ML20337A040

Summary of November 17, 2020, Teleconference with Tennessee Valley Authority Regarding Planned License Amendment Request for Technical Specification 5.9.9, Steam Generator Tube Inspection Report

ML20337A040
Person / Time
Site:	Watts Bar
Issue date:	12/15/2020
From:	Kimberly Green Plant Licensing Branch II
To:	Tennessee Valley Authority
Green K
References
EPID L-2020-LRM-0107
Download: ML20337A040 (5)

Text

December 15, 2020 LICENSEE: Tennessee Valley Authority FACILITY: Watts Bar Nuclear Plant, Unit 2

SUMMARY

OF NOVEMBER 17, 2020, TELECONFERENCE WITH TENNESSEE VALLEY AUTHORITY REGARDING PLANNED LICENSE AMENDMENT REQUEST FOR TECHNICAL SPECIFICATION 5.9.9, STEAM GENERATOR TUBE INSPECTION REPORT (EPID L-2020-LRM-0107)

On November 17, 2020, the U.S. Nuclear Regulatory Commission (NRC) staff conducted a Category 1 public teleconference with representatives of Tennessee Valley Authority (TVA).

The purpose of the call was to discuss TVAs planned license amendment request (LAR) to revise Watts Bar Nuclear Plant (Watts Bar), Unit 2, Technical Specification (TS) 5.9.9, Steam Generator Tube Inspection Report.

The meeting notice and agenda, dated November 9, 2020, are available at Agencywide Documents Access and Management System (ADAMS) Accession No. ML20315A399. TVAs presentation slides for the meeting are available at ADAMS Accession No. ML20329A372. A list of participants is enclosed.

TVA stated that it plans to submit an LAR to revise TS 5.9.9 to add a reporting requirement for the use of the Probability of Prior Cycle Detection (POPCD) methodology. The current alternate repair criteria in use is Generic Letter (GL) 95-05, Voltage-Based Repair Criteria for Westinghouse Steam Generator Tubes Affected by Outside Diameter Stress Corrosion Cracking.

Watts Bar, Unit 2, recently completed refueling outage 3 (U2R3), which was the third inservice inspection for the Unit 2 steam generators (SGs). The Unit 2 SGs are Model D3 with Alloy 600 mill annealed tubes. Based on the inspections, TVA determined that SG-3 did not pass the GL 95-05 criteria for conditional probability of burst. TVA recounted the identified SG tube degradation mechanisms based on the U2R3 inspections, which included mechanical wear, circumferential outer diameter stress corrosion cracking (ODSCC), axial ODSCC, and axial primary water stress corrosion cracking. Based on the results of the inspections, TVA concluded that the condition monitoring requirements were met for all degradation mechanisms except for the conditional probability of burst in SG-3 associated with axial ODSCC at tube support plates (TSPs). The GL 95-05 criteria were developed specifically for this degradation mechanism. The NRC staff asked if axial ODSCC at TSPs was detected during the previous outage. TVA stated that some axial ODSCC indications at TSPs were detected and plugged in the previous outage (U2R2) because the use of GL 95-05 at Watts Bar was not approved at the time. TVA further stated that all 14 tubes with axial ODSCC detected indications that exceeded the GL 95-05 repair criteria were plugged during this refueling outage.

TVA described the probability of detection (POD) of ODSCC from GL 95-05, Attachment 1, Section 2.b.1, which requires the beginning of cycle distribution of bobbin probe inspection indications to be scaled upward by a factor of 1/POD to conservatively account for non-detected crack indications that are assumed to be returned to service. The generic letter states that the POD should be assumed to have a value of 0.6, or as an alternative, an NRC approved POD function can be used, if such a function becomes available. TVA pointed out that substantial industry data shows a POD of 1.0 for indications in the range of 3 - 4 volts, and according to information in EPRI NP-7490, Addendum 7, no undetected indication has exceeded 3.2 volts.

The NRC staff asked if Watts Bar, Unit 2 was implementing a POD of 1 as part of an alternate NRC approved function, and TVA indicated it was not. TVA stated that based on GL 95-05 preliminary operational assessment predictions, the use of a POD of 0.6 is limiting for Watts Bar, Unit 2, i.e., that the U2R3 inspection results did not support a cycle length of 90 days with the use of a POD of 0.6. TVA is using a short-term POD of 1.0 in their operational assessment. TVA calculated two cases for POD = 1.0: one case for indications greater than or equal to 3.2 volts and a second case for indications greater than or equal to 8 volts. In the long-term, TVA wants to use the POPCD methodology for the POD. As shown on Slide 10, depending on the bobbin coil voltage that the POD of 1.0 value is applied to, SG-3 can operate either 180 effective full power days (EFPD) or 240 EFPD before mid-cycle inspections would be needed for SG-3. If a POPCD methodology is applied, SG-3 can operate for approximately 270 EFPD. TVA pointed out that Slide 10 contains an error. The POD column for SG-2 should read the same as the entry for SG-1.

