ML23090A142
| ML23090A142 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 04/03/2023 |
| From: | John Lamb NRC/NRR/DORL/LPL2-1 |
| To: | Brown R Southern Nuclear Operating Co |
| References | |
| EPID L-2023-NFO-0002 | |
| Download: ML23090A142 (1) | |
Text
April 3, 2023 Mr. R. Keith Brown Regulatory Affairs Director Southern Nuclear Operating Co., Inc.
3535 Colonnade Parkway Birmingham, AL 35243
SUBJECT:
VOGTLE ELECTRIC GENERATING PLANT, UNIT 1 -
SUMMARY
OF CONFERENCE CALL REGARDING THE SPRING 2022 STEAM GENERATOR TUBE INSPECTIONS (EPID L-2023-NFO-0002)
Dear Mr. Brown:
On March 16, 2023, the U.S. Nuclear Regulatory Commission staff participated in a conference call with representatives of Southern Nuclear Operating Company regarding the ongoing steam generator tube inspection activities at Vogtle Electric Generating Plant, Unit 1.
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. 50-424
Enclosures:
- 1. Summary of Conference Call
- 2. List of Attendees
- 3. Discussion Points cc: Listserv
SUMMARY
OF CONFERENCE CALL HELD ON MARCH 16, 2023, REGARDING SPRING 2023 STEAM GENERATOR TUBE INSPECTIONS AT VOGTLE ELECTRIC GENERATING PLANT, UNIT 1 DOCKET NO. 50-424 Introduction On March 16, 2023, 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 1, during the spring 2023 refueling outage (RFO 1R24).
The discussion points for the conference call held on March 16, 2023, were contained in the email dated February 24, 2023 (Agencywide Documents Access and Management System Accession No. ML23055A226). The attendees for the conference call are contained in.
By letter dated January 5, 2022 (ML21316A055), the NRC staff issued Amendment No. 211 to Vogtle, Unit 1. The amendment revised the Vogtle Steam Generator (SG) Program and the Steam Generator Tube Inspection Report technical specifications based on Technical Specifications Task Force (TSTF) Traveler TSTF-577, Revision 1, Revised Frequencies for Steam Generator Tube Inspections (TSTF-577) (ML21060B434), and the associated NRC staff safety evaluation of TSTF-577 (ML21098A188). The SG tube inspection scope for 1R24 included an enhanced probe inspection approach to support implementation of the TSTF-577.
Vogtle, Unit 1, has four Westinghouse Model F SGs, each of which contains 5,626 U-bend thermally treated Alloy 600 tubes. Each tube has a nominal outside diameter (OD) of 0.688 inches and a nominal wall thickness of 0.040 inches. During SG fabrication, the tubes were hydraulically expanded, at both ends, over the full depth of the tubesheet. Stainless steel tube support plates (TSP), which have broached quatrefoil holes, support the vertical section of the tubes, and anti-vibration bars (AVBs) support the U-bend section of the tubes.
March 16, 2023, Conference Call Information provided by the licensee in support of the conference call on March 16, 2023, is provided as Attachment 2. The NRC staff notes that this inspection information is preliminary and subject to change upon final data analysis.
At the time of the call, approximately 88 percent of the eddy current data acquisition and 84 percent of the eddy current analysis had been completed.
Highlights of the eddy current inspection scope for each SG include:
o A 100 percent full length bobbin/array combination probe examination of all Row 6 and higher in-service tubes. A 100 percent bobbin/array probe examination of hot leg (HL) and cold leg (CL) straight portions in Rows 1-5 and U-bends of Rows 3-5.
o +PointTM rotating probe inspections on:
All Row 1 and 2 U-bends (top TSP HL to top TSP CL).
All HL top of tubesheet (TTS) tubes +3 inches to -3 inches depth.
Special interest diagnostics of bobbin/array I Codes (i.e., 3 letter eddy current inspection result codes ending in I).
All dents/dings greater than or equal to 2 volts.
All overexpansion indications, and all bulge indications greater than 42 volts, within the HL tubesheet and above the H-star (H*) region At the time of the call, the licensee had identified:
o A total of 800 AVB wear indications in the 4 SGs with the greatest wear depth measured as 36 percent through-wall.
o One new indication of foreign object wear (depth was not yet available).
o Three potential cracks in SG3 in the HL at the TTS. Confirmation of these indications will be made using the Ghent Probe.
o Two confirmed circumferential outside diameter stress corrosion cracks (ODSCC) at the HL TTS in SG4.
o One confirmed axial ODSCC crack in an overexpansion area within the HL tubesheet. This indication was approximately 1.24 inches below the TTS.
