ML24260A032

NRR E-mail Capture - Request for Additional Information Regarding the Watts Bar Unit 2 Steam Generator Tube Inspection Report for U2R5

ML24260A032
Person / Time
Site:	Watts Bar
Issue date:	09/10/2024
From:	Kimberly Green NRC/NRR/DORL/LPL2-2
To:	Hughes S Tennessee Valley Authority
References
L-2024-LRO-0022
Download: ML24260A032 (5)

Text

From: Kimberly Green Sent: Tuesday, September 10, 2024 10:55 AM To: Hughes, Shawna Marie

Subject:

Request for Additional Information regarding the Watts Bar Unit 2 Steam Generator Tube Inspection Report for U2R5 (EPID L-2024-LRO-0022)

Attachments: Non-Prop RAI for U2R5 SGTI Report - Final_Redacted.pdf

Dear Shawna Hughes,

By letter dated May 16, 2024 (ADAMS Accession No. ML24137A267), Tennessee Valley Authority (TVA) submitted the 180 Day Steam Generator Inspection Report for the Watts Bar Nuclear Plant, Unit 2, Cycle 5 outage.

The U.S. Nuclear Regulatory Commission (NRC) staff is reviewing the report and has identified areas where additional information is needed to complete its review. A draft request for additional information (RAI) was previously transmitted to you via the BOX - Enterprise File Synchronization and Sharing service (BOX-EFSS) application on August 12, 2024, because the file contained proprietary information. At TVAs request, a clarification call was held on September 4, 2024, to clarify the NRC staffs requests. Based on the discussion during that call, the NRC staff has reworded RAI 1.a and 1.b, which do not contain proprietary information, to provide clarity. Additions are shown in red text and deletions are shown in red text with strikeout.

RAI 1

Provide the following:

a. If known, describe the root cause(s) More details concerning the reasons for the greater than anticipated wear at the ATSG observed during U2R5, including if the hot leg and cold leg tube wear haves different causes. If the root cause has not yet been determined, provide any insights that have been gained about the potential reason(s) for the tube wear.

b. For the tubes that were preventively plugged, describe A description of the shape of the deeper wear scars (e.g., tapered, flat.)

The redacted, non-proprietary version of the RAI is attached. The version containing proprietary information has been transmitted to you via the BOX-EFSS.

A response to the attached RAI (non-proprietary) is requested within 30 days of the date of this email. The NRC staff considers that timely responses to RAIs help ensure sufficient time is available for staff review and contribute toward the NRCs goal of efficient and effective use of staff resources. If circumstances result in the need to revise the requested response date, please me at (301) 415-1627 or via email at Kimberly.Green@nrc.gov.

Kimberly Green Senior Project Manager Division of Operating Reactor Licensing U.S. Nuclear Regulatory Commission 301-415-1627

Hearing Identifier: NRR_DRMA Email Number: 2604

Mail Envelope Properties (SA1PR09MB916332A9D4AC0E9926A42DD48F9A2)

Subject:

Request for Additional Information regarding the Watts Bar Unit 2 Steam Generator Tube Inspection Report for U2R5 (EPID L-2024-LRO-0022)

Sent Date: 9/10/2024 10:54:57 AM Received Date: 9/10/2024 10:54:00 AM From: Kimberly Green

Created By: Kimberly.Green@nrc.gov

Recipients:

"Hughes, Shawna Marie" <smhughes@tva.gov>

Tracking Status: None

Post Office: SA1PR09MB9163.namprd09.prod.outlook.com

Files Size Date & Time MESSAGE 2303 9/10/2024 10:54:00 AM Non-Prop RAI for U2R5 SGTI Report - Final_Redacted.pdf 71330

Options Priority: Normal Return Notification: No Reply Requested: No Sensitivity: Normal Expiration Date:

OFFICIAL USE ONLY - PROPRIETARY INFORMATION

REQUEST FOR ADDITIONAL INFORMATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION WATTS BAR UNIT 2 - CYCLE 5 STEAM GENERATOR TUBE INSPECTION REPORT TENNESSEE VALLEY AUTHORITY WATTS BAR NUCLEAR PLANT, UNIT 2 DOCKET NO. 50-391

=

Background===

By letter dated May 16, 2024 (ADAMS Accession No. ML24137A267), TVA (the licensee),

submitted information summarizing the results of the fall 2023 steam generator (SG) inspections performed at Watts Bar Nuclear Plant, Unit 2 (WBN 2), during the Unit 2 Cycle 5 refueling outage (U2R5). To complete its review of the inspection report, the U.S. Nuclear Regulatory Commission (NRC) staff requests the following additional information.

Regulatory Basis

All pressurized-water reactors have Technical Specifications (TS) according to Section 50.36 of Title 10 of the Code of Federal Regulations that include a SG Program with specific criteria for the structural and leakage integrity, repair, and inspection of SG tubes. WBN 2 TS Section 5.9.9 requires that a report be submitted within 180 days after the initial entry into hot shutdown (Mode 4) following completion of an inspection of the SGs performed in accordance with TS 5.7.2.12, which requires that a SG Program be established and implemented to ensure SG tube integrity is maintained. The TS 5.7.2.12 (d) states, in part, In addition to meeting the requirements of d.1, d.2, and d.3 below, the inspection scope, inspection methods, and inspection intervals shall be such as to ensure that SG tube integrity is maintained until the next SG inspection.

RAI 1

The WBN 2 inspection during the fall 2023 outage (U2R5) was the first inspection of the SGs following replacement in 2022. The Westinghouse Model 68AXP replacement SGs had operated for about 1.33 effective full power years (EFPY) at the time of the U2R5 outage. Based on the inspection results, 56 tubes were plugged due to wear at horizontal advanced tube support grids (ATSG). Condition monitoring was met for tube wear at the ATSG with a maximum wear depth of 28 percent through-wall. The steam generator inspection report also identifies a sub-population of perimeter tubes as having a different wear rate from the interior tubes.

Provide the following:

a. If known, describe the root cause(s) for the greater than anticipated wear at the ATSG observed during U2R5, including if the hot leg and cold leg tube wear have different causes. If the root cause has not yet been determined, provide any insights that have been gained about the potential reason(s) for the tube wear.

b. For the tubes that were preventively plugged, describe the shape of the wear scars (e.g., tapered, flat).

1

OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - PROPRIETARY INFORMATION

RAI 2

Section 9 of the WBN 2 tube inspection report discusses two operational assessment methods to predict tube integrity conditions at the next scheduled inspection. The deterministic model evaluated all SGs while the fully probabilistic model determined the probability of burst and probability of leakage only for the limiting steam generator (SG2). Results for both the deterministic and the probabilistic analyses (ATSG Wear) are close to the acceptance criteria for a projected 2.7 EFPY interval. When considering tube wear, Revision 5 of the EPRI Steam Generator Integrity Assessment Guidelines states:

((

))

Given the uncertainty associated with projecting the greater than expected tube wear rates experienced at some of the ATSGs during the first operating cycle for the replacement SGs, please discuss the date and provide justification for the next planned SG tube inspection.

2

OFFICIAL USE ONLY - PROPRIETARY INFORMATION