ML20322A009
| ML20322A009 | |
| Person / Time | |
|---|---|
| Site: | Limerick  |
| Issue date: | 12/10/2020 |
| From: | James Danna Plant Licensing Branch 1 |
| To: | Bryan Hanson Exelon Generation Co, Exelon Nuclear |
| Sreenivas V, NRR/DORL/LPLI, 415-2597 | |
| References | |
| EPID L-2020-LLR-0043 | |
| Download: ML20322A009 (12) | |
Text
December 10, 2020 Mr. Bryan C. Hanson Senior Vice President Exelon Generation Company, LLC President and Chief Nuclear Officer Exelon Nuclear 4300 Winfield Road Warrenville, IL 60555
SUBJECT:
LIMERICK GENERATING STATION, UNITS 1 AND 2 - ISSUANCE OF ALTERNATIVE REQUESTS 41-VRR-8 AND 41-VRR-7 REGARDING CERTAIN INSERVICE TESTING PROGRAM REQUIREMENTS FOR SAFETY RELIEF VALVES (EPID L-2020-LLR-0043)
Dear Mr. Hanson:
By letter dated February 5, 2020 (Agencywide Documents and Access Management System (ADAMS) Accession No. ML20036E488), as supplemented by letters dated May 27, 2020, and June 26, 2020 (ADAMS Accession Nos. ML20149K328 and ML20178A514, respectively), Exelon Generation Company, LLC (the licensee) proposed an alternative to its Inservice Testing (IST)
Program. In particular, the licensee requested implementation of alternative requests 41-VRR-8 and 41-VRR-7 with respect to certain IST requirements for safety relief valves in the American Society of Mechanical Engineers (ASME) Operation and Maintenance of Nuclear Power Plants, Division 1, OM Code: Section IST (OM Code), for the IST Program at Limerick Generating Station (Limerick), Units 1 and 2, during the fourth 10-year IST Program interval.
Specifically, pursuant to the requirements of Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(z)(1), Acceptable level of quality and safety, the licensee requested to implement proposed alternatives 41-VRR-8 and 41-VRR-7 on the basis that these testing alternatives for specific safety relief valves will provide an acceptable level of quality and safety.
The U.S. Nuclear Regulatory Commission (NRC) staff has determined that proposed alternative requests 41-VRR-8 and 41-VRR-7 provide an acceptable level of quality and safety for the testing of the safety relief valves. Accordingly, the NRC staff concludes that the licensee has adequately addressed the regulatory requirements set forth in 10 CFR 50.55a(z)(1) for 41-VRR-8 and 41-VRR-7. Therefore, the NRC staff authorizes the use of alternative requests 41-VRR-8 and 41-VRR-7 for the remainder of fourth 10-year IST program interval at Limerick, Units 1 and 2, which began on January 8, 2020, and is scheduled to end on January 7, 2030.
All other ASME OM Code requirements for which relief was not specifically requested and approved remain applicable.
B. Hanson
If you have any questions, please contact the Limerick project manager, V. Sreenivas, at 301-415-2597 or V.Sreenivas@nrc.gov.
Sincerely, James G. Danna, Chief Plant Licensing Branch I Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-352 and 50-353
Enclosure:
Safety Evaluation cc: Listserv James G.
Danna Digitally signed by James G. Danna Date: 2020.12.10 19:47:23 -05'00'
Enclosure SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION ALTERNATIVE REQUESTS 41-VRR-8 AND 41-VRR-7 FOURTH 10-YEAR INSERVICE TESTING PROGRAM INTERVAL EXELON GENERATING COMPANY, LLC LIMERICK GENERATING STATION, UNITS 1 AND 2 DOCKET NOS. 50-352 AND 50-353
1.0 INTRODUCTION
By letter dated February 5, 2020 (Agencywide Documents and Access Management System (ADAMS) Accession No. ML20036E488), as supplemented by letters dated May 27, 2020, and June 26, 2020 (ADAMS Accession Nos. ML20149K328 and ML20178A514, respectively),
Exelon Generation Company, LLC (Exelon, the licensee) submitted requests to the U.S. Nuclear Regulatory Commission (NRC) for alternatives to its Inservice Testing (IST)
Program. In particular, the licensee requested implementation of alternative requests 41-VRR-8 and 41-VRR-7 with respect to certain IST requirements for safety relief valves (SRVs) in the American Society of Mechanical Engineers (ASME) Operation and Maintenance of Nuclear Power Plants, Division 1, OM Code: Section IST (OM Code), for the IST Program at Limerick Generating Station (Limerick), Units 1 and 2, during the fourth 10-year IST Program interval.
Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(z)(1)), the licensee requested to implement proposed alternatives 41-VRR-8 and 41-VRR-7 on the basis that these testing alternatives for specific SRVs will provide an acceptable level of quality and safety.
In its submittal dated February 5, 2020, the licensee proposed alternative request GVVR-9 related to use of ASME OM Code Case OMN-17, Alternative Rules for Testing ASME Class 1 Pressure Relief/Safety Relief Valves. The NRC staff noted that the identification number GVVR-9 is being used by the licensee for a different request during the fourth 10-year IST Program interval. In response, the licensee submitted the supplemental letter dated May 27, 2020, which changed this alternative request number from GVVR-9 to 41-VRR-8.
2.0 REGULATORY EVALUATION
The NRC regulations in 10 CFR 50.55a(f)(4), Inservice testing standards requirement for operating plants, state, in part, that:
Throughout the service life of a boiling or pressurized water-cooled nuclear power facility, pumps and valves that are within the scope of the ASME OM Code must meet the inservice test requirements (except design and access provisions) set forth in the ASME OM Code and addenda that become effective subsequent to editions and addenda specified in [10 CFR 50.55a(f)(2) and (3)] and that are incorporated by reference in [10 CFR 50.55a(a)(1)(iv)], to the extent practical within the limitations of design, geometry, and materials of construction of the components.
The NRC regulations in 10 CFR 50.55a(z) state, in part, that alternatives to the requirements of paragraph (f) of 10 CFR 50.55a may be used, when authorized by the NRC, if the licensee demonstrates (1) the proposed alternatives would provide 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.
The Limerick, Units 1 and 2, fourth 10-year IST Program interval began on January 8, 2020, and is scheduled to end on January 7, 2030. The applicable ASME OM Code edition for the Limerick, Units 1 and 2, fourth 10-Year IST Program interval is the 2012 Edition, which is incorporated by reference in 10 CFR 50.55a with conditions.
3.0 TECHNICAL EVALUATION
3.1 Licensees Alternative Request 41-VRR-8 ASME OM Code, subsection ISTA, General Requirements, paragraph ISTA-3130, Applicable of Code Cases, subparagraph (b), states that Code Cases shall be applicable to the edition and addenda in the test plan. Pursuant to 10 CFR 50.55a, Codes and standards, paragraph (z)(1), the licensee requested an alternative to ISTA-3130(b) requirements for implementing Code Case OMN-17, "Alternative Rules for Testing ASME Class 1 Pressure Relief/Safety Valves" (Reference 2). The basis of this request is that the proposed alternative would provide an acceptable level of quality and safety.
ASME OM Code Case OMN-17 provides alternative rules for the testing of ASME BPV Code Class 1 SRVs in lieu of the required frequencies specified in ASME OM Code, Mandatory Appendix I, paragraph I-1320. ASME OM Code, Mandatory Appendix I, Inservice Testing of Pressure Relief Devices in Light-Water Reactor Nuclear Plants, paragraph I-1320, Test Frequencies, Class 1 Pressure Relief Valves, states, in part, that Class 1 pressure relief valves shall be tested at least once every 5 years, starting with initial electric power generation.
ASME OM Code Case OMN-17 specifies that alternative test frequency requirements may be used in lieu of the requirements in ASME OM Code, Mandatory Appendix I, paragraph I-1320.
The licensee requested to use proposed alternative 41-VRR-8 for the main steam line (MSL)
ASME Boiler and Pressure Vessel Code (BPV Code) Class 1 SRVs as specified in Table 1 below.
