ML24194A022
| ML24194A022 | |
| Person / Time | |
|---|---|
| Site: | Byron, Braidwood  |
| Issue date: | 07/22/2024 |
| From: | Jeffrey Whited Plant Licensing Branch III |
| To: | Rhoades D Exelon Generation Co |
| Wiebe J | |
| References | |
| EPID L-2023-LLR-0062 | |
| Download: ML24194A022 (1) | |
Text
July 22, 2024 David P. Rhoades Senior Vice President Constellation Energy Generation, LLC President and Chief Nuclear Officer Constellation Nuclear 4300 Winfield Road Warrenville, IL 60555
SUBJECT:
BRAIDWOOD STATION, UNITS 1 AND 2; AND BYRON STATION, UNIT NOS. 1 AND 2 - ISSUANCE OF RELIEF RE: PROPOSED ALTERNATIVE REQUEST ASSOCIATED WITH PRESSURIZER EXAMINATIONS (EPID L-2023-LLR-0062)
Dear David Rhoades:
By letter dated November 1, 2023 (Agencywide Documents Access and Management System Accession Nos. ML23305A069), as supplemented by letter dated March 22, 2024 (ML24082A185), Constellation Energy Generation, LLC (the licensee), submitted requests for the Braidwood Station, Units 1 and 2 (Braidwood), and Byron Station, Units 1 and 2 (Byron), to the U.S. Nuclear Regulatory Commission (NRC or Commission) for proposed alternatives to certain requirements of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (BPV) Code (ASME Code),Section XI.
Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR),
paragraph 50.55a(z)(1), Acceptable level of quality and safety, the licensee proposed to defer the ASME Code,Section XI, inspection requirements pertaining to pressurizer welds from the current 10-year requirement to the end of the currently licensed operating periods of the subject units. The regulation in 10 CFR 50.55a(z)(1) requires the licensee to demonstrate that the proposed alternatives provide an acceptable level of quality and safety.
The proposed alternatives are based probabilistic fracture mechanics and a proposed performance monitoring plan. The licensee requested to use the proposed alternative I4R-15, Revision 1, for Braidwood, and I4R-21, Revision 1, for Byron. These proposed alternatives concern pressurizer circumferential and longitudinal shell-to-head welds and nozzle-to-vessel welds examinations. In the March 22, 2024, supplement letter, the licensee stated that the proposed performance monitoring plan has been modified to ensure that a sample of at least 25 percent of the ASME Code required examinations are conducted, and that the duration of the proposed alternative is being revised from the fifth inservice inspection interval to the end of the current operating licenses for Braidwood and Byron.
The NRC staff has reviewed the subject request and concludes, as set forth in the enclosed safety evaluation, that the licensee has adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a(z)(1). Therefore, the NRC staff authorizes the use of proposed alternatives I4R-15, Revision 1, for Braidwood, and I4R-21, Revision 1, for Byron.
All other ASME BPV Code,Section XI, requirements for which relief was not specifically requested and approved remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
If you have any questions, please contact the Senior Project Manager, Scott Wall, at 301-415-2855 or e-mail at Scott.Wall@nrc.gov.
Sincerely, Jeffrey A. Whited, Chief Plant Licensing Branch III Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. STN 50-456, STN 50-457, STN 50-454, and STN 50-455
Enclosure:
Safety Evaluation cc: Listserv Jeffrey A.
Whited Digitally signed by Jeffrey A. Whited Date: 2024.07.22 12:49:36 -04'00'
Enclosure SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION REQUESTS FOR ALTERNATIVE REGARDING INSPECTION INTERVAL EXTENSION FOR PRESSURIZER WELDS CONSTELLATION ENERGY GENERATION, LLC BRAIDWOOD STATION, UNITS 1 AND 2 BYRON STATION, UNIT NOS. 1 AND 2 DOCKET NOS. STN 50-456, STN 50-457, STN 50-454, AND STN 50-455 INTRODUCTION By letter dated November 1, 2023 (Agencywide Documents Access and Management System Accession Nos. ML23305A069), as supplemented by letter dated March 22, 2024 (ML24082A185), Constellation Energy Generation, LLC (the licensee or CEG), submitted requests for the Braidwood Station, Units 1 and 2 (Braidwood), and Byron Station, Unit Nos. 1 and 2 (Byron), to the U.S. Nuclear Regulatory Commission (NRC or Commission) for proposed alternatives to certain requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI.
Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR), paragraph 50.55a(z)(1), Acceptable level of quality and safety, the licensee proposed to defer the ASME Code,Section XI, inspection requirements pertaining to pressurizer (PZR) welds from the current 10-year requirement to the end of the currently licensed operating periods of the subject units. The licensee requested to use the proposed alternative I4R-15, Revision 1, for Braidwood, and I4R-21, Revision 1, for Byron. These proposed alternatives concern PZR circumferential and longitudinal shell-to-head welds and nozzle-to-vessel welds examinations and are based on probabilistic fracture mechanics (PFM) and a proposed performance monitoring plan. In the March 22, 2024, supplement letter, the licensee stated that the proposed performance monitoring plan has been modified to ensure that a sample of at least 25 percent of the ASME Code required examinations are conducted, and that the duration of the proposed alternative is being revised from the fifth inservice inspection (ISI) interval to the end of the current operating licenses for Braidwood and Byron.
2.0 REGULATORY EVALUATION
The PZR pressure-retaining welds at the subject CEG units are ASME Code Class 1 components, whose ISIs are performed in accordance with the applicable edition of Section XI, Rules for Inservice Inspection of Nuclear Power Plant Components, of the ASME Code, as required by 10 CFR 50.55a(g).
The regulations in 10 CFR 50.55a(g)(4) state, in part, that 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.
3.0 TECHNICAL EVALUATION
3.1 Licensee's Proposed Alternative
=
Applicable Code Edition and Addenda===
The current ISI interval and associated codes of record for the subject plants are summarized in Table 1.
Table 1: Section XI Codes of Record for Subject Plants Plant Interval Current Edition and Addenda Interval Start1 Interval End1 Braidwood Fourth 2013 Edition August 29, 2018 (Unit 1)
November 5, 2018 (Unit 2)
July 28, 2028 (Unit 1)
October 16, 2028 (Unit 2)
Braidwood Fifth Established 18 months prior to 5th interval start date in accordance with 10 CFR 50.55a(g)(4)(ii)
July 29, 2028 (Unit 1)
October 17, 2018 (Unit 2)
July 28, 2038 (Unit 1)
October 16, 2038 (Unit 2)
Byron Fourth 2007 Edition with the 2008 Addenda July 16, 2016 July 15, 2025 Byron Fifth 2019 Edition July 16, 2025 July 15, 2035 Note 1: The fifth ISI interval start and end dates are estimates based on the current ISI interval. Interval start and end dates and may be adjusted as allowed by ASME Code,Section XI. Start and end dates for the sixth ISI interval, as well as the ASME Code,Section XI, code of record, will be determined in accordance with the requirements of 10 CFR 50.55a(g)(4)(ii).
American Society of Mechanical Engineers (ASME) Code Components Affected ASME Code Class:
Class 1 Examination Category:
B-B, Pressure Retaining Welds in Vessels Other Than Reactor Vessels B-D, Full Penetration Welded Nozzles in Vessels Item Numbers:
B2.11 for PZR circumferential welds B2.12 for PZR longitudinal welds B3.110 for PZR nozzle-to-vessel welds Component IDs:
The tables in Section 1 of Attachment 2 to the submittals list the component identifications (IDs) affected for each subject plant.
ASME Code Requirements for Which Alternative Is Requested For ASME Code Class 1 welds in the PZR, the ISI requirements are those specified in subarticle IWB-2500 of the ASME Code,Section XI, which requires the licensee to perform volumetric examinations as specified in ASME Code,Section XI, Table IWB-2500-1, for each Examination Category and Item No. listed below once every 10-year ISI interval:
Examination Category B-B, Item No. B2.11, PZR Shell-to-Head Welds, Circumferential Examination Category B-B, Item No. B2.12, PZR Shell-to-Head Welds, Longitudinal Examination Category B-D, Item The NRC staff confirmed that the ASME Code ISI requirements listed above did not change in the latest edition of ASME Code,Section XI, incorporated by reference in 10 CFR 50.55a.
Proposed Alternative In Section 5 of Attachment 2 to the submittal and supplement, the licensee described the proposed alternative, summarized as follows.
The licensee is requesting an inspection alternative to the examination requirements of the ASME Code,Section XI, described above. The proposed alternative is to defer the inspection of the subject examination items from the current ASME Code,Section XI, requirements to the end of the currently approved period of extended operation Braidwood and Byron, as summarized in Table 1 of Attachment 2 to supplement. The alternative request includes a description of a performance monitoring plan, graphically shown in Attachment 2 to the supplement and reproduced in Figure 1 below.
Reason for Proposed Alternative In Section 4 of Attachment 2 to the submittal and supplement, the licensee stated that the Electric Power Research Institute (EPRI) performed assessments in the following non-proprietary report of the basis for the ASME Code,Section XI, examination requirements for the subject PZR welds.
