ML25240B625
| ML25240B625 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 08/28/2025 |
| From: | Jonathan Brown Constellation Energy Generation |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML25240B627 | List: |
| References | |
| Download: ML25240B625 (1) | |
Text
WEB-BASED PROPOSED ALTERNATIVE SUBMISSION 10 CFR 50.55a(z)(1)
Submission Date: 08/28/2025 Submitted By: Jesse Brown Submission Availability: Publicly Available Licensee: Constellation Energy Generation, Llc - 36090 Plant Unit(s) and Docket No(s): Calvert Cliffs 2 ( 05000318 )Calvert Cliffs 1 ( 05000317 )
Licensee
Contact:
Jesse Brown (267)-533-6355 jesse.brown@constellation.com Project
Title:
Proposed Alternative for Implementation of Extended Reactor Vessel Inservice Inspection Intervals for Calvert Cliffs Unit 1 and Unit 2 Request Type:
Inservice Inspection (ISI) or Inservice Testing (IST)
Inservice Inpection (ISI)
Requested Completion Date:
August 31, 2026 Proposed Alternative Number or Identifier:
ISI-05-01
Brief Description of Proposed Alternative In accordance with 10 CFR 50.55a(z)(1), Constellation Energy Generation, LLC (CEG), requests NRC approval of a proposed alternative to the requirement of the IWB-2411 Inspection Program, that volumetric examination of essentially 100% of reactor vessel pressure-retaining Examination Category B-A and B-D welds be performed once each 10-year interval for Calvert Cliffs Unit 1 and Unit 2. Specifically, CEG is requesting an extension of the interval between examinations of Category B-A and B-D welds from 10 years to up to 22 years.
There are no regulatory commitments contained in this submittal.
Proposed Duration of Alternative (in terms of ISI/IST Program Interval with Start and End Dates):
This request is applicable to the Calvert Cliffs Unit 1 and Unit 2 ISI program for the fifth and sixth inspection intervals.
5th interval:
- start 7/1/2019
- end 6/30/2029 6th interval:
- start 7/1/2029
- end 6/30/2041 based on implementation of Code Case N-921 Applicable ASME Code Requirements IWB-2411, Inspection Program, requires volumetric examination of essentially 100% of reactor vessel pressure-retaining welds identified in Table IWB-2500-1 once each 10-year interval. The fifth ISI interval is scheduled to end on June 30, 2029, for Calvert Cliffs Unit 1 and Unit 2. The applicable Code for the sixth ISI interval will be selected in accordance with the requirements of 10 CFR 50.55a.
Applicable American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (BPV Code),
or ASME Operation and Maintenanceof Nuclear Power Plants (OM Code), Edition and Addenda ASME Boiler & Pressure Vessel Code,Section XI, "Rules for Inservice Inspection of Nuclear Power Plant Components", 2013 Edition. (Reference 1).
Current ISI or IST Program Interval Number and Start/End Dates
The current fifth ISI interval started on July 01, 2019 and is scheduled to end on June 30, 2029.
Applicable ASME Code Components and/or System Description The affected component is the Calvert Cliffs Unit 1 and Unit 2 reactor vessel (RV), specifically, the following American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (BPV) Code,Section XI (Reference
- 1) examination categories and item numbers covering examinations of the RVs. These examination categories and item numbers are from IWB-2500 and Table IWB-2500-1 of the ASME BPV Code,Section XI.
Category B-A welds are defined as Pressure Retaining Welds in Reactor Vessel.
Category B-D welds are defined as Full Penetration Welded Nozzles in Vessels.
Examination Category Item No. Description B-A B1.11 Circumferential Shell Welds B-A B1.12 Longitudinal Shell Welds B-A B1.21 Circumferential Head Welds B-A B1.22 Meridional Head Welds B-A B1.30 Shell-to-Flange Weld B-A B1.40 Head-to-Flange Weld B-D B3.90 Nozzle-to-Vessel Welds B-D B3.100 Nozzle Inside Radius Section (Throughout this request, the above examination categories are referred to as the subject examinations and the ASME BPV Code,Section XI, is referred to as the Code.)
=
Reason for Request===
An alternative for Calvert Cliffs Unit 1 and Unit 2 is requested from the requirement of the IWB-2411 Inspection Program, that volumetric examination of essentially 100% of reactor vessel pressure-retaining Examination Category B-A and B-D welds be performed once each 10-year interval. Extension of the interval between examinations of Category B-A and B-D welds from 10 years to up to 22 years will result in a reduction in person-rem exposure and examination costs.
