ML23135A787
| ML23135A787 | |
| Person / Time | |
|---|---|
| Site: | Beaver Valley |
| Issue date: | 05/19/2023 |
| From: | Sujata Goetz Plant Licensing Branch 1 |
| To: | Blair B Energy Harbor Nuclear Corp |
| Goetz S | |
| References | |
| EPID L-2023-LRO-0013 | |
| Download: ML23135A787 (6) | |
Text
May 19, 2023 Mr. Barry N. Blair Site Vice President Energy Harbor Nuclear Corp.
Beaver Valley Power Station Mail Stop P-BV-SSB P.O. Box 4, Route 168 Shippingport, PA 15077-0004
SUBJECT:
BEAVER VALLEY POWER STATION, UNIT 2 -
SUMMARY
OF CONFERENCE CALLS REGARDING THE SPRING 2023 STEAM GENERATOR TUBE INSPECTIONS (EPID L-2023-LRO-0013)
Dear Mr. Blair:
On April 19, and May 1, 2023, the U.S. Nuclear Regulatory Commission staff and representatives from Energy Harbor Nuclear Corp. participated in conference calls to discuss the ongoing steam generator tube inspection activities at Beaver Valley Power Station, Unit 2 during refueling outage 23.
A summary of the conference calls is attached as an enclosure to this letter.
If you have any questions, please contact me at 301-415-8004 or via e-mail at Sujata.Goetz@nrc.gov.
Sincerely,
/RA/
Sujata Goetz, Project Manager Plant Licensing Branch I Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-412
Enclosure:
Summary of Conference Calls cc: Listserv
Enclosure
SUMMARY
OF CONFERENCE CALLS ENERGY HARBOR NUCLEAR CORP.
ENERGY HARBOR NUCLEAR GENERATION LLC DOCKET NO. 50-412 BEAVER VALLEY POWER STATION, UNIT NO. 2 On April 19, and May 1, 2023, the U.S. Nuclear Regulatory Commission (NRC) staff participated in conference calls with Energy Harbor Nuclear Corp., regarding the ongoing steam generator (SG) tube inspection activities at Beaver Valley Power Station, Unit 2 (Beaver Valley, Unit 2) during refueling outage 23 (2R23).
Beaver Valley, Unit 2 is a three-loop plant with Westinghouse Model 51M SGs. Each SG contains 3,376 mill-annealed alloy 600 tubes with a nominal outside diameter of 0.875 inches and a nominal wall thickness of 0.050 inches. The tubes are supported by carbon steel tube support plates (TSPs) and alloy 600 anti-vibration bars (AVBs). The tubes were roll expanded for the full depth of the tubesheet. The entire length of tube interior within the tubesheet was shot-peened on both the hot-leg and cold-leg side of the SG prior to operation. The U-bend region of the small radius tubes was in-situ stress-relieved prior to operation.
In addition to the depth-based tube repair criteria, the licensee is also authorized to apply the Generic Letter (GL) 95-05 voltage-based tube alternate repair criteria for predominantly axially-oriented outside diameter stress corrosion cracking (ODSCC) within the TSPs (Agencywide Documents Access and Management System (ADAMS) Accession No. ML031070113). The licensee is also authorized to leave flaws within the tubesheet region in service, provided they satisfy the F* repair criterion (ML12143A445).
April 19, 2023, conference call is summarized below:
At the time of the call, 91 percent of the base inspection eddy current data acquisition and analysis were complete, and 60 to 80 percent of special interest eddy current data acquisition and analysis were complete. No indications had required in situ pressure testing and 50 tubes were potential candidates for plugging or sleeving.
At the time of the call the following degradation mechanisms had been identified:
o 138 AVB wear indications in 80 tubes. Most of the indications were in SGs 2A and 2B, with only 4 in SG 2C. One indication in SG 2B met the 40 percent through-wall (TW) repair limit in the technical specifications. It was noted that this indication was approximately 37 to 38 percent TW at the prior inspection. The largest indications in SG 2A and SG 2C were 35 percent TW and 17 percent TW, respectively. The licensee stated that all AVB wear indications met the condition monitoring limit of 62 percent TW.
o Two Flow Distribution Baffle/TSP wear indications in SG 2C. At the time of the call these indications had not been depth sized but historically they were 20 and 22 percent TW with little growth from the prior inspection.
o Three historical volumetric indications in the freespan that had not been depth sized at the time of the call. The licensee noted that during the last outage there were 11 historical volumetric indications with depths ranging from 10 to 31 percent TW with no evidence of foreign objects (FOs) being present.
o A total of 1,343 axial ODSCC indications (also called distorted support indications or DSIs) at TSPs had been detected and were evaluated using the GL 95-05 voltage-based alternate repair criteria. The largest DSI observed was 1.44 volts. All of these indications were below the repair limits.
o At the time of the call, 46 (23 in SG 2A, 19 in SG 2B, and 4 in SG 2C) circumferential ODSCC indications in the hot-leg top-of-tubesheet expansion transition region had been detected. The +PointTM probe voltages for these indications ranged from 0.06 to 0.25 volts. The maximum depth measurements by phase analysis ranged from 0 to 94 percent TW and the measured circumferential crack arc lengths ranged from 27 to 246 degrees. None met the initial voltage screening criteria for in situ pressure testing.
