ML25328A069
| ML25328A069 | |
| Person / Time | |
|---|---|
| Site: | Mcguire |
| Issue date: | 12/05/2025 |
| From: | Markley M NRC/NRR/DORL/LPL2-1 |
| To: | Pigott E Duke Energy Carolinas |
| References | |
| EPID L-2025-LLR-0026 | |
| Download: ML25328A069 (0) | |
Text
December 5, 2025 Edward Pigott Site Vice President Duke Energy Carolinas, LLC McGuire Nuclear Station 12700 Hagers Ferry Road Huntersville, NC 28078-8985
SUBJECT:
WILLIAM B. MCGUIRE NUCLEAR STATION, UNIT NO. 2 - AUTHORIZATION OF RELIEF REQUEST RA-24-0290 FOR VOLUMETRIC EXAMINATION OF CLASS 1 & 2 COMPONENTS (EPID L-2025-LLR-0026)
Dear Mr. Pigott:
By letter dated February 27, 2025, Duke Energy Carolinas, LLC (the licensee) submitted a request to the Nuclear Regulatory Commission (NRC) for relief from American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (BPV Code),Section XI requirements at McGuire Nuclear Station (MNS), Unit No 2.
Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(g)(5)(iii),
the licensee submitted relief request RA-24-0290 on the basis that conformance with these ASME BPV Code,Section XI, requirements is impractical as conformance would require extensive structural modifications to the component or surrounding structure. The U.S. Nuclear Regulatory Commission (NRC) staff has completed its review and concludes that Duke Energy has adequately demonstrated that conformance with the regulatory requirements set forth in 10 CFR 50.55a, Codes and standards, for the Code of Record Interval that implements the 2007 Edition through the 2008 Addenda of the ASME BPV Code,Section XI, is impractical for the McGuire Nuclear Station, Unit 2. The NRC staff further determined that the combination of the limited examination coverage, periodic system pressure tests, and periodic walkdowns provide reasonable assurance of the structural integrity of the subject welds. Therefore, the NRC authorizes relief RA-24-0290 in accordance with paragraph (f)(6)(i) of 10 CFR 50.55a for the Fourth ISI interval at McGuire, Unit 2, that started on July 15, 2014, and ended on February 29, 2024.
All other ASME BPV Code and ASME Code for Operation and Maintenance of Nuclear Power Plants (OM Code) requirements for which relief was not specifically requested and approved remain applicable.
If you have any questions, please contact John Klos, MNS Licensing Project Manager, at (301) 415-5136 or via email at John.Klos@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. 50-370
Enclosure:
Safety Evaluation cc: Listserv MICHAEL MARKLEY Digitally signed by MICHAEL MARKLEY Date: 2025.12.05 08:01:38 -05'00'
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELIEF REQUEST RA-24-0290 ALTERNATIVE WELD EXAMINATION COVERAGE MCGUIRE NUCLEAR STATION UNIT 2 DUKE ENERGY DOCKET NO. 50-370
1.0 INTRODUCTION
By letter dated February 27, 2025 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML25058A128), Duke Energy Carolinas, LLC (the licensee), requested relief from the requirements of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (BPV Code),Section XI for McGuire Nuclear Station, Unit 2.
The licensee submitted the Relief Request RA-24-0290 in accordance with Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(g)(5)(iii) for the Fourth 10-year inservice inspection (ISI) interval at McGuire, Unit 2, because the licensee had determined that compliance with the examination requirements of the ASME BPV Code,Section XI, was impractical.
and Enclosure 2 to the licensees letter dated February 27, 2025, contain Relief Request RA-24-0290 and examination data, respectively (hereafter referred to as Enclosure 1 and Enclosure 2).
2.0 REGULATORY EVALUATION
The regulations in 10 CFR 50.55a(g)(4), Inservice inspection standards requirement for operating plants, states, in part, that ASME BPV 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 Section XI, Rules for Inservice Inspection of Nuclear Power Plant Components, of the applicable editions and addenda of the ASME BPV Code to the extent practical within the limitations of design, geometry, and materials of construction of the components. The regulations also require that inservice examination of components and system pressure tests conducted during the first 10-year interval and subsequent intervals comply with the requirements in the latest Edition and Addenda of Section XI of the ASME Code, incorporated by reference in 10 CFR 50.55a(b), 18 months prior to the start of the 120-month interval, subject to the limitations and modifications listed therein.
