ML23018A164
| ML23018A164 | |
| Person / Time | |
|---|---|
| Site: | Surry  |
| Issue date: | 01/17/2023 |
| From: | John Klos Plant Licensing Branch II |
| To: | Geoffrey Miller Dominion Energy Co |
| Klos, J | |
| References | |
| Download: ML23018A164 (1) | |
Text
John Klos From: John Klos Sent: Tuesday, January 17, 2023 2:35 PM To: gary.d.miller@dominionenergy.com Cc: John Klos
Subject:
Formal issuance of RAIs for Surry ISI alternative for SG Welds, 30 day calendar response period Importance: High
- Gary, By letter dated November 17, 2022 (Agencywide Document Access and Management System Accession Number ML22322A158), Virginia Electric and Power Company (the licensee) submitted to the United States Nuclear Regulatory Commission (NRC), a proposed alternative to the inservice inspection (ISI) requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code) of the pressurizer (PZR) and steam generator (SG) welds of Surry Power Station (SPS), Units 1 and 2.
The NRC staff needs additional information to complete its review and approval of the licensees submittal.
These requests for additional information (RAIs) are now released formally with a 30-day calendar response period; thereby, these RAIs are due on Friday February 17, 2023.
Specifically, pursuant to Title 10 of the Code of Federal Regulations, Part 50, Section 55a, Paragraph (z)(1)
(10 CFR 50.55a(z)(1)), the licensee is proposing to increase the ISI interval for the PZR and SG welds of SPS, Units 1 and 2, from the current ASME Code,Section XI 10-year requirements by deferring the PZR and SG examinations for the following:
For SPS Unit 1, PZR and SGs: through the sixth 10-year ISI interval, and For SPS Unit 2, PZR and SGs, for the remainder of the third period of the fifth 10-year ISI interval through the sixth 10-year ISI interval The licensee referred to the results of the probabilistic fracture mechanics (PFM) analyses in the following Electric Power Research Institute (EPRI) non-proprietary reports as the primary basis for the deferral of the ISI examinations:
EPRI Technical Report 3002015905, Technical Bases for Inspection Requirements for PWR [Pressurized Water Reactor] Pressurizer Head, Shell-to-Head, and Nozzle-to-Vessel Welds, 2019 (hereinafter referred to as EPRI report 15905, ADAMS Accession No. ML21021A271).
EPRI Technical Report 3002015906, Technical Bases for Inspection Requirements for PWR Steam Generator Class 1 Nozzle-to-Vessel Welds and Class 1 and Class 2 Vessel Head, Shell, Tubesheet-to-Head and Tubesheet-to-Shell Welds, 2019 (hereinafter referred to as EPRI report 15906, ADAMS Accession No. ML20225A141).
EPRI Technical Report 3002014590, Technical Bases for Inspection Requirements for PWR Steam Generator Class 1 Feedwater and Main Steam Nozzle-to-Shell Welds and Nozzle Inside Radius Sections, 2019 (hereinafter referred to as EPRI report 14590, ADAMS Accession No. ML19347B107).
Regulatory Basis 1
The NRC has established requirements in 10 CFR Part 50 to protect the structural integrity of structures and components in nuclear power plants. Among these requirements are the ISI requirements of Section XI of the ASME Code incorporated by reference in 10 CFR 50.55a to ensure that adequate structural integrity of PZR and SG vessels (including their welds) is maintained through the service life of the vessels. Therefore, the regulatory basis for the following requests for additional information (RAIs) has to do with demonstrating that the proposed alternative ISI requirements would ensure adequate structural integrity of the PZR and SG welds of SPS, Units 1 and 2, and thereby would provide an acceptable level of quality and safety per 10 CFR 50.55a(z)(1) for the welds.
