ML20351A219

Summary of Conference Calls Regarding the Fall 2020 Steam Generator Tube Inspections

ML20351A219
Person / Time
Site:	Watts Bar
Issue date:	01/11/2021
From:	Kimberly Green Plant Licensing Branch II
To:	Jim Barstow Tennessee Valley Authority
Green K
References
EPID L-2020-NFO-0004
Download: ML20351A219 (7)

Text

January 11, 2021 Mr. James Barstow Vice President, Nuclear Regulatory Affairs and Support Services Tennessee Valley Authority 1101 Market Street, LP 4A-C Chattanooga, TN 37402-2801

SUBJECT:

WATTS BAR NUCLEAR PLANT, UNIT 2 -

SUMMARY

OF CONFERENCE CALLS REGARDING THE FALL 2020, STEAM GENERATOR TUBE INSPECTIONS (EPID L-2020-NFO-0004)

Dear Mr. Barstow:

On November 6 and 12, 2020, conference calls were held between the U.S. Nuclear Regulatory Commission (NRC) staff and representatives from the Tennessee Valley Authority (TVA, the licensee) regarding the steam generator (SG) tube inspection activities at Watts Bar Nuclear Plant, Unit 2, during refueling outage 3. A list of participants is provided as Enclosure 1. A summary of the conference calls is provided as Enclosure 2.

If you have any questions, please contact me at 301-415-1627 or via e-mail at Kimberly.Green@nrc.gov.

Sincerely,

/RA/

Kimberly J. Green, Senior Project Manager Plant Licensing Branch II-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-391

Enclosures:

As stated cc: Listserv

LIST OF PARTICIPANTS NOVEMBER 6 AND 12, 2020, CONFERENCE CALLS WITH TENNESSEE VALLEY AUTHORITY WATTS BAR NUCLEAR PLANT, UNIT 2 FALL 2020 STEAM GENERATOR INSPECTIONS U.S. Nuclear Regulatory Commission Kim Green Andrew Johnson Greg Makar Steve Bloom Alexander Butcavage Mike Magyar Paul Klein (11/12 only)

Wesley Deschaine (11/12 only)

Tennessee Valley Authority Russell Wells Dean Baker Jeremy Mayo Anne Robinson-Givens Keith Dietrich Jesse Baron (11/6 only)

Michael Bradley (11/6 only)

Daniel Folsom (11/6 only)

Tracy Orf (11/12 only)

Gordon Williams (11/12 only)

Bradley Dolan (11/12 only)

Tony Brown (11/12 only)

James Polickoski (11/12 only)

Westinghouse Jay Smith (11/6 only)

Levi Marcus (11/6 only)

Enclosure 1

SUMMARY

OF NOVEMBER 6 AND 12, 2020, CONFERENCE CALLS TENNESSEE VALLEY AUTHORITY WATTS BAR NUCLEAR PLANT, UNIT 2 DOCKET NO. 50-391 FALL 2020 STEAM GENERATOR TUBE INSPECTIONS On November 6 and 12, 2020, the staff of the Corrosion and Steam Generator Branch (NCSG) of the Division of New and Renewed Licenses (DNRL) participated in a conference call with representatives from the Tennessee Valley Authority (TVA, the licensee) and its vendor, Westinghouse, regarding the ongoing steam generator (SG) tube inspection activities at Watts Bar Nuclear Plant (Watts Bar), Unit 2, during refueling outage 3 (RFO 3).

The four Model D3 SGs at Watts Bar, Unit 2, were designed by Westinghouse. Each SG contains 4,674 mill-annealed tubes with a nominal outside diameter of 0.75 inches and a nominal wall thickness of 0.043 inches. The SGs have an integral preheater with flow distribution baffles. The tubes are supported by carbon steel drilled tube support plates (TSP).

Information provided by the licensee during the November 6, 2020, conference call is summarized below:

The licensee indicated they were implementing the Generic Letter (GL) 95-05, Voltage-Based Criteria for Westinghouse Steam Generator Tubes Affected by Outside Diameter Stress Corrosion Cracking, alternate repair criteria (ARC) for the first time during the current refueling outage.

No indications of primary-to-secondary leakage were observed during the recently completed cycle. No secondary side pressure tests were performed during the outage.

No exceptions were taken to the industry guidelines. No in-situ pressure tests or tube pulls were planned.

Inspections were performed in all four SGs. At the time of the call, the licensee stated that the SG tube inspections were approximately 99 percent complete. The inspection scope included:

o A 100-percent full-length bobbin probe examination in all open tubes, except for the row 1-4 U-bends, which were inspected with a +PointTM probe from the top TSP on hot leg (HL) side to the top TSP on the cold leg (CL) side of the SG.

o A special interest +PointTM probe examination of tube locations with non-resolved bobbin and/or array probe signals.

o 100 percent +PointTM examination at the HL top-of-tubesheet (TTS), plus or minus two inches.

