ML21253A082
| ML21253A082 | |
| Person / Time | |
|---|---|
| Site: | Catawba  |
| Issue date: | 09/20/2021 |
| From: | Markley M Plant Licensing Branch II |
| To: | Simril R Duke Energy Carolinas |
| Stone Z | |
| References | |
| EPID L-2021-LLR-0028 | |
| Download: ML21253A082 (8) | |
Text
September 20, 2021 Mr. Robert T. Simril Site Vice President Catawba Nuclear Station Duke Energy Carolinas, LLC 4800 Concord Road York, SC 29745
SUBJECT:
CATAWBA NUCLEAR STATION, UNIT 2 - PROPOSED ALTERNATIVE REQUEST RA-21-0145 TO USE REACTOR VESSEL HEAD PENETRATION EMBEDDED FLAW REPAIR METHOD (EPID L-2021-LLR-0028)
Dear Mr. Simril:
By letter dated April 23, 2021, as supplemented by letter dated April 24, 2021, Duke Energy Carolinas, LLC (Duke Energy, the licensee) submitted a request to the U.S. Nuclear Regulatory Commission (NRC) for a proposed alternative to the requirements of American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (BPV Code) regarding alternative requirements for repair of reactor vessel closure head (RVCH) penetration at Catawba Nuclear Station, Unit 2. Duke Energy requested authorization to repair the J-groove weld of RVCH penetration #74 using an embedded flaw repair process as an alternative to the defect removal and weld repair provisions of ASME Section XI, IWA-4000 and ASME Section III, NB-4450.
The licensee submitted the proposed alternative pursuant to Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Section 50.55a(z)(1) on the basis that its alternative requirements for repair of the J-groove weld of RVCH penetration provides an acceptable level of quality and safety.
On April 24, 2021, the NRC staff verbally authorized the proposed alternative RA-21-0145 for one cycle of operation at Catawba Nuclear Station, Unit 2, until the end of Cycle 25 that is scheduled to end in fall 2022 The NRC staff has reviewed the proposed alternative 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 alternative request RA-21-0145 for Catawba Nuclear Station, Unit 2.
All other ASME Code,Section XI, requirements for which relief was not specifically requested and authorized herein by the NRC staff remain applicable including the third-party review by the Authorized Nuclear Inservice Inspector.
R. T. Simril If you have any questions, please contact the Project Manager, Zackary Stone, at (301) 415-0615 or by e-mail at Zackary.Stone@nrc.gov.
Sincerely, Michael T. Digitally signed by Michael T. Markley Markley Date: 2021.09.20 08:28:25 -04'00' Michael T. Markley, Chief Plant Licensing Branch II-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No: 50-414
Enclosure:
Safety Evaluation cc: Listserv
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION PROPOSED ALTERNATIVE REQUEST RA-21-0145 TO USE REACTOR VESSEL HEAD PENETRATION EMBEDDED FLAW REPAIR METHOD RENEWED FACILITY OPERATING LICENSE NO. NPF-52 DUKE ENERGY CAROLINAS, LLC CATAWBA NUCLEAR STATION, UNIT 2 DOCKET NO. 50-414
1.0 INTRODUCTION
By letter dated April 23, 2021 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML21113A215), as supplemented by letter dated April 24, 2021 (ADAMS Accession No. ML21114A000), Duke Energy Carolinas, LLC (Duke Energy, the licensee) submitted a request to the U.S. Nuclear Regulatory Commission (NRC) for a proposed alternative to the requirements of American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (BPV Code) regarding alternative requirements for repair of reactor vessel closure head (RVCH) penetration at Catawba Nuclear Station, Unit 2 (CNS). Duke Energy requested authorization to repair the J-groove weld of RVCH penetration #74 using an embedded flaw repair process as an alternative to the defect removal and weld repair provisions of ASME Section XI, IWA-4000 and ASME Section III, NB-4450.
The licensee submitted the proposed alternative pursuant to Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Section 50.55a(z)(1) on the basis that its alternative requirements for repair of the J-groove weld of RVCH penetration provides an acceptable level of quality and safety.
On April 24, 2021 (ADAMS Accession No. ML21117A129), the NRC staff verbally authorized the proposed alternative RA-21-0145 for one cycle of operation at CNS, Unit 2, until the end of Cycle 25 that is scheduled to end in fall 2022
2.0 REGULATORY EVALUATION
Regulations in 10 CFR 50.55a(g)(4) state, in part, that 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 Section XI of the applicable editions and addenda of the ASME Code to the extent practical within the limitations of design, geometry, and materials of construction of the components.
Regulations in 10 CFR 50.55a(g)(6)(ii)(D) state, in part, that holders of operating licenses or combined licenses for pressurized-water reactors as of or after June 3, 2020 shall implement the requirements of ASME BPV Code Case N-729-6 instead of ASME BPV Code Case N-729-4, subject to the conditions specified in paragraphs (g)(6)(ii)(D)(2) through (8) of this section, by no later than one year after June 3, 2020. All previous NRC-approved alternatives from the requirements of paragraph (g)(6)(ii)(D) of this section remain valid.
