ML23199A312

Revision to the Reactor Vessel Material Surveillance Capsule Withdrawal Schedule

ML23199A312
Person / Time
Site:	Diablo Canyon
Issue date:	07/20/2023
From:	Jennifer Dixon-Herrity Plant Licensing Branch IV
To:	Gerfen P Pacific Gas & Electric Co
Lee S, 301-415-3158
References
EPID L-2023-LLL-0012
Download: ML23199A312 (8)

Text

July 20, 2023 Ms. Paula Gerfen Senior Vice President, Generation and Chief Nuclear Officer Pacific Gas and Electric Company Diablo Canyon Power Plant P.O. Box 56, Mail Code 104/6 Avila Beach, CA 93424

SUBJECT:

DIABLO CANYON NUCLEAR POWER PLANT, UNIT 1 - REVISION TO THE REACTOR VESSEL MATERIAL SURVEILLANCE CAPSULE WITHDRAWAL SCHEDULE (EPID L-2023-LLL-0012)

Dear Ms. Gerfen:

By letter dated May 15, 2023 (Agencywide Documents Access and Management System Accession No. ML23135A217), Pacific Gas and Electric Company (the licensee) requested revision of the reactor vessel material surveillance capsule withdrawal schedule for the Diablo Canyon Nuclear Power Plant (Diablo Canyon), Unit 1, in accordance with Title 10 of the Code of Federal Regulations Part 50, Domestic Licensing of Production and Utilization Facilities, Appendix H, Reactor Vessel Material Surveillance Program Requirements,Section III.B.3.

The licensee has already fulfilled its reactor vessel material surveillance requirements for Diablo Canyon, Unit 1 for the current operating license period (i.e., 40 years), but is proactively addressing surveillance data needs to support the potential for the submission of a license renewal application. The NRC staff has reviewed the licensees request and concludes, as set forth in the enclosed safety evaluation, that the modified reactor vessel material surveillance capsule withdrawal schedule for Diablo Canyon, Unit 1 is acceptable for implementation.

However, the NRC staff does not make any conclusion regarding the future use of the subject capsule in any potential future licensing applications or license periods.

P. Gerfen If you have any questions, please contact Samson Lee at 301-415-3168 or via email at Samson.Lee@nrc.gov.

Sincerely, Digitally signed by Jennifer L. Jennifer L. Dixon-Herrity Date: 2023.07.20 Dixon-Herrity 13:58:23 -04'00' Jennifer L. Dixon-Herrity, Chief Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-275

Enclosure:

Safety Evaluation cc: Listserv

SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION REQUEST FOR REVISION TO REACTOR VESSEL MATERIAL SURVEILLANCE PROGRAM WITHDRAWAL SCHEDULE PACIFIC GAS AND ELECTRIC COMPANY DIABLO CANYON NUCLEAR POWER PLANT, UNIT 1 DOCKET NO. 50-275

1.0 INTRODUCTION

By letter dated May 15, 2023 (Agencywide Documents Access and Management System Accession No. ML23135A217), Pacific Gas and Electric Company (PG&E, the licensee) requested revision of the reactor vessel material surveillance capsule withdrawal schedule for the Diablo Canyon Nuclear Power Plant (Diablo Canyon), Unit 1, in accordance with Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Domestic Licensing of Production and Utilization Facilities, Appendix H, Reactor Vessel Material Surveillance Program Requirements,Section III.B.3. Specifically, the licensee proposed to revise the reactor vessel material surveillance capsule withdrawal schedule so that supplemental surveillance Capsule B is changed from a standby capsule to being withdrawn at approximately 33.58-34.97 plant effective full power years (EFPY). The licensee explained that the corresponding projected neutron fluences for supplemental surveillance Capsule B will be 3.39E x 1019 neutrons per square centimeter (n/cm2) if it is withdrawn during the Diablo Canyon, Unit 1 24th refueling outage (1R24) or 3.56E x 1019 n/cm2 if it is withdrawn during the Diablo Canyon, Unit 1 25th refueling outage (1R25).

2.0 REGULATORY EVALUATION

The regulations and guidance relevant to this request are the following.

Section I of Appendix H to 10 CFR Part 50, which states, in part:

The purpose of the [reactor vessel] material surveillance program required by this appendix is to monitor changes in the fracture toughness properties of ferritic materials in the reactor vessel beltline region of light water nuclear power reactors which result from exposure of these materials to neutron irradiation and the thermal environment. Under the program, fracture toughness test data are Enclosure

obtained from material specimens exposed in surveillance capsules, which are withdrawn periodically from the reactor vessel.

Section III.B.1 of Appendix H to 10 CFR Part 50, which states, in part:

The design of the surveillance program and the withdrawal schedule must meet the requirements of the edition of ASTM E 185 [an industry standard by ASTM International, formerly known as American Society for Testing and Materials] that is current on the issue date of the ASME code [American Society of Mechanical Engineers Boiler and Pressure Vessel Code] to which the reactor vessel was purchased; . later editions of ASTM E 185 may be used, but including only those editions through 1982.

