ML21263A004

Review of the Fall 2020 Steam Generator Tube Inspection Report

ML21263A004
Person / Time
Site:	Watts Bar
Issue date:	09/24/2021
From:	Kimberly Green Plant Licensing Branch II
To:	Jim Barstow Tennessee Valley Authority
Green K
References
EPID L-2021-LRO-0023
Download: ML21263A004 (4)

Text

September 24, 2021 Mr. James Barstow Vice President, Nuclear Regulatory Affairs and Support Services Tennessee Valley Authority 1101 Market Street, LP 4A-C Chattanooga, TN 37402-2801

SUBJECT:

WATTS BAR NUCLEAR PLANT, UNIT 2 - REVIEW OF THE FALL 2020 STEAM GENERATOR TUBE INSPECTION REPORT (EPID L-2021-LRO-0023)

Dear Mr. Barstow:

By letter dated May 10, 2021, Tennessee Valley Authority (TVA) submitted information summarizing the results of the fall 2020 steam generator (SG) inspections performed at Watts Bar Nuclear Plant (Watts Bar), Unit 2 during refueling outage 3. In addition to this report review, the U.S. Nuclear Regulatory Commission (NRC) staff summarized conference calls regarding the fall 2020 SG tube inspections at Watts Bar, Unit 2, in a letter dated January 11, 2021.

The NRC staff has completed its review of the information provided and concludes that TVA provided the information required by the Watts Bar Nuclear Plant, Unit 2, technical specifications and that no follow-up is needed at this time. The staffs review is enclosed.

If you have any questions, please contact me at 301-415-1627 or via e-mail at Kimberly.Green@nrc.gov.

Sincerely,

/RA/

Kimberly J. Green, Senior Project Manager Plant Licensing Branch II-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-391

Enclosure:

As stated cc: Listserv

REVIEW OF THE FALL 2020 STEAM GENERATOR TUBE INSPECTION REPORT TENNESSEE VALLEY AUTHORITY WATTS BAR NUCLEAR PLANT, UNIT 2 DOCKET NO. 50-391 By letter dated May 10, 2021 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML21130A040), Tennessee Valley Authority (the licensee) submitted information summarizing the results of the fall 2020 steam generator (SG) inspections performed at Watts Bar Nuclear Plant (Watts Bar), Unit 2, during refueling outage 3 (RFO 3). In addition to this report review, the U.S. Nuclear Regulatory Commission (NRC) staff summarized conference calls regarding the fall 2020 SG tube inspections at Watts Bar 2, in a letter dated January 11, 2021 (ADAMS Accession No. ML20351A219).

Watts Bar, Unit 2 has four Westinghouse Model D3 SGs, each of which contains 4,674 mill-annealed Alloy 600 tubes. Each tube has a nominal outside diameter of 0.75 inches and a nominal wall thickness of 0.043 inches. The tubes are supported by anti-vibration bars and carbon steel drilled tube support plates (TSPs). Each SG has an integral preheater section with flow distribution baffle plates.

The licensee provided the scope, extent, methods, and results of its SG tube inspections in the document referenced above. In addition, the licensee described corrective actions taken in response to the inspection findings.

Based on the review of the information provided, the NRC staff has the following observations:

Four new degradation mechanisms were found during RFO 3, including axial outside diameter stress corrosion cracking (ODSCC) at hot-leg top-of-tubesheet expansion transitions, axial and circumferential ODSCC at tube freespan dings, and axial primary water stress corrosion cracking at hot-leg top-of-tubesheet expansion transitions.

A total of 189 tubes were plugged during RFO 3. All tubes with observed degradation satisfied the condition monitoring criteria for structural and leakage integrity with the exception of some tubes with axial ODSCC at TSP intersections, which were evaluated in accordance with NRC Generic Letter 95-05, Voltage-Based Alternate Repair Criteria and provided separately in a 90-day report dated July 20, 2021 (ADAMS Accession No. ML21202A062).

As a result of the observed axial ODSCC at TSP intersections, the licensees operational assessment concluded that it would not be able to run for a typical 18-month operational cycle and a mid-cycle shutdown and inspection would be required. The licensee plans to install new SGs in the spring of 2022.

Enclosure

Based on a review of the information provided, the NRC staff concludes that the licensee provided the information required by the Watts Bar Nuclear Plant, Unit 2 technical specifications. In addition, the 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.

ML21263A004 OFFICE NRR/DORL/LPL2-2/PM NRR/DORL/LPL2-2/LA NRR/DNRL/NCSG/BC*

NAME KGreen RButler SBloom DATE 09/17/2021 09/22/2021 09/14/2021 OFFICE NRR/DORL/LPL2-2/BC NRR/DORL/LPL2-2/PM NAME DWrona KGreen DATE 09/23/2021 09/24/2021