RS-24-106, County Station, Units 1 and 2, Request RV-04, Proposed Alternative to Modify Reactor Pressure Vessel Safety Relief Valve Testing Sampling Requirements Per Inservice Test Program
| ML24331A109 | |
| Person / Time | |
|---|---|
| Site: | LaSalle  |
| Issue date: | 11/25/2024 |
| From: | Steinman R Constellation Energy Generation |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| RS-24-106 | |
| Download: ML24331A109 (1) | |
Text
4300 Winfield Road Warrenville, IL 60555 630 657 2000 Office November 25, 2024 10 CFR 50.55a RS-24-106 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555-0001 LaSalle County Station, Units 1 and 2 Renewed Facility Operating License Nos. NPF-11 and NPF-18 NRC Docket Nos. 50-373 and 50-374
Subject:
Request RV-04, Proposed Alternative to Modify Reactor Pressure Vessel Safety Relief Valve Testing Sampling Requirements per Inservice Test Program In accordance with 10 CFR 50.55a, "Codes and standards," paragraph (z)(1), Constellation Energy Generation, LLC (CEG) requests U.S. Nuclear Regulatory Commission (NRC) approval of the attached alternative associated with the Inservice Testing (IST) Program for LaSalle County Station (LSCS), Units 1 and 2. This request proposes to modify the American Society of Mechanical Engineers (ASME) Operations and Maintenance (OM) Code Case OMN-17, Revision 1 minimum of 20% of the valves from each valve group shall be tested within any 24-month interval with 40% of the valves from each valve group shall be tested within any 48-month interval. The basis for this request is that implementation of the Constellation Safety Relief Valve (SRV) Best Practices Maintenance Program has resulted in high confidence for the SRVs maintaining their set point within tolerance over a six-year period without requiring a minimum of 20% of the valves from each valve group to be tested within any 24-month interval.
The proposed alternative provides an acceptable level of quality and safety, equivalent to compliance with ASME OM requirements.
CEG requests authorization of this request by November 25, 2025. There are no regulatory commitments contained within this letter.
Should you have any questions concerning this letter, please contact Jared Smith at 779-231-6155.
Respectfully, Rebecca L. Steinman Sr. Manager Licensing Constellation Energy Generation, LLC
- Steinman, Rebecca Lee Digitally signed by Steinman, Rebecca Lee Date: 2024.11.25 14:09:55
-06'00'
U.S. Nuclear Regulatory Commission November 25, 2024 Page 2
Attachment:
Request RV-04, Proposed Alternative to Modify Safety Relief Valve Testing Sampling Requirements per Inservice Test Program cc:
Regional Administrator - NRC Region III NRC Project Manager - LaSalle County Station NRC Senior Resident Inspector - LaSalle County Station Illinois Emergency Management Agency - Department of Nuclear Safety
ATTACHMENT LaSalle County Station Units 1 and 2 10 CFR 50.55a Request RV-04, Proposed Alternative to Modify Reactor Pressure Vessel Safety Relief Valve Testing Sampling Requirements per Inservice Test Program (Page 1 of 7)
10 CFR 50.55a Request RV-04, Proposed Alternative for LaSalle County Station, Units 1 and 2, Revision 0 (Page 2 of 7)
- 1.
ASME Code Components Affected The LaSalle County Station (LSCS) Main Steam Safety/Relief Valves (SRVs), as listed in the following table:
Component Description Class Category 1B21-F013C Main Steam Line Safety/Relief Valve 1
C 1B21-F013D Main Steam Line Safety/Relief Valve 1
C 1B21-F013E Main Steam Line Safety/Relief Valve 1
C 1B21-F013F Main Steam Line Safety/Relief Valve 1
C 1B21-F013H Main Steam Line Safety/Relief Valve 1
C 1B21-F013K Main Steam Line Safety/Relief Valve 1
C 1B21-F013L Main Steam Line Safety/Relief Valve 1
C 1B21-F013M Main Steam Line Safety/Relief Valve 1
C 1B21-F013P Main Steam Line Safety/Relief Valve 1
C 1B21-F013R Main Steam Line Safety/Relief Valve 1
C 1B21-F013S Main Steam Line Safety/Relief Valve 1
C 1B21-F013U Main Steam Line Safety/Relief Valve 1
C 1B21-F013V Main Steam Line Safety/Relief Valve 1
C 2B21-F013C Main Steam Line Safety/Relief Valve 1
C 2B21-F013D Main Steam Line Safety/Relief Valve 1
C 2B21-F013E Main Steam Line Safety/Relief Valve 1
C 2B21-F013F Main Steam Line Safety/Relief Valve 1
C 2B21-F013H Main Steam Line Safety/Relief Valve 1
C 2B21-F013K Main Steam Line Safety/Relief Valve 1
C 2B21-F013L Main Steam Line Safety/Relief Valve 1
C 2B21-F013M Main Steam Line Safety/Relief Valve 1
C 2B21-F013P Main Steam Line Safety/Relief Valve 1
C 2B21-F013R Main Steam Line Safety/Relief Valve 1
C 2B21-F013S Main Steam Line Safety/Relief Valve 1
C 2B21-F013U Main Steam Line Safety/Relief Valve 1
C 2B21-F013V Main Steam Line Safety/Relief Valve 1
C
- 2.