Section III.B.3 of Appendix H to 10 CFR Part 50, which states:

A proposed withdrawal schedule must be submitted with a technical justification as specified in [10 CFR] 50.4. The proposed schedule must be approved prior to implementation.

U.S. Nuclear Regulatory Commission (NRC, the Commission) Administrative Letter 97-04, NRC Staff Approval for Changes to 10 CFR Part 50, Appendix H, Reactor Vessel Surveillance Specimen Withdrawal Schedules, dated September 30, 1997 (ML031210296), which states, in part:

The Commission found that while 10 CFR Part 50, Appendix H, II.B.3 requires prior NRC approval for all withdrawal schedule changes, only certain changes require license amendments as the process to be followed for such approval.

Specifically, those changes that do not conform to the ASTM standard referenced in Appendix H (ASTM E-185, Standard Practice for Conducting Surveillance Tests for Light-Water Cooled Nuclear Power Reactor Vessels) will require approval by the license amendment process, whereas changes that conform to the ASTM standard require only staff verification of such conformance.

NUREG-1801, Revision 2, Generic Aging Lessons Learned (GALL) Report, dated December 2010 (ML103490041), which lists generic aging management reviews of systems, structures, and components (SSCs) that may be in the scope of a license renewal application (LRA) and identifies aging management programs that are determined to be acceptable to manage aging effects of these SSCs.

3.0 TECHNICAL EVALUATION

3.1 Licensees Proposal for Diablo Canyon, Unit 1 In its submittal for Diablo Canyon, Unit 1, dated May 15, 2023, the licensee indicated that the reactor vessel material surveillance program withdrawal schedule is located in the Updated Final Safety Analysis Report (UFSAR), Revision 26, dated September 2021 (Package ML21306A142), and that the proposed change would revise the supplemental surveillance Capsule B from being a standby capsule to being scheduled for withdrawal during the 1R24 (fall 2023) or the 1R25 (spring 2025) (i.e., at 33.58 or 34.97 EFPY, respectively). The licensee explained that the equivalent exposure on supplemental surveillance Capsule B if it is

withdrawn during the 1R24 will have a projected neutron fluence of 3.39E x 1019 n/cm2 or during the 1R25 will have a projected neutron fluence of 3.56 x 1019 n/cm2. As reflected in enclosure 2 of the submittal, the licensee provided the proposed changes to the Diablo Canyon, Unit 1 reactor vessel material surveillance program withdrawal schedule in table 5.2-22 of the Diablo Canyon UFSAR.

3.2 NRC Staff Review Section III.B.1 of Appendix H to 10 CFR Part 50 states, in part, that:

The design of the surveillance program and the withdrawal schedule must meet the requirements of the edition of the ASTM E 185 that is current on the issue date of the ASME code to which the reactor vessel was purchased; for reactor vessels purchased after 1982, the design of the surveillance program and the withdrawal schedule must meet the requirements of ASTM E 185-82 [Standard Practice for Conducting Surveillance Tests for Light-Water Cooled Nuclear Power Reactor Vessels]. For reactor vessels purchased in or before 1982, later editions of ASTM E 185 may be used, but including only those editions through 1982.

The licensee stated that the ASTM E 185 edition of record for Diablo Canyon, Unit 1 is ASTM E 185-70, Standard Recommended Practice for Surveillance Tests for Nuclear Reactor Vessels, and that a Diablo Canyon, Unit 1 supplemental reactor vessel material surveillance program capsule withdrawal schedule was requested by letter dated March 31, 1992, and approved by the NRC by letter dated September 4, 1992 (ML16341G687).

ASTM E 185-70 recommends that capsules be withdrawn at three or more separate times, specifically including that one capsule be removed at a neutron fluence corresponding to the neutron exposure of the reactor vessel at no greater than 30 percent of the design life and one other capsule removed at a neutron exposure corresponding to the neutron fluence of the reactor vessel near the end of its design life. As of June 2023, the licensee has withdrawn and tested a total of three surveillance capsules (i.e., Capsules S, Y, and V) for Diablo Canyon, Unit 1. The test results from the latest surveillance capsule (i.e., Capsule V) are documented in WCAP-15958, Revision 0, Analysis of Capsule V from Pacific Gas and Electric Company Diablo Canyon Unit 1 Reactor Vessel Radiation Surveillance Program, dated January 2003 (Package ML031400352). Per UFSAR table 5.2-22, Capsule V received a neutron fluence of 1.36 x 1019 n/cm2 after an irradiation time of 14.3 EFPY. This report indicates that the calculated and best estimate neutron fluence at the vessel inner radius at the end of 40 years of plant operation (i.e., 32 EFPY) are 1.26 x 1019 n/cm2 and 1.14 x 1019 n/cm2, respectively.