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 authorized by the NRC if the licensee demonstrates that: (1) the proposed alternative provides 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 The Licensees Proposed Alternative RA-21-0145 3.1.1 ASME Code Components Affected The affected component is ASME Code Class 1, RVCH penetration #74.
3.1.2 Applicable Code Editions and Addenda The applicable ASME Code,Section XI, Edition and Addenda for the fourth 10-year Inservice Inspection Interval (ISI) at CNS, Unit 2, is the 2007 Edition through 2008 Addenda. The fourth ISI interval at CNS, Unit 2, began on August 19, 2015, and is scheduled to end on February 24, 2026. Examinations of the RVCH penetrations are performed in accordance with 10 CFR 50.55a(g)(6)(ii)(D), which specifies the use of ASME Code Case N-729-6, with conditions.
The licensee stated that the Construction Code applicable to the repair of weld defects on the RVCH is the 1989 Edition of ASME Code,Section III, and the RPV Construction Code is ASME Code,Section III, 1971 Edition through Winter 1972 Addenda.
3.1.3 Appliable Code Requirement Section XI, of ASME Code, IWA-4000, contains requirements for the removal of defects from and welded repairs performed on ASME Code components. Paragraph IWA 4421 states, in part, that defects be removed or mitigated in accordance with the requirements in IWA-4461 (by thermal methods), IWA-4462 (by mechanical processing) or IWA-4411 (by welding or brazing).
Specifically, paragraph IWA-4411 requires that welding, brazing, fabrication, and installation shall be performed in accordance with the Owners Requirements and the Construction Code of the item, with additional provisions allowing the use of later editions or addenda of the Construction Code.
Section III, of ASME Code, paragraph NB-4451, provides the general requirements for removal and repair of weld metal defects. In addition, ASME Code,Section III, paragraph NB-4452 and subparagraph NB-4453.1 specify the requirements for eliminating weld surface defects and the requirements for excavating weld defects for repair activities, respectively.
3.1.4 Reason for Request During the Unit 2 refueling outage, C2R24, the licensee identified a relevant indication in the RVCH penetration #74 J-groove weld. The licensee stated, based on the change in backwall reflectivity observed during the volumetric ultrasonic leak path assessment and the relevant indication detected by both supplemental surface examination methods (eddy current testing and liquid penetrant), repair of the J-groove weld would be required during the C2R24 refueling outage.
3.1.5 Licensees Proposed Alternative The licensee proposed to repair the J-groove weld of RVCH penetration #74 using an embedded flaw repair process as an alternative to the defect removal and weld repair provisions of ASME Section XI, IWA-4000 and ASME Section III, NB-4450. The proposed embedded flaw repair process is in accordance with the NRC approved WCAP-15987-P-A, Technical Basis for the Embedded Flaw Process for Repair of Reactor Vessel Head Penetrations, Revision 2 (ADAMS Accession Nos. ML040290246), with some modifications, to repair the weld.
3.1.6 Licensees Basis of the Proposed Alternative The licensee proposed that repairing the weld in accordance with WCAP-15987-P-A, Revision 2, provides an acceptable level of quality and safety, as described in the NRC safety evaluation, dated July 3, 2003 (ADAMS Accession No. ML031840237). The repair weld material (Alloy 52/52M) is considered highly resistant to primary water stress corrosion cracking (PWSCC) and isolates the subject J-groove weld from the reactor coolant environment, thereby preventing the occurrence of PWSCC.
In lieu of the examination requirements identified for J-groove welds in the NRC safety evaluation of WCAP-15987-P, Revision 2, the licensee proposed examination requirements consistent with the NRC regulations in 10 CRF 50.55a(g)(6)(ii)(D), which mandates the use of ASME Code Case N-729-6, with conditions. The licensee proposed that these inservice examinations will confirm the acceptability of the repair weld.
The fracture mechanics assessment for the subject penetration nozzle was performed to evaluate the potential fatigue crack growth of a conservatively postulated J-groove weld flaw into the RVCH. The licensee proposed that the results of this evaluation confirmed that the growth of a postulated fatigue crack did not affect the structural integrity of the closure head and penetration, consistent with the conclusion of WCAP-15987-P-A, Revision 2. The licensee also proposes that the conservative fatigue crack growth evaluation also confirms that the repair weld is sufficient to maintain the seal weld integrity for the period of the relief request (until fall 2022).
3.2 NRC Staff Evaluation The NRC staff reviewed the following information: (1) proposed repair method; (2) consistency of the repair, examination and flaw evaluation methods with those described in the WCAP 15987-P-A report and current NRC regulations under 10 CFR 50.55a(g)(6)(ii)(D); (3) corrosion resistance of repair weld material (Alloy 52/52M) exposed to reactor coolant; and (4) flaw assessment for one cycle of operation.
