NL-24-0020, Plan, Unit 1 Responses to NRC Request for Additional Information for Refueling Outage 1R24 Steam Generator Tube Inspection Report

Plan, Unit 1 Responses to NRC Request for Additional Information for Refueling Outage 1R24 Steam Generator Tube Inspection Report

ML24022A222
Person / Time
Site:	Vogtle
Issue date:	01/22/2024
From:	Coleman J Southern Nuclear Operating Co
To:	Office of Nuclear Reactor Regulation, Document Control Desk
Shared Package
ML24022A220	List: NL-24-0020, Plan, Unit 1 Responses to NRC Request for Additional Information for Refueling Outage 1R24 Steam Generator Tube Inspection Report
References
NL-24-0020
Download: ML24022A222 (1)

Text

~ Southern Nuclear January 22, 2024 Docket No.:

50-424 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D. C. 20555-0001 Regulatory Affairs Vogtle Electric Generating Plant - Unit 1 3535 Colonnade Parkway Birmingham, AL 35243 205 992 5000 NL-24-0020 Responses to NRC Request for Additional Information for Refueling Outage 1 R24 Steam Generator Tube Inspection Report Ladies and Gentlemen:

By letter dated September 22, 2023 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML23265A249), Southern Nuclear Operating Company (SNC) submitted the Steam Generator (SG) Tube Inspection Report for the SG tube inspection performed during the twenty-fourth refueling outage on Vogtle Electric Generating Plant (Vogtle),

Unit 1 (1 R24) in accordance with the requirements of Vogtle Technical Specification 5.6.10 as updated by TS Amendment 211 (ML21316A055).

After reviewing the report, the NRC staff requested response to the request for additional information (RAI) given below.

On November 29, 2023, the NRC staff provided draft RAI questions to SNC to make sure that the RAls were understandable, the regulatory basis was clear, to ensure there is no proprietary information, and to determine if the information was previously docketed. On December 8, 2023, SNC stated that it would provide the RAI response within 45 days (January 22, 2024). to this letter provides the SNC Responses to the NRC Request for Additional Information for Refueling Outage 1 R24 Steam Generator Tube Inspection Report. This enclosure contains proprietary information as defined by 10 CFR 2.390. Westinghouse Electric Company LLC ("Westinghouse"), as the owner of the proprietary information, has executed the enclosed affidavit, which identifies that the enclosed proprietary information has been withheld from public disclosure.

The proprietary information was provided to Southern Nuclear (SNC) in a Westinghouse transmittal which included the affidavit provided as Enclosure 1 to this letter, as well as a non-proprietary version of the Responses to the NRC Request for Additional Information, which is provided as Enclosure 3. The proprietary information has been faithfully reproduced in the enclosed documentation, such that, the affidavit remains applicable. to this letter contains Proprietary Information to be withheld from public disclosure per 10 CFR 2.390. When separated from Enclosure 2 this transmittal document is decontrolled.

U.S. Nuclear Regulatory Commission NL 0020 Page 2 Westinghouse hereby requests that the enclosed proprietary information provided in Enclosure 2 to this letter be withheld from public disclosure in accordance with the provisions of 10 CFR 2.390.

This letter contains no regulatory commitments. If you have any questions, please contact Ryan Joyce at (205) 992-6468.

Respectfully submitted, Jamie Coleman Regulatory Affairs Director JMC/dsp/cbg

Enclosures:

1.

CAW-24-001, Affidavit for GAE-NRCD-RF-LR-000002 (Non-Proprietary)

2.

GAE-NRCD-RF-LR-000002 P-Attachment, Revision 0 (PROPRIETARY)

3.

GAE-NRCD-RF-LR-000002 NP-Attachment, Revision 0 (Non-Proprietary) cc:

Regional Administrator, Region II NRR Project Manager - Vogtle 1 & 2 Senior Resident Inspector - Vogtle 1 & 2 RType: CVC?000 to this letter contains Proprietary Information to be withheld from public disclosure per 10 CFR 2.390. When separated from Enclosure 2 this transmittal document is decontrolled.