Although sizing had not yet been completed at the time of the call, the licensee subsequently provided the maximum depth of 74 precent through-wall. This is a new degradation mechanism for Vogtle, Unit 1.
At the time of the call all indications met the condition monitoring limits demonstrating that tube integrity was maintained. No in-situ pressure tests had been performed and none were planned.
Foreign object search and retrieval (FOSAR) inspection was complete in SG1 and SG4.
FOSAR inspection was in progress in SG2 and SG3. Additional information for foreign objects may be found in Table 1 of Attachment 2.
SNC estimated all SG work would be completed by March 18, 2023.
Subsequent to the outage phone call, the licensee provided a response to several outage call questions from the NRC staff that were not answered during the call.
Included in the response was the following information:
o Eight tubes with single circumferential indications (SCI) by +Point' at the TTS during RFO 1R23 were also examined with the array probe for information. One tube was called SCI by all analysts reviewing the array data. One analyst made an SCI call in four other tubes. No analysts identified an SCI by array probe in the other three tubes.
o Vogtle, Unit 1 has experienced tube denting at the upper support plate of the tube bundle and has incorporated inspection data from a similar plant into their site-specific performance demonstration.
o Indications are reviewed back to 1999-2000 when reviewing bobbin data and typically back to the earliest rotating probe test data for a given tube when reviewing rotating probe data.
o Unit 1 experienced ODSCC at a ding located above the top support on the HL (7H+2.51 inches). The approximate maximum depth of ODSCC measured 38 percent through-wall. This is a new degradation mechanism for Unit 1 but has occurred previously in Unit 2.
Summary The NRC staff did not identify any issues that required follow-up action at this time. The NRC staff asked to be notified in the event that in situ pressure testing of tube indications was planned. The licensee response after the outage stated that no in situ pressure testing was required.
ATTENDEES OF CONFERENCE CALL HELD ON MARCH 16, 2023, REGARDING SPRING 2023 STEAM GENERATOR TUBE INSPECTIONS AT VOGTLE ELECTRIC GENERATING PLANT, UNIT 1 DOCKET NO. 50-424 NAME ORGANIZATION John G. Lamb U.S. Nuclear Regulatory Commission (NRC)
Paul Klein NRC Greg Makar NRC Andrew Johnson NRC Steve Bloom NRC Tom Morrissey NRC Michael Magyar NRC Steve Downey NRC DeLisa Pournaras Southern Nuclear Operating Company (SNC)
Amy Chamberlain SNC Keith Brown SNC Jonathan Thompson SNC Brett Evans SNC Michelle Alger SNC Chris Gamblin SNC Cotasha Blackburn SNC David Suddaby Westinghouse
PRELIMINARY STEAM GENERATOR TUBE INSPECTION DISCUSSION POINTS VOGTLE, UNIT 1, SPRING 2023 REFUELING OUTAGE STEAM GENERATOR TUBE INSPECTION DISCUSSION POINTS The following discussion points have been prepared to facilitate the conference call arranged with the licensee to discuss the results of the steam generator tube inspections to be conducted during the upcoming spring 2023, Vogtle, Unit 1, RFO. This conference call is scheduled to occur towards the end of the planned SG tube inspections, but before the unit completes the inspections and repairs.
The NRC staff plans to document a publicly available summary of the conference call, as well as any material that is provided in support of the call.
- 1. Discuss any trends in the amount of primary-to-secondary leakage observed during the recently completed cycle.
- a. No primary-to-secondary leakage during previous inspection cycle.
- 2. Discuss whether any secondary side pressure tests were performed during the outage and the associated results.
- a. None
- 3. Discuss any exceptions taken to the industry guidelines.
- a. None
- 4. For each steam generator, provide a description of the inspections performed including the areas examined and the probes used (e.g., dents/dings, sleeves, expansion-transition, U-bends with a rotating probe), the scope of the inspection (e.g., 100 percent of dents/dings greater than 5 volts and a 20 percent sample between 2 and 5 volts), and the expansion criteria.