The regulation in 10 CFR 50.55a(g)(5)(iii) states, ISI program update: Notification of impractical ISI Code requirements, states 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 in support of the determinations. Determination 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 inservice inspection interval for which the request is being submitted. Requests for relief made in accordance with this section must be submitted to the NRC no later than 12 months after the expiration of the initial 120-month inspection interval or subsequent month inspection interval for which relief is sought.
The regulation in 10 CFR 50.55a(g)(6)(i), Impractical IST requirements; Granting of relief, states 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.
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 the NRC to grant the reliefs requested by the licensee.
3.0 TECHNICAL EVALUATION
3.1 Licensees Request RA-24-0290 3.1.1 ASME BPV Code Components Affected In its submittal dated February 27, 2025, the licensee stated that the ASME Code components are Class 1 and Class 2 welds in Examination Categories: B-D, C-A, and R-A, and Item Numbers B3.110, C1.30, and R1.11 (Socket Welds), respectively. The examination requirements are specified in the ASME Code,Section XI, IWA-2200(c), IWB-2500, Table IWB-2500-1, IWC-2500, and Table IWC-2500-1.
The ASME Code Case N-716 Table 1, Note 8 provides additional requirements for the inspection of the socket welds under Inspection Item R1.11.
3.1.2 Applicable Code Edition and Addenda The McGuire, Unit 2, Fourth Inservice Inspection Interval is based on the ASME BPV Code,Section XI, 2007 Edition through the 2008 Addenda.
The licensee examined the subject welds in accordance with the requirements of ASME Code,Section XI, Appendix VIII, Performance Demonstration for Ultrasonic Examination Systems, as amended and mandated by 10 CFR 50.55a. In the case of limited examination coverage, the licensee made efforts to obtain additional coverage. Table 1 of the Relief Request RA-24-0290 identifies those welds that were examined in accordance with the requirements of ASME BPV Code,Section XI, Appendix VIII.
3.1.3 Applicable Code Requirements Examination Category B-D, Item Number B3.110, per Table IWB-2500-1, requires a volumetric examination of all nozzle-to-vessel welds as shown in Figure IWB-2500-7(b).
Examination Category C-A, Item Number C1.30, per Table IWC-2500-1, requires a volumetric examination of all tubesheet-to-shell welds as shown in Figure IWC-2500-2.
Examination Category R-A, Item Number R1.11, per Table 1, Note 8 of ASME Code Case N-716, requires a volumetric examination of piping base metal within 1/2 inch of the toe of the weld, and the fitting itself shall receive a visual examination VT-2. By letter dated August 13, 2013 (ML13234A069), the licensee submitted Relief Request 13-MNS-002 requesting to use ASME Code Case N-716 for Periods 1 and 2 of the 4th ISI Interval at McGuire, Unit 2. By letter dated July 14, 2014 (ML14188C348), the NRC approved Relief Request 13-MNS-002.
The ASME BPV Code,Section XI, IWA-2200(c) specifies that All nondestructive examinations of the required examination surface or volume shall be conducted to the maximum extent practical. When performing visual examination VT-1, surface, radiographic, or ultrasonic examination on a component with defined surface or volume, essentially 100% of the required surface or volume shall be examined. Essentially 100% coverage is achieved when the applicable examination coverage is greater than 90%; however, in no case shall the examination be terminated when greater than 90% coverage is achieved, if additional coverage of the required examination surface or volume is practical 3.1.4 Impracticality and Burden of Compliance In Section 4.0 of its submittal dated February 27, 2025, the licensee stated 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 early plants design and construction. A design modification would be required to obtain ASME Code required coverage. Therefore, it is impractical for MNS Unit 2 to satisfy the ASME Section XI code requirements to perform a volumetric examination of the components listed in Table 1 due to the physical component configuration and interference from permanent plant equipment.