Applicable Code Edition and Addenda
The Fourth 10-year interval of the LSCS Inservice Testing (IST) Program is based on the American Society of Mechanical Engineers (ASME) Code for Operation and Maintenance of Nuclear Power Plants (OM Code) - 2004 Edition with Addenda through OMb-2006.
10 CFR 50.55a Request RV-04, Proposed Alternative for LaSalle County Station, Units 1 and 2, Revision 0 (Page 3 of 7)
- 3.
Applicable Code Requirement
Division 1, Mandatory Appendix I, Inservice Testing of Pressure Relief Devices in Light-Water Reactor Nuclear Power Plants, paragraph I-1320, Test Frequencies, Class 1 Pressure Relief Valves, subparagraph (a) 5-Year Test Interval, states:
Class 1 pressure relief valves shall be tested at least once every 5 years, starting with initial electric power generation. No maximum limit is specified for the number of valves to be tested within each interval; however, a minimum of 20% of the valves from each valve group shall be tested within any 24-mo interval. This 20% shall consist of valves that have not been tested during the current 5-year interval, if they exist. The test interval for any installed valve shall not exceed 5 years.
ASME OM Code Case OMN-17, Revision 1, Alternative Rules for Testing ASME Class 1 Pressure Relief/Safety Valves, (Reference 1) Section 1, Test Frequencies, Class 1 Pressure Relief Valves, paragraph (a), 72-Month Test Interval, states:
Class 1 pressure relief valves and PWR Main Steam Safety Valves shall be tested at least once every 72 months (6 years), starting with initial electric power generation. A minimum of 20% of the valves from each valve group shall be tested within any 24-month interval. This 20% shall consist of valves that have not been tested during the current 72-month interval, if they exist. The test interval for any individual valve that is in service shall not exceed 72 months except that a 6-month grace period is allowed to coincide with refueling outages to accommodate extended shutdown periods for ASME OM Code 2015 Edition and prior. For ASME OM Code 2017 Edition and later ISTA-3170 may be utilized to accommodate extended shutdown periods.
- 4.
Reason for Request
In accordance with 10 CFR 50.55a, Codes and standards, paragraph (z)(1), an alternative is proposed to SRV testing requirements of the ASME OM-2004 Code.
The basis of the request is that an SRV set pressure performance assessment supports conclusion that the proposed alternative would provide an acceptable level of quality and safety.
At LSCS the nuclear pressure relief system consists of SRVs located on the main steam lines between the reactor vessel and the first isolation valve within the drywell.
These valves protect against overpressure of the reactor coolant system. The SRVs provide three main protection functions:
- a.
Overpressure relief operation - The valves open automatically to limit a pressure rise.
- b.
Overpressure safety operation - The valves function as safety valves and open (self-actuated operation if not already automatically opened for relief operation) to prevent nuclear system over-pressurization.
- c.
Depressurization operation - The automatic depressurization system (ADS) valves open automatically as part of the emergency core cooling system (ECCS) for events involving small breaks in the nuclear system process barrier (reactor coolant pressure boundary).
10 CFR 50.55a Request RV-04, Proposed Alternative for LaSalle County Station, Units 1 and 2, Revision 0 (Page 4 of 7)
The as-found test of SRVs in the safety mode tests the valves ability to open when steam pressure at the valve inlet overcomes the spring force holding the valve closed. This mode satisfies the ASME Code requirements. SRVs at LSCS are Crosby style 6xRx10 HB-65-BP. Each unit has 13 SRVs installed. It is noted that in Amendment Nos. 232 and 218 to the Operating Licenses of LSCS Units 1 and 2, respectively (Reference 3), the NRC approved a license amendment for Technical Specification 3.4.4. to change the SRV setpoint tolerance to +3% above SRV nameplate pressure and -5% below SRV nameplate pressure. These valves are classified into the same IST program group. Mandatory Appendix I, paragraph I-1320 requires the installed SRVs to be tested at least once every five years starting with initial electric power generation, while ASME OM Code Case OMN-17, Revision 1 requires the SRVs to be tested at least once every 72 months (6 years), starting with initial electric power generation. LSCS is currently operating on a 24-month refueling cycle.
