ML24305A149
| ML24305A149 | |
| Person / Time | |
|---|---|
| Site: | Oconee  (DPR-047) |
| Issue date: | 11/04/2024 |
| From: | Shawn Williams Plant Licensing Branch II |
| To: | Snider S Duke Energy Carolinas |
| Williams S | |
| References | |
| EPID L-2024-LRO-0019 | |
| Download: ML24305A149 (1) | |
Text
November 4, 2024 Steven M. Snider Site Vice President, Oconee Nuclear Station Duke Energy Carolinas, LLC 7800 Rochester Highway Seneca, SC 29672-0752
SUBJECT:
OCONEE NUCLEAR STATION, UNIT 2 - REVIEW OF THE FALL 2023 STEAM GENERATOR TUBE INSPECTION REPORT (O2R31) (EPID L-2024-LRO-0019)
Dear Steven Snider:
By letter dated May 14, 2024, Duke Energy (the licensee) submitted information summarizing the results of the fall 2023 steam generator inspections performed at Oconee Nuclear Station, Unit 2, during refueling outage 31 (O2R31).
The U.S. Nuclear Regulatory Commission (NRC) staff has completed its review of the report and concludes that the licensee provided the information required by their technical specifications and that no additional follow-up is required at this time. The NRC staffs review is enclosed.
If you have any questions, please contact me at 301-415-1009 or via e-mail at Shawn.Williams@nrc.gov.
Sincerely, Shawn Williams, Senior Project Manager Plant Licensing Branch II-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-270
Enclosure:
Review of Steam Generator Tube Inspection Report cc: Listserv SHAWN WILLIAMS Digitally signed by SHAWN WILLIAMS Date: 2024.11.04 14:39:38 -05'00'
Enclosure OCONEE NUCLEAR STATION, UNIT 2 NRC STAFF REVIEW OF THE FALL 2023 STEAM GENERATOR TUBE INSPECTION REPORT (O2R31)
DOCKET NO. 50-270 By letter dated May 14, 2024 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML24135A389), Duke Energy (the licensee) submitted information summarizing the results of the fall 2023 steam generator (SG) inspections performed at Oconee Nuclear Station, Unit 2, during refueling outage 31 (O2R31).
Oconee, Unit 2, has two replacement once-through steam generators (OTSGs) designed and fabricated by Babcock and Wilcox International. Each OTSG has 15,631 thermally treated Alloy 690 tubes with a nominal outside diameter of 0.625 inches and a nominal wall thickness of 0.038 inches. The tubes were hydraulically expanded for 13 inches from the tube end into the 22-inch thick tubesheet. Tube support is provided by 15 stainless steel horizontal tube support plates (TSPs) with trifoil broached openings. The 14th TSP also has some drilled holes.
The licensee provided the scope, extent, methods, and results of the SG tube inspections in the letters referenced above. In addition, the licensee described corrective actions (e.g., tube plugging) taken in response to the inspection findings.
After reviewing the information provided, the NRC staff noted the following:
During O2R31 (fall 2023), the licensee changed the depth reporting threshold for drilled TSP tube wear indications from 10 percent through-wall (TW) to 11 percent. The licensee reported that the upper 95th percentile growth rate for drilled-hole TSP tube wear has been increasing over the past three outages with the maximum observed during the most recent operating cycle (O2R31) of 2.75 percent TW per effective full power year (EFPY).
During O2R31, the licensee assigned a Historical No Change (HNC) code to 35 tube-to-tube wear (TTW) indications in the 2A SG and to 24 TTW indications in the 2B SG that had been inspected at least three previous times with the array probe and which showed no change in the bobbin probe signal. By comparison, in O2R30, 33 HNC indications were assigned in SG 2A and 24 were assigned in SG 2B.
No new indications of TTW were reported but there were 14 repeat indications of TTW from bobbin probe examination. The array probe was able to distinguish these indications as 4 indications in 4 tubes in SG 2A and 12 indications in 10 tubes in SG 2B, for a total of 16 repeat indications.
One indication of presumed foreign object wear (13 percent TW) was reported in SG 2A slightly above the 13th TSP. Three foreign objects were found and removed in both SGs.
In SG 2A, 23 tubes were plugged due to tube wear at TSP locations, and in SG 2B, 14 tubes were plugged due to tube wear at TSP locations.
Based on a review of the information provided, the NRC staff concludes that the licensee provided the information required by their technical specifications. In addition, the NRC staff concludes that there are no technical issues that warrant follow-up action currently, since 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.
Principal Contributor: Andrew Johnson, NRR
ML24305A149 OFFICE NRR/DORL/LPL2-1/PM NRR/DORL/LPL2-1/LA NRR/DNRL/NCSG/BC NAME SWilliams KGoldstein SBloom DATE 10/31/2024 11/01/2024 10/30/2024 OFFICE NRR/DORL/LPL2-1/BC*
NRR/DORL/LPL2-1/PM NAME MMarkley SWilliams DATE 11/04/2024 11/04/2024