Table 1 provides a summary of the examination limitations for each component for which relief is requested. The tables also indicate the outage the component was examined, the coverage percentage obtained for each component, and other pertinent design information. These tables are the cumulative lists of the limited ASME Section XI examinations performed during the Fourth ISI interval. provides nondestructive examination (NDE) data and coverage plots that detail the examination limitations.
Accordingly, pursuant to 10 CFR 50.55a(g)(5)(iii), Duke Energy has determined that conformance with the code requirement of essentially 100% coverage of weld volume or area examined was impractical due to various constraints and limitations as stated above. Duke Energy requests NRC approval of the proposed alternative as stated below.
In Section 6.0 of its submittal dated February 27, 2025, the licensee stated, in part, that, Radiography (RT) is not a desired option because it is limited in its ability to detect service-induced flaws. Use of other manual or automated UT techniques, whether conventional or phased array, were considered, but would not increase coverage due to limitation created by the component configuration.
3.1.5 Proposed Alternative In Section 6.0 of its submittal dated February 27, 2025, the licensee stated, in part, On the basis that obtaining the required examination coverage is impractical due to physical obstructions and limitations imposed by original plant design and fabrication including socket weld configurations, no alternative examination for additional ultrasonic testing (UT) examination coverage is proposed. As a minimum, all components completed the required examination(s) to the extent practical with regard to the limited component configuration or lack of access available. The examinations conducted confirmed satisfactory results resulting in no unacceptable flaws present, even though essentially 100% coverage was not attained. Duke Energy has concluded that completed UT examinations in conjunction with VT-2 system pressure tests are an acceptable alternative that provides reasonable assurance of continued structural integrity 3.1.6 Duration of Proposed Alternative This request is proposed for the Fourth Inservice Inspection Interval at McGuire, Unit 2, that started on July 15, 2014, and ended on February 29, 2024.
3.2
NRC Staff Evaluation
3.2.1 Evaluation of Examination Category B-D For Examination Category B-D, Item No. B3.110, the licensee was not able to achieve the essentially 100 percent examination coverage for pressurizer surge nozzle-to-head weld 2PZR-10. Figure IWB-2500-7(b) of the ASME BPV Code,Section XI specifies the required examination volume for the weld and base metal (portions of pressurizer shell and nozzle adjacent to the weld).
To perform the examination, the licensee used 35°, 45° and 60° shear wave transducer and 0° longitudinal transducer as discussed in Enclosure 2. The NRC staff determined that the licensee has properly documented the information of the four transducers on the UT calibration sheets, including calibration block, instrument setting, scan directions, couplant, reference block and search unit specifications.
The NRC staff reviewed the examination coverage calculation and transducer scanning diagrams as presented in Enclosure 2 and determined that the licensee aggregated coverage in the weld, base metal and zero-degree scan resulted in an examination coverage of 81.2% of the required volume.
The licensee stated that the examination was limited due to location of the pressurizer heater bundles and nozzle configuration. The NRC staff noted that the pressurizer is fitted with 20 heater wells and each well obstructs 2 inches of the surge nozzle-to-head weld length from UT scan; thus, the total examination coverage blockage is 40 inches (2 inches x 20 wells) out of a total weld length of 76 inches. The licensee also stated that the required examination volume of the base metal was also limited due to the heater wells. The licensee reported that it did not detect any unacceptable indications in the examined volume. The licensee considered using phased array UT method, but the required size of transducers proved to be prohibitive to the examination.
The NRC staff determined that the licensee performed the ASME BPV Code Section XI required examination to the maximum extent practical as documented in Enclosure 2. The licensee reported that there are currently no alternative examination techniques available to increase coverage. The NRC staff determined that the licensee is required to perform Class 1 system leakage tests which require VT-2 visual examinations prior to plant start from each refueling outage in accordance with the ASME Code,Section XI, IWA-5000 and IWB-5000. The NRC staff found that this required system leakage test and associated visual examination provide a defense-in-depth measure to monitor the structural integrity of weld 2PZR-10. The NRC staff additionally found that the VT-2 examination -- as part of the system leakage test in conjunction with the examined volume described above -- provides reassurance that any generic degradation mechanisms that may be occurring in weld 2PZR-10 will be identified.