Table 1 Components Description ASME BPV Code Class ASME OM Category PSV-41-1F013A MSL SRV on MSL A 1
C PSV-41-1F013B MSL SRV on MSL B 1
C PSV-41-1F013C MSL SRV on MSL C 1
C PSV-41-1F013D MSL SRV on MSL D 1
C PSV-41-1F013E MSL SRV on MSL A 1
C PSV-41-1F013F MSL SRV on MSL B 1
C PSV-41-1F013G MSL SRV on MSL C 1
C PSV-41-1F013H MSL SRV on MSL D 1
C PSV-41-1F013J MSL SRV on MSL A 1
C PSV-41-1F013K MSL SRV on MSL B 1
C PSV-41-1F013L MSL SRV on MSL C 1
C PSV-41-1F013M MSL SRV on MSL D 1
C PSV-41-1F013N MSL SRV on MSL B 1
C PSV-41-1F013S MSL SRV on MSL D 1
C PSV-41-2F013A MSL SRV on MSL A 1
C PSV-41-2F013B MSL SRV on MSL B 1
C PSV-41-2F013C MSL SRV on MSL C 1
C PSV-41-2F013D MSL SRV on MSL D 1
C PSV-41-2F013E MSL SRV on MSL A 1
C PSV-41-2F013F MSL SRV on MSL B 1
C PSV-41-2F013G MSL SRV on MSL C 1
C PSV-41-2F013H MSL SRV on MSL D 1
C PSV-41-2F013J MSL SRV on MSL A 1
C PSV-41-2F013K MSL SRV on MSL B 1
C PSV-41-2F013L MSL SRV on MSL C 1
C PSV-41-2F013M MSL SRV on MSL D 1
C PSV-41-2F013N MSL SRV on MSL B 1
C PSV-41-2F013S MSL SRV on MSL D 1
C
=
Reason for Request===
ASME OM Code Case OMN-17 is unconditionally approved for use in Regulatory Guide (RG) 1.192, Revision 3, Operation and Maintenance Code Case Acceptability, ASME OM Code (ADAMS Accession No. ML19128A261). The Limerick, Units 1 and 2, OM Code of record for the fourth 10-year IST Program interval is the ASME OM Code, 2012 Edition.
However, Code Case OMN-17 states in the Applicability section that it is applicable to the ASME OM Code, 1995 Edition through the 2006 Addenda. As Limerick, Units 1 and 2, will be implementing the ASME OM Code, 2012 Edition, the licensee proposes to implement Code Case OMN-17 for the MSL SRVs.
Code Case OMN-17 allows for extending the test frequencies of the ASME BPV Code Class 1 MSL SRVs to a 72-month (6-year) test interval, with a grace period of 6 months, providing that all of the provisions in Code Case OMN-17 continue to be satisfied.
The licensee proposes that the ASME BPV Code Class 1 MSL SRVs listed in Table 1 of this SE be tested per Code Case OMN-17 at least once every three refueling cycles, with a minimum of
20 percent of the SRVs tested within any 24-month interval. This 20 percent test group would consist of SRVs (complete assemblies) that have not been tested during the current 72-month interval, if they exist. The test interval for any individual SRV would not exceed 72 months, except that a 6-month grace period would be allowed to coincide with refueling outages (RFOs) to accommodate extended shutdown periods. The licensee states that Limerick, Units 1 and 2, will continue to satisfy all of the specified provisions in Code Case OMN-17.
NRC Staff Evaluation
The NRC staff reviewed the information in alternative request 41-VRR-8. The Limerick, Units 1 and 2, MSL SRVs are ASME BPV Code Class 1 SRVs that provide overpressure protection for the main steam system.
The 2012 Edition of the ASME OM Code, subsection ISTC, paragraph ISTC-5240, specifies that SRVs shall meet the IST requirements of Mandatory Appendix I. Mandatory Appendix I, paragraph I-1320, requires, in part, that Class 1 pressure relief valves shall be tested at least once every 5 years, starting with initial electric power generation. The licensee proposes to implement ASME OM Code Case OMN-17, which allows a test interval of 6 years plus a 6-month grace period. Specifically, the licensee proposes to apply Code Case OMN-17 to the 2012 Edition of the ASME OM Code and to use the test interval of 6 years plus a 6-month grace period.