The NRC staff asked if a POD of 0.6 is used, how long would the plant be able to operate before mid-cycle tube inspections would be required, and if that timeframe was close to 90 days. TVA responded that the use of a POD of 0.6 does not support 90 days, and that the time would be much less than 90 days.

TVA described the POPCD methodology and stated that it is calculated as the ratio of indications reported at the prior inspection to the total indications found at the subsequent inspection. The premise of POPCD is that all indications can contribute significantly to burst and leakage for GL 95-05 can be confirmed with a rotating pancake coil or equivalent detection technique. It also treats all new indications found during an inspection as having been undetected at the prior inspection. TVA stated that the POPCD is supported by an industry database of 42 inspections with 9 inspections of high noise plant data.

TVA described the noise considerations for the Watts Bar, Unit 2 SGs. The TSP ODSCC indications are dominantly located near the center of the TSP. The NRC staff asked what is meant by dominantly located near the center. TVA replied that it means the indications tend to occur near the middle third of the TSP. According to TVA, the Watts Bar, Unit 2 SGs have relatively low bobbin noise measurements at the TSP center. TVA performed noise monitoring during U2R3. Based on preliminary results using POPCD, there is potential improved detection of axial ODSCC at the TSP center for large voltage indications. The NRC asked if there were any indications that were outside of the TSPs. TVA stated that there were no indications outside of the TSPs.

TVA stated that it will use a POD of 1.0 in the short term for indications greater than or equal to 8 volts or possibly for greater than or equal to 3.2 volts. TVA will submit an LAR to request use of the POPCD methodology and that it is evaluating the use of Watts Bar, Unit 1 data to support the use of Unit 2-specific POPCD. The NRC staff asked if TVA thought there would be a significant difference between the use of a generic industry POPCD and a plant-specific

POPCD. TVA responded that it did not believe the results would be significantly different. The NRC staff also asked what TVAs basis is for temporarily using a POD of 1.0. TVA stated that it will submit one LAR that will request the use of POPCD until the SGs are replaced. The NRC staff asked for clarification on TVAs response, if the POPCD methodology will only be used for the upcoming cycle. TVA stated that it is considering a number of options, but one of the options is to replace the SGs during the next refueling outage.

TVA recounted the regulatory precedent for the use of the POPCD methodology. The NRC has previously approved the use of the POPCD methodology at Sequoyah, Unit 2 and Diablo Canyon Power Plant, Unit 2. TVA plans to submit an LAR that mimics the TS changes for these two plants LARs. TVA stated that it has reviewed the two LARs, the requests for additional information, and responses associated with these LARs and will address the issues, as applicable, in the proposed LAR. TVA plans to submit the LAR for Watts Bar, Unit 2 to the NRC by December 18, 2020, and will ask for approval by February 8, 2021, with implementation by February 14, 2021, which is 90 days from when Watts Bar, Unit 2 entered Mode 4. The NRC staff asked why TVA believed that approval is needed within 90 days. TVA responded that it is based on the current 90-day reporting requirement in the Watts Bar, Unit 2 TS 5.9.9, and on the precedent for Diablo Canyon, Unit 2.

No comments or public meeting feedback were received. No regulatory decisions were made at this meeting.

Please direct any inquiries to me at 301-415-1627 or by e-mail to Kimberly.Green@nrc.gov.

/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

Enclosure:

List of Participants cc: Listserv

LIST OF PARTICIPANTS NOVEMBER 17, 2020, TELECONFERENCE WITH TENNESSEE VALLEY AUTHORITY REGARDING WATTS BAR NUCLEAR PLANT, UNIT 2 PLANNED LICENSE AMENDMENT REQUEST TO REVISE TECHNICAL SPECIFICATION 5.9.9 Name Organization Kim Green U.S. Nuclear Regulatory Commission (NRC)

Tom Stephen NRC Wes Deschaine NRC Vic Cusumano NRC Clint Ashley NRC Al Butcavage NRC Brendan Collins NRC Mike Magyar NRC Steve Bloom NRC Andy Johnson NRC Paul Klein NRC Greg Makar NRC Undine Shoop NRC Kayla Gamin NRC Tison Campbell NRC Jennifer Scro NRC Ching Ng NRC Antonios Zoulis NRC Russ Wells Tennessee Valley Authority (TVA)

Kim Hulvey TVA Anne Robinson-Givens TVA Jeremy Mayo TVA Gordon Williams TVA Andy Taylor TVA Dean Baker TVA Jim Polickoski TVA Jesse Baron TVA Dan Folsom TVA Jon Johnson TVA Mimi King-Patterson TVA Bill Victor TVA Enclosure

ML20337A040 *via e-mail OFFICE DORL/LPL2-2/PM DORL/LPL2-2/LA* DNLR/NCSG/BC* DORL/LPL2-2/BC* DORL/LPL2-2/PM*

NAME KGreen BAbeywickrama SBloom UShoop KGreen DATE 12/3/2020 12/2/2020 12/3/2020 12/14/2020 12/15/2020