Based on a review of the surveillance capsules that have already been withdrawn and tested for Diablo Canyon, Unit 1, the NRC staff notes that additional capsules are not needed to satisfy the requirements of Appendix H to 10 CFR Part 50 and ASTM E 185-70 for the current operating license period (i.e., 40 years). As such, the licensees compliance with Appendix H to 10 CFR Part 50 and ASTM E 185-70 with respect to the current operating license period for Diablo Canyon, Unit 1 forms no part of the NRC staffs evaluation of the licensees proposed revision to the withdrawal schedule for supplemental surveillance Capsule B, which is discussed below.

By letter dated October 31, 2022 (ML22304A691), the licensee requested that the NRC resume its review of a previously withdrawn LRA for Diablo Canyon, and if that request is not granted, the licensee requested approval to submit a new LRA for Diablo Canyon by December 31, 2023, and still receive timely renewal protection under 10 CFR 2.109(b). By letter dated March 2, 2023 (Package ML23026A102), the NRC staff granted an exemption for Diablo Canyon such that if PG&E submits an LRA no later than December 31, 2023, and if the staff finds it acceptable for docketing, the existing operating licenses for Diablo Canyon will be in timely renewal under the NRCs regulations until the NRC has made a final determination on the LRA.

Given that there is the potential for the licensee to submit an LRA for Diablo Canyon, the NRC staff understands the requested revision of the reactor vessel material surveillance capsule withdrawal schedule for Diablo Canyon, Unit 1 to be proactively addressing surveillance data needs to support the potential for the submission of an LRA and, therefore, addresses the request based on this understanding.

The NRC staff notes that NUREG-1801, Revision 2 provides the recommendation of aging management programs that the staff determined are adequate for the period of extended operation. Specifically, NUREG-1801, Revision 2, section XI.M31, Reactor Vessel Surveillance, recommends that the program withdraws one capsule at an outage in which the capsule receives a neutron fluence of between one and two times the peak reactor vessel wall neutron fluence at the end of the period of extended operation. In its submittal, the licensee stated that the projected maximum neutron fluence calculated for the potential license renewal period (i.e., 60 years of plant operation) at Diablo Canyon, Unit 1 is 2.01 x 1019 n/cm2 (E>1 MeV). The NRC staff notes that the proposed withdrawal of supplemental surveillance Capsule B during the 1R24 or 1R25 would equate to the capsule being exposed to either a neutron fluence of 3.39 x 1019 n/cm2 or 3.56 x 1019 n/cm2, respectively (i.e., 1.69 times to 1.77 times the maximum fluence expectations for 60 years of operation).

The licensee has already fulfilled its reactor vessel material surveillance requirements for Diablo Canyon, Unit 1 for the current operating license period (i.e., 40 years), but is proactively addressing surveillance data needs to support the potential for the submission of an LRA. The proposed revised withdrawal schedule for supplemental surveillance Capsule B will accomplish addressing (1) the underlying purpose of Appendix H to 10 CFR Part 50 (i.e., monitor changes in the fracture toughness properties of the reactor pressure vessel) and (2) recommendations in NUREG-1801, Revision 2, for the period of extended operation (i.e., 60 years). Therefore, the NRC staff finds that the licensees proposed revised withdrawal schedule for supplemental surveillance Capsule B to be tested following its withdrawal during the 1R24 or 1R25 (in fall 2023 or spring 2025, respectively) is acceptable. The NRC staff concludes that the withdrawal and testing of supplemental surveillance Capsule B supplements the requirements of the reactor vessel material surveillance program for the current license period at Diablo Canyon, Unit 1. The NRC staff notes that a report containing the test results for supplemental surveillance Capsule B must be reported to the NRC within 18 months of the capsule withdrawal in accordance with Section IV.A of Appendix H to 10 CFR Part 50.

4.0 CONCLUSION

Based on the above evaluation, the NRC staff concludes that the proposed revised surveillance capsule withdrawal schedule for supplemental surveillance Capsule B for Diablo Canyon, Unit 1 to be withdrawn during the 1R24 (fall 2023) or 1R25 (spring 2025) (i.e., 33.58 or 34.97 EFPY, respectively) is acceptable; therefore, the NRC staff approves this surveillance capsule withdrawal schedule. However, the NRC staff does not make any conclusion regarding the future use of the subject capsule in any potential future licensing applications or license periods.

Principal Contributors: O. Yee, NRR C. Fairbanks, NRR Date: July 20, 2023

ML23199A312 *concurrence via email OFFICE NRR/DORL/LPL4/PM NRR/DORL/LPL4/LA* NRR/DNRL/NVIB/BC*

NAME SLee PBlechman ABuford DATE 7/18/2023 7/19/2023 6/27/2023 OFFICE NRR/DORL/LPL4/BC*

NAME JDixon-Herrity DATE 7/20/2023