ML23326A259

Review of the Fall 2022 Steam Generator Tube Inspection Report

ML23326A259
Person / Time
Site:	South Texas
Issue date:	12/05/2023
From:	Dennis Galvin Plant Licensing Branch IV
To:	Gerry Powell South Texas
Galvin D
References
EPID L-2023-LRO-0029
Download: ML23326A259 (4)

Text

December 5, 2023 Mr. G. T. Powell President and Chief Executive Officer STP Nuclear Operating Company P.O. Box 289 Wadsworth, TX 77483

SUBJECT:

SOUTH TEXAS PROJECT, UNIT 2 - REVIEW OF THE FALL 2022 STEAM GENERATOR TUBE INSPECTION REPORT (EPID L-2023-LRO-0029)

Dear Mr. Powell:

By letter dated April 24, 2023 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML23114A341), as supplemented by letter dated August 9, 2023 (ML23221A300), STP Nuclear Operating Company (STPNOC, the licensee), submitted information summarizing the results of the fall 2022 steam generator inspections at South Texas Project, Unit 2. These inspections were performed during the 22nd refueling outage (2RE22).

The information was submitted in accordance with South Texas Project, Unit 2 Technical Specification (TS) 6.8.3o, Steam Generator (SG) Program.

The U.S. Nuclear Regulatory Commission (NRC) staff has completed its review of the STPNOC submittals and concludes that the licensee provided the information required by South Texas Project, Unit 2 TS 6.8.3o. The NRC staff did not identify additional issues that warrant followup actions. The NRC staffs review summary is enclosed.

If you have any questions, please contact me at 301-415-6256 or by email at Dennis.Galvin@nrc.gov.

Sincerely,

/RA/

Dennis J. Galvin, Project Manager Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-499

Enclosure:

Review of Steam Generator Tube Inspection Report cc: Listserv

REVIEW OF THE FALL 2022 STEAM GENERATOR TUBE INSPECTION REPORT STP NUCLEAR OPERATING COMPANY SOUTH TEXAS PROJECT, UNIT 2 DOCKET NO. 50-499 By letter dated April 24, 2023 (ML23114A341), as supplemented by letter dated August 9, 2023 (ML23221A300), South Texas Nuclear Operating Company (the licensee), submitted information summarizing the results of the fall 2022 steam generator (SG) inspections performed at South Texas Project, Unit 2 (STP, Unit 2). The inspections were performed during refueling outage 22 (2RE22).

STP, Unit 2 is a four-loop pressurized-water reactor with Westinghouse Model Delta 94 SGs.

These SGs have been in service for approximately 17 effective full power years of operation at 2RE22. Each SG contains 7,585 thermally treated Alloy 690 tubes with a nominal outside diameter of 0.6875 inches and a nominal wall thickness of 0.040 inches. The tubes are supported by stainless steel flow distribution baffles, broached trefoil stainless steel tube support plates (TSPs) and stainless steel anti-vibration bars. The tubes were hydraulically expanded at both ends for the full depth of the tubesheet. The U-bend region of tube rows 1 to 17 received a thermal stress relief prior to operation.

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, such as tube plugging, 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 licensee provided a revised SG inspection report to clarify that there was a total of ten indications of tube wear at the TSPs. Six of the ten indications had been tracked during previous outages and met the reporting threshold requirement at 2RE22. The deepest wear indication measured 13 percent through-wall, which is well below the tube plugging criteria.

Pitting is an assumed existing degradation mechanism in STP, Unit 2. Pitting has not been identified in STP, Unit 2, but as part of the resolution of the sludge pile volumetric indication that was found in STP, Unit 1 during the 1RE19 inspection, STP, Unit 2 treated pitting as an existing degradation mechanism, until two consecutive inspections without any new sludge pile volumetric indications. Since there have now been two consecutive inspections at STP, Unit 2 without sludge pile volumetric indications, the expanded scope for pitting will be removed from the base inspection scope. Sludge pile volumetric indications will become a potential degradation mechanism for the next STP, Unit 2 inspection.

No tubes were plugged during 2RE22. A total of ten tubes are plugged in the STP, Unit 2 SGs.

Enclosure

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 current technical issues that warrant additional follow-up action. 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.

ML23326A259 *via e-mail OFFICE NRR/DORL/LPL4/PM NRR/DORL/LPL4/LA* NRR/DNRL/NCSG/BC*

NAME DGalvin PBlechman SBloom DATE 11/22/2023 11/29/2023 8/14/2023 OFFICE NRR/DORL/LPL4/BC* NRR/DORL/LPL4/PM*

NAME JRankin DGalvin DATE 12/5/2023 12/5/2023