ML25269A064
| ML25269A064 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 09/30/2025 |
| From: | John Lamb NRC/NRR/DORL/LPL2-1 |
| To: | Coleman J Southern Nuclear Operating Co |
| References | |
| EPID L-2025-NFO-0019 | |
| Download: ML25269A064 (1) | |
Text
September 30, 2025 Ms. Jamie M. Coleman Regulatory Affairs Director Southern Nuclear Operating Co., Inc.
3535 Colonnade Parkway Birmingham, AL 35243
SUBJECT:
VOGTLE ELECTRIC GENERATING PLANT, UNIT 4 -
SUMMARY
OF CONFERENCE CALL REGARDING THE FALL 2025 STEAM GENERATOR TUBE INSPECTIONS (EPID L-2025-NFO-0019)
Dear Ms. Coleman:
On September 17, 2025, the U.S. Nuclear Regulatory Commission (NRC) staff participated in a conference call with representatives of Southern Nuclear Operating Company (SNC) regarding the ongoing steam generator (SG) tube inspection activities at Vogtle Electric Generating Plant, Unit 4, during its first refueling outage.
A summary of the conference call is provided in the enclosure.
If you have any questions, please contact me at (301) 415-3100 or via email at John.Lamb@nrc.gov Sincerely,
/RA/
John G. Lamb, Senior Project Manager Plant Licensing Branch II-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No.52-026 Attachments:
- 1. Summary of Conference Call
- 2. List of Attendees cc: Listserv
SUMMARY
OF CONFERENCE CALL HELD ON SEPTEMBER 17, 2025, REGARDING FALL 2025 STEAM GENERATOR TUBE INSPECTIONS AT VOGTLE ELECTRIC GENERATING PLANT, UNIT 4 DOCKET NO.52-026 Introduction On September 17, 2025, the U.S. Nuclear Regulatory Commission (NRC) staff participated in a conference call with representatives of Southern Nuclear Operating Company, Inc. (SNC, the licensee), regarding the ongoing steam generator (SG) tube inspection activities at Vogtle Electric Generating Plant (Vogtle), Unit 4, during the first refueling outage (RFO 4R01). The discussion points for the conference call held on September 17, 2025, were contained in the email dated August 7, 2025 (Agencywide Documents Access and Management System Accession No. ML25219A764). The attendees for the conference call are contained in.
Vogtle, Unit 4, is a two-loop plant with Westinghouse Model D-125 SGs. Each SG contains 10,025 thermally treated Alloy 690 tubes with a nominal outside diameter of 0.688 inches and a nominal wall thickness 0.040 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 stainless steel tube support plates (TSPs) with trifoil broaches holes. The U-bend portions of the tubes are supported by stainless-steel anti-vibration bars. The first 17 rows of tubes received stress relief heat treatment.
Conference Call on September 17, 2025 A summary of the information shared by SNC and responses to questions asked by the NRC staff on the call on September 17, 2025, are provided below:
There was no observed primary-to-secondary leakage in the previous operating cycle.
At the time of the call, no secondary side pressure tests had been performed or were planned.
No exceptions to industry guidelines were taken.
The licensee stated that the scope of the SG inspections included the following:
100 percent bobbin probe exam from tube end to tube end, for rows 3 and higher.
100 percent bobbin probe exam for straight leg portions of rows 1 and 2.
100 percent +PointTM exam of row 1 and 2 U-bends (from the top tube support plate (TSP) on the hot-leg (HL) to the top TSP on the cold-leg (CL)).
100 percent +PointTM exam of tube bundle periphery (4 tubes deep) and no-tube lane at the top of the tubesheet (TTS) (+/-3 inches), HL and CL. This includes tubes with velocities 14 feet/second.
100 percent +PointTM exam of dents and dings 2 volts bobbin.
100 percent +PointTM exam of all bobbin I-codes.
100 percent +PointTM exam of all new volumetric indications from anti-vibration bar (AVB), TSP, Foreign Objects (FO), and possible loose parts.
100 percent +PointTM exam of all new proximity, bulge, overexpansion, and permeability variation indications 1 volt bobbin.
The licensee provided the following preliminary summary of the number of indications identified to date, for each degradation mode:
AVB tube wear indications: SG 1 - 10 indications; SG 2 - 0 indications TSP tube wear indications: SG 1 - 160 indications; SG 2 - 60 indications In response to a question from the NRC staff, SNC stated that shallower TSP flaws tended to be tapered in profile, while deeper flaws tended to be flat in profile.
The preliminary summary of the most significant indications and an assessment of tube integrity included:
Structural and leakage integrity were maintained in the previous operating cycle.
Maximum AVB tube wear was 11 percent through-wall (TW); the condition monitoring (CM) limit was 47.4 percent TW.
Maximum TSP tube wear was 32 percent TW; the CM limit was 46.1 percent TW.
New degradation modes not previously seen at Vogtle, Unit 4.
