ML21012A203

NRR E-mail Capture - Request for Additional Information Regarding Tva'S Request to Revise the Watts Bar UFSAR to Use Alternate Probability of Detection

ML21012A203
Person / Time
Site:	Watts Bar
Issue date:	01/11/2021
From:	Kimberly Green NRC/NRR/DORL/LPL2-2
To:	Wells R Tennessee Valley Authority
References
L-2020-LLA-0273
Download: ML21012A203 (4)

Text

From: Green, Kimberly Sent: Monday, January 11, 2021 4:52 PM To: Wells, Russell Douglas Cc: Shoop, Undine; Haeg, Luke

Subject:

Request for Additional Information Regarding TVA's Request to Revise the Watts Bar UFSAR to Use Alternate Probability of Detection (EPID L-2020-LLA-0273)

Attachments: RAI Non-Proprietary_Redacted.pdf

Dear Mr. Wells,

By letter dated December 23, 2020 (Agencywide Documents Access and Management System (ADAMS)

Accession No. ML20358A141), Tennessee Valley Authority (TVA) submitted a license amendment request (LAR) for the Watts Bar Nuclear Plant (Watts Bar), Unit 2. The proposed amendment would revise the Watts Bar Updated Final Safety Analysis Report 5.5.2.4, Tests and Inspections, for Unit 2 only, to identify the probabilities of detection that will be used in the voltage-based alternate repair criteria for axial outer diameter stress corrosion cracking until the Unit 2 steam generators are replaced.

The U.S. Nuclear Regulatory Commission (NRC) staff is reviewing your submittal 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 on January 8, 2021, via BOX due to the proprietary nature of one of the requests. A clarification call was held on January 11, 2021, to clarify the NRC staffs requests. As a result of the clarification call, the NRC staff determined that RAI 5.b was unnecessary. The redacted, non-proprietary version of the RAI is attached. The version containing proprietary information will be transmitted to you via the NRCs BOX - Enterprise File Synchronization and Sharing service.

Due to the expedited nature of the LAR, a response to the attached RAI (non-proprietary) is requested no later than January 19, 2021.

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.

Sincerely, Kimberly J. Green, Senior Project Manager Plant Licensing Branch II-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation

Hearing Identifier: NRR_DRMA Email Number: 966 Mail Envelope Properties (MN2PR09MB573905D5590C37FBE9C08DCA8FAB0)

Subject:

Request for Additional Information Regarding TVA's Request to Revise the Watts Bar UFSAR to Use Alternate Probability of Detection (EPID L-2020-LLA-0273)

Sent Date: 1/11/2021 4:51:47 PM Received Date: 1/11/2021 4:51:47 PM From: Green, Kimberly Created By: Kimberly.Green@nrc.gov Recipients:

"Shoop, Undine" <Undine.Shoop@nrc.gov>

Tracking Status: None "Haeg, Luke" <Lucas.Haeg@nrc.gov>

Tracking Status: None "Wells, Russell Douglas" <rdwells0@tva.gov>

Tracking Status: None Post Office: MN2PR09MB5739.namprd09.prod.outlook.com Files Size Date & Time MESSAGE 2036 1/11/2021 4:51:47 PM RAI Non-Proprietary_Redacted.pdf 83735 Options Priority: Normal Return Notification: No Reply Requested: No Sensitivity: Normal Expiration Date:

OFFICIAL USE ONLY PROPRIETARY INFORMATION REQUEST FOR ADDITIONAL INFORMATION TENNESSEE VALLEY AUTHORITY WATTS BAR NUCLEAR PLANT, UNIT 2 DOCKET NO. 50-391 USE OF ALTERNATE METHOD OF DETERMINING PROBABILITY OF DETECTION FOR STEAM GENERATORS INTRODUCTION By letter dated December 23, 2020 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML20358A141), Tennessee Valley Authority requested a license amendment to change Section 5.5.2.4, Tests and Inspections, of the Updated Final Safety Analysis Report (UFSAR) for Watts Bar Nuclear Plant (Watts Bar), Unit 2. The proposed changes would assign alternative probability of detection (POD) values for the eddy current bobbin probe inspections of steam generator (SG) tubes performed according to Generic Letter (GL) 95-05, Voltage-Based Repair Criteria for Westinghouse Steam Generator Tubes Affected by Outside Diameter Stress Corrosion Cracking [ODSCC]. These inspections and the associated POD values are used in determining if the SG tubes meet the regulatory requirements for structural and leakage integrity.

