ML24057A037
| ML24057A037 | |
| Person / Time | |
|---|---|
| Site: | Braidwood  |
| Issue date: | 03/26/2024 |
| From: | Jeffrey Whited NRC/NRR/DORL/LPL3 |
| To: | Rhoades D Constellation Energy Generation, Constellation Nuclear |
| Wiebe J, NRR/DORL/LPL3 | |
| References | |
| EPID L-2024-LLR-0000 | |
| Download: ML24057A037 (1) | |
Text
March 26, 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 - PROPOSED ALTERNATIVE FROM CERTAIN REQUIREMENTS CONTAINED IN THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS BOILER AND PRESSURE VESSEL CODE, SECTION XI (EPID L-2024-LLR-0000)
Dear David Rhoades:
By letter dated January 11, 2024 (Agencywide Documents and Access Management System (ADAMS) Accession No. ML24012A003), as supplemented by letter dated February 13, 2024 (ML24044A120), Constellation Energy Generation, LLC (CEG or the licensee) requested a proposed alternative from the minimum percentage requirements contained in the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code), section XI, table IWC-2411-1, for the second inspection period which would require examination of two components in refueling outage A1R24 (April 2024) at Braidwood Station (Braidwood), Unit 1, and examination of three components in refueling outage A2R24 (October 2024) at Braidwood, Unit 2.
Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(z)(2), the licensee requested to use the alternative on the basis that complying with the specified requirement would result in hardship or unusual difficulty.
The U.S. Nuclear Regulatory Commission (NRC) staff has reviewed the subject request and concludes, as set forth in the enclosed safety evaluation, that that the proposed alternative will not affect structural integrity of the subject components and that compliance with the specified requirements results in a hardship or unusual difficulty without a compensating increase in quality or safety. The staff concludes that the licensee has adequately addressed the regulatory requirements set forth in 10 CFR 50.55a(z)(2). Therefore, the NRC staff authorizes the use of proposed alternative I4R-18 for the second inspection period of the fourth inservice inspection interval at Braidwood, Units 1 and 2.
All other ASME 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 Project Manager Joel S. Wiebe at 301-415-6606 or Joel.Wiebe@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 and STN 50-457
Enclosure:
Safety Evaluation cc: Listserv Jeffrey A.
Whited Digitally signed by Jeffrey A. Whited Date: 2024.03.26 14:22:55 -04'00'
Enclosure SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION PROPOSED ALTERNATIVE I4R-18 TO INSERVICE INSPECTION OF STEAM GENERATOR SHELL WELDS CONSTELLATION ENERGY GENERATION, LLC BRAIDWOOD STATION UNITS 1 AND 2 DOCKET NOS. STN 50-456 AND STN 50-457
1.0 INTRODUCTION
By letter dated January 11, 2024 (Agencywide Documents and Access Management System (ADAMS) Accession No. ML24012A003) and supplement dated February 13, 2024 (ML24044A120), Constellation Energy Generation, LLC (CEG or the licensee) requested a proposed alternative from the minimum percentage requirements contained in the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code), section XI, table IWC-2411-1, for the second inspection period which would require examination of two components in refueling outage A1R24 (April 2024) at Braidwood Station (Braidwood), Unit 1, and examination of three components in refueling outage A2R24 (October 2024) at Braidwood, Unit 2.
Pursuant to Title 10 of the Code of Federal Regulations, part 50, (10 CFR 50.55a(z)(2)), the licensee submitted for U.S. Nuclear Regulatory Commission (NRC) review and approval proposed alternative I4R-18 for Braidwood, Units 1 and 2.
2.0 REGULATORY EVALUATION
Pursuant to 10 CFR 50.55a(g)(4), ASME Code Class 1, 2, and 3 components (including supports) must meet the requirements, except the design and access provisions and the preservice examination requirements, set forth in the ASME Code, section XI, Rules for In-service Inspection [ISI] of Nuclear Power Plant Components, to the extent practical within the limitations of design, geometry, and materials of construction of the components. The regulations require that inservice examination of components and system pressure tests conducted during the first 10-year interval and subsequent intervals comply with the requirements in the latest Edition and Addenda of Section XI of the ASME Code, incorporated by reference in 10 CFR 50.55a(b), 18 months prior to the start of the 120-month interval, subject to the limitations and modifications listed therein.
Pursuant to 10 CFR 50.55a(z) it states, in part, that alternatives to the requirements of paragraphs (b) through (h) of 10 CFR 50.55a or portions thereof may be used when authorized by the Director, Office of Nuclear Reactor Regulation. A proposed alternative must be submitted and authorized prior to implementation. The applicant or licensee must demonstrate that: (1)
Acceptable level of quality and safety. The proposed alternative would provide an acceptable level of quality and safety; or (2) Hardship without a compensating increase in quality and safety. Compliance with the specified requirements of this section would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
3.0 TECHNICAL EVALUATION
3.1 ASME Code Component(s) Affected The affected components are steam generator pressure retaining welds, full penetration welded nozzles, and nozzle-to-shell welds.
