ML25132A310
| ML25132A310 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  (DPR-051, NPF-006) |
| Issue date: | 05/12/2025 |
| From: | Dennis Galvin Plant Licensing Branch IV |
| To: | Keele R Entergy Operations |
| Galvin, Dennis | |
| References | |
| EPID L-2025-LLR-0002 | |
| Download: ML25132A310 (5) | |
Text
From:
Dennis Galvin To:
Riley Keele, Jr. (rkeele@entergy.com)
Cc:
Couture III, Philip; Clark, Robert; Tony Nakanishi
Subject:
Arkansas Nuclear One, Units 1 and 2 - Request for Additional Information - Alternative Requests ANO1-ISI-24-02 and ANO2-ISI-24-02 Related to Pressurizer Weld Examination (EPID L-2025-LLA-0002)
Date:
Monday, May 12, 2025 4:54:00 PM Attachments:
L-2025-LLR-0002 2025-05-12 ANO PA Pressurizer Welds - RAI Issued.pdf
Dear Mr. Keele,
By letter dated January 13, 2025 (Agencywide Documents and Access Management System (ADAMS) Accession No. ML25013A293), Entergy Operations, Inc. (Entergy, the licensee) requested approval of proposed alternatives for Arkansas Nuclear One Units 1 and 2 (ANO-1 and ANO-2, respectively). Specifically, the proposed Alternative Requests ANO1-ISI-24-02 and ANO2-ISI-24-02 are related to alternative examination of pressurizer welds under Examination Category B-B, Item Numbers B2.11 and B2.12, and Examination Category B-D, Item Number B3.110 of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI, Table IWB-2500-1.
The Nuclear Regulatory Commission (NRC) staff reviewed the submittal and determined that additional information is required for the staff to complete its review of the application.
The requests for additional information (RAIs) were transmitted to the licensee in draft form on May 8, 2025. On May 12, 2025, you indicated that a clarification call was not needed and that you could respond in 45 days, or June 26, 2025. The NRC staff agrees with this date.
Sincerely,
Dennis Galvin Project Manager / Agency 2.206 Petition Coordinator U.S. Nuclear Regulatory Commission Office of Nuclear Reactor Regulation Division of Operating Reactor Licensing Plant Licensing Branch IV 301-415-6256
REQUEST FOR ADDITIONAL INFORMATION ALTERNATIVE REQUESTS ANO1-ISI-24-02 AND ANO2-ISI-24-02 RELATED TO PRESSURIZER WELD EXAMINATION ENTERGY OPERATIONS INC.
ARKANSAS NUCLEAR ONE UNIT NOS. 1 AND 2 DOCKET NOS. 50-313 AND 50-368 1.0 Introduction By letter dated January 13, 2025 (Agencywide Documents and Access Management System (ADAMS) Accession No. ML25013A293), Entergy Operations, Inc. (Entergy, the licensee) requested approval of proposed alternatives for Arkansas Nuclear One Units 1 and 2 (ANO-1 and ANO-2, respectively). Specifically, the proposed Alternative Requests ANO1-ISI-24-02 and ANO2-ISI-24-02 are related to alternative examination of pressurizer welds under Examination Category B-B, Item Numbers B2.11 and B2.12, and Examination Category B-D, Item Number B3.110 of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI, Table IWB-2500-1.
2.0 Regulatory Basis The pressurizer pressure-retaining welds and nozzles are ASME Code Class 1 components, with Inservice Inspections (ISIs) performed in accordance with the applicable edition of Section XI, of ASME Code as required by 10 CFR 50.55a(g). The regulations in 10 CFR 50.55a(g)(4) state, in part, components that are classified as ASME Code Class 1, 2, and 3 must meet the requirements, except the design and access provisions and the preservice examination requirements, set forth in the ASME Code,Section XI, to the extent practical within the limitations of design, geometry, and materials of construction of the components. The regulations in 10 CFR 50.55a(z) state, in part, that alternatives to the requirements in paragraphs (b) through (h) of 10 CFR 50.55a may be used when authorized by the NRC if the licensee demonstrates that: (1) the proposed alternative would provide an acceptable level of quality and safety, or (2) compliance with the specified requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
To complete its review, the U.S. Nuclear Regulatory Commission (NRC) staff requests for additional information.