Regulatory Requirements Fundamental regulatory requirements with respect to the integrity of the SG tubing are established in Title 10 of the Code of Federal Regulations (10 CFR) Part 50. Specifically, the general design criteria (GDC) in Appendix A, General Design Criteria for Nuclear Power Plants, to 10 CFR Part 50 provide regulatory requirements that state the reactor coolant pressure boundary shall have an extremely low probability of abnormal leakage, of rapidly propagating failure, and of gross rupture (GDC 14), shall be designed with sufficient margin (GDCs 15 and 31), shall be of the highest quality standards practical (GDC 30), and shall be designed to permit periodic inspection and testingto assess their structural and leak tight integrity (GDC 32). Section 3.1.2 of the Watts Bar UFSAR addresses conformance with the GDC in Appendix A to 10 CFR Part 50 (ADAMS Accession No. ML19176A129).

INFORMATION REQUESTED In order to complete its evaluation of whether the proposed changes meet the requirements described above, the U.S. Nuclear Regulatory Commission staff requests the following information.

1. Section 2.2, Evaluation of Proposed Changes, of Enclosure 1 states that using the standard GL 95-05 evaluation methods (i.e., POD = 0.6 for all indications) SG3 and SG4 did not meet the criteria for a full cycle operational assessment, and that different POD values must be used to support continued operation. With respect to meeting the SG tube structural and leakage integrity requirements, identify the period for which the OFFICIAL USE ONLY PROPRIETARY INFORMATION

OFFICIAL USE ONLY PROPRIETARY INFORMATION proposed POD values support continued operation and the criteria that will not be met after that time.

2. The technical basis for the proposed POD depends on relationships between the bobbin probe eddy current indication peak-to-peak voltage (Vpp) and vertical maximum voltage (Vvm). Confirm the NRC staffs understanding that the bobbin probe voltage values discussed in Section 3.3 of Enclosure 1 and in the proposed revision to the UFSAR are Vpp values.

3. Regarding eddy current signal-to-noise (S/N) ratio, clarify the statement in Enclosure 2, Section 2.1.1, that ((

)).

4. Please provide the following information about Enclosure 3, Figure 1, ETSS I28411S/N-POD Data Points and Regression Curve.

a. If any points from ETSS I28411 are not included in Figure 1, discuss the reason for excluding them. For example, ETSS I28411 appears to have more values for PODs of 0.1 and 0.2 than are shown in Figure 1.

b. Describe how the noise was determined in order to calculate the S/N values used to generate Figure 1. Also, clarify whether the tube noise value referenced in the last paragraph on page 5 of Enclosure 3 is a tube from Watts Bar, Unit 2 or a tube used in the development of ETSS I28411.

5. Enclosure 3, Section 2.2, Data Union Software (DUS) Flaw Injection, includes figures comparing injected eddy current flaw signals (3.2 volts and 6.0 volts) to the noise signal amplitude (1.54 Vvm) at the tube with the highest noise signal.

Discuss the source of the noise signals and injected signals compared to the actual inspection measurements from the plant in the U2R3 inspection. Explain if the 3.2 volt and 6.0 volt injected signals are the 3.21 volt and 6.06 volt indications listed in Table 1 of Enclosure 1. If not, describe their origin.

6. Confirm that the references to Section 3.1 and Section 3.2 in Section 3.0, Summary of Results and Conclusions, of Enclosure 3 are meant to refer to Sections 2.1 and 2.2.

OFFICIAL USE ONLY PROPRIETARY INFORMATION