NL-22-0549, Responses to NRC Request for Additional Information for Refueling Outage 1R23 Steam Generator Tube Inspection Report
| ML22200A301 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 07/19/2022 |
| From: | Joyce R Southern Nuclear Operating Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML22200A300 | List: |
| References | |
| NL-22-0549 | |
| Download: ML22200A301 (14) | |
Text
3535 Colonnade Parkway Birmingham, AL 35243 205
992 tel 205 992 7601 fax UPMR\FH@southernco.com NL-22-0549 July 1 , 2022 Docket No.:
50-424 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D. C. 20555-0001 Vogtle Electric Generating Plant - Unit 1 Responses to NRC Request for Additional Information for Refueling Outage 1R23 Steam Generator Tube Inspection Report Ladies and Gentlemen:
By letter dated April 1, 2022 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML22091A261), Southern Nuclear Operating Company (SNC) submitted information summarizing the results of the fall 2021 steam generator (SG) inspections performed at Vogtle Electric Generating Plant (Vogtle), Unit 1, during the twenty-third refueling outage (1R23).
After reviewing the report, the NRC staff requested response to the request for additional information (RAI) given below.
On May 27, 2022, the NRC staff provided a draft RAI question to SNC to make sure that the RAI was understandable, the regulatory basis was clear, to ensure there is no proprietary information, and to determine if the information was previously docketed. On June 6, 2022, a clarifying call was held and SNC stated that it would provide the RAI response within 45 days (July 21, 2022). to this letter provides the SNC Responses to the NRC Request for Additional Information for Refueling Outage 1R23 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.
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. 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-22-0549 Page 2 This letter contains no regulatory commitments. If you have any questions, please contact Amy Chamberlain at (205) 992-6361.
Respectfully submitted, 5\DQ-R\FH
/LFHQVLQJ0DQDJHU 50-/dsp/cbg
Enclosures:
- 1. Affidavit CAW-22-024 (Non-Proprietary) 2.
GAE-NRCD-RF-LR-000001 P-Attachment, Revision 0 (PROPRIETARY) 3.
GAE-NRCD-RF-LR-000001 NP-Attachment, Revision 0 (Non-Proprietary)
Cc: Regional Administrator, Region II NRR Project Manager - Vogtle 1 & 2 Senior Resident Inspector - Vogtle 1 & 2 RType: CVC7000 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 1R23 Steam Generator Tube Inspection Report Affidavit CAW-22-024 (Non-Proprietary)
- This record was final approved on 7/14/2022, 5:05:50 PM. (This statement was added by the PRIME system upon its validation)
Westinghouse Non-Proprietary Class 3 AFFIDAVIT CAW-22-024 Page 1 of 3 COMMONWEALTH OF PENNSYLVANIA:
COUNTY OF BUTLER:
(1)
I, Zachary S. Harper, 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-000001 P-Attachment, Revision 0, Vogtle Electric Generating Plant, Unit 1, Responses to Request for Additional Information for Refueling Outage 1R23 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.
(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 Westinghouses 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 to NL-22-0549
- This record was final approved on 7/14/2022, 5:05:50 PM. (This statement was added by the PRIME system upon its validation)
Westinghouse Non-Proprietary Class 3 AFFIDAVIT CAW-22-024 Page 2 of 3 others to use the information to meet NRC requirements for licensing documentation without purchasing the right to use the information.
(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.
(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 of lower-case letters (a) through (f) located as a superscript immediately following the brackets enclosing each item of to NL-22-0549
- This record was final approved on 7/14/2022, 5:05:50 PM. (This statement was added by the PRIME system upon its validation)
Westinghouse Non-Proprietary Class 3 AFFIDAVIT CAW-22-024 Page 3 of 3 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.