A performance assessment of the LSCS Crosby style 6xRx10 HB-65-BP SRVs as-found and as-left test results concluded that there is reasonable assurance that each SRV will retain the set pressure within the required drift tolerances on a six-year interval with the proposed modification to the required testing of 20% of the relief valves within a 24-month interval. Modifying the SRV testing scope to 40% of the relief valves within a 48-month interval will allow LSCS the scheduling flexibility to contribute to the principals of maintaining radiation dose As Low As Reasonably Achievable (ALARA) by allowing LSCS to reduce radiological exposure incurred during SRV removal, testing, and re-installation by approximately 5 REM for the station over a ten-year IST interval.
- 5.
Proposed Alternative and Basis for Use Constellation proposes that the subject SRVs be tested at least once every 6 (six) years, as granted by ASME Code Case OMN-17, Revision 1, without the requirement of testing 20% of the valves in a 24-month interval. Constellation proposes the approval of an alternative per 10 CFR 50.55a(z)(1) to replace the minimum requirement of 20% of the valves in the group being tested within a 24-month interval with a minimum requirement of 40% of the valves in the group being tested with a 48-month interval.
Due to primary containment layout limitations, LSCS must sequentially access the valves in a strategic manner. The North side has seven SRVs, while the South side has six. When removing the valves, LSCS must commence removal activities with the valves closer to the entrance in order to reach the valves further from the entrance.
Reducing or eliminating that scope of valves being removed solely to support other valve testing resultantly decreases LSCS radiological exposure by approximately 1.6 REM on average including the supporting scaffold and ductwork activities in the drywell. This scoping allowance will enable LSCS to perform a single refueling outage within a 6-year interval without being required to test any of the SRVs. The additional requirements stipulated within ASME Code Case OMN-17, Revision 1 will be retained.
Following the revised guidance of SRV maintenance best practices and the implementation of these practices throughout the fleet, SRV reliability has increased, resulting in decreased SRV test failures.
10 CFR 50.55a Request RV-04, Proposed Alternative for LaSalle County Station, Units 1 and 2, Revision 0 (Page 5 of 7)
LSCS valve performance has consistently improved since 2018, when the SRV Best Practices Maintenance Program was implemented. As a part of LSCS best practice implementation in March of 2018, a 6-point spindle runout measurement was incorporated in order to minimize setpoint drift. Valves installed beginning with L2R17 in 2019 were the first valves to incorporate the 6-point spindle runout measurement.
These valves were then removed and tested during L2R19 (2023) and L1R20 (2024).
The improved valve performance can be attributed to the implementation of the Constellation SRV Best Practices Maintenance Program. This program is comprised of methods and philosophies concerning maintenance, inspection and techniques which uses the SRV manufacturer's recommended maintenance practices and enhancements identified by Constellation that have been broadly termed "Best Practices." This includes as-left testing for setpoint and seat leakage and are described in more detail within Reference 4. Constellation SRV Best Practices are developed from the application of the EPRl/NMAC Safety and Relief Valve Testing and Maintenance Guide (Reference 2) and from Constellation fleet Operational Experience (OE). The Constellation SRV Best Practices have been implemented through Constellation oversight of the valve vendor's test and rebuild processes.
Code Case OMN-17, Revision 1 includes a requirement that at least 20% of the SRVs be tested every 24 months, with these 20% scope made up of SRVs which have not been tested during the previous 72-month interval, if they exist. Testing of a minimum number of SRVs from each valve group within any 24-month interval is intended to have some SRVs tested throughout the six-year interval that would allow for more timely discovery of performance issues than would happen if all the testing was scheduled at the end of the six-year interval. This amendment request proposes to modify the 20% and 24-month testing requirement and instead test 40% of the valves in a 48-month interval. When considering LSCS has the same valve installed on both Units 1 and 2 and refueling outages are staggered, as-found test results for the SRVs will be obtained a minimum of 12 months to a maximum of 36 months after previous testing was performed. Any test or material condition findings that could impact the valves at both units will be evaluated in the Corrective Action Program (CAP) for the unsatisfactory valves as well as the other valves in the group in order to mitigate further potential issues.