Line by line depth profiling of select indications was in progress.
o Six axial ODSCC indications in six tubes at the hot-leg expansion transition region had been detected. The largest indication had a +PointTM probe voltage of 0.39 volts, depth of 62 percent TW, and measured axial crack length ranging from 0.10 to 0.15 inch. None met the initial voltage screening criteria for in situ pressure testing. Line by line depth profiling of select indications was in progress.
The licensee stated that no indications had been detected in Alloy 800 nickel banded mechanical tubesheet sleeves.
The two cold leg thinning indications, one reported in 2R21 and the other reported in 2R22, were confirmed and measured 11 and 18 percent TW. No additional indications of cold leg thinning had been detected.
Three FOs had been found and will remain in the SGs; a small wire bristle in SG 2A and a sludge rock and a piece of weld slag in SG 2B. The wire bristle in SG 2A was fixed within hard scale. In SG 2B, the sludge rock was historical and confined within four tubes and the piece of weld slag was historical and wedged between two tubes. No tube damage was associated with the FOs.
Visual examination of the channel heads included the divider plate to channel head weld, divider plate to stub runner weld, tubesheet to channel head Z-seam area, and cladding.
Secondary side inspection and maintenance activities included or will include the following:
o Inspections of steam drum components and feedwater/J-nozzles planned for SG 2B.
These inspections had not started at the time of the call.
o Visual inspection of the tubesheet elevation included the annulus, blowdown lane, and selected in-bundle tube locations. At the time of the call the inspections had been completed in SGs 2A and 2B, and inspections in SG 2C had not started. Minor erosion on the first of five tube-lance blocking devices in SGs 2A and 2B is an existing condition that is being monitored each outage.
o Sludge lancing had been completed in SGs 2A (40 pounds of deposits removed) and 2B (36 pounds of deposits removed) and was in progress in SG 2C.
The licensee indicated that probe equivalency between the 0.630 probe and the 0.720 probe was done by testing the same tubes with each probe. The voltage differences were determined to be 10 percent or less.
At the time of the call, the licensee planned to de-plug and return to service approximately 70 to 100 tubes in SGs A and B.
After the April 19, 2023, conference call, the licensee informed the NRC staff that circumferential ODSCC at the cold-leg top-of-tubesheet expansion transition was detected in two de-plugged tubes in SG 2B, one tube in Row 19, Column 41 (R19C41) and one tube in R19C44, which were previously plugged in spring 2014 and spring 2008, respectively.
Circumferential ODSCC occurring on the cold leg is a new degradation mechanism for Beaver Valley, Unit 2. On May 1, 2023, NCSG staff participated in a conference call with the licensee to discuss this new degradation mechanism.
May 1, 2023, conference call is summarized below:
The indications were detected with a +PointTM rotating probe and confirmed with a Ghent rotating probe.
The two de-plugged tubes in SG 2B were initially plugged and stabilized due to hot-leg top-of-tubesheet cracking.
The licensee informed the NRC that circumferential ODSCC at the cold-leg top-of-tubesheet expansion transition had also been detected in one de-plugged tube in SG 2A (R27C39).
This tube was de-plugged during 2R22. The licensee noted that they identified a precursor signal from the historical lookback at the 2R22 +PointTM probe inspection data and that there was little change in the indication.
All of the circumferential ODSCC indications found were located slightly below the top-of-tubesheet at the bottom of the expansion transition (i.e., in the crevice region). The percent degraded area ranged from 4 to 15 percent, the circumferential crack arc lengths ranged from 29 to 135 degrees, and the depth ranged from 40 to 57 percent TW.
The scope of tubes inspected was expanded in SGs 2A and 2B to include examinations in the region where this degradation mechanism occurs based on the hot-leg side of the SGs (i.e., the kidney zone and sludge pile area). At the time of the call, the licensee was performing cold-leg top-of-tubesheet examinations on 100 percent of the in-service tubes in the targeted region with a rotating probe (approximately 1800 tubes in each SG).
The licensee stated that the new degradation mechanism had only been found in de-plugged tubes and modeling showed plugged tubes undergo higher stresses at the bottom of the expansion transition during operating cycles after plugging. Since there are no de-plugged tubes in SG 2C, and since 20 percent of the cold-leg top-of-tubesheet had been inspected in 2R22 and 2R23 with a rotating probe (covering approximately 34 percent of the in-service tubes in the targeted region), additional inspections were not performed in SG 2C.
At the time of the discovery of the new degradation mechanism, the SG 2C manway covers had been installed and tensioned.
The three tubes with circumferential ODSCC at the cold-leg top-of-tubesheet expansion transition have been plugged and stabilized.
The NRC staff did not identify any issues that require follow-up action at this time.
- by memorandum OFFICE NRR/DORL/LPL1/PM NRR/DORL/LPL1/LA NRR/DNRL/NCSG/BC NAME SGoetz KZeleznock SBloom DATE 05/15/2023 05/18/2023 05/8/2023 OFFICE NRR/DORL/LPL1/BC NRR/DORL/LPL1/PM NAME HGonzález (MMarshall for)
SGoetz DATE 05/18/2023 05/19/2023