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: 7/14/2022 Zachary S. Harper, Manager Licensing Engineering
__________ to NL-22-0549
Vogtle Electric Generating Plant - Unit 1 Responses to NRC Request for Additional Information for Refueling Outage 1R23 Steam Generator Tube Inspection Report GAE-NRCD-RF-LR-000001 NP-Attachment, Revision 0 (Non-Proprietary)
- This record was final approved on 7/13/2022, 4:44:47 PM. (This statement was added by the PRIME system upon its validation)
Westinghouse Non-Proprietary Class 3
GAE-NRCD-RF-LR-000001 NP-Attachment Page 1 of 7
Rev. 0 Westinghouse Electric Company GAE-NRCD-RF-LR-000001 NP-Attachment Revision 0 Vogtle Electric Generating Plant, Unit 1 - Responses to NRC Request for Additional Information for Refueling Outage 1R23 Steam Generator Tube Inspection Report July 2022 Author:
David A. Suddaby*
Component Design and Management Programs Verifier:
Mitchell D. Krinock*
Component Design and Management Programs Reviewer:
Gary W. Whiteman*
Licensing Engineering Approved:
Robert S. Chappo, Jr.*, Manager Component Design and Management Programs
©2022 Westinghouse Electric Company LLC All Rights Reserved
- Electronically approved records are authenticated in the Electronic Document Management System. to NL-22-0549
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Westinghouse Non-Proprietary Class 3
GAE-NRCD-RF-LR-000001 NP-Attachment Page 2 of 7
Rev. 0 Vogtle Electric Generating Plant, Unit 1 - Responses to NRC Request for Additional Information for Refueling Outage 1R23 Steam Generator Tube Inspection Report REQUEST FOR ADDITIONAL INFORMATION (RAI)
By letter dated April 1, 2022 (Agencywide Documents Access and Management System (ADAMS)
Accession No. ML22091A261), Southern Nuclear Operating Company (SNC, the licensee) submitted information summarizing the results of the fall 2021 steam generator (SG) inspections performed at Vogtle Electric Generating Plant (Vogtle), Unit 1, during the twenty-third refueling outage (RFO) (1R23).
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. 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 NRC staff requests the following additional information:
- 1. Vogtle, Unit 1, has recurring circumferential outside diameter stress corrosion cracking (ODSCC) at the hot leg top of tubesheet in the expansion transition. The 1R23 inspection report (Table 6) provides information about eight tubes with ODSCC in the hot leg top of tubesheet region. Knowing the indication location, SNC reviewed previous inspection data to determine if an eddy current precursor signal was present. Review of previous inspection data is valuable since it helps with early recognition of ODSCC indications and informs growth rate estimates. Previously, a tube in Vogtle, Unit 1, SG 4, with circumferential ODSCC at the top of the tubesheet, was pulled from the SG in 2008 and destructively analyzed (ML100560265).
Comparison of the destructive analysis results to the eddy current analysis results confirmed the challenges related to detection of shallow stress corrosion cracking (SCC) cracks.
- a. Based on the information gained from eddy current analysis (including review of previous inspection data) and laboratory analysis of the pulled tube, please discuss the depth of circumferential ODSCC in the tubesheet expansion transition region that is associated with reliable detection.
- b. If arc length is included as an input for the operational assessment (OA) of circumferential ODSCC in the tubesheet expansion transition region, please discuss how the OA accounts for the differences that were previously observed between destructive analysis results and eddy current measurements.
Response 1a:
In support of the 1R23 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 4 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 1 and 2 cycles. The next planned inspection for this degradation mechanism is 1R24 (Spring 2023).
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 to NL-22-0549
- This record was final approved on 7/13/2022, 4:44:47 PM. (This statement was added by the PRIME system upon its validation)
Westinghouse Non-Proprietary Class 3
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Rev. 0 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 4). The MAPOD model combines the +POINT probe detection voltage amplitude to true depth distribution correlation (Ahat) with the site-specific top of tubesheet expansion transition noise distribution to generate a site-specific noise-based POD curve for maximum flaw depth.
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 correlation of measured voltage amplitudes to true flaw max depth. Figure 1 provides the results of the Vogtle specific MAPOD simulation for circumferential ODSCC at tubesheet expansion transitions for maximum depth. Based on the resulting POD curve from the MAPOD simulation, the 50th percentile maximum depth is [
]b. The 95th percentile maximum depth is [
]b.
A review was performed of the Vogtle Unit 1 database of reanalyzed circumferential ODSCC flaws at the expansion transition. These data are primarily from the A600TT Feasibility Study (Reference 3),
supplemented with the 1R23 flaws. Figure 2 shows the population of flaw maximum depths that have been detected by the +Point probe and sized using ETSS 21410.1. The counts include lookback sizing, where the flaw was detectable within the historical data available.. The majority of the circumferential ODSCC flaws detected in the Vogtle Unit 1 expansion transition were sized between 70-80% TW. This is reasonable because this flaw size is readily detectable (>95th percentile of the POD curve). However, there is also a large population of flaws <40%TW; showing that the +Point probe is able to detect flaws sized at 20-40%TW maximum depth at Vogtle Unit 1.