Vogtle Electric Generating Plant - Unit 1 Responses to NRC Request for Additional Information for Refueling Outage 1 R24 Steam Generator Tube Inspection Report CAW-24-001, Affidavit for GAE-NRCD-RF-LR-000002 (Non-Proprietary) to NL-24-0020 Commonwealth of Pennsylvania:

County of Butler:

Westinghouse Non-Proprietary Class 3 AFFIDAVIT CAW-24-001 (1)

I, Zachary Harper, Manager, Licensing Engineering, have been specifically delegated and authorized to apply for withholding and execute this Affidavit on behalf of Westinghouse Electric Company LLC (Westinghouse).

(2)

I am requesting the proprietary portions of GAE-NRCD-RF-LR-000002 P-Attachment, Revision 0, "Vogtle Electric Generating Plant, Unit 1 - Responses to NRC Request for Additional Information for Refueling Outage 1R24 Steam Generator Tube Inspection Report," be withheld from public disclosure under 10 CFR 2.390.

(3)

I have personal knowledge of the criteria and procedures utilized by Westinghouse in designating information as a trade secret, privileged, or as confidential commercial or financial information.

Page 1 of3 (4)

Pursuant to 10 CFR 2.390, the following is furnished for consideration by the Commission in determining whether the information sought to be withheld from public disclosure should be withheld.

(i)

The information sought to be withheld from public disclosure is owned and has been held in confidence by Westinghouse and is not customarily disclosed to the public.

(ii)

The information sought to be withheld is being transmitted to the Commission in confidence and, to Westinghouse's knowledge, is not available in public sources.

(iii)

Westinghouse notes that a showing of substantial harm is no longer an applicable criterion for analyzing whether a document should be withheld from public disclosure. Nevertheless, public disclosure of this proprietary information is likely to cause substantial harm to the competitive position of Westinghouse because it would enhance the ability of competitors to provide similar technical evaluation justifications and licensing defense services for commercial power reactors without commensurate expenses. Also, public disclosure of the information would enable others to use the information to meet NRC requirements for licensing documentation without purchasing the right to use the information.

• • • This record was final approved on 01 /16/2024 15:39:33. (This statement was added by the PRIME system upon its validation) to NL-24-0020 Westinghouse Non-Proprietary Class 3 AFFIDAVIT CAW-24-001 (5)

Westinghouse has policies in place to identify proprietary information. Under that system, information is held in confidence if it falls in one or more of several types, the release of which might result in the loss of an existing or potential competitive advantage, as follows:

(a)

The information reveals the distinguishing aspects of a process ( or component, structure, tool, method, etc.) where prevention of its use by any of Westinghouse's competitors without license from Westinghouse constitutes a competitive economic advantage over other companies.

Page 2 of3 (b)

It consists of supporting data, including test data, relative to a process ( or component, structure, tool, method, etc.), the application of which data secures a competitive economic advantage ( e.g., by optimization or improved marketability).

( c)

Its use by a competitor would reduce his expenditure of resources or improve his competitive position in the design, manufacture, shipment, installation, assurance of quality, or licensing a similar product.

( d)

It reveals cost or price information, production capacities, budget levels, or commercial strategies of Westinghouse, its customers or suppliers.

( e)

It reveals aspects of past, present, or future Westinghouse or customer funded development plans and programs of potential commercial value to Westinghouse.

(f)

It contains patentable ideas, for which patent protection may be desirable.

(6)

The attached documents are bracketed and marked to indicate the bases for withholding. The justification for withholding is indicated in both versions by means oflower-case letters (a) through (f) located as a superscript immediately following the brackets enclosing each item of information being identified as proprietary or in the margin opposite such information. These lower-case letters refer to the types of information Westinghouse customarily holds in confidence identified in Sections (5)(a) through (f) of this Affidavit.

• • • This record was final approved on 01/16/2024 15:39:33. (This statement was added by the PRIME system upon its validation) to NL-24-0020 Westinghouse Non-Proprietary Class 3 AFFIDAVIT CAW-24-001 I declare that the averments of fact set forth in this Affidavit are true and correct to the best of my knowledge, information, and belief. I declare under penalty of perjury that the foregoing is true and correct.