The Calvert Cliffs Unit 2 reactor vessel inspection interval was previously extended from a 10-year to a 20 year inspection interval for the Category B-A and B-D welds until the end-of-license (EOL) date of August 13, 2036 per the U.S. NRC safety evaluation report (Reference 2). However, the NRC staff typically grants ISI interval extensions on an interval-by-interval basis. Thus, to maintain consistency with the technical basis in WCAP-16168-NP-A, Revision 3, Calvert Cliffs Unit 2 is resubmitting the proposed alternative using the most recent information and methodologies applicable to the data and calculated values provided in Table 2-2 and Table 3-2.
Full Description of Proposed Alternative Unit 1:
Constellation proposes not to perform the ASME Code required volumetric examination of the Calvert Cliffs Unit 1 reactor vessel full penetration pressure-retaining Examination Category B-A and B-D welds for the fifth ISI interval, currently scheduled for Spring 2028. Constellation will perform the next ASME Code required volumetric examination of the Calvert Cliffs Unit 1 reactor vessel full penetration pressure-retaining Examination Category B-A and B-D welds in the sixth ISI interval no later than Spring 2040. The proposed inspection date is within plus or minus one refueling outage of the date in the latest revised implementation plan, OG-10-238 (Reference 3), which reflects the next inspection being performed in 2038.
Unit 2:
Constellation proposes not to perform the ASME Code required volumetric examination of the Calvert Cliffs Unit 2 reactor vessel full penetration pressure-retaining Examination Category B-A and B-D welds for the fifth ISI interval.
Constellation will perform the next ASME Code required volumetric examination of the Calvert Cliffs Unit 2 reactor vessel full penetration pressure-retaining Examination Category B-A and B-D welds in the sixth ISI interval no later than Spring 2041. The proposed inspection date is within plus or minus one refueling outage of the date in the latest revised implementation plan, OG-10-238 (Reference 3), which reflects the next inspection being performed in 2039.
Description of Basis for Use In accordance with 10 CFR 50.55a(z)(1), an alternate inspection interval is requested on the basis that the current interval can be revised with negligible change in risk by satisfying the risk criteria specified in Regulatory Guide 1.174 (Reference 4) and provide an acceptable level of quality and safety.
The methodology used to conduct this analysis is based on that defined in the study WCAP-16168-NP-A, Revision 3, Risk-Informed Extension of the Reactor Vessel In-service Inspection Interval (Reference 5). This study focuses on risk assessments of materials within the beltline and extended beltline regions of the RV wall. The results of the calculations for Calvert Cliffs Unit 1 and Unit 2 were compared to those obtained from the Combustion Engineering (CE) pilot plant evaluated in WCAP-16168-NP-A, Revision 3. Appendix A of the WCAP identifies the parameters to be compared. Demonstrating that the parameters for Calvert Cliffs Unit 1 and 2 are bounded by the results of the CE pilot plant qualifies Calvert Cliffs Unit 1 and 2 for an ISI interval extension.
The current 5th ISI interval for Calvert Cliffs Unit 1 and Unit 2 is a 10-year duration. During the 6th ISI interval, Calvert Cliffs Unit 1 and Unit 2 are planning to implement ASME Section XI Code Case N-921 (Reference 6), which permits a 12-year duration for the ISI interval, resulting in a 22-year inspection interval. This alternative is justified based on the risk assessment performed in WCAP-16168-NP-A, Revision 3 (Reference 5), Section 3.4 for the CE pilot plant.
Based on the results in Table 4-1 of Reference 5, it was demonstrated that the contribution of eliminating future inspections after the initial 10-year ISI meets the prescribed regulatory criteria for assessing risk (i.e., change in core damage frequency [CDF] and large early release frequency [LERF] less than 1x10-7 per reactor year per page 4-6 of Reference 5). Extension of the interval between examinations of Category B-A and B-D welds from 10 years to up to 22 years provides sufficient margin based on the conclusions from WCAP-16168-NP-A, Revision 3.
Table 1-1 and 1-2 list the critical parameters investigated in the WCAP and compares the results of the CE pilot plant to those of Calvert Cliffs Unit 1 and Unit 2. Tables 2-1, 2-2, 3-1 and 3-2 provide additional information that was requested by the NRC and included in Appendix A of Reference 5.
Include Any Additional Information None Precedents
- 1. Point Beach Nuclear Plant, Units 1 and 2 - Approval of Relief Requests 1-RR-13 and 2-RR-13 Regarding Extension of Inspection Interval for Reactor Pressure Welds from 10 to 20 years (EPID L-2019-LLR-0060), dated March 4, 2020, ADAMS Accession Number ML20036F261.
- 2. St. Lucie Plant, Unit 2 - Authorization of RR#15 Regarding Extension of ASME Requirements Related to Reactor Pressure Vessel Weld Examinations from 10 to 20 years (EPID L-2020-LLR-0283), dated September 30, 2021, ADAMS Accession Number ML21236A131.