3.0 Request for Additional Information
RAI-01
Background
The proposed alternative references probabilistic fracture mechanics (PFM) to support the deferral of the pressurizer weld ISI examinations. The NRC staff notes that leveraging PFM
2 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 pressurizer 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 pressurizer welds.
The NRC staff has determined that, when considering the proposed deferral of examinations, adequate performance monitoring through inspections is needed to ensure that the assumptions of the PFM model remain valid, and that novel or unexpected degradation is detected and dispositioned in a timely fashion. Further, the NRC staff has communicated concepts that licensees can implement on a fleet-wide basis to develop a performance monitoring plan and bolster the technical basis for alternative requests (see presentation slide packages dated January 30, 2023, and April 27, 2023, at ML23033A667 and ML23114A034, respectively). In its public meeting on June 27, 2024, the NRC staff discussed its position regarding the need for adequate performance monitoring of components as part of the risk-informed materials assessment project (ML24193A005).
The staffs position is that the number of welds that are proposed to be examined and the required number of welds to be examined for the ISI intervals should have been converted to the pressurizer Equivalent that would result in inspections of at least 25% of the number of pressurizers required to be inspected by the ASME Code. The examples of an adequate inspection sample size based on similar alternative requests that the staff has approved in the past are documented in NRC safety evaluations such as ML23256A088 and ML24179A326, respectively. The NRC staff noted that although the referenced submittals are related to the steam generator weld examinations, the concept of the 25% sample examination is the same as for the pressurizer weld examinations.
To address performance monitoring, Section 5.1.6 of the proposed alternatives state that ANO-1 has performed five examinations on a total population of ten components in the current fifth 10-year ISI interval as discussed in Enclosure, Attachment 1 of the proposed alternatives. The licensee stated that ANO-1 has performed 50% of the pressurizer weld examinations in the current fifth 10-year ISI. Section 5.1.6 further states that ANO-2 has performed one examination on a total population of seven components in the current fifth 10-year ISI interval as discussed in Enclosure, Attachment 2. Section 5.1.6 explains that ANO-2 is scheduled to examine weld 05-002 during the sixth 10-year ISI interval, third period, as shown in Enclosure, Attachment 6.
The NRC staff noted that for the ASME B-B and B-D Examination Category, ANO-1 has examined 5 out of 10 (50%) of its of weld population in the fifth ISI interval, and ANO-2 has examined only 1 of the 7 (~14%) of its weld population in the fifth ISI interval, plus a commitment to exam one more weld in the sixth ISI interval, equating to ~28% weld examination across fifth and sixth intervals for ANO-2. The weld population of ANO-1 and ANO-2 may be combined to determine the minimum number of examinations necessary for adequate performance monitoring. ANO-1 and ANO-2 pressurizers are fabricated using similar low-alloy steels, utilizing ASME qualified weld material and welding techniques, therefore the weld examinations for ANO-1 and ANO-2 can be combined for a sample population. The ASME Code requirement is that during an inservice inspection interval for one pressurizer, 100% of the welds as specified in the Code be inspected. Given that ANO-1 and ANO-2 are distinct pressurizers, and the alternative extends across the fifth and sixth interval, the ASME Code requirement mandates examination of pressurizers over the fifth and sixth ISI intervals at ANO-1 and ANO-2, equating to four total pressurizer examinations. The staff position is that licensees are permitted
3 to inspect 25% of the total pressurizer examination, which equates to inspecting one pressurizer across both ISI intervals for ANO-1 and ANO-2.