Based on the above, the NRC staff finds that the volume of examination coverage obtained during the UT examinations along with ongoing Class 1 system leakage tests during every refueling outage provide adequate assurance that the licensee could identify and disposition any flaw(s) that might have propagated through weld 2PZR-10 via the corrective action program.
3.2.2 Evaluation of Examination Category C-A For Examination Category C-A, Item No. C1.30, the licensee could not achieve the essentially 100 percent examination coverage for steam generator tubesheet-to-shell weld 2ACSHX-SH-48. Figure IWC-2500-2 of the ASME BPV Code,Section XI specifies the required examination volume for the weld and base metal (portions of the tubesheet and shell adjacent to the weld). To perform the examination, the licensee used 35° shear wave transducer and 0° longitudinal transducer for the examination as discussed in Enclosure 2. The NRC staff determined that the licensee has properly documented the information of the two transducers on the UT calibration sheets, including calibration block, instrument setting, scan directions, couplant, reference block and search unit specifications.
The NRC staff reviewed the examination coverage calculation and transducer scanning diagrams in Enclosure 2 and determined that out of a total weld length of 175 inches, a total of 133 inches of weld 2ACSHX-SH-48 was obstructed from the UT scan. The licensee was able to examine 42 inches of the weld (175 inches - 133 inches). The NRC staff confirmed that the licensee achieved 24% of the required volume (42 inches /175 inches). The licensee stated that the examination was limited due to the interference of the permanent support structure adjacent to the weld. The licensee did not detect any unacceptable indications in the examined volume.
The NRC staff determined that the licensee has performed the ASME Code Section XI required examination to the maximum extent practical. The licensee stated that there are no alternative examination techniques currently available to increase coverage. The NRC staff noted that the licensee is required to perform Class 2 system leakage test and associated VT-2 visual examinations prior to plant startup in accordance with IWA-5000 and IWC-5000 of the ASME Code,Section XI. The NRC staff found that the VT-2 examination as part of the system leakage test in conjunction with the examined volume described above provides reassurance that any generic degradation mechanisms that may be occurring in weld 2ACSHX-SH-48 will be identified.
Based on the above, the NRC staff finds that the examination coverage obtained during the UT examinations along with ongoing Class 2 system leakage tests during every refueling outage provide reasonable assurance that the licensee could identify and disposition any flaw(s) that might have propagated through the steam generator tubesheet-to-shell weld 2ACSHX-SH-48 via the corrective action program.
3.3 Evaluation of Examination Category R-A For Examination Category R-A, Item No. R1.11, the licensee was not able to achieve essentially 100 percent examination coverage for multiple Class 1 socket welds, as documented in Table 1 of Relief Request RA-24-0290. Table 1, Note 8 of ASME Code Case N-716 requires a volumetric examination of the piping base metal within 1/2 inch of the toe of the socket weld and a VT-2 visual examination of the fitting itself.
The NRC staff reviewed the UT data, coverage calculations, and scanning diagrams provided in. The examinations were conducted using 38° and 45° shear wave transducers, and 0° longitudinal transducers, with the licensee documenting calibration blocks, scan directions, couplant, and instrument settings. The component identification, weld description, and reported coverage results are presented in Table A below.