Exam Probe Extent 100%
Full-length X-Probe (bobbin &
array)
Tube end to tube end, for Row 6 and higher Straight leg portion of hot leg (HL) and cold leg (CL) (Rows 1-5)
Inspection scope has been developed with enhanced probes to support implementation of TSTF-577 Note: this scope covers the tube support plate (TSP) intersections of high stress (2-sigma) tubes, loose parts, and any possible loose parts (PLPs) 100%
Low Row U-bend Bobbin Candy cane from CL Rows 3-5 Array Only
+Point Row 1 and Row 2 U-bends from the top TSP on the HL to the top TSP on the CL 100%
Tubesheet Expansion Transition
+Point HL tubes from top of tubesheet (TTS) (+3/-3 inches)
Note: the full-length X-Probe inspection covers the remainder of the tubesheet to the H* distance.
Dents (DNT)
+Point 100% of DNT 2.0 volts Dings (DNG)
+Point 100% of DNG 2.0 volts Bulges (BLG)
+Point 100% of HL BLG > 42 volts (excluding those below H* distance)
Over-expansions (OXP)
+Point 100% of HL OXP (excluding those below H* distance)
Special Interest (Diagnostic)
+Point All I-Codes (DNI, NQI, etc.)
As needed to support tube integrity evaluations Tube slippage Bobbin H* Tube slippage monitoring Plug Visual Inspection Camera All plugs inspected Cleanliness and Foreign Object Search and Retrieval (FOSAR)
Camera Secondary side in-bundle, annulus, tube lane, as well as PLP indications Primary Channel Head Visual Camera Visual inspection in all SGs of channel head primary side HL and CL in accordance NSAL 12-1 inclusive of the entire divider plate to channel head weld and all visible clad surfaces. The known anomaly in the CL channel head of SG-1 will be evaluated for a change from the analyzed condition during this inspection.
- 5. For each area examined (e.g., tube supports, dent/dings, sleeves, etc.), provide the following:
- a. A summary of the number of indications identified to date for each degradation mode (e.g., number of circumferential primary water stress corrosion cracking indications at the expansion transition).
- i. Anti-Vibration Bar (AVB) Wear:
SG1: ~113 indications SG2: ~227 indications SG3: ~265 indications SG4: ~195 indications ii. TSP Wear:
SG4: One (1) Historic TSP wear indication iii. Historical Foreign Object Wear (FOW) / Secondary Side Cleaning Loss (SSCL):
SG1: Ten (10) Historic FOW, 2 SSCL indications SG2: One (1) Historic FOW indication SG3: One (1) Historic FOW indication, 1 new FOW indication SG4: Zero (0) indications iv. Other indications of interest:
SG3: Three (3) I codes at TTS awaiting confirmation with Ghent probe.
Sizing has not been completed.
SG4: Two (2) confirmed Circumferential Outside Diameter Stress Corrosion Cracking (ODSCC) at TTS One (1) confirmed Axial ODSCC within the tubesheet at OXP Sizing has not been completed.
- b. For the most significant indications in each area, provide an estimate of the severity of the indication (e.g., voltage, depth, and length of the indication), including whether tube integrity (structural and accident induced leakage integrity) was maintained during the previous operating cycle. In addition, discuss any analyses performed specifically for the most significant indications to demonstrate tube integrity.
- i. Structural and leakage integrity was maintained during the previous inspection interval ii. Max AVB wear, 36% TW, less than CM limit iii. Max TSP wear, awaiting sizing. 1R23 indication was 19%TW, no growth expected iv. Max historical FOW / SSCL 38%, less than CM limit.
- c. Discuss whether any location exhibited a degradation mode that had not previously been observed at this location at this unit (e.g., observed circumferential primary water stress corrosion cracking at the expansion transition for the first time at this unit).
- i.
One (1) confirmed Axial ODSCC within the tubesheet at OXP and sizing has not been completed.
- 6. Describe repair/plugging plans.
- a. Any tube wear over 40% TW will be plugged on detection, any confirmed crack will be plugged on detection, and any additional tubes will be plugged on an as-needed basis to support tube integrity engineering.
- 7. Describe in-situ pressure test and tube pull plans and results (as applicable and if available).
- a. There are currently no indications that require in-situ pressure testing. For any confirmed cracks, line by line sizing will be completed to start the screening process.
The line by line sizing information will then be used in parallel with the Vogtle 1R24 Degradation Assessment instructions for in-situ pressure test screening.
- b. No tube pulls are planned to be performed.
- 8. Discuss the following regarding loose parts:
- a. The inspections performed to detect loose parts.
- i.
TTS Visual Inspection in all SGs ii.
Sludge Lance in all SGs iii.
FOSAR TTS in all SGs
- b. A description of any loose parts detected and their location within the SG (including the source or nature of the loose part, if known).
- i.
See Table 1
- c. If the loose parts were removed from the SG.