AVB and TSP tube wear are new degradation mechanisms - Refueling outage 4R01 is the first inspection for Vogtle, Unit 4. However, these degradation mechanisms were not unexpected by the licensee.
The licensee described the examinations and results of inspections performed in the low row tubes and how the results will be considered in the operational assessment. Operating experience with some very large SGs has revealed an increased susceptibility to aggressive wear from tube supports on tubes in the low rows.
SNC understood that the AP1000 SGs had susceptible regions for TSP and AVB tube wear before the start of the inspection outage, so 100 percent of the low-row areas were inspected by bobbin and the low row U-bends were inspected with a +PointTM probe.
The inspection plan was front-loaded with the susceptible regions to detect tube wear early.
Indications of TSP tube wear were detected in both SGs, while indications of AVB tube wear were detected only in SG 1. For TSP tube wear, approximately 49 percent of the indications were in row 1, approximately 31 percent were in row 2, and approximately 20 percent were in rows 3 and above. These patterns are consistent with domestic and international operating experience.
A subset of 12 tubes (2 groups of 6 tubes) in both SGs, adjacent to two flow slots at the top TSP (TSP 10), experienced accelerated wear compared to the rest of the tube bundle. The two groups of six tubes may be treated as outlier sub-population in the OA.
Describe repair/plugging plans.
An estimate of tube plugging had not been generated at the time of the call. Any tube wear 40 percent TW will be plugged, and additional tubes will be plugged as needed to support the operational assessment.
Tubes with accelerated growth rates or confirmed FO tube wear with a part still present will be stabilized and plugged.
Describe in-situ pressure test and tube pull plans and results (as applicable and if available).
At the time of the call, there were no indications that required in-situ pressure testing, and no tube pulls were planned.
The following activities were performed regarding loose parts:
Sludge lancing in both SGs.
TTS visual inspections in both SGs.
Foreign object search and retrieval (FOSAR) at TTS in both SGs.
The results of the loose parts activities included:
Three FOs were found in SG 1: two pieces of gasket material and one sludge rock. The FOs did not threaten tube integrity. The gasket pieces were retrieved, and the sludge rock was left in place.
Four FOs were found in SG 2: one piece of wire, one wire bristle, one piece of gasket material, and one sludge rock. The FOs did not threaten tube integrity. The wire and wire bristle were retrieved; the gasket material and sludge rock were left in place.
There was no damage reported from any loose parts.
The results of secondary side inspection and maintenance activities included:
Steam drum visual inspections, including the upper internal components, feedrings, and spray cans, will be performed in both SGs.
Visual inspection of deposit loading was performed at TSP 10 in both SGs, with satisfactory results.
Sludge analysis for both SGs will be performed after the outage.
Scale profiling for SG 2 will be performed after the outage.
SNC stated there were no unexpected or unusual results.
Regarding the schedule for the remainder of the current outage:
At the time of the call, eddy current inspections in all SGs were estimated to be completed later that day, September 17, 2025.
Sludge lancing and FOSAR were complete.
Steam drum inspections were estimated to be completed by September 20, 2025.
In response to a question from the NRC staff, the licensee stated that they are currently planning to perform the next tube inspection during the next RFO.
Summary The NRC staff did not identify any issues that require follow-up action at this time.
ATTENDEES OF CONFERENCE CALL HELD ON SEPEMBER 17, 2025, REGARDING FALL 2025 STEAM GENERATOR TUBE INSPECTIONS AT VOGTLE ELECTRIC GENERATING PLANT, UNIT 4 DOCKET NO.52-026 NAME ORGANIZATION John G. Lamb U.S. Nuclear Regulatory Commission (NRC)
Paul Klein NRC Greg Makar NRC Andrew Johnson NRC Steve Bloom NRC Leslie Terry NRC Mike Markley NRC Theo Fanelli NRC Michael Magyar NRC Steve Downey NRC Zach Turner NRC Paula Cooper NRC Eric Magnuson NRC JPParent NRC Ken Lowery Southern Nuclear Operating Company (SNC)
Ryan Joyce SNC Jonathan Thompson SNC Brett Evans SNC Michelle Alger SNC Chris Gamblin SNC Cotasha Blackburn SNC Corey Thomas SNC Aaron Knighton SNC Kara Stacy SNC Jordan Rice SNC David Suddaby Westinghouse Robert Chappo Westinghouse Mitchell Krinock Westinghouse
ML25269A069 (Package)
ML25269A064 (Summary)
ML25219A764 (Discussion Points Email)
- via eConcurrence NRR-106 OFFICE NRR/DORL/LPL2-1/PM NRR/DORL/LPL2-1/LA*
NRR/DNRL/NCSG/BC NAME JLamb KZeleznock SBloom DATE 9/26/2025 9/30/2025 9/25/2025 OFFICE NRR/DORL/LPL2-1/BC*
NRR/DORL/LPL2-1/PM*
NAME MMarkley JLamb DATE 9/30/2025 9/30/2025