LSCS will continue to implement all other requirements contained within ASME Code Case OMN-17, Revision 1. During outages when a partial complement of SRVs is replaced, those SRVs removed shall be as-found tested prior to resumption of electrical generation. To support identification of common cause issues, two additional SRVs shall be tested for each SRV that fails to meet the set +3%/-5% tolerance acceptance criteria. If either of these two additional SRVs are found to not meet their set pressure acceptance criteria, then all remaining SRVs within the same group shall be tested.
LSCS shall also continue to disassemble and inspect each subject SRV following as-found set pressure testing to verify that parts are free of defects resulting from time-related degradation or service-induced wear. Each valve shall also be disassembled and inspected prior to as-left testing and installation to the Constellation Best Practice Maintenance Program requirements provided above as well as all other requirements stipulated in ASME OM Code Case OMN-17, Revision 1.
10 CFR 50.55a Request RV-04, Proposed Alternative for LaSalle County Station, Units 1 and 2, Revision 0 (Page 6 of 7)
A total of eighty-two (82) valves have been tested since 2014, with all valves having passed their as-found lift test. Table 1 shows the total number of tested valves per outage and the number of valves passing the as-found lift test.
Based on the application of the Constellation SRV Best Practices Maintenance Program, the past performance of the SRVs at LSCS demonstrates reasonable assurance that the SRVs will remain within the set point tolerance with the proposed modified test scoping of 40% of valves over a 48-month period. This proposal provides an alternative which would maintain an acceptable level of valve operational readiness, provide an acceptable level of quality and safety pursuant to 10 CFR 50.55a(z)(1) and provide for reduced occupational radiological exposure.
Table 1: SRV Testing Performance Year Outage TotalValvesTested TotalValvesTestedSatisfactorily 2014 L1R15 6
6 2015 L2R15 9
9 2016 L1R16 7
7 2017 L2R16 10 10 2018 L1R17 10 10 2019 L2R17 7
7 2020 L1R18 7
7 2021 L2R18 6
6 2022 L1R19 6
6 2023 L2R19 7
7 2024 L1R20 7
7
- 6.
Duration of Proposed Alternative The proposed alternative will be utilized for the remainder of the current Fourth Ten-Year IST interval (Start: October 12, 2017, End: October 11, 2027).
- 7.
Precedent References 5 and 6 document previously approved alternatives that include the SRV scoping modification requested herein.
10 CFR 50.55a Request RV-04, Proposed Alternative for LaSalle County Station, Units 1 and 2, Revision 0 (Page 7 of 7)
- 8.
References
- 1. ASME OM Code Case OMN-17, Revision 1, Alternative Rules for Testing ASME Class 1 Pressure Relief/Safety Valves
- 2. Electric Power Research Institute / Nuclear Maintenance Applications Center (EPRl/NMAC) Safety and Relief Valve Testing and Maintenance Guide, Revision of TR-105872, Technical Report 3002005362, August 2015
- 3. Letter from Bhalchandra K. Vaidya (U.S. Nuclear Regulatory Commission) to Bryan Hanson (Exelon Generation Company), LaSalle County Station, Units 1 and 2-Issuance of Amendments to Renewed Facility Operating Licenses RE: License Amendment Request to Revise the Technical Specifications Surveillance Requirement 3.4.4.1 and the Lower Setpoint Tolerances for Safety/Relief Valves, dated December 19, 2018 (Accession Number ML18278A030)
- 4. Letter from David P. Helker (Exelon Generation Company) to U.S.
Nuclear Regulatory Commission) Proposed Alternative to Extend Reactor Pressure Vessel Safety Relief Valve Testing Frequency -
Response to Request for Additional Information, dated June 12, 2020 (Accession Number ML20164A188)
- 5. Letter from Nancy L. Salgado (U.S. Nuclear Regulatory Commission) to David Rhoades (Exelon Generation Company), Proposed Alternatives to Extend the Safety Relief Valve Testing Interval, dated January 14, 2021(Accession Number ML21005A061)
- 6. Letter from Jeffrey A. Whited (U.S. Nuclear Regulatory Commission) to Shawn Hafen (Northern States Power Company - Minnesota),
Proposed Alternative Request VR-09 to the Inservice Testing Requirements of the ASME OM Code for Main Steam Safety Relief Valves, dated August 27, 2024 (Accession Number ML24222A182)