ML24102A121

Summary of Conference Call with Tennessee Valley Authority Regarding Sequoyah Nuclear Plant, Unit 1 Spring 2024 Steam Generator Tube Inspections

ML24102A121
Person / Time
Site:	Sequoyah
Issue date:	04/18/2024
From:	Perry Buckberg Plant Licensing Branch II
To:	Jim Barstow Tennessee Valley Authority
Buckberg, P
References
EPID L-2024-NFO-0004
Download: ML24102A121 (1)

Text

April 18, 2024

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

SUMMARY

OF CONFERENCE CALL WITH TENNESSEE VALLEY AUTHORITY REGARDING SEQUOYAH NUCLEAR PLANT, UNIT 1 SPRING 2024 STEAM GENERATOR TUBE INSPECTIONS ( EPID: L-2024-NFO-0004)

Dear James Barstow:

On April 4, 2024, the U.S. Nuclear Regulatory Commission staff participated in a conference call with representatives of the Tennessee Valley Authority regarding the ongoing Sequoyah Nuclear Plant, Unit No. 1 steam generator inspections.

A list of the conference call participants is contained in Enclosure 1. A list of questions and responses discussed during the call are in Enclosure 2.

If you have any questions regarding this summary, please contact me at 301-415-1383, or at Perry.Buckberg@nrc.gov.

Sincerely,

/RA/

Perry H. Buckberg, Senior Project Manager Plant Licensing Branch II-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation

Docket No. 50-327

Enclosures:

1. List of Participants

2. Conference Call Summary

cc: Listserv LIST OF PARTICIPANTS APRIL 4, 2024, CONFERENCE CALL TENNESSEE VALLEY AUTHORITY SEQUOYAH NUCLEAR POWER PLANT, UNIT NO. 1 SPRING 2024 STEAM GENERATOR INSPECTIONS

Nuclear Regulatory Commission

Perry Buckberg Andrew Johnson Greg Makar Steven Bloom Alex Price Paul Klein Michael Magyar Peter Meier

Tennessee Valley Authority

Connor Rigsby Scott Bowman Jesse Baron David Suddaby Daniel Folsom Jeremy Mayo Emmett Camp Ryan Spencer Andrew McNeil Anne Robinson-Givens

Enclosure 1

SUMMARY

OF CONFERENCE CALL SEQUOYAH NUCLEAR PLANT, UNIT 1 SPRING 2024 STEAM GENERATOR TUBE INSPECTIONS DOCKET NO. 50-327

On April 4, 2024, the Nuclear Regulatory Commission staff of the Corrosion and Steam Generator Branch (NCSG) of the Division of New and Renewed Licenses participated in a conference call with Tennessee Valley Authority (the licensee), regarding the ongoing steam generator (SG) tube inspection activities at Sequoyah Nuclear Plant, Unit 1 (Sequoyah, Unit 1) during refueling outage 26 (1R26).

Sequoyah, Unit 1, is a four-loop plant with Westinghouse Model 57AG SGs. Each SG contains 4,983 thermally treated Alloy 690 tubes with a nominal outside diameter of 0.750 inches and a nominal wall thickness 0.043 inches. The tubes were hydraulically expanded into the tubesheet through the full thickness of the tubesheet, and the straight sections of the tubes are supported by seven stainless steel advanced tube support grids (ATSGs). The U-bend portions of the tubes are supported by anti-vibration bars composed of ventilated flat bar support trees with varying numbers of diagonal and vertical straps, depending on tube location. The low row (small U-bend radius) tubes received a stress relief heat treatment over their entire length following bending.

Highlights from the April 4, 2024, conference call are summarized below:

At the time of the call, the licensee expected that eddy current data acquisition would be completed within a day. The bobbin probe inspections were nearly complete, and most of the remaining acquisition was for special interest array probe inspection. Eddy current data analysis was ongoing. No leakage was observed during the preceding operating cycle, and no indications had required in situ pressure testing.

The base scope of the inspection was full-length bobbin probe inspection of all tubes in all four SGs and array probe inspection of the periphery, five to six tubes deep, from the tubesheet up to the first horizontal support in all four SGs. The array probe was also being used for resolving bobbin I codes, examining dents and dings, and performing special interest examinations.

The only two degradation mechanisms that had been detected at the time of the call were wear at ATSGs and wear at U-bend supports.

A total of 418 indications of wear at ATSG and U-bend supports had been detected. The maximum depth was 22 percent through-wall (TW), as sized by bobbin and array probes, at a U-bend support vertical strap in SG 1. That indication was sized at 28 percent TW at the previous inspection in 2016, which was performed using different calibration standards.

The largest new indication, at a U-bend support vertical strap in SG 4, was 21 percent TW as sized by bobbin and array probes. Analysis of prior inspection data revealed no significant indication. This indication had a significantly larger TW depth than any other new indication. The NRC staff asked what the 95 th percentile probability of detection (POD) was

Enclosure 2

for detection of wear at vertical straps. The licensee stated that noise processing was still in progress and provided a preliminary 95 th percentile POD of approximately 10 percent TW.

No wear from loose parts or foreign objects had been detected. A total of 17 possible loose part indications were being resolved in the foreign object search and retrieval (FOSAR) process. FOSAR was being performed at the top of the tubesheet in all four SGs at the periphery, the tube lanes, and two full columns on each side of the bundle. Foreign objects included gasket pieces, wire bristles, sludge rocks, and weld slag. Some objects had been removed, and removal efforts were ongoing.

For U-bend wear, based on the maximum depth of 22 percent TW and corresponding length of 1.5 inches, the licensee stated that all indications met the condition monitoring limit of 48.9 percent TW. Similarly, for ATSG wear, based on a maximum depth of 17 percent TW and a corresponding length of 0.37 inches, the licensee stated all indications met the condition monitoring limit of 58.6 percent TW.

The resolution process was ongoing, and no tubes had been identified for plugging at the time of the call. The 22 and 21 percent TW U-bend indications were being considered for plugging.

Sludge lancing had been completed in SG 1 (34 pounds of deposits removed), SG 2 (39 pounds of deposits removed), and SG 4 (55 pounds of deposits removed), and was in progress in SG 3.

Scale profiling was being performed in SG 1 and would be trended with the last outage profiling data.

The NRC staff did not identify any issues that require follow-up action at this time.

ML24053A030 (Request for Call)

ML24102A121 (Meeting Summary)

ML24102A127 (Package)

OFFICE NRR/DORL/LPL2-2/PM NRR/DORL/LPL2-2/LA NRR/DNRL/NCSG/BC NAME PBuckberg ABaxter SBloom DATE 4/11/2024 4/11/2024 4/09/2024 OFFICE NRR/DORL/LPL2-2/BC NRR/DORL/LPL2-2/PM NAME DWrona PBuckberg DATE 04/12/2024 04/18/2024