The NRC approved WCAP-15987-P-A, Revision 2, as a topical report to be used for referencing in licensing applications to request implementation of the embedded flaw repair process. The process embeds PWSCC flaws found in Alloy 600 RVCH penetration nozzles and J-groove welds under a non-structural seal weld which is more resistant to PWSCC. The licensees proposal identified Alloy 52/52M as the seal weld material to be used. The NRC staff have performed extensive testing to verify the increased resistance to PWSCC of these materials over the past 10 years at Argonne National Laboratory and Pacific Northwest National Laboratory and find them acceptable for use in this application. Consistent with the NRC-approved WCAP-15987-P-A, the NRC staff finds that seal weld repair technique of flaws of the type identified by the licensee in the J-groove weld of RVCH penetration #74 would provide an acceptable level of safety and quality.
The NRC staff reviewed the licensees proposed alternative for non-destructive examination requirements of the seal weld and future ISI requirements. During the time in which WCAP-15987 was approved by the NRC staff, the regulatory requirements for upper head inspection were found under NRC Order EA-03-009 (ADAMS Accession No. ML030410402).
In September 2008, by rule, the NRC established 10 CFR 50.55a(g)(6)(ii)(D) which defined the regulatory requirements for upper head inspections as using ASME Code Case N-729-1, with conditions, and rescinded NRC Order EA-03-009. In July 2017, by rule, the NRC modified 10 CFR 50.55a(g)(6)(ii)(D) to replace ASME Code Case N-729-1 with ASME Code Case N-729-4 and in June 2020, by rule, the NRC modified 10 CFR 50.55a(g)(6)(ii)(D) to replace ASME Code Case N-729-4 with ASME Code Case N-729-6.
The licensees proposed alternative modified the original embedded flaw repair process to address these changes in examination requirements since the approval of WCAP-15987.
The licensee proposed alternative examination requirements to be consistent with the NRC regulations in 10 CFR 50.55a(g)(6)(ii)(D), which mandates the use of ASME Code Case N-729-6, with conditions, for the examination of RVCH penetration nozzles and welds. The NRC staff verified that the examination types and frequencies were consistent with the current regulatory requirements and latest approvals of use of the embedded flaw repair process for other licensees. The NRC staff finds that the examinations will provide reasonable assurance of the structural integrity of the RVCH through the requested duration of the licensees proposed alternative and is, therefore, acceptable.
The licensees proposed alternative is for one cycle of operation until the fall 2022 refueling outage at CNS, Unit 2. Typically, the embedded flaw repair process is a longer-term repair.
The NRC staff have previously authorized the embedded flaw repair for greater than 10 years of design life. However, due to the identification of the flaw during the spring 2021 refueling outage at CNS, Unit 2, the licensee was unable to complete the full flaw analysis required by WCAP-15987-P-A, Revision 2, to establish the full design lifetime of the repair. The licensee instead provided a flaw assessment utilizing the full design requirements of the repair technique and justifying operation for one cycle of operation. The NRC staff reviewed this assessment and found the design parameters of the repair consistent with previous NRC approved versions in multiple applications which were approved for longer periods of time. Further, no structural failures have occurred in an embedded flaw repaired penetration nozzle or J-groove weld in similar applications in pressurized water reactors in over 20 years of service. Given the similar design criteria and performance history, the NRC staff finds the embedded flaw repair proposed by the licensee for the J-groove weld of RVCH penetration #74 provides reasonable assurance of structural integrity for one cycle of operation and is, therefore, acceptable.
The NRC staff finds that the licensees repair, examination and flaw assessment methods are consistent with the guidance in the NRC-approved WCAP-15987-P-A, Revision 2, and the inspection requirements specified in ASME Code Case N-729-6, as conditioned in 10 CFR 50.55a(g)(6)(ii)(D). The NRC staff determined that the proposed repair would restore the primary system pressure boundary and provide reasonable assurance of structural integrity of the reactor vessel closure head and repaired penetration #74 for one cycle of operation, as requested in the licensees proposed alternative. Therefore, the NRC staff concludes the licensees proposed alternative provides an acceptable level of quality and safety.
4.0 CONCLUSION
The NRC staff has reviewed alternative request RA-21-0145 and concludes, as set forth in this 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 alternative RA-21-0145 at Catawba Nuclear Station, Unit 2, for one cycle of operation that will end in fall 2022.
All other ASME BPV 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 Contributor: Jay Collins, NRR Date: September 20, 2021
ML21253A082 OFFICE NRR/DORL/LPL2-1/PM NRR/DORL/LPL2-1/LA NRR/DNRL/NPHP/BC NAME ZStone KGoldstein MMitchell DATE 9/14/2021 9/14/2021 9/01/2021 OFFICE NRR/DORL/LPL2-1/BC NRR/DORL/LPL2-1/PM NAME MMarkley ZStone DATE 9/20/2021 9/20/2021