The affected components are classified under the ASME Code, section XI. Table IWC-2500-1, Examination Category C-A, Pressure Retaining Welds in Pressure Vessels and Examination Category C-B, Pressure Retaining Nozzle Welds in Pressure Vessels.
Under Examination Category C-A, the applicable item numbers. for proposed alternative I4R-18 are C1.10, shell circumferential welds; and C1.20, head circumferential welds.
Under Examination Category C-B, applicable item number for proposed alternative I4R-18 is C2.21, nozzle-to-shell (nozzle-to-head or nozzle-to-nozzle) weld.
Section 1 of proposed alternative I4R-18 in the submittal dated January 11, 2024, indicates that Item Number C2.22, nozzle inside radius section, is an affected component. In the supplement dated February 13, 2024, the licensee removed nozzle inside radius section from the proposed alternative. Therefore, Item Number C2.22 is no longer being considered as an affected component under proposed alternative I4R-18.
The specific weld Identification numbers and descriptions are shown in the following two submittals:
(1) Letter from D. Gudger (Constellation Energy Generation, LLC) to U.S. Nuclear Regulatory Commission, Proposed Alternative for Examinations of Examination Categories B-B, B-D, and C-A Steam Generator Pressure Retaining Welds and Full Penetration Welded Nozzles, dated October 11, 2023 (ML23284A259).
(2). Letter from D. Gudger (Constellation Energy Generation, LLC) to U.S. Nuclear Regulatory Commission, Proposed Alternative for Examinations of Examination Category C-B Steam Generator Nozzle-to-Shell Welds and Nozzle Inside Radius Sections, dated October 10, 2023 (ML23283A003).
3.2 Applicable ASME Code,Section XI, Edition and Addenda The code of record for the fourth ISI interval is the 2013 Edition of the ASME Code, section XI, for Braidwood, Units 1 and 2.
The fourth ISI interval for Braidwood, Unit 1, started on August 29, 2018, and will end on July 28, 2028. The fourth ISI interval for Braidwood, Unit 2, started on November 5, 2018, and will end on October 16, 2028.
3.3
Applicable Code Requirement
For Examination Categories C-A and C-B steam generator welds, the ASME Code, section XI, subparagraph IWC-2411(a), and table IWC-2411-1, specify that at least 50 percent of the required inspections be conducted by the end of the second inspection period of each ISI interval.
3.4
Reason for Request
As shown in above letters dated October 10 and 11, 2023, the licensee submitted proposed alternatives associated with alternative examination of steam generator welds and nozzle inner radii at Braidwood, Units 1 and 2; Byron Station, Unit Nos. 1 and 2; Calvert Cliffs Nuclear Power Plant, Units 1 and 2; and R. E. Ginna Nuclear Power Plant. These letters proposed to defer any further examination of these steam generator components during the current ISI intervals based on the probabilistic fracture mechanics analysis and the proposed performance monitoring plan.
In proposed alternative I4R-18, the licensee proposed to achieve less than the ASME Code, table IWC-2411-1, required examination percentage for the second inspection period of the current fourth ISI interval. The licensee requested approval of the proposed alternative I4R-18 on the basis that performing these examinations creates undue hardship based upon the letters dated October 10 and 11, 2023, and as compared to performing the examinations of the subject components along with the other required examinations based upon the requirements of table IWC-2500-1 and table IWC-2411-1, in the third period of the fourth ISI interval.
3.5 Proposed Alternative and Basis for Use The licensee proposed an alternative from the minimum percentage inspection requirements contained in the ASME Code, table IWC-2411-1, for the second inspection period of the fourth ISI interval at Braidwood, Units 1 and 2. Specifically, the licensee requested not to perform certain steam generator weld examinations for two components in A1R24 at Braidwood, Unit 1, and three components in A2R24 at Braidwood, Unit 2.
The licensee stated that A1R24 and A2R24 are the last opportunity to perform examinations of the subject Category C-A and C-B welds to satisfy the inspection requirements for the second inspection period of the fourth ISI interval at Braidwood, Units 1 and 2. The licensee further stated that the rules of IWA-2430 do not allow the second inspection period of the fourth ISI interval to be extended more than one year to incorporate another refueling outage. Table IWC-2411-1 requires examination of at least 50 percent of the Categories C-A and C-B components by the end of the second inspection period.
The licensee stated that performing any of the Category C-A and Category C-B steam generator examinations during the 2024 refueling outages will eliminate the benefit of the proposed alternatives for Braidwood as discussed in its letters dated October 10 and 11, 2023.
The licensee stated that due to common support tasks (scaffold, insulation removal, etc.) and personnel to access and examine the steam generator welds, there is little benefit to separating the Category C-A and Category C-B welds for the sole purpose of maintaining compliance with the table IWC-2411-1 examination requirements. The licensee stated that all remaining Categories C-A and C-B examinations would be performed during the third inspection period to take full advantage of the common support tasks if the proposed alternatives in its letters dated October 10 and 11, 2023, are not approved.
