ML24305A166
| ML24305A166 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 11/06/2024 |
| From: | John Lamb NRC/NRR/DORL/LPL2-1 |
| To: | Coleman J Southern Nuclear Operating Co |
| References | |
| EPID L-2024-NFO-0009 | |
| Download: ML24305A166 (1) | |
Text
November 6, 2024 Ms. Jamie M. Coleman Regulatory Affairs Director Southern Nuclear Operating Co., Inc.
3535 Colonnade Parkway Birmingham, AL 35243
SUBJECT:
VOGTLE ELECTRIC GENERATING PLANT, UNIT 3 -
SUMMARY
OF CONFERENCE CALL REGARDING THE FALL 2024 STEAM GENERATOR TUBE INSPECTIONS (EPID L-2024-NFO-0009)
Dear Ms. Coleman:
On October 28, 2024, 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 3, 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.52-025 Attachments:
- 1. Summary of Conference Call
- 2. List of Attendees cc: Listserv
SUMMARY
OF CONFERENCE CALL HELD ON OCTOBER 28, 2024, REGARDING FALL 2024 STEAM GENERATOR TUBE INSPECTIONS AT VOGTLE ELECTRIC GENERATING PLANT, UNIT 3 DOCKET NO.52-025 Introduction On October 28, 2024, 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 3, during the first refueling outage (RFO 3R01). The discussion points for the conference call held on October 28, 2024, were contained in the email dated September 17, 2024 (Agencywide Documents Access and Management System Accession No. ML24261B928). The attendees for the conference call are contained in.
Vogtle, Unit 3, 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 a stress relief heat treatment.
October 28, 2024, Conference Call A summary of the information shared by SNC and responses to questions asked by the NRC staff in the October 28, 2024, call are provided below:
At the time of the call, the overall inspection effort was approximately 80 percent complete.
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:
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). Includes tubes with velocities 14 feet/second.
100 percent +PointTM exam of dents and dings 3 volts.
100 percent +PointTM exam of pre-service wear indications (1 in SG 1, 2 in SG 2).
100 percent +PointTM exam of all new volumetric indications from anti-vibration bars (AVB), TSP, and Foreign Objects (FO).
100 percent +PointTM exam of all possible loose part (PLP) indications at TTS (1-tube box).
100 percent +PointTM exam of existing FO (1-tube box) and new FO (2-tube box).
100 percent +PointTM exam of all bobbin I-codes.
100 percent +PointTM exam of all new proximity indications and bobbin indications 1 volt in the U-bends.
100 percent +PointTM exam of all geometry (GEO), bulge (BLG), overexpansion (OXP),
obstruction (OBS), and restriction (RES) indications.
100 percent +PointTM exam of all permeability variations 1 volt.
SNC provided the following preliminary summary of the number of indications identified to date, for each degradation mode:
AVB tube wear indications: SG 1 - 22 indications; SG 2 - 50 indications TSP tube wear indications: SG 1 - 97 indications; SG 2 - 65 indications Anomalous tube indications from manufacturing: SG 1 - 1 indication from pre-service inspection (PSI); SG 2 - 2 indications from PSI.
The preliminary summary of the most significant indications and an assessment of tube integrity included:
Structural and leakage integrity maintained in the previous operating cycle Maximum AVB tube wear was 15 percent through-wall (TW); Condition monitoring (CM) limit was 47.9 percent TW Maximum TSP tube wear was 28 percent TW; CM limit was 46.5 percent TW Maximum anomalous manufacturing indication was 11 percent TW; CM limit was 50.2 percent TW New degradation modes not previously seen at this unit:
AVB and TSP tube wear are new degradation mechanisms - Refueling outage 3R01 is the 1st inspection for Vogtle, Unit 3.
A discussion of the inspection results that focus on the operating experience of very large SGs that have shown an increased susceptibility to aggressive wear from tube supports on tubes in the low rows. 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.
SNC acknowledged 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.
