ML23331A798

Review of the Fall 2022 Steam Generator Tube Inspection Report (01R32)

ML23331A798
Person / Time
Site:	Oconee
Issue date:	12/14/2023
From:	Shawn Williams Plant Licensing Branch II
To:	Snider S Duke Energy Carolinas
Williams S
References
EPID L-2023-LRO-0037
Download: ML23331A798 (4)

Text

December 14, 2023 Mr. 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 1 - REVIEW OF THE FALL 2022 STEAM GENERATOR TUBE INSPECTION REPORT (O1R32) (EPID L-2023-LRO-0037)

Dear Mr. Snider:

By letter dated May 18, 2023, Duke Energy (the licensee) submitted information summarizing the results of the Fall 2022 steam generator inspections performed at Oconee Nuclear Station, Unit 1, during refueling outage 32 (O1R32).

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,

/RA/

Shawn A. Williams, Senior Project Manager Plant Licensing Branch II-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-269

Enclosure:

Review of Steam Generator Tube Inspection Report cc: Listserv

OCONEE NUCLEAR STATION, UNIT 1 NRC STAFF REVIEW OF THE FALL 2022 STEAM GENERATOR TUBE INSPECTION REPORT (O1R32)

DOCKET NO. 50-269 By letter dated May 18, 2023 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML23138A099), Duke Energy (the licensee) submitted information summarizing the results of the fall 2022 steam generator (SG) inspections performed at Oconee Nuclear Station, Unit 1, during refueling outage 32 (O1R32, hereafter referred to as RFO32). By letter dated November 22, 2022 (ML22321A158), the Nuclear Regulatory Commission (NRC) staff documented a conference call held with the licensee on November 8, 2022, during RFO32.

Oconee, Unit 1, 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 trefoil broached openings. Some of the openings in the 14th TSP are 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:

The licensees formula for calculating the percent degraded area (PDA) of the wear indications at the drilled hole locations in the 14th TSP was an approximation rather than a standard cross-sectional area formula. This formula was used for calculating both the condition monitoring (CM) limit and the measured PDA of the maximum depth wear indication at the 14th TSP. Using this approximation for the CM limit resulted in a conservative calculation, since the resulting CM limit was smaller than that calculated using the standard cross-sectional area formula. However, for the maximum depth wear indication, the calculated PDA was smaller than that calculated using the standard cross-sectional area formula, and thus, was slightly non-conservative. In this case, however, there was sufficient margin such that calculation of the PDA by either method was acceptable for demonstrating tube integrity.

Enclosure

During RFO32, the licensee continued using the fixed curve for bobbin depth sizing and the new depth reporting threshold of TSP wear indications, both of which were implemented in RFO31. The new depth reporting threshold of TSP wear indications located at broached-hole TSPs is 8 percent through-wall; the previous depth reporting threshold was 5 percent. This change eliminates reporting small signals from tube noise or mix residual, in comparison to true tube wear. For the same reason, the licensee also increased the depth reporting threshold of TSP wear indications located at drilled hole TSPs from 8 percent to 11 percent for the first time in RFO32, which affected reporting of a limited number of indications at the 14th TSP.

In SG 1A, 28 tubes were plugged due to wear at TSP intersections. In SG 1B, 14 tubes were plugged due to wear at TSP intersections.

There was one indication of presumed foreign object wear in one tube in SG 1A, located at the top of the lower tubesheet. A foreign object in this location was removed from the SG. There were 23 foreign objects found in the two SGs. Fifteen of the foreign objects were removed and the remaining were evaluated for continued operation.

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

ML23331A798 OFFICE NRR/DORL/LPL2-1/PM NRR/DORL/LPL2-1/PM NRR/DORL/LPL2-1/LA NAME JMinzerBryant SWilliams KGoldstein DATE 12/11/2023 12/11/2023 12/13/2023 OFFICE NRR/DNRL/NCSG/BC NRR/DORL/LPL2-1/BC* NRR/DORL/LPL2-1/PM NAME SBloom MMarkley SWilliams DATE 12/08/2023 12/14/2023 12/14/2023