONS Technical Specification (TS) 3.4.15, RCS Leakage Detection Instrumentation, ensures early detection of any RCS pressure boundary leakage and compliance with ONS TS 3.4.13, RCS Operational Leakage.

The NRC staff determined that the examinations performed, despite the limited coverage obtained by the licensee, provide reasonable assurance of the structural integrity for the subject component welds in Examination Category C-A, Item Numbers C1.20 and C1.30. Furthermore, the continued performance of the periodic required VT-2 visual examinations during the system pressure tests provides additional assurance of structural integrity and leak tightness of the subject welds and that any generic degradation mechanisms that may be occurring in these components will be identified and dispositioned via the corrective action program. Full compliance with the ASME Code requirements for these welds is impractical and would constitute a burden on the licensee without a commensurate increase in safety. Based on the above, the NRC staff finds that there is reasonable assurance of structural integrity and the risk associated with authorizing the requested relief would be acceptably low. Therefore, the NRC concludes that the licensees request concerning Examination Category C-A items is acceptable.

3.3 Examination Category C-F-1 ASME Code Requirement The ASME Code,Section XI, Table IWC-2500-1, Examination Category C-F-1, Item Number C5.11, requires surface and volumetric examinations of applicable circumferential welds. As provided by the licensee, ONS, Unit 1 did not implement a Risk-Informed ISI (RI-ISI) program in accordance with ASME Code Case N-716-1 until the start of the second period of the fifth 10-year ISI interval; therefore, ASME Code,Section XI examinations were required for the applicable C-F-1 welds during the first period of the interval. ONS Units 2 and 3 implemented RI-ISI programs for the entire fifth ISI interval and, therefore, have no limited examinations associated with Examination Category C-F-1 welds. Relief Request RA-23-0309 specifically included the following C-F-1 welds for the fifth 10-year ISI interval program at ONS, Unit 1.

ONS Unit ASME Code Examination Category ASME Code

• Item Component Description Licensee s

Componen t

Number Percentag e

Coverage Obtained Unit 1 C-F-1 C5.11 Pipe to Valve ILP-208-4 75%

Unit 1 C-F-1 C5.11 Pipe to Flow Restrictor ILP-210-72 50%

Unit 1 C-F-1 C5.11 Pipe to Flow Restrictor ILP-210-73 50%

Impracticality of Compliance The licensee requested relief pursuant to 10 CFR 50.55a(g)(5)(iii) on the basis that conformance with the ASME Code,Section XI requirements is impractical. Specifically, the licensee explained that achieving the ASME Code-required surface and volumetric examination coverage would require extensive structural modifications to the component or surrounding structures. The licensee further noted that these inspection limitations are attributable to the original plant design and construction and that permanent plant equipment and component configurations physically restrict access to the subject welds. As a result, obtaining additional examination coverage would necessitate design modifications, which the licensee indicated are impractical for ONS Units 1.

Proposed Alternative Consistent with Sections 6.0, 6.1, and 6.2, of the relief request, the licensee proposed that no alternative examination method for additional ultrasonic testing (UT) coverage be implemented.

The licensee noted that obtaining additional volumetric examination coverage is impractical due to physical obstructions and limitations imposed by the original plant design and fabrication.

Radiographic testing was not selected because of its limited capability to detect service-induced flaws. The licensee further noted that other manual or automated UT techniques, including phased array UT, were considered but would not increase examination coverage due to component configuration constraints.

The licensee performed the ASME Code,Section XI required volumetric examinations to the maximum extent practical, as documented in Tables 1 of the relief request. In addition, VT-2 visual examinations associated with Class 2 system leakage tests are performed periodically.

The licensee explained that the volumetric examination coverage obtained, together with ongoing leakage testing, provides reasonable assurance that any flaw(s) propagating through the subject welds would be identified and addressed through the corrective action program.

NRC Staff Evaluation

The NRC staff reviewed the licensees request for relief from the ASME Code,Section XI examination requirements for Examination Category C-F-1 welds. The staff notes that the subject welds are limited in number and that examinations were performed to the maximum extent practical, consistent with the physical constraints imposed by the plants original design and the presence of permanent plant equipment. To increase examination coverage beyond that obtained would require redesign or replacement of the subject components, which would impose a burden on the licensee. Accordingly, the NRC staff finds that achieving the ASME Code-required surface and volumetric examination coverage is impractical.

Full compliance with the ASME Code requirements for these welds would be impractical and constitute a burden on the licensee without a commensurate increase in level of quality and safety. Based on the volumetric examination coverage obtained, the results of ASME Code-required system pressure testing, and the ongoing VT-2 leakage monitoring, the NRC staff finds that there is reasonable assurance of structural integrity and the risk associated with authorizing the request would be acceptably low. Therefore, the NRC concludes that the licensees request concerning Examination Category items C-F-1 welds is acceptable.