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 (hereafter EPRI report 15905, ML21021A271).
The assessments include a survey of inspection results from 74 domestic and international nuclear units and flaw tolerance evaluations using PFM and deterministic fracture mechanics (DFM). The licensee stated that the EPRI report concluded that the current ASME Code,Section XI, ISI frequency of 10 years can be increased significantly with no impact to plant safety, and that this is the basis for which an alternate inspection frequency is being requested.
The NRC staff noted that EPRI report 15905 was not submitted or reviewed as a topical report.
The NRC staff reviewed the proposed alternative request as a plant-specific alternative for the subject plants. The NRC did not review the EPRI report for generic use, and this review does not extend beyond the plant-specific authorization.
Basis for Proposed Alternative In Section 5 of Attachment 2 to the supplement, the licensee referred to the results of the PFM analyses in EPRI report 15905 and the performance monitoring plan as the bases for the proposed alternative.
Duration of Proposed Alternative In Section 6 of Attachment 2 to the supplement, the licensee stated that the proposed alternatives are requested for Braidwood and Byron for the remainder of their currently approved operating licenses, which are scheduled to end on October 17, 2046 (Braidwood, Unit 1), December 18, 2047 (Braidwood, Unit 2), October 31, 2044 (Byron, Unit No.1), and November 6, 2046 (Byron, Unit No. 2).
3.2
NRC Staff Evaluation
By letter dated May 12, 2021 (ML21133A297), the licensee (Exelon at the time) submitted the first versions (Revision 0) of alternative requests I4R-15 (Braidwood) and I4R-21 (Byron). By letter dated November 10, 2022 (ML22307A246), the NRC authorized these requests for the remainder of the fourth ISI intervals of Braidwood and Byron. The NRC staff compared the content of I4R-15, Revision 1, and I4R-21, Revision 1, with that of I4R-15, Revision 0, and I4R-21, Revision 0, and determined that, excepting the information on the performance monitoring plan, the content of I4R-15, Revision 1, and I4R-21, Revision 1, is identical to the corresponding first versions with respect to geometric configurations, materials, transients, and inspection histories of the subject PZR welds of Braidwood and Byron. In the inspection histories of the subject PZR welds in Tables 2 and 3 of Attachment 2 to the supplement, the licensee referenced the NRCs November 10, 2022, authorization for the fourth ISI interval.
Because the relevant content of I4R-15, Revision 1, and I4R-21, Revision 1, are identical to that I4R-15, Revision 0, and I4R-21, Revision 0, except for the noted differences (i.e., performance monitoring plan and referencing of the NRC fourth ISI interval authorization), the NRC staff focused on evaluating the proposed performance monitoring plan contained in the current requests. The NRC staff documented its plant-specific evaluation of the PFM and DFM technical bases contained in EPRI report 15905 in sections 1 through 10 of the NRC staffs safety evaluation (SE) dated November 10, 2022 (ML22307A246).
Figure 1: Licensees Proposed Alternative and Performance Monitoring Plan for PZR Welds 3.3 Performance Monitoring Plan Performance monitoring, such as ISI programs, is a necessary component described by the NRC five principles of risk-informed decision making. Analyses, such as PFM, work along with performance monitoring to provide a mutually supporting and diverse basis for facility condition and maintenance that is within its licensing basis. An adequate performance monitoring program must provide direct evidence of the presence and extent of degradation, validation of continued appropriateness of associated analyses, and a timely method to detect novel/unexpected degradation. The NRC staff described these characteristics at several public meetings (e.g., ML22060A277, ML23033A667, and ML23114A034).
In Section 5 of Attachment 2 to the supplement in the section titled Performance Monitoring Requirements, the licensee described the performance monitoring plan for the subject alternative requests. The licensees performance monitoring plan is graphically shown in to the supplement and reproduced in Figure 1 of this SE.
The NRC staff reviewed the proposed performance monitoring plan in terms of number of PZRs, rather than in terms of number of required Item No. examinations. ASME Code,Section XI, requires that one PZR (i.e., all welds specified in the ASME Code,Section XI, for the PZR) be examined per unit per ISI interval. Accordingly, Table 2 shows the NRC staffs calculation of the number of total PZRs required to be examined by the ASME Code,Section XI, for the licensees proposed alternative.
Table 2: Calculation of Total ASME Code Required PZRs Site
- of units
units x intervals Braidwood 2
2 4
Byron 2
2 4
Total 8
The NRC staff determined, through binomial statistics and Monte Carlo methods, that a 25 percent sample of the total ASME Code required number of PZRs would be an adequate performance monitoring sample over the subject alternative period. This leads to a sample of 0.25 x 8 = 2 PZRs.