Executed on: 1/16/2024

1. .¥s 1gne e ectromca y y Zachary Harper Page 3 of3

• • • This record was final approved on 01/16/2024 15:39:33. (This statement was added by the PRIME system upon its validation)

Vogtle Electric Generating Plant - Unit 1 Responses to NRC Request for Additional Information for Refueling Outage 1 R24 Steam Generator Tube Inspection Report GAE-NRCD-RF-LR-000002 NP-Attachment, Revision 0 (Non-Proprietary) to NL-24-0020 Westinghouse Non-Proprietary Class 3 Westinghouse Electric Company GAE-NRCD-RF-LR-000002 NP-Attachment Revision 0 Vogtle Electric Generating Plant, Unit 1 - Responses to NRC Request for Additional Information for Refueling Outage 1R24 Steam Generator Tube Inspection Report January 2024 Author:

David A. Suddaby*

Component Design and Management Programs Verifier:

Jay R. Smith*

Component Design and Management Programs Reviewer:

Gary W. Whiteman*

Licensing Engineering Approved:

Robert S. Chappo, Jr.*, Manager Component Design and Management Programs

©2024 Westinghouse Electric Company LLC All Rights Reserved

• Electronically approved records are authenticated in the Electronic Document Management System.

GAE-NRCD-RF-LR-000002 NP-Attachment Rev. 0 Page 1 of 9

• • • This record was final approved on 01/17/2024 10:58:57. (This statement was added by the PRIME system upon its validation) to NL-24-0020 Westinghouse Non-Proprietary Class 3 Vogtle Electric Generating Plant, Unit 1 - Responses to NRC Request for Additional Information for Refueling Outage 1R24 Steam Generator Tube Inspection Report REQUEST FOR ADDITIONAL INFORMATION (RAI)

By letter dated September 22, 2023 (Agencywide Documents Access and Management System (ADAMS)

Accession No. ML23265A249), Southern Nuclear Operating Company (SNC, the licensee), submitted information summarizing the results of the spring 2023 steam generator (SG) inspections performed at Vogtle Electric Generating Plant (Vogtle), Unit 1, during the twenty-fourth refueling outage (1R24).

All pressurized water reactors have Technical Specifications (TS) according to § 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. Vogtle, Unit 1, TS Section 5. 6.10 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 Section 5.5.9, which requires that a SG Program be established and implemented to ensure SG tube integrity is maintained.

To complete its review of the inspection report, the U.S. Nuclear Regulatory Commission (NRC) staff requests the following additional information:

Vogtle, Unit 1, has recurring circumferential outside diameter stress corrosion cracking (ODSCC) at the hot leg top of tubesheet in the expansion transition. The 1R24 inspection report (Table 8) provides information about five tubes with ODS CC in the hot leg top of tubesheet expansion transition region. This topic has been the subject of a previous NRC staff Request for Additional Information (RAI) dated June 6, 2022 (ML22157A090). During the review of the previous 1R23 inspection report dated April 1, 2022 (ML22091A261), the NRC staff issued an RAI related to the depth of circumferential ODSCC associated with reliable eddy current detection. The SNC response dated July 19, 2023 (ML22200A301), indicated that the ODSCC detection and sizing was based on examination technique specification sheet (ETSS) 21410.1. In addition, the response stated a site-specific probability of detection (POD) function was developed using the Electric Power Research Institute (EPRI) MAPOD (model assisted probability of detection) Code. The RAI response also provided proprietary 50th percentile and 95th percentile maximum depth values of the POD curve from the MAPOD simulation.

During the review of the 1 R24 SG inspection report, the NRC staff compiled the hot leg expansion transition circumferential ODSCC maximum depths reported from 1Rl4 to 1R24. These maximum depths did not include data from look-back sizing, which would bias the detected depths in a nonconservative manner.

The NRC staff determined the approximate reported maximum depths where 50 percent of the cracks had been detected for three different cases: (1) all data from 1Rl4 through 1R24; (2) data from the more recent 1R20 to 1R24 outages; and (3) data from all inspections that had an inspection in the prior (N-1) refueling outage. The maximum depth where 50 percent of the cracks had been reported for each of these three cases was significantly greater than the proprietary 50th percentile depth provided in the 1R23 RAI response.

While the NRC staff understands that an empirically based analysis of a small dataset will result in a different outcome from a statistical model such as MAPOD, additional information is needed for the NRC staff to complete the review.

a) For the ETSS of interest, the site-specific POD function developed with MAPOD seems to be optimistic relative to the unit's historical probe performance for ODSCC at the hot leg expansion transition region. Please discuss what steps were taken during and after development of the POD function to ensure the results are reasonably consistent with probe performance.