3.4 Examination Category C-F-2 ASME Code Requirement The ASME Code,Section XI, Table IWC-2500-1, Examination Category C-F-2, Item Number C5.51, requires surface and volumetric examinations of applicable circumferential welds. As provided by the licensee, ONS Unit 1 did not implement a Risk-Informed ISI (RI-ISI) program in accordance with ASME Code Case N-716-1 until the start of the second period of the fifth 10-year ISI interval; therefore, ASME Code,Section XI examinations were required for the applicable C-F-2 welds during the first period of the interval. ONS Units 2 and 3 implemented RI-ISI programs for the entire fifth ISI interval and, therefore, have no limited examinations associated with Examination Category C-F-2 welds. Relief Request RA-23-0309 specifically included the following C-F-2 weld for the fifth 10-year ISI interval program at ONS, Unit 1.

ONS Unit ASME Code Examination Category ASME Code

• Item Component Description Licensees Component Number Percentage Coverage Obtained Unit 1 C-F-2 C5.51 Pipe to Valve 1-20B-21-16-7 88.5%

Impracticality of Compliance The licensee requested relief pursuant to 10 CFR 50.55a(g)(5)(iii) on the basis that conformance with the ASME Code,Section XI requirements is impractical. The licensee noted that meeting the ASME Code-required surface and volumetric examination coverage would require extensive structural modifications to the component or surrounding structures. The licensee stated that these limitations are attributable to the original plant design and construction, as well as interference from permanent plant equipment that restricts physical access to the subject welds. As a result, achieving the ASME Code-required examination coverage would necessitate design modifications, which the licensee indicated are impractical for ONS, Units 1, 2, and 3.

Proposed Alternative Consistent with Sections 6.0, 6.1, and 6.3 of the relief request, the licensee proposed that no alternative examination method for additional ultrasonic testing (UT) coverage be implemented.

The licensee noted that additional UT coverage is impractical due to physical obstructions and limitations imposed by the original plant design and fabrication. Radiographic testing was not selected because of its limited capability to detect service-induced flaws. The licensee further noted that other manual or automated UT techniques, including phased array UT, were considered but would not increase examination coverage due to component configuration limitations.

The licensee performed ASME Section XI Code-required volumetric examinations to the maximum extent practical, as documented in Tables 1of the relief request. In addition, VT-2 visual examinations associated with Class 2 system leakage tests are performed periodically.

The licensee explained that the volumetric examination coverage obtained, together with ongoing leakage testing, provides reasonable assurance that any flaw(s) propagating through the subject welds would be identified and addressed through the corrective action program.

NRC Staff Evaluation

The NRC staff evaluated the licensees request for relief from the ASME Code,Section XI examination requirements for Examination Category C-F-2 welds. The staff notes that volumetric examinations were performed to the maximum extent practical and were supplemented by periodic VT-2 visual examinations associated with Class 2 system leakage tests. To increase examination coverage beyond that obtained would require redesign or replacement of the subject components, which would impose a burden on the licensee.

Accordingly, the NRC staff finds that achieving the ASME Code-required surface and volumetric examination coverage would be impractical and constitute a burden on the licensee without a commensurate increase in the level of quality and safety. Based on the volumetric examination coverage obtained, the results of ASME Code-required system pressure testing, and the ongoing VT-2 leakage monitoring, the NRC staff finds that the examinations performed to the extent practical provide reasonable assurance of the structural integrity and the risk associated with authorizing the request would be acceptably low. Therefore, the NRC concludes that the licensees request concerning Examination Category C-F-2 welds is acceptable.

3.5 Examination Category F-A ASME Code Requirement Relief request RA-23-0309 requests relief for the Reactor Pressure Vessel (RPV) support skirt for the fifth 10-year ISI interval program at ONS. Specifically, the licensee requested relief for the following components:

ONS Unit ASME Code Examination Category ASME Code

• Item Component Description Licensees Component Number Unit 1 F-A F1.40 RPV Welded Support Skirt 1-RPV-WR36 Unit 2 F-A F1.40 RPV Welded Support Skirt 2-RPV-WR36 Unit 3 F-A F1.40 RPV Welded Support Skirt 3-RPV-WR36 The RPV support skirt is an ASME Code Class 1 support that is subject to the examination requirements of Examination Category F-A in Table IWF-2500-1 of the 2007 Edition of the ASME Code,Section XI, through the 2008 Addenda. The ASME Code,Section XI, Table IWF-2500-1, Examination Category F-A requires a VT-3 visual examination of 100 percent of the RPV support skirt (Item No. F1.40) once each 10-year inspection interval.

Impracticality of Compliance In its letter dated July 14, 2025, the licensee explained that performing the VT-3 visual examination of essentially 100 percent of the RPV support skirt as required by the ASME Code is impractical due to the existence of insulation panels that partially obstruct the visual examination surfaces.