RAI-1
Issue The licensee referenced probabilistic and deterministic analyses in the above EPRI reports to estimate potential fatigue growth in the subject PZR and SG welds. The licensee presented plant-specific information to demonstrate that the referenced analyses in the EPRI reports would bound the subject PZR and SG welds, including high-level results from previous ISI of the welds. The licensee also provided limited discussion of performance monitoring, primarily focused on justifying application of the EPRI analyses to the proposed ISI interval extension for the subject PZR and SG welds (i.e., that leakage would be detected).
Leveraging PFM analyses to define the basis for risk-informing inspection requirements requires knowledge of both the current and future behavior of the material degradation and the associated uncertainties applicable to the subject PZR and SG welds. Confidence in the results of these analyses hinges on the assurance that the PFM model adequately represents, and will continue to represent, the degradation behavior in the subject PZR and SG welds. The NRC staff has determined that, when considering extended examination intervals, adequate performance monitoring through inspections is needed to ensure that the PFM model continues to predict the material behavior and that novel or unexpected degradation is detected and dispositioned in a timely fashion.
In Section 5.0 of the submittal, the licensee stated SPS, Units 1 and 2, are currently in the third period of the fifth 10-year ISI interval. Unit 1 will have completed the required fifth interval ISI examinations of the PZR and SGs at the time of the approval of this request. The ISI examinations of the Unit 2 PZR and SGs for the third period, fifth interval will not be completed by the requested approval date for the proposed alternative.
The proposed alternative is to increase the inspection interval for these examination items from the current ASME Code Section XI 10-year requirement by deferring the PZR and SG examinations for the following:
For SPS Unit 1, PZR and SGs: through the sixth 10-year ISI interval, and For SPS Unit 2, PZR and SGs, for the remainder of the third period of the fifth 10-year ISI interval through the sixth 10-year ISI interval.
The staff noted that some of the PZR and SGs components in SPS, Unit 2, addressed in the licensees proposed alternative will be in operation for more than 20 years without inspections, but no performance monitoring scheme was provided for these components.
The licensee also discusses the system leakage test as providing further assurance of safety for the proposed alternative. However, the NRC staff notes that the visual examinations performed during system leakage tests may not provide sufficient information to ensure that the PFM model continues to predict the material behavior and that emergent degradation is discovered and dispositioned in a timely fashion. Specifically, visual examinations may not directly detect pertinent integrity conditions (e.g., presence or extent of degradation); may not provide direct detection of aging effects prior to potential loss of structure or intended function; and do not provide sufficient validating data necessary to confirm the modeling of degradation behavior in the subject PZR and SG welds.
Request 2
- 1) Identify the PZR and SGs components in SPS, Unit 2, as requested in the proposed alternative for deferral of the examination requirements for the remainder of the third period of the fifth 10-year ISI interval through the sixth 10 year ISI interval, that would result in the components being in operation for more than 20 years without inspections.
a) Describe the performance monitoring that will be implemented with this proposed alternative to ensure that the PFM model adequately represents, and will continue to represent, the degradation behavior in the subject components commensurate with the duration of the requested alternative (i.e., plant-specific end date).
b) Explain how this performance monitoring will provide, over the extended examination interval, (1) direct evidence of the presence and extent of degradation, (2) validation and confirmation of the continued adequacy of the PFM model; and (3) timely detection of novel or unexpected degradation.
c) If through this performance monitoring, indications are detected that exceed the acceptance standards of ASME Code,Section XI, IWB-3500, confirm that they will be evaluated as required by ASME Code,Section XI (which includes requirements for successive inspections and additional examinations) and describe other actions (if any) that may be taken in the plant's corrective action program to ensure that the integrity of the component is adequately maintained.
RAI-2
Issue In Section 5.0 of the submittal, the licensee stated SPS, Units 1 and 2, are currently in the third period of the fifth 10-year ISI interval. Unit 1 will have completed the required fifth interval ISI examinations of the PZR and SGs at the time of the approval of this request. The ISI examinations of the Unit 2 PZR and SGs for the third period, fifth interval will not be completed by the requested approval date for the proposed alternative.