GAE-NRCD-RF-LR-000002 NP-Attachment Rev. 0 Page 2 of9

• • • This record was final approved on 01 /17/2024 10:58:57. (This statement was added by the PRIME system upon its validation) to NL-24-0020 Westinghouse Non-Proprietary Class 3 b) Did the site-specific POD function developed for ETSS 21410.1 at the top of tubesheet expansion region receive a peer review? If so, please discuss the organization that performed the peer review and the scope of the peer review.

c) The 1R23 and 1R24 SG tube inspection reports indicate that enhanced probe inspections were performed of tubes with potentially increased susceptibility to degradation. Please specify if any of the tubes with stress corrosion cracking indications in 1R23 and 1R24 occurred in potentially high stress tubes (e.g., -2 sigma tubes).

GAE-NRCD-RF-LR-000002 NP-Attachment Rev. 0 Page 3 of 9

• • • This record was final approved on 01 /17/2024 10:58:57. (This statement was added by the PRIME system upon its validation) to NL-24-0020 Westinghouse Non-Proprietary Class 3 a) For the ETSS of interest, the site-specific POD function developed with MAPOD seems to be optimistic relative to the unit's historical probe performance for ODSCC at the hot leg expansion transition region.

Please discuss what steps were taken during and after development of the POD function to ensure the results are reasonably consistent with probe performance.

Response a:

In support of the 1 R24 SG Tube Inspection Report (Reference 1 ), a fully probabilistic whole bundle analysis was performed for circumferential ODSCC at the expansion transition. The analysis assessed the SG performance criteria for probability of burst (POB), probability of leakage (POL), burst pressure, and accident induced leakage performance criteria (AILPC) following the guidance of Revision 5 of the Electric Power Research Institute (EPRI) steam generator (SG) Integrity Assessment Guidelines (IAGL) (Reference 2). The operational assessment performed the forward-looking tube burst and leakage projections for 2 cycles. The next planned inspection for this degradation mechanism is 1R26 (Spring 2026).

The fully probabilistic full bundle analysis starts with development of the probability of detection (POD) distribution. For circumferential ODSCC at the hot leg expansion transition, the +POINT probe detection and sizing technique applied during inspections at Vogtle was examination technique specification sheet (ETSS) 21410.1.

A site-specific POD function for maximum flaw depth was developed using the EPRI MAPOD code (Reference 3). During development of the site-specific POD curve for maximum flaw depth, the +POINT probe detection voltage amplitude to true depth distribution regression (Ahat) were combined with the site-specific top of tubesheet expansion transition noise distribution. The Ahat data from ETSS 21410.1 includes true depths from both lab cracks and pulled tube data. In this way, the Vogtle Unit 1 specific POD distribution accounts for the regression of measured voltage amplitudes to true flaw max depth. The 1R24 noise was collected, processed, and compared with historical noise trends. In general, the noise levels at the top of tubesheet (TTS) have been consistent at Vogtle Unit 1. However, during the development of the POD curve, it was noted that the 1R21 hot leg (HL) TTS noise bounded the 1R24 noise. As an additional measure of conservatism, the 1R21 HL TTS noise was utilized.

Figure 1 provides the results of the Vogtle specific MAPOD simulation for circumferential ODSCC at tubesheet expansion transitions for maximum depth (MD). Based on the resulting POD curve from the MAPOD simulation, the 50th percentile MD is [

t The 95th percentile MD is [

t In order to ensure the POD curve is reasonably consistent with probe performance, a simulated inspection was performed, following methodology described by Section 8.3 of the EPRI SG IAGL (Reference 2). [

The POD curve is one input to the fully probabilistic operational assessment (OA) methodology. In order to ensure the POD curve is reasonably consistent with probe performance, the OA methodology is benchmarked. The benchmarking followed the methodology prescribed by Section 8.3 of the EPRI SG IAGL (Reference 2). Benchmarking of the fully probabilistic OA methods for this mechanism was completed by comparing OA simulation results from prior outages with actual detection results. The 1R23 I-cycle OA utilized the POD curve described above (Figure 1). The 1R24 prediction for detected depths, lengths, PDA, and quantities were compared to actual outage results from 1R24. It was found that [

GAE-NRCD-RF-LR-000002 NP-Attachment Rev. 0 Page 4 of9

• • • This record was final approved on 01 /17/2024 10:58:57. (This statement was added by the PRIME system upon its validation) to NL-24-0020 Westinghouse Non-Proprietary Class 3

]"'c The POD curve also affects the simulated quantity of flaws detected during the simulation. [

] a,c The benchmarking developed confidence that the overall OA process will accurately and conservatively predict future SG conditions.