Based on the information in Section 5.1.6 of the proposed alternatives, the staff determined that the number of proposed inspections would be less than the staffs position of 25% of the total Code-required pressurizer examinations (the equivalent of 100% of one pressurizer, i.e., = 1 Pressurizer Equivalent) required to be conducted over the duration of the requested alternatives at ANO-1 and ANO-2. The equivalent total inspected sample size across ANO-1 (50%) and ANO-2 (~28%) over the 5th and 6th ISI interval is currently committed to inspect only a total of seven welds, which is equivalent to 0.78 of 1 Pressurizer Equivalent, which does not meet the staff position of 1 Pressurizer Equivalent.
Requests (a) Provide a technical justification describing the minimum sample size, utilizing calculations for a number of examinations greater than or equal to 1 Pressurizer Equivalent according to the staff position, or other methodology as least as conservative as the staff position, in the proposed performance monitoring plan that is necessary to provide a 25% or greater sampling of the entire population of pressurizer welds. Include a description of how the sample size is consistent with, or if using a different methodology, at least as conservative as, the documented staff position for acceptable levels of performance monitoring demonstrated by the above NRC-approved precedents.
(b) Explain how the proposed 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.
RAI-02
Background
If through the proposed performance monitoring, indications are detected in subject pressurizer welds that exceed the acceptance standards of the ASME Code,Section XI, IWB-3500, scope expansion may be appropriate to assess extent of condition. Furthermore, if this performance monitoring plan or industry-wide operating experience indicates that a new or novel degradation mechanism is possible in pressurizer welds, scope expansion may be appropriate to ensure that no such mechanism is occurring in the subject plants. Section 5.1.6 of the proposed alternatives discuss the additional examinations if unacceptable indications are detected in the ANO pressurizer welds. However, Section 5.1.6 does not mention the sample expansion beyond the reactor unit in question. Examples of previously approved inspection sample expansion scope beyond the reactor unit in question can be found in the following references (1). Duke Energy response to staffs RAI-1 (c) and (d) in its letter dated July 20, 2023 (ML23201A140), (2) NRC safety evaluation for Duke Energy fleet (ML23256A088), (3). NRC safety evaluation for Vogtle nuclear plant (ML20352A155), and (4) NRC safety evaluation for Constellation fleet (ML24179A326). These examples are related to steam generator weld examinations, but the additional examination strategy is applicable to the pressurizer weld examination at ANO-1 and ANO-2.
4 Request Clarify whether the licensee intends to perform additional examinations of the pressurizer welds beyond the reactor unit where unexpected degradation was found as part of the proposed alternative examination schedules. If the licensee does intend to expand scope to other reactor units, describe the timing and number of additional examinations. If the licensee does not intend to expand scope of inspection to other reactor units, provide justification on how the proposed alternative requests address extent of condition for unexpected degradation.
RAI-03
Background
Enclosure, Attachment 1, ANO-1 Plant-Specific Applicability. of the proposed alternatives provide Table 1-3, ANO-1 Inspection History. This table details the previous inspections that ANO-1 received for the relevant ASME Code Class 1, Examination Categories B-B and B-D components. The NRC staff noted that two different ASME Item numbers are assigned to the same weld Component Item in Table 1-3. For example, for Component ID 05-002, row 6 indicates Item No. B2.11, whereas row 7 indicates B2.12. For Component ID 05-012, row 11 indicates Item No. B2.12, whereas row 12 indicates B3.110.
Request(s)
Please clarify the (a) ASME Examination Category and (b) the ASME item for Component IDs05-002 and 05-012 in row 6/row 7 and row 11/row 12 of Table 1-3 in Attachment 1.
RAI-04
Background
Enclosure, Attachment 1, ANO-1 Plant-Specific Applicability, provides Table 1-3 titled ANO-1 Inspection History. This table details the previous inspections that ANO-1 received for the relevant ASME Code Class 1, B-B and B-D ASME category components. The item contained in row 18, Item No.: B3.110, Component ID: 05-021, Exam Date: 4/28/2007, interval/Period/Outage: 3rd/3rd/1R20, includes an inspection coverage of < 90%.
Request Please clarify if the examination coverage was > 90%, or if it was < 90%. If the coverage was
< 90%, please provide how much coverage was achieved during the inspection of the item found in row 18 of Table 1-3 in Attachment 1.