Both SGs contained TSP and AVB tube wear indications. For TSP tube wear, approximately 50 percent of the indications were in row 1, approximately 28 percent were in row 2, and approximately 22 percent were in rows 3 and above. For AVB tube wear, approximately 6 percent of the indications were in row 1, approximately 12 percent were in row 2, approximately 9 percent were in row 3, and approximately 74 percent were in rows 4 and above. In rows 4 and above, the AVB tube wear indications were found preferentially in the higher rows and towards the central columns but spread out in no discernible pattern. The locations of both the TSP and AVB tube wear indications followed the noted domestic and international operating experience.
Since rows 1 and 2 contain most of the TSP tube wear indications, separate growth distributions were created and analyzed from a sub-population perspective. The impact of this sub-population on the 95th percentile of the whole tube population was analyzed and found to be minimal. Additional consideration for use of a TSP tube wear sub-population will be explored after all data acquisition is complete. The use of sub-populations to analyze the AVB tube wear was not necessary, based on the acquired inspection data.
In response to a question from the NRC staff, the licensee indicated that most of the TSP tube wear indications were tapered wear, and a few were flat wear indications.
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 on detection and additional tubes will be plugged to support the operational assessment. Tubes with accelerated growth rates or confirmed FO tube wear with a part still present, will also be stabilized.
Describe in-situ pressure test and tube pull plans and results (as applicable and if available).
As of 8:00 am on October 28, there were no indications that required in-situ pressure testing.
No tube pulls are planned to be performed.
The following inspections were taken regarding loose parts:
Sludge lancing in all SGs TTS visual inspections in all SGs Foreign object search and retrieval (FOSAR) at TTS in all SGs.
The loose parts inspection results included:
Eleven new FOs were found in SG 1. The FOs did not threaten tube integrity (e.g., they were gasket material, sludge rocks, wire bristles) and left in place.
Six new FOs were found in SG 2. The FOs did not threaten tube integrity (e.g., they were gasket material, sludge rocks, wire bristles) and left in place.
There was no damage reported from any loose parts.
The results of secondary side inspection and maintenance activities included:
Steam drum inspections will be performed, including the feedring.
Sludge analysis will be performed after the outage.
Scale profiling on SG 2 will be performed after the outage.
Regarding any unexpected or unusual results:
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 on Tuesday, October 29, 2024.
Sludge lancing and FOSAR are complete.
Steam drum inspections estimated to be complete by Friday, November 1, 2024.
In response to a question from the NRC staff, the licensee stated that during fabrication of the SGs, rows 1 - 17 were stress relieved.
In response to a question from the NRC staff, the licensee stated that they do have plant-specific broached TSP wear calibration standards.
In response to a question from the NRC staff, the licensee stated that the operational assessment recommendation for the timing of the next tube inspection will consider international AP1000 experience as well as recent U.S. operating experience with tube wear at tube support locations.
Summary The NRC staff did not identify any issues that require follow-up action at this time.
ATTENDEES OF CONFERENCE CALL HELD ON OCTOBER 28, 2024, REGARDING FALL 2024 STEAM GENERATOR TUBE INSPECTIONS AT VOGTLE ELECTRIC GENERATING PLANT, UNIT 3 DOCKET NO.52-025 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 Bill Truss NRC Michael Magyar NRC Steve Downey NRC Zach Turner NRC Paula Cooper NRC Eric Magnuson NRC Theo Fanelli 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 Kara Stacy SNC Jordan Rice SNC David Suddaby Westinghouse Robert Chappo Westinghouse Mitchell Krinock Westinghouse
ML24305A166 (Summary)
ML24261B928 (Discussion Points Email)
ML24295A376 (Package)
OFFICE NRR/DORL/LPL2-1/PM NRR/DORL/LPL2-1/LA NRR/DNRL/NCSG/BC NAME JLamb KGoldstein SBloom DATE 10/30/2024 11/01/2024 10/30/2024 OFFICE NRR/DORL/LPL2-1/BC NRR/DORL/LPL2-1/PM NAME MMarkley JLamb DATE 11/06/2024 11/06/2024