Table A - ASME Code,Section XI, Examination Category R-A (Unit 2)
ASME Code Item Component ID Weld Description Percent Coverage Obtained R1.11 2NC2FW45-6 (M2.R1.11.3050) 2D Loop 1.5 Pipe-to-Coupling Socket Weld 80 R1.11 2NC2FW45-7 (M2.R1.11.3051) 2D Loop 1.5 Pipe-to-Coupling Socket Weld 80 R1.11 2NC2FW45-12 (M2.R1.11.3119) 2D Loop 1.5 Pipe-to-Coupling Socket Weld 80 R1.11 2NC2FW45-13 (M2.R1.11.3120) 2D Loop 1.5 Pipe-to-Coupling Socket Weld 80 R1.11 2NC2FW40-14 (M2.R1.11.3043) 2D Loop 1.5 Pipe-to-Coupling Socket Weld 80 Table A - ASME Code,Section XI, Examination Category R-A (Unit 2)
ASME Code Item Component ID Weld Description Percent Coverage Obtained R1.11 2NC2FW40-15 (M2.R1.11.3121) 2D Loop 2 Pipe-to-Coupling Socket Weld 15 R1.11 2NI2FW89-7 (M2.R1.11.3099) 2D Loop 2 Pipe-to-Coupling Socket Weld 80 R1.11 2NI2FW89-8 (M2.R1.11.3100) 2D Loop 2 Pipe-to-Coupling Socket Weld 80 R1.11 2NC2FW40-13 (M2.R1.11.3042) 2D Loop 1.5 Pipe-to-Coupling Socket Weld N/A For 2NC2FW40-13, a direct preservice UT examination could not be performed after reconfiguration and field installation due to its close proximity with socket weld 2NC2FW40-14.
However, during fabrication of weld 2NC2FW40-14, the UT base metal examination covered a portion of the required exam volume for 2NC2FW40-13. This resulted in 47.5 percent aggregate coverage of the base metal associated with 2NC2FW40-13 prior to welding. The NRC staff noted that these limitations stem from the engineering change that reconfigured the cold-leg injection piping after flaws were identified and attributed to thermal-fatigue damage from back-leakage through the original check valves. Replacement with larger 2-inch check valves, associated piping reconfiguration, and installation of permanent rupture restraints created close spacing and interferences that restricted UT access. ASME BPV Code,Section III construction-code dye-penetrant surface examinations were performed on 2NC2FW40-13 &
2NC2FW40-14 and achieved 100 percent coverage with no relevant conditions. After installation, the required base metal exam volume could not be re-examined due to geometric constraints. The associated VT-2 visual examination of the socket weld and fitting was performed during the Class 1 system leakage test and revealed no relevant conditions.
The NRC staff also determined that the limited UT coverage resulted from physical interferences such as adjacent valves, couplings, rupture restraints, and piping reconfiguration associated with the replacement. These design constraints reduced scanning access and prevented full volumetric coverage.
The NRC staff further noted that no unacceptable indications were identified in any of the volumetric or surface examinations. The licensee is also required to perform Class 1 system leakage tests, including VT-2 visual examinations, prior to plant startup from each refueling outage, in accordance with the ASME Code,Section XI, IWA-5000 and IWB-5000.
The NRC staff finds that the combination of (1) volumetric UT coverage to the extent practical, (2) 100 percent surface examinations performed during construction, and (3) ongoing Class 1 system leakage tests with VT-2 visual examinations during every refueling outage, provides reasonable assurance that any flaws that may propagate through these socket welds would be identified and dispositioned in the corrective action program.
4.0 CONCLUSION
Based on the above, the NRC staff determined that compliance with the ASME BPV Code,Section XI examination coverage requirements for the subject welds during the fourth ISI interval at McGuire, Unit 2, was impractical. The NRC staff further determined that the combination of the limited examination coverage, periodic system pressure tests, and periodic walkdowns provide reasonable assurance of the structural integrity of the subject welds.
Accordingly, the NRC staff finds that the licensee has adequately addressed all the regulatory requirements set forth in 10 CFR 50.55a(g)(5)(iii). The NRC staff concludes 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 giving due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility. Therefore, the NRC staff authorizes Relief Request RA-24-0290 from the examination requirements for the subject welds for the fourth 10-year ISI interval at McGuire, Unit 2, which started on July 15, 2014, and ended on February 29, 2024.
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: Omar Khan, NRR John Tsao, NRR Date of Issuance: December 5, 2025
- via eConcurrence NRR-028 OFFICE NRR/DORL/LLPB/PM NRR/DORL/LPL2-1/PM NRR/DORL/LPL2-1/LA NAME JDelosreyes JKlos KZeleznock DATE 11/24/2025 11/24/2025 11/25/2025 OFFICE NRR/DNRL/NPHP/BC NRR/DORL/LPL2-1/BC NRR/DORL/LPL2-1/PM NAME MMitchell MMarkley JKlos DATE 11/26/2025 12/5/2025 12/5/2025