A circumferential ODSCC flaw was analyzed in a pulled tube report (Reference 5). The flaw was detected at 1R14 (2008) in SG4 R12C98. The laboratory eddy current test (ECT) and destructive examination for this flaw indicate that shallow portions of the crack (i.e., <40%TW) were not reported (Table 3-1 in combination with Figure 9-18 of Reference 5). There is some indication in the ECT graphics (Figure 3-10 through Figure 3-13 of Reference 5) that the shallow components of the crack are present but may be below the noise threshold for this particular location. The laboratory ECT was performed with an older analog tester, which tended to have elevated noise levels compared to the modern digital testers.
The factors that contribute to flaw detection in the field at Vogtle Unit 1 are generally unchanged since the 2008 inspection when the tube was pulled. The same or similar equipment and ECT setups are currently being used in the field. The primary driver for noise is the geometry of the expansion transition, which is unique to each tube, but consistent between inspections. As previously mentioned, the tester can also be a source of noise; with Vogtle Unit 1 utilizing the modern digital tester in the field during the 2008 and subsequent inspections. Therefore, the overall signal-to-noise ratios for circumferential flaws at the expansion transition should be consistent at Vogtle Unit 1 for the +Point probe. Site-specific technique qualifications are performed prior to each outage to ensure Vogtle Unit 1 noise levels are less than those measured in the ETSS 21410.1 qualification data sets.
As noted above, the geometry conditions and ability for the probe to detect flaws in the field are generally unchanged since 2008, with detection of specific depths being dependent on signal-to-noise at a flaw location. However, there have been improvements in the ECT data analysis techniques that have improved SCC reportability since 2008. Recent EPRI guidance (Reference 6) provides information about analyst training on complex signals, historical data review procedures, and guidance on deletion of reported indications of degradation. The guidance has led to updates to the site-specific performance demonstration, which have increased analyst sensitivity to SCC. As a result, there has been a general increase in reporting of SCC at Vogtle Unit 1, which often results in reporting of shallow cracking because they are identified soon after initiation.
to NL-22-0549
- This record was final approved on 7/13/2022, 4:44:47 PM. (This statement was added by the PRIME system upon its validation) to NL-22-0549
- This record was final approved on 7/13/2022, 4:44:47 PM. (This statement was added by the PRIME system upon its validation)
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Rev. 0
Figure 2. Vogtle Unit 1 Circ. ODSCC at Expansion Transition Flaw Max Depth Distribution Response 1b:
In support of the 1R23 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 POB, POL, burst pressure, and AILPC following the guidance of Revision 4 of the EPRI SG IAGL (Reference 2). The operational assessment performed the forward-looking tube burst and leakage projections for 1 and 2 cycles. The next planned inspection for this degradation mechanism is 1R24 (Spring 2023).
The beginning of cycle (BOC) undetected flaw total length is an input to the fully probabilistic OA. The BOC undetected flaw total length was derived from [
]a Figure 3 provides the simulated total length distribution for assumed undetected flaws at BOC.
Indication length growth was applied to the BOC undetected length distribution and flaws initiated during the OA duration. Additionally, benchmarking was performed by comparing OA simulation results for prior outages with actual detection results. The predicted end of cycle (EOC) depths, lengths, percent degraded area, and quantities were compared to actual outage results. It was found that the measured flaw lengths are well bounded by the predicted EOC distributions (including the peak flaw versus the worst-case prediction distribution). This benchmarking developed confidence that the simulation process can accurately and conservatively predict future SG conditions. to NL-22-0549
- This record was final approved on 7/13/2022, 4:44:47 PM. (This statement was added by the PRIME system upon its validation)
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Rev. 0 Figure 3. Circ. ODSCC at Expansion Transition Flaw BOC Total Length Distributions a,b to NL-22-0549
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Rev. 0 References
- 1. Vogtle Electric Generating Plant, Unit 1, Refueling Outage 1R23 Steam Generator Tube Inspection Report (ML22091A261), April 1, 2022.
- 2. Steam Generator Management Program: Steam Generator Integrity Assessment Guidelines, Revision 4. EPRI, Palo Alto, CA: 2016. 3002007571.
- 3. Steam Generator Management Program: Feasibility Study for Multi-Cycle 600TT Operational Assessments. EPRI, Palo Alto, CA: 2020. 3002018258.
- 4. EPRI Computer Software 3002010334, Steam Generator Management Program: Model Assisted Probability of Detection Using R (MAPOD-R) Version 2.1, 2017.
- 5. Supplement to 1R14 Steam Generator Inspection Report - Tube Pull Examination Results,, ML100560268
- 6. Steam Generator Management Program, SGMP-20-11, Information Pertaining to Recent Stress Corrosion Cracking Located Within A600TT Tubing and Action Items in Support of TSTF-577, EPRI, Palo Alto, CA: 2020. to NL-22-0549