Application of ASME OM Code Cases is addressed in 10 CFR 50.55a(b)(6) through reference to RG 1.192, Revision 3, which lists acceptable Code cases for implementation in IST programs. RG 1.192, Revision 3, lists Code Case OMN-17 as acceptable for use without conditions. Code Case OMN-17 specifies that it is applicable to the 1995 Edition through the 2006 Addenda of the ASME OM Code. The NRC staff considers the use of Code Case OMN-17 to be acceptable when implementing the 2012 Edition of the ASME OM Code.
The NRC staff review of the 2012 Edition of the ASME OM Code and Code Case OMN-17 confirmed that there are no changes in the applicable Code sections referenced within Code Case OMN-17. Based on this evaluation, the NRC staff has determined that the licensees proposed alternative 41-VRR-8 provides an acceptable level of quality and safety for the testing of the SRVs as listed in Table-1 of this SE for the duration of the current IST Program interval at Limerick, Units 1 and 2. Therefore, the NRC staff concludes that the licensee has adequately addressed the regulatory requirements set forth in 10 CFR 50.55a(z)(1) for 41-VRR-8.
3.2 Licensees Alternative Request 41-VRR-7 The licensee requested an alternative to the SRV testing requirements of the ASME OM Code, subsection ISTC, and the provisions in Code Case OMN-17 (alternative request 41-VRR-8).
ASME OM Code, subsection ISTC, paragraph ISTC-5240, states that Safety relief valves shall meet the inservice test requirements of the Mandatory Appendix I of this division.
ASME OM Code, Mandatory Appendix I, 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-yr
interval, if they exist. The test interval for any installed valve shall not exceed 5 yr. The 5-yr test interval shall begin from the date of the as-left set pressure test for each valve.
ASME OM Code Case OMN-17 specifies alternative test frequencies that may be used in lieu of the requirements in ASME OM Code, Mandatory Appendix I, paragraph I-1320.
The licensee requested to use proposed alternative 41-VRR-7 for the ASME BPV Code Class 1 MSL SRVs as specified in Table 2 below.
Table 2 Components Description ASME BPV Code Class ASME OM Category PSV-41-1F013A MSL SRV on MSL A 1
C PSV-41-1F013B MSL SRV on MSL B 1
C PSV-41-1F013C MSL SRV on MSL C 1
C PSV-41-1F013D MSL SRV on MSL D 1
C PSV-41-1F013E MSL SRV on MSL A 1
C PSV-41-1F013F MSL SRV on MSL B 1
C PSV-41-1F013G MSL SRV on MSL C 1
C PSV-41-1F013H MSL SRV on MSL D 1
C PSV-41-1F013J MSL SRV on MSL A 1
C PSV-41-1F013K MSL SRV on MSL B 1
C PSV-41-1F013L MSL SRV on MSL C 1
C PSV-41-1F013M MSL SRV on MSL D 1
C PSV-41-1F013N MSL SRV on MSL B 1
C PSV-41-1F013S MSL SRV on MSL D 1
C PSV-41-2F013A MSL SRV on MSL A 1
C PSV-41-2F013B MSL SRV on MSL B 1
C PSV-41-2F013C MSL SRV on MSL C 1
C PSV-41-2F013D MSL SRV on MSL D 1
C PSV-41-2F013E MSL SRV on MSL A 1
C PSV-41-2F013F MSL SRV on MSL B 1
C PSV-41-2F013G MSL SRV on MSL C 1
C PSV-41-2F013H MSL SRV on MSL D 1
C PSV-41-2F013J MSL SRV on MSL A 1
C PSV-41-2F013K MSL SRV on MSL B 1
C PSV-41-2F013L MSL SRV on MSL C 1
C PSV-41-2F013M MSL SRV on MSL D 1
C PSV-41-2F013N MSL SRV on MSL B 1
C PSV-41-2F013S MSL SRV on MSL D 1
C
=
Reason for Request===
At Limerick, Units 1 and 2, there are 14 Target Rock 3-stage Model 98-67F SRVs installed on the MSLs inside the drywell on each unit. These SRVs are classified within the same IST Program valve group. ASME OM Code, Mandatory Appendix I, subparagraph I-1320(a),
requires that these SRVs have a 5-year test interval. These SRVs are tested every outage in order to comply with the requirement that at least 20 percent of the SRVs are tested every
24 months. This 20 percent group consists of SRVs that have not been tested during the current 5-year interval, if they exist. The test interval for any individual SRV shall not exceed 5 years. Limerick, Units 1 and 2, operate on 24-month refueling cycles.