Enclosure 2

o A 50 percent combination bobbin and array probe examination from the CL TTS up to the C06 TSP in a checkerboard pattern.

o A 100 percent +PointTM or array probe examination of HL dings and dings 5 volts on the HL side and the U-bends, up to the top TSP on the CL side.

o A 25 percent +PointTM or array examination of dents and dings 2 volts.

o A 100 percent +PointTM examination of any dent or ding within one inch of a manufacturing burnish mark.

o A 100 percent +PointTM or array examination of mixed residual signals >1 volt.

o A 100 percent +PointTM or array examination of tubes surrounding known foreign object locations and of all tubes within a two-tube pitch surrounding foreign object wear or possible loose part locations.

o A 100 percent +PointTM examination of bobbin probe proximity signals 1.25 volts.

o A 100 percent visual examination of installed tube plugs on both the HL and CL sides.

o A visual exam of the primary channel head bowl that was consistent with the requirements of the Westinghouse Nuclear Safety Advisory Letter 12-1. There was no change to the indication in SG 1 noted previously during RFO 2, which had been determined to be acceptable for at least six cycles of operation during RFO 1.

Anti-vibration bar wear and TSP wear were identified in the outage, but neither form of degradation was a challenge to the structural integrity performance criteria. The licensee reported finding:

o Circumferential Outside Diameter Stress Corrosion Cracking (ODSCC) -

70 indications o Axial ODSCC - 5 indications not applicable to the GL 95-05 ARC o Circumferential ODSCC associated with dings - 2 indications o Axial ODSCC associated with dings - 2 indications o TSP Indications addressed by GL 95-05 ARC Axial ODSCC at TSPs:

1221 distorted support indications (DSI) 315 single axial indications 12 DSI greater than the upper repair limit of 2.8 volts 3 DSI excluded from the GL 95-05 alternate repair criteria due to seismic plus loss of coolant accident

At the time of the call, the licensee planned to stabilize 71 tubes and to plug 191 tubes.

There was no plan to install sleeves during this outage.

No in situ pressure tests were scheduled or planned for the outage.

Foreign object search and retrieval (FOSAR) secondary side inspections were performed in all four SGs to characterize and remove loose parts. The FOSAR included the annulus and no-tube lane, and 100 percent of the HL TTS. A checkerboard pattern was used on the CL side. Findings of some small wires and sludge rocks were all that was reported. A small wire-bristle at row 19 column 59 was lodged in a small sludge pile and could not be removed.

Sludge lancing was performed in all SGs during the outage, and approximately 10 - 13 pounds of sludge were removed from each SG.

When compared to the original D3 SGs at Watts Bar, Unit 1, the Unit 2 SGs are experiencing more cracking at TSPs than at the TTS. The licensee indicated that they were reaching out to industry experts on Condition Monitoring to confirm the Watts Bar, Unit 2, analysis. The licensee confirmed that the amount of cracking indications noted could potentially accelerate the planned SG replacement to RFO 4 from RFO 5.

The licensee plans to stabilize and plug tubes in the days following the call with the U.S. Nuclear Regulatory Commission (NRC).

Information provided by the licensee during the November 12, 2020, conference call is summarized below:

Since the previous call on November 6, 2020, axial primary water stress corrosion cracking indications had been identified at the HL TTS, during the independent quality data analyst resolution process.

SG 3 did not meet Condition Monitoring requirements for the conditional probability of burst, as part of the GL 95-05 ARC. The licensee had already completed their 8-hour NRC notification as required by Title 10 Code of Federal Regulations, Section 50.72.

The increase to the large early release frequency was calculated to be approximately 1 x 10-11 /year.

The final plugging list contained 189 tubes. Most of these tubes were in SG 3, which had 122 tubes to be plugged. SGs 1, 2, and 4 had 9, 22, and 36 tubes to be plugged, respectively. SG 3 had 400 DSI indications at TSPs. The tubes plugged in SG 3 included 3 tubes excluded from the GL 95-05 ARC due to seismic plus loss-of-coolant accident loads, and 10 indications that were greater than the upper repair limit.

The single largest indication was approximately 9.3 volts. The NRC regional inspector requested the licensee to provide the historical eddy current data from this tube for comparison.

The licensee is working to determine if they will submit a license amendment to incorporate the probability of prior cycle detection methodology as part of the GL 95-05 operational assessment for the next operating cycle.

The licensee stated that they would be entering Mode 4 in the morning of November 14, 2020, and asked if the NRC staff had any concerns. The NRC staff did not identify any issues that required follow-up action at the time of the call.

Subsequent to the call on November 12, 2020, discussions were held with Region II and the licensee regarding the methodology used for calculating the probability of detection in the GL 95-05 ARC used by the licensee. The results of the discussions are summarized in the quarterly inspection report for Watts Bar, Unit 2, No. 2020004.

ML20351A219 *by e-mail OFFICE NRR/DORL/LPL2-2/PM NRR/DORL/LPL2-2/LA NRR/DNRL/NCSG/BC*

NAME KGreen BAbeywickrama SBoom DATE 12/21/2020 12/21/2020 12/07/2020 OFFICE NRR/DORL/LPL2-2/BC NRR/DORL/LPL2-2/PM NAME UShoop KGreen DATE 01/08/2021 01/11/2021