According to the licensee, the likelihood of an unknown degradation mechanism having gone undetected and/or starting to initiate and a flaw resulting from this degradation mechanism growing to sufficient size to threaten the integrity of the subject welds before the next inspection is acceptably low based on the limited application and duration of this alternative request.
3.6 Duration of Proposed Alternative The licensee requested that the proposed alternative I4R-18 be applicable for the second inspection period of the current fourth ISI interval at Braidwood, Units 1 and 2.
3.7
NRC Staff Evaluation
The ASME Code, section XI, IWC-2411(a), states, in part, that The required examinations in each examination category shall be completed during each inspection interval in accordance with Table IWC-2411-1...If there are less than three items or welds to be examined in an Examination Category, the items or welds may be examined in any two periods, or in any one period if there is only one item or weld, in lieu of the percentage requirements of Table IWC-2411-1 The ASME Code, section XI, table IWC-2411-1 stipulates that for the second inspection period, the minimum examination completed should be 50 percent of the component population. The maximum examination credited is 75 percent of the component population. As stated above, the licensee requested not to perform the examination of the subject welds for satisfying the required examination of 50 percent of the component population.
The NRC staff notes that the licensees submittal dated October 10, 2023, contains proposed alternative I4R-16, Revision 1, for Braidwood, Units 1 and 2. Proposed alternative I4R-16, Revision 1, is related to an alternate examination of Item Numbers C2.21 among other welds.
The licensees submittal dated October 11, 2023, contains proposed alternative I4R-17, Revision 1, for Braidwood, Units 1 and 2. Proposed alternative I4R-17, Revision 1, is related to an alternate examination of Item Numbers C1.10 and C1.20 among other welds. These two alternatives contain information that is applicable to the C1.10, C1.20, and C2.21 welds covered in proposed alternative I4R-18 including its supplement.
Based on this discussion, the NRC staff determined that the likelihood of an unknown degradation mechanism having gone undetected and/or starting to initiate, and a flaw resulting from this degradation mechanism growing to sufficient size to challenge the integrity of the subject welds before the next inspection is acceptably low based on the limited application and duration of this alternative request (i.e., the application of the alternative is limited to two welds in Unit 1 and three welds in Unit 2 and to the second period of the fourth ISI interval). The NRC staff further noted that approval of the alternative does not constitute an undue increase in risk and consequently is not associated with a compensating increase in the level of quality and safety.
The NRC staff reviewed the results of the last inspection of the subject welds at both units as shown in proposed alternatives I4R-16, Revision 1, and I4R-17, Revision 1. The NRC staff noted that the plant-specific history shows that no recordable indications have been identified in the subject welds during multiple ISI inspections. In addition, the NRC determined that there is no currently known active degradation mechanism in the subject welds such that a one-time alternative to the table IWC-2411-1 requirements for a single inspection period during the fourth ISI interval would lead to an undue increase in risk.
The NRC staff finds that requiring the licensee to meet the ASME Code, section XI, subparagraph IWC-2411(a) and table IWC-2411-1 minimum inspections requirements would result in a high radiological dose without a compensating increase in quality and safety. This is compounded by additional effort associated with having to schedule the appropriate personnel and equipment for an imminent outage.
The NRC staff determined that even though the licensee proposed not to perform the required examination of the affected components during the second inspection period of the fourth ISI interval, the licensee is required to examine 100 percent of the affected welds that are required to be examined during the third inspection period of the fourth ISI interval in accordance with the ASME Code, table IWC-2411-1.
Based on the above evaluation, the NRC staff finds that compliance with the inspection requirements of the ASME Code, section XI, tables IWC-2411(a) and IWC-2411-1 for the second inspection period during the fourth ISI interval constitutes a hardship without a compensating increase in quality and safety. The NRC staff finds that the licensees basis for requesting an alternative based on hardship satisfies the requirements of 10 CFR 50.55a(z)(2),
and, therefore, is acceptable.
4.0 CONCLUSION
Based on the above evaluation, the NRC staff concludes that the proposed alternative will not affect structural integrity of the subject components and that compliance with the specified requirements results in a hardship or unusual difficulty without a compensating increase in quality or safety. The NRC staff concludes that the licensee has adequately addressed the regulatory requirements set forth in 10 CFR 50.55a(z)(2). Therefore, the NRC staff authorizes the use of proposed alternative I4R-18 for the second inspection period of the fourth ISI interval at Braidwood Units 1 and 2.
The NRC staff notes that this safety evaluation does affect the NRC staffs review and its resulting licensing action on proposed alternative I4R-16, Revision 1, and I4R-17, Revision 1.
All other ASME Code, section XI, requirements for which an alternative was not specifically requested and authorized remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
Principal Contributors: John Tsao, NRR David Dijamco, NRR Date: March 26, 2024
ML24057A037 NRR-028 OFFICE NRR/DORL/LPL3/PM NRR/DORL/LPL3/LA NRR/DNRL/NVIB/BC NRR/DORL/LPL3/BC NAME JWiebe SRohrer ABuford JWhited DATE 2/26/2024 2/26/24 2/23/2024 3/26/2024