The OA process (including the POD curve) will be benchmarked again at the next planned inspection. If the measured flaw depths are not reasonably represented by the 2-cycle simulation distributions of the 1R24 OA, the POD curve would be a good candidate for adjustment in the next OA.

GAE-NRCD-RF-LR-000002 NP-Attachment Rev. 0 Page 5 of9

• • • This record was final approved on 01 /17/2024 10:58:57. (This statement was added by the PRIME system upon its validation) to NL-24-0020 Westinghouse Non-Prop1ietaiy Class 3 Figure 1. ETSS 21410.1 Circumferential ODSCC POD Distribution for Maximum Depth GAE-NRCD-RF-LR-000002 NP-Attachment Rev. 0 Page 6 of9 a,b,c to NL-24-0020 Westinghouse Non-Proprietary Class 3 Figure 2. Max Depth Distribution for Circ. ODSCC at Expansion Transition - Reported vs Simulated GAE-NRCD-RF-LR-000002 NP-Attachment Rev. 0 Page 7 of 9

• • • This record was final approved on 01 /17/2024 10:58:57. (This statement was added by the PRIME system upon its validation) a,b,c to NL-24-0020 Westinghouse Non-Proprietary Class 3 b) Did the site-specific POD function developed for ETSS 21410.1 at the top of tubesheet expansion region receive a peer review? If so, please discuss the organization that performed the peer review and the scope of the peer review.

Response b: The site-specific POD and the overall OA methodology received independent verification by Westinghouse engineering. The Westinghouse independent verification scope included all of the elements of the POD, including the Ahat regression, noise distributions, MAPOD execution, and any follow-up work done to ensure the results are reasonably consistent with probe performance. Additionally, the final POD function was reviewed by SNC and the independent qualified data analyst (IQDA) to ensure it was reasonably consistent with probe performance. The POD function for circ. ODSCC at expansion transition described above [

]"*

0 The 1R23 180-day report RAI responses included description of this POD curve, which was reviewed and accepted by NRC staff in ML22220Al34 (Reference 4).

c) The 1R23 and 1R24 SG tube inspection reports indicate that enhanced probe inspections were performed of tubes with potentially increased susceptibility to degradation. Please specify if any of the tubes with stress corrosion cracking indications in 1R23 and 1R24 occurred in potentially high stress tubes (e.g., -2 sigma tubes).

Response c: No tubes with SCC indications in 1R23 or 1R24 occurred in potentially high stress tubes.

GAE-NRCD-RF-LR-000002 NP-Attachment Rev. 0 Page 8 of 9

• • • This record was final approved on 01 /17/2024 10:58:57. (This statement was added by the PRIME system upon its validation) to NL-24-0020 Westinghouse Non-Proprietary Class 3 References

1. Vogtle Electric Generating Plant, Unit 1, Refueling Outage 1 R24 Steam Generator Tube Inspection Report (ML23265A249), September 22, 2023.

2. Steam Generator Management Program: Steam Generator Integrity Assessment Guidelines, Revision 5. EPRI, Palo Alto, CA: 2021. 3002020909.

3. EPRI Computer Software 3002010334, "Steam Generator Management Program: Model Assisted Probability of Detection Using R (MAPOD-R) Version 2.1," 2017.

4. Nuclear Regulatory Commission

Document, ML22220Al34, "VOGTLE ELECTRIC GENERATING PLANT, UNIT 1 - REVIEW OF THE REFUELING OUTAGE 1R23 (FALL 2021) STEAM GENERATOR TUBE INSPECTION REPORT (EPID L-2022-LRO-0030),"

August 9, 2022.

GAE-NRCD-RF-LR-000002 NP-Attachment Rev. 0 Page 9 of9

• • • This record was final approved on 01/17/2024 10:58:57. (This statement was added by the PRIME system upon its validation)