The proposed alternative is to increase the inspection interval for these examination items from the current ASME Code Section XI 10-year requirement by deferring the PZR and SG examinations for the following:
For SPS Unit 1, PZR and SGs: through the sixth 10-year ISI interval, and For SPS Unit 2, PZR and SGs, for the remainder of the third period of the fifth 10-year ISI interval through the sixth 10-year ISI interval.
Since Unit 1 did not complete the required fifth interval ISI examinations of the PZR and SGs at the time of the submittal, the staff was not able to consider these inspection results during its review. However, the staff noted in its submittal, the licensee did not explain the actions it would take to verify the validity and applicability of the PFM analyses in the EPRI reports cited in its proposed alternative based on the potential for indications and/or flaws for the upcoming required fifth interval ISI examinations of the PZR and SGs for Unit 1.
Request
- 1. Identify the PZR and SG components at Unit 1 in the scope of the proposed alternative that will be inspected prior to end of the fifth 10-year ISI interval.
- 2. For these components, discuss the process that will be used to verify the validity and applicability of the PFM analyses in the EPRI reports cited in its proposed alternative should indications and/or flaws be identified during the upcoming required fifth interval ISI examinations of the Unit 1 PZR and SGs
RAI-3
Issue Section 9 of the EPRI reports for the respective components provide criteria that must be met for the report results to be applied to a specific PWR plant. One such criterion from these EPRI reports indicate that the materials of the components must be low-alloy ferritic steels that conform to the requirements of ASME Code,Section XI, Appendix G, Paragraph G-2110.
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The 2019 edition of ASME Code,Section XI, Appendix G, Paragraph G-2110 indicates that Figure G-2210-1 (Figure G-2210-1M) is based on specimens of SA-533 Grade B Class 1, and SA-508-1, SA-508-2, and SA-508-3 steel. It further indicates that Figure G-2210-1 (Figure G-2210-1M) may be used for:
- 1) ferritic steels that meet the requirements of NB-2331 and have a specified minimum yield strength at room temperature of 50 ksi (350 MPa) or less, or
- 2) materials in Table G-2110-1 that meet the requirements of NB-2331.
The staff noted fabrication materials for some of the SG and PZR components addressed in the licensees proposed alternative are not specifically addressed in ASME Code Section XI, Appendix G, Paragraph G-2110 for development of Figure G-2210-1. Table A1 of Attachment 1 to the licensees submittal indicates the following:
o The SPS, Units 1 and 2, PZR upper and lower heads and nozzles are fabricated from SA-216, Grade WCC, cast carbon steel material. The PZR shells are fabricated of SA-302, grade B, carbon steel material.
o The SPS, Units 1 and 2, SG lower heads are fabricated of SA-216, Grade WCC, carbon steel. The tubesheets are fabricated of SA-508, Class 2a material. The SG lower shells are fabricated of SA-533, Grade A, Class 2 material.
o The SPS, Units 1 and 2, SG vessel upper heads and shells are fabricated of SA-533, Grade A, Class 1 material.
o The material for the upper head and shell material is SA-533, Grade A, Class 1.
For these materials, the licensees proposed alternative did not sufficiently address the information necessary to demonstrate conformance to ASME Code Section XI, Appendix G, Paragraph G-2110.
Request For the materials in the licensees proposed alternative that are not explicitly addressed in ASME Code Section XI, Appendix G, Paragraph G-2110 for development of Figure G-2210-1, provide sufficient justification to demonstrate the following :
(1) the requirements of NB-2331 are met and (2) have a specified minimum yield strength at room temperature of 50 ksi (350 MPa) or less, if the material is not identified in Table G-2110-1 of ASME Code Section XI, Appendix G.
Thanks in advance, John Klos DORL Mcguire, Surry Licensing Project Manager U.S. NRC, Office of Nuclear Reactor Regulation (NRR),
Division of Operating Reactor Licensing (DORL),
NRC/NRR/DORL/LPL2-1, MS O9E3 Washington, DC 20555-0001 301.415.5136, John.Klos@NRC.gov 4