ML25227A208
| ML25227A208 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 09/18/2025 |
| From: | Shawn Williams NRC/NRR/DORL/LPL2-1 |
| To: | Duke Energy Carolinas |
| References | |
| EPID L-2025-LRM-0104 | |
| Download: ML25227A208 (1) | |
Text
September 18, 2025 LICENSEE:
Duke Energy Carolinas, LLC FACILITY:
Oconee Nuclear Station, Units 1, 2, and 3
SUBJECT:
SUMMARY
OF SEPTEMBER 10, 2025, PUBLIC MEETING WITH DUKE ENERGY CAROLINAS, LLC, REGARDING PRE-APPLICATION MEETING TO DISCUSS PROPOSED ALTERNATIVE FOR EXTENDING VOLUMETRIC EXAMINATION INTERVAL OF HIGH PRESSURE INJECTION NOZZLE WELDS (EPID L-2025-LRM-0104)
On September 10, 2025, an Observation public meeting (teleconference), was held between the U.S. Nuclear Regulatory Commission (NRC) and representatives of Duke Energy Carolinas, LLC (Duke Energy, the licensee). The purpose of the meeting was for Duke Energy to discuss a proposed alternative for Oconee Nuclear Station, Units 1, 2 and 3, to extend the volumetric ultrasonic examination interval for seven High Pressure Injection (HPI) nozzle Alloy 82/182 welds from every other inspection period, not to exceed 7 years, to once per Inservice Inspection (ISI) interval, not to exceed 13 years between examinations.
The meeting notice and agenda, dated August 4, 2025, are available in the Agencywide Documents Access and Management System (ADAMS) at Accession No. ML25252A081. A list of attendees is provided as an Enclosure. The licensees presentation is available in ADAMS at Accession No. ML25233A159.
Teleconference During the meeting, Duke Energy presented its proposed alternative request to reduce the frequency of encoded ultrasonic testing (UT) for seven Alloy 82/182 cold leg HPI nozzle-to-safe-end welds. The licensee explained that the current requirement under Title 10 of the Code of Federal Regulations (10 CFR) Section 50.55a(g)(6)(ii)(F)(1) requires use of ASME Code Case (CC) N-770-7, Alternative Examination Requirements and Acceptance Standards for Class 1 PWR Piping and Vessel Nozzle Butt Welds Fabricated with UNS N06082 or UNS W86182 Weld Filler Material With or Without Application of Listed Mitigation Activities,Section XI, Division 1, dated December 4, 2020, subject to conditions. Specifically, Condition 13 mandates encoded UT every second inspection period (maximum 7 years). Due to Oconees 24-month refueling cycle, this effectively results in a 6-year examination frequency The proposed alternative would reduce the encoded UT exam frequency to once per ISI interval (maximum 13 years), aligning with the frequency allowed for larger-bore welds under Item B-2 of CC N-770-7. The licensee stated that a plant-specific circumferential crack growth analysis supports this change, showing that the time to reach the allowable flaw size exceeds 13 years.
The analysis includes a conservative assumption of a 70% through-wall weld repair from the outside diameter. This request represents a first-of-a-kind submittal for this type of inspection relief, se3. Tog approval of an alternative that would remain in effect through the end of the current operating licenses for all three Oconee units, extending as late as 2054 for Unit 3.To maintain defense-in-depth, Duke Energy proposes to perform a manual (unencoded) phased array UT examinations every other outage (every 4 years) in accordance with Generic Letter 85-20, Evaluation of Stress Corrosion Cracking of Small Diameter Instrumentation and Thermowell Nozzles. Visual examinations (VT-2) are also performed during system pressure tests.
The NRC staff asked several clarifying questions and offered suggestions, including:
Clarify the technical differences between manual phased array UT, which is typically used to detect thermal fatigue under GL 85-20, and encoded phased array UT, which is required under Code Case N-770 to detect primary water stress corrosion cracking (PWSCC).
Requested a summary of past weld cracking, replacements, and relevant operating experience.
Confirm that the proposed manual (non-encoded) ultrasonic examinations are consistent with NEI 03-08, Guideline for the Management of Materials Issues, and relevant Electric Power Research Institute (EPRI) guidance, including EPRI Report 3002012244, Ultrasonic Examination of Dissimilar Metal Welds (Revision 3), which supports the use of manual phased array UT as a defense-in-depth measure and EPRI Report 3002015981, Human Factors in Manual Ultrasonic Testing, which highlights best practices and challenges associated with manual UT in field conditions. These references support the acceptability of the proposed examination strategy and align with NRC expectations for non-encoded UT practices.
Suggested that the licensee consider requesting relief from 10 CFR 50.55a(g)(6)(ii)(F),
specifically Condition 13, rather than from a specific revision of Code Case N-770. This would avoid tying the approval to a particular version (e.g., N-770-7) and ensures the relief remains valid if the code case is updated (e.g., to N-770-11).
While Duke is proposing to request relief under 10 CFR 50.55a(z)(1) (acceptable level of quality and safety), NRC staff noted that (z)(2) (hardship) could also be considered, especially due to vendor mobilization and dose concerns. The licensee noted that Arkansas Nuclear One (ANO) had a similar case that was initially submitted under (z)(1) but later supplemented under (z)(2).
The NRC staff questioned if the licensees assumption of a 70% through-wall weld repair from the outside diameter in the weld residual stress analysis is more conservative than the 50% depth typically assumed in industry guidance, including Electric Power Research Institute (EPRI) Report MRP-287, Guidance for Bounding Flaw Evaluations of Dissimilar Metal Piping Welds in PWR Plants, and related ASME Code Cases. The NRC staff suggested that Duke Energy confirm that this assumption is bounding and consistent with applicable guidance. The NRC staff also asked whether the assumed weld repair was localized or 360-degree, as this distinction affects the residual stress profile and flaw growth behavior. Duke Energy stated that it would review the calculation and provide clarification in the relief request.
Public Questions to NRC No members of the public were in attendance.
Closing No regulatory decisions or commitments were made during the meeting.
Please direct any inquiries to shawn.williams@nrc.gov.
/RA/
Shawn Williams, Senior Project Manager Plant Licensing Branch, II-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-269, 50-270, 50-287
Enclosure:
List of Attendees cc: Listserv
LIST OF ATTENDEES SEPTEMBER 10, 2025, PUBLIC MEETING WITH DUKE ENERGY CAROLINAS REGARDING A PRE-APPLICATION MEETING TO DISCUSS PROPOSED ALTERNATIVE FOR EXTENDING VOLUMETRIC EXAMINATION INTERVAL OCONEE NUCLEAR STATION, UNITS 1, 2, AND 3 Nuclear Regulatory Commission Staff Shawn Williams Michael Markley Jay Collins Stephen Cumblidge Duke Energy Carolinas Participants Ryan Treadway Joshua Duc Jordan Vaughan Austin Keller Angela Staller
ADAMS Package: ML25227A206 Meeting Notice: ML25252A081 Meeting Summary: ML25227A208
- via eConcurrence NRC-001 OFFICE NRR/DORL/LPL2-1/PM*
NRR/DORL/LPL1/LA*
NRR/DNRL/NPHP/BC*
NAME SWilliams KZeleznock MMitchell DATE 9/12/2025 9/16/2025 9/16/2025 OFFICE NRR/DORL/LPL2-1/BC*
NRR/DORL/LPL2-1/PM*
NAME MMarkley SWilliams DATE 9/17/2025 9/18/2025