ML25058A262
| ML25058A262 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 02/28/2025 |
| From: | Samson Lee Plant Licensing Branch IV |
| To: | Gerfen P Pacific Gas & Electric Co |
| Lee S, 301-415-3158 | |
| References | |
| EPID L-2025-LRO-0003 | |
| Download: ML25058A262 (1) | |
Text
February 28, 2025 Paula Gerfen Senior Vice President, Generation and Chief Nuclear Officer Pacific Gas and Electric Company Diablo Canyon Nuclear Power Plant P.O. Box 56, Mail Code 104/6 Avila Beach, CA 93424
SUBJECT:
DIABLO CANYON NUCLEAR POWER PLANT, UNIT 1 - REVIEW OF FALL 2023 STEAM GENERATOR TUBE INSPECTION REPORT (EPID L-2025-LRO-0003)
Dear Paula Gerfen:
By letter dated May 8, 2024 (Agencywide Documents Access and Management System Accession No. ML24130A020), Pacific Gas and Electric Company (the licensee) submitted information summarizing the results of the fall 2023 steam generator tube inservice inspections performed at Diablo Canyon Nuclear Power Plant, Unit 1. These inspections were performed during refueling outage 24. The steam generator tube inspection report was submitted in accordance with Technical Specification 5.6.10, Steam Generator Tube Inspection Report.
Based on its review, the U.S. Nuclear Regulatory Commission (NRC) staff concludes that the licensee has provided the information required by Technical Specification 5.6.10, and that no follow-up is required at this time. A summary of the NRC staffs review is enclosed.
If you have any questions, please contact me at 301-415-3168 or via email at Samson.Lee@nrc.gov.
Sincerely,
/RA/
Samson S. Lee, Project Manager Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-275
Enclosure:
Review of the Steam Generator Tube Inspection Report cc: Listserv
Enclosure REVIEW OF FALL 2023 STEAM GENERATOR TUBE INSPECTION REPORT PACIFIC GAS AND ELECTRIC COMPANY DIABLO CANYON NUCLEAR POWER PLANT, UNIT 1 DOCKET NO. 50-275 By letter dated May 8, 2024 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML24130A020), Pacific Gas and Electric Company (the licensee) submitted information summarizing the results of the fall 2023 steam generator (SG) inspections performed at Diablo Canyon Nuclear Power Plant (Diablo Canyon), Unit 1. These inspections were performed during refueling outage 24 (1R24). The SG tube inspection report was submitted in accordance with Diablo Canyon Technical Specification (TS) 5.6.10, Steam Generator Tube Inspection Report.
Diablo Canyon, Unit 1, has four Westinghouse Model D54 replacement SGs manufactured by ENSA. Each SG has 4,444 thermally treated Alloy 690 tubes with an outside diameter of 0.75 inches and a nominal wall thickness of 0.043 inches. The straight portion of the SG tubes is supported by eight stainless steel broached trefoil tube support plates (TSPs). Stainless steel anti-vibration bars (AVBs) support the U-bend portion of the SG tubes.
The licensee provided the scope, extent, methods, and results of the SG tube inspections in the letter dated May 8, 2024. In addition, the licensee described corrective actions (e.g., tube plugging), if any were taken in response to the inspection findings.
Based on the review of the information provided, the U.S. Nuclear Regulatory Commission (NRC) staff has the following observations:
The only degradation mechanism detected during the 1R24 outage was tube wear from support structures. The maximum measured wear depth was 19 percent through-wall for wear both at TSPs and at AVBs. No tubes were plugged in 1R24. The operational assessment evaluated both forms of wear for 96 effective full-power months using a deterministic method. For wear at TSPs and AVBs, the structural and leakage criteria were met with margin.
Top of tubesheet visual inspection and foreign object search and retrieval were performed following sludge lancing. Five foreign objects were detected but did not cause tube wear according to rotating probe inspections. Two objects were retrieved. Three objects (two metallic) were not retrieved but were evaluated and determined to be acceptable to remain in place.
Visual inspection of the upper secondary-side internals performed in all four SGs found no evidence of flow accelerated corrosion, erosion corrosion, or other anomalies. Visual inspection was performed in the channel head bowl of all SGs, including the divider plate assemblies, tube-to-tubesheet welds, channel heads, and tubesheets. No discolorations or defects were noted.
Eddy current deposit mapping was performed for the third time. Deposit mapping and feedwater iron transport are used to support trending of tube deposits. The amount of deposits was determined to be well below any thresholds for tube bundle cleaning.
Based on a review of the information provided, the NRC staff concludes that the licensee provided the information required by Diablo Canyon TS 5.6.10. In addition, the NRC staff concludes that there are no technical issues that warrant follow-up action at this time, because the inspections appear to be consistent with the objective of detecting potential tube degradation and the inspection results appear to be consistent with industry operating experience at similarly designed and operated units.
- concurrence via email OFFICE NRR/DORL/LPL4/PM NRR/DORL/LPL4/LA*
NRR/DNRL/NCSG/BC*
NAME SLee PBlechman SBloom DATE 02/27/2025 02/28/2025 02/26/2025 OFFICE NRR/DORL/LPL4/BC*
NRR/DORL/LPL4/PM*
NAME TNakanishi SLee DATE 02/28/2025 02/28/2025