- 3. Oconee Nuclear Station, Units 1, 2, and 3 - Authorization and Safety Evaluation for Alternative reactor Pressure Vessel Inservice Inspection Intervals (EPID L-2021-LLR-0004), dated November 19, 2021, ADAMS Accession Number ML21281A141.
- 4. Turkey Point Nuclear Generating Unit Nos. 3 and 4 - Authorization of Relief Request Nos. 8 and 9 Regarding Extension of Inspection Interval for Reactor Pressure Vessel Welds (EPID L-2021-LLR-0038), dated May 10, 2022, ADAMS Accession Number ML22123A192.
References
- 1. ASME Boiler & Pressure Vessel Code,Section XI, "Rules for Inservice Inspection of Nuclear Power Plant Components", 2013 Edition.
- 2. Safety Evaluation for Relief Requests ISI-020 and 021 Reactor Vessel Weld Examination Extension - Calvert Cliffs Nuclear Power Plant, Unit No. 2 (TAC Nos. MD9773 and MD9774), dated April 8, 2009 (ADAMS Accession Number ML090920077).
- 3. PWROG Letter OG-10-238, Revision to the Revised Plan for Plant Specific Implementation of Extended Inservice Inspection Interval per WCAP-16168-NP, Revision 1, Risk-Informed Extension of the Reactor Vessel In-Service Inspection Interval. PA-MSC-0120, PWR Owners Group, July 12, 2010 (ADAMS Accession Number ML11153A033).
- 4. NRC Regulatory Guide 1.174, Revision 1, An Approach for Using Probabilistic Risk Assessment in Risk Informed Decisions on Plant-Specific Changes to the Licensing Basis, U.S. Nuclear Regulatory Commission, November 2002 (ADAMS Accession Number ML023240437).
- 5. Westinghouse Report, WCAP-16168-NP-A, Revision 3, Risk-Informed Extension of the Reactor Vessel In-service Inspection Interval, October 2011 (ADAMS Accession Number ML11306A084).
- 6. ASME Code Case N-921, Alternative 12-yr Inspection Interval Duration Section XI, Division 1, ASME International, dated September 28, 2021.
- 7. NUREG-1874, Recommended Screening Limits for Pressurized Thermal Shock (PTS), U.S. Nuclear Regulatory Commission, March 2010 (ADAMS Accession Number ML15222A848).
- 8. NRC Letter Report, Generalization of Plant-Specific Pressurized Thermal Shock (PTS) Risk Results to Additional Plants, U.S. Nuclear Regulatory Commission, December 14, 2004 (ADAMS Accession Number ML042880482).
- 9. Code of Federal Regulations, 10 CFR Part 50.61a, Alternate Fracture Toughness Requirements for Protection Against Pressurized Thermal Shock Events, U.S. Nuclear Regulatory Commission, Washington D.C., Federal Register, Volume 75, No. 1, dated January 4, 2010 and with corrections to part (g), Volume 75, No. 22, dated February 3, 2010, Volume 75, No. 44, dated March 8, 2010, and Volume 75, No. 227, dated November 26, 2010.
- 10. Joseph M. Farley, Unit 1, Alternative to Inservice Inspection (CAC No. MF6475), dated February 1, 2016 (ADAMS Accession Number ML16013A348).
- 11. Westinghouse Report, WCAP-18624-NP, Revision 0, Analysis of Capsule 83° from the Calvert Cliffs Unit 1 Reactor Vessel Radiation Surveillance Program, April 2021(ADAMS Accession Number ML21210A325).
- 12. Westinghouse Report, WCAP-18958-NP, Revision 0, Analysis of Capsule 83° from the Calvert Cliffs Unit No. 2 Reactor Vessel Radiation Surveillance Program, August 2024 (ADAMS Accession Number ML24240A246).
- 13. NRC Regulatory Guide 1.99, Revision 2, Radiation Embrittlement of Reactor Vessel Materials, U.S. Nuclear Regulatory Commission, May 1988 (ADAMS Accession Number ML003740284).
- 14. Calvert Cliffs Report, CRVSP, Revision 7, Comprehensive Reactor Vessel Surveillance Program, April 27, 2016.
- 15. Calvert Cliffs Nuclear Power Plant Engineering Change Package ECP-25-000173, "Incorporate Calculations and Evaluations Needed for Updates to the Reactor Vessel Surveillance Program - Extend Reactor Vessel ISI Interval".
Attachments Table_1-1.pdf Table_1-2.pdf Table_2-1.pdf Table_2-2.pdf Table_3-1.pdf Table_3-2.pdf