The use of ASME OM Code Case OMN-17 extends the ASME OM Code, Mandatory Appendix I, subparagraph I-1320(a), 5-year test interval to 6 years, along with the potential use of a 6-month grace period. This Code case allows the licensee to test all of the SRVs listed in Table 2 of this SE over three RFOs instead of two RFOs, which could reduce the number of SRVs tested over three RFOs by seven SRVs per unit.
The licensee conducted a performance assessment of the SRVs listed in Table 2 of this SE and determined that there is reasonable assurance that these SRVs will retain their set pressure within the required drift tolerances if the test interval is extended from 5 years to 8 years. Also, extending the test interval will reduce the occupational radiological dose that is incurred during the removal, testing, and reinstallation of these SRVs.
Proposed Alternative The licensee proposes to extend the minimum test interval for the SRVs listed in Table 2 of this SE from the 5 years permitted by ASME OM Code, Mandatory Appendix I, subparagraph I-1320(a), and the 6 years allowed by Code Case OMN-17 to 8 years from the date of the as-left set pressure test for each SRV. The licensee plans to implement Code Case OMN-17 and proposes two modifications to the Code case provisions. The first modification would be to extend the test interval from 6 years to 8 years, with an allowed 6-month grace period. The test interval will not exceed 81/2 years. With the current plant operating cycles, the maximum time interval between tests for the SRVs at both units would be 36 months. The second modification proposes to change the minimum number of SRVs from each valve group to be tested from 20 percent within any 24-month interval to 40 percent within any 48-month interval, with the 40 percent population consisting of SRVs that have not been tested during the previous 96-month interval, if any exist. All of the other provisions of Code Case OMN-17 will be retained and implemented.
The licensee stated that it began implementing an SRV Best Practices Maintenance Program at Limerick, Units 1 and 2, in 2010, and the licensee has made several enhancements to the program since then. The elements of this program include spring testing, lapping techniques and tools, set pressure adjustment methodology precision, average delay time trending, and internal component condition variations. The program document and licensee-approved vendor procedures are updated to incorporate advances in technology and operating experience from the licensees corporate fleet, the original equipment manufacturer, and the industry. The setpoint drift performance of the SRVs has improved as a result of this program. The licensee reported that it had performed an assessment of the SRVs recently, and the licensee determined that there is reasonable assurance that each SRV will retain the set pressure within the required drift tolerances through an 8-year interval.
All of the Exelon Target Rock 3-Stage SRVs used at the Dresden (Model 74-67F), Peach Bottom (Models73-67F and 74-67F), Quad Cities (Model 74-67F) and Limerick (Model 98-67F) stations are the same base model (i.e., Target Rock 3-Stage Safety Relief Valve Model 67F).
The licensee has been collecting, trending, and analyzing SRV test, maintenance, inspection, and performance data since 2014 for the following plants:
Dresden, Units 2 and 3 (74-67F)
Peach Bottom, Units 2 and 3 (73-67F and 74-67F)
Quad Cities, Units 1 and 2 (74-67F)
Limerick, Units 1 and 2 (98-67F)
The licensee stated that trending and analyzing test data between the plants that have the same SRV model reduce the effective maximum elapsed time between the same model tests. In this case, it would be Target Rock Model 74-67F at Dresden, Units 2 and 3; Target Rock Model 74-67F at Quad Cities, Units 1 and 2; and Target Rock Models73-67F and 74-67F at Peach Bottom, Units 2 and 3; and Target Rock Model 98-67F at Limerick, Units 1 and 2. Also, prior to the implementation of this alternative request, an SRV Best Practices