The licensee stated that the Byron, Unit No. 2, PZR (consisting of 10 weld examinations) will be selected for performance monitoring examinations in the fifth ISI interval. For the sixth ISI interval, the licensee stated that either the Braidwood, Unit 1, or Braidwood, Unit 2, PZR will be selected for performance monitoring examinations, with the number of components selected for examinations being the same as for Byron, Unit No. 2 (i.e., 10 weld examinations). This performance monitoring amounts to two PZRs (10 weld examinations per PZR) for the proposed alternatives, which meets the minimum sample of two PZRs. Consequently, the NRC staff finds that the quantity of examinations over the subject alternative period is acceptable.
The NRC staff reviewed the timing of examinations to ensure that the proposed examinations in the performance monitoring plan would provide a reasonably continuous source of data supporting the characteristics of acceptable performance monitoring. Specifically, data would continue to become available on a cadence reasonably commensurate with ASME Code requirements, but on a four-unit basis rather than an individual unit basis. Based on the proposed examinations during the alternative periods, and periods in which unmodified ASME Code inspections requirements would be in force, the NRC staff finds that the examinations proposed in the performance monitoring plan will provide an appropriately continuous stream of data.
As part of the proposed performance monitoring plan, the licensee described actions it would take in the event that new unacceptable indications are identified as part of performance monitoring activities. The licensee stated that detected indications would be evaluated according to the rules of ASME Code,Section XI (which include additional examination and successive inspection requirements), and the Constellation corrective action program. These additional activities are described in detail in pages 19 and 20 of Attachment 2 to the supplement.
In addition, the licensee described system leakage tests as providing further assurance of safety for the proposed alternatives. The NRC staff noted that the visual examinations performed during system leakage tests may not directly detect the 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 welds. However, the NRC staff noted that leakage tests provide complementary additional performance monitoring to the ISI examinations. This additional assurance increases confidence that the proposed quantity of examinations, in concert with other on-going activities, will provide an acceptable level of performance monitoring for the subject PZR components.
Based on the above discussion, the NRC staff determined that inspections for the subject PZR components could be deferred during the proposed period because an adequate level of performance monitoring is maintained for the components.
4.0 CONCLUSION
As set forth above, the NRC staff determined that the licensees proposed alternative, as discussed above, for the requested PZR components provides an acceptable level of quality and safety. Accordingly, the NRC staff concludes that the licensee has adequately addressed all the regulatory requirements set forth in 10 CFR 50.55a(z)(1). Therefore, the NRC staff authorizes the use of proposed alternatives I4R-15, Revision 1, for Braidwood, and I4R-21, Revision 1, for Byron, for the remainder of their currently approved operating licenses, which are scheduled to end on October 17, 2046 (Braidwood, Unit 1), December 18, 2047 (Braidwood, Unit 2), October 31, 2044 (Byron, Unit No.1), and November 6, 2046 (Byron, Unit No. 2).
All other ASME Code,Section XI, requirements for which relief has not been specifically requested and approved in this relief request remain applicable, including third party review by the Authorized Nuclear Inservice Inspector.
Principal Contributors: D. Dijamco, NRR D. Widrevitz, NRR Date: July 22, 2024
SUBJECT:
BRAIDWOOD STATION, UNITS 1 AND 2; AND BYRON STATION, UNIT NOS. 1 AND 2 - ISSUANCE OF RELIEF RE: PROPOSED ALTERNATIVE REQUEST ASSOCIATED WITH PRESSURIZER EXAMINATIONS (EPID L-2023-LLR-0062) DATED JULY 22, 2024 DISTRIBUTION:
PUBLIC RidsNrrDorlLpl1 Resource RidsNrrDorlLpl3 Resource RidsRgn1MailCenter Resource RidsRgn3MailCenter Resource RidsNrrLASLent Resource RidsNrrLASRohrer Resource RidsNrrLAKZeleznock Resource RidsNrrLAKEntz Resource RidsAcrs_MailCTR Resource RidsNrrPMConstellation Resource RidsNrrPMBraidwood Resource RidsNrrPMByron Resource RidsNrrDnrlNvib Resource DDijamco, NRR DWidrevitz, NRR Accession No.: ML24194A022
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NAME SWall SRohrer ABuford DATE 07/11/2024 07/15/2024 07/09/2024 OFFICE NRR/DORL/LPL3/BC NRR/DORL/LPL3/PM NAME JWhited SWall DATE 07/19/2024 07/22/2024 OFFICIAL RECORD COPY