- i.
See Table 1
- d. Indications of tube damage associated with the loose parts.
- a. There has been one (1) new FOW indication in SG 3, awaiting special interest testing for sizing
- 9. Discuss the scope and results of any secondary side inspection and maintenance activities (e.g., in-bundle visual inspections, feedring inspections, sludge lancing, assessing deposit loading, etc.).
- a. See responses to Question 8
- 10. Discuss any unexpected or unusual results.
- a. See response to Question 5c
- 11. Provide the schedule for steam generator-related activities during the remainder of the current outage.
- b. Secondary activities are estimated to be completed on 3/18.
Table 1 SGNo.
ForeignObject No.
RetrievalStatus Priority ForeignObject Description Leg/Region Beginning Row End Row Beginning Col End Col IsLegacy Length (In.)
Width (In.)
Height (In.)
Diameter (In.)
SG1 1001 Retrieved 1
GasketMaterial HotLeg 65 65 65 65 New 2
0.25 0.125
SG1 1002 WillNotRetrieve 3
WireBristle Tubelane 60 60 1
1 Legacy 0.2
0.01 SG1 1003 WillNotRetrieve 3
SludgeRock HotLeg 36 37 15 15 New 0.292 0.292 0.65
SG1 1004 Retrieved 1
GasketMaterial HotLeg 43 44 56 57 New 2.06 0.25 0.125
SG1 1005 Retrieved 1
GasketMaterial HotLeg 60 60 61 63 New 2.937 0.25 0.125
SG1 1006 WillNotRetrieve 3
SludgeRock HotLeg 26 27 112 113 Legacy 0.292 0.292 0.4
SG1 1007 WillNotRetrieve 3
SludgeRock HotLeg 24 25 110 111 New 0.292 0.292 0.25
SG1 1008 WillNotRetrieve 3
SludgeRock ColdLeg 57 57 49 50 Legacy 0.292 0.25 0.3
SG1 1009 WillNotRetrieve 3
SludgeRock ColdLeg 46 46 96 97 New 0.292 0.292 0.292
SG1 1010 WillNotRetrieve 3
SludgeRock Tubelane 0
0 90 91 New 0.6875 0.292 0.292
SG1 1011 WillNotRetrieve 3
SludgeRock ColdLeg 3
4 51 52 New 0.292 0.292 0.2
SG1 1012 WillNotRetrieve 3
SludgeRock HotLeg 16 17 28 29 New 0.292 0.292 0.292
SG1 1013 WillNotRetrieve 3
SludgeRock ColdLeg 49 50 62 63 New 0.3 0.3 0.3
SG1 1014 WillNotRetrieve 3
SludgeRock HotLeg 36 36 87 88 Legacy 0.2 0.7 0.293
SG3 3001 Note1 0
GasketMaterial HotLeg 15 16 53 54 New 0.06 0.06 0.04
SG3 3002 Note1 0
WireBristle HotLeg 15 16 53 54 New 0.01 0.01 0.01
SG3 3003 Note1 0
Washer HotLeg 15 16 57 58 New 0.292 0.292 0.292
SG4 4001 WillNotRetrieve 3
SludgeRock HotLeg 9
9 58 59 New 0.25 0.292 0.25
SG4 4002 Retrieved 2
GasketMaterial HotLeg
63 64 New 1.5 0.25 0.125
SG4 4003 WillNotRetrieve 3
SludgeRock HotLeg 55 55 72 73 New 0.292 0.292 0.325
SG4 4004 Retrieved 2
GasketMaterial ColdLeg
58 59 New 2
0.25 0.125
SG4 4005 WillNotRetrieve 3
SludgeRock ColdLeg 58 59 67 68 Legacy 0.292 0.2 0.292
SG4 4006 WillNotRetrieve 3
SludgeRock ColdLeg 55 54 73 74 New 0.292 0.292 0.292
SG4 4007 WillNotRetrieve 3
SludgeRock ColdLeg 52
66 67 New 0.4 0.292 0.292
Note 1: FOSAR on SG-3 still in progress, SG-2 awaiting start.
ML23090A142 OFFICE NRR/DORL/LPL2-1/PM NRR/DORL/LPL2-1/LA NRR/DNRL/NCSG/BC NAME JLamb KGoldstein SBloom DATE 03/29/2023 04/03/2023 03/29/2023 OFFICE NRR/DORL/LPL2-1/BC NRR/DORL/LPL2-1/PM NAME MMarkley JLamb DATE 04/03/2023 04/03/2023