Although these insulation panels can be removed, the result of removing the insulation to perform visual examination of essentially 100 percent of the RPV support skirt would be excessive personnel radiation dose and additional personnel safety risk. Below are details as stated in the licensees relief request:

The minimum estimated radiation dose associated with obtaining the maximum available coverage on the exterior and interior surfaces of the support skirt is approximately 282.4 rem for each Unit.

In order to remove the bottom row of mirror insulation needed to access the entire exterior surface of the support skirt, removal of additional rows of mirror insulation is necessary because they are supported by the bottom row of insulation. The upper rows of these insulation panels can slip when the supporting row of insulation is removed, creating a potential personnel safety risk.

Even if all insulation panels are to be removed, there will still be some portions of the skirt interior and exterior surfaces that cannot be examined because of permanent attachments to the support skirt to which the insulation is attached. Compliance would require redesigning the insulation support attachments. The estimated radiation dose associated with the redesign and replacement of the insulation packages, however, has not been estimated.

Proposed Alternative In its letter dated July 14, 2025, the licensee in lieu of performing the 100 percent VT-3 examination of the welded support skirt proposes the following alternative:

For each Unit, a VT-3 visual examination was performed on accessible surfaces of the RPV support skirt. The calculated coverage is approximately 65.6-66 percent of the support surface areas within the examination boundary specified in Figure IWF-1300-1(c).

The VT-3 visual examinations were performed using personnel, equipment, and procedures qualified in accordance with the ASME Code,Section XI, 2007 Edition with the 2008 Addenda.

There were no unacceptable conditions or indications detected during these examinations.

NRC Staff Evaluation

The ASME Code,Section XI, Table IWF-2500-1, Examination Category F-A, requires a VT-3 visual examination of 100 percent of the RPV support skirt. The VT-3 visual examination is conducted to observe the general mechanical and structural condition of the support skirt to ensure that it can continue to perform its intended function of providing load-bearing support to the RPV and internal components. The VT-3 examination provides a means of detecting gross structural deformation, misalignments, and missing parts for the support items; it is not intended for detecting localized flaws or other small-scale degradation such as stress-corrosion cracking.

The ASME Code specifies a VT-3 because the support skirt is not susceptible to the types of localized aging effects that would require, at a minimum, a high-resolution visual examination (such as a VT-1 visual) of all accessible surfaces. The licensee proposed as an alternative to the above ASME Code,Section XI, examination requirements, that the VT-3 visual examination of 65.6-66 percent of the interior and exterior surfaces of the support skirt can be examined on accessible surfaces, without removal and reinstallation of the insulation panels.

The licensee has shown that it is impractical to meet the ASME Code-required 100 percent VT-3 visual examination coverage for the RPV support skirt due to limiting insulation design configurations and high radiation exposures. Based on the VT-3 visual examination coverage of 65.6-66 percent of the interior and exterior surfaces of the RPV support skirt obtained, the NRC finds there is reasonable assurance to conclude that if significant service-induced degradation such as seismic-induced deformation, buckling, or misalignments had occurred, evidence of it would have been detected by the examinations that were performed. Furthermore, the NRC staff concludes that the VT-3 examinations performed provide reasonable assurance of structural integrity of the subject component and that the risk associated with authorizing the request would be acceptably low. Therefore, the NRC concludes that the licensees request concerning Examination Category F-A is acceptable.

4.0 CONCLUSION

The NRC staff has reviewed the subject request and concludes, as set forth in the enclosed safety evaluation, that granting relief pursuant to 10 CFR 50.55a(g)(6)(i) is authorized by law and will not endanger life or property, or the common defense and security, and is otherwise in the public interest given due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility. Furthermore, the NRC staff has concluded that the examinations performed to the extent practical provide reasonable assurance of structural integrity of the subject components. Accordingly, the NRC staff concludes that the licensee has adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a(g)(5)(iii).

Therefore, the NRC staff grants relief pursuant to 10 CFR 50.55a(g)(6)(i) for the subject limited examinations, as described in relief request RA-23-0309, for the fifth 10-year ISI interval at ONS. All other ASME BPV Code Section XI requirements for which relief was not specifically requested and approved remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.

Principal Contributors: On Yee, NRR Omar Khan, NRR Andrew Prinaris, NRR Si Hwan Park, NRR John Tsao, NRR Date: January 28, 2026

ML25266A040 NRR-028 OFFICE NRR/LPL2-1/PM NRR/LPL2-1/LA NRR/DNRL/NVIB/BC NRR/DNRL/NPHP/BC NAME SWilliams KZeleznock ABuford MMitchell DATE 1/22/2026 1/23/2026 1/23/2026 1/23/2026 OFFICE NRR/DEX/ESEB NRR/LPL2-1/BC NAME ITseng MMarkley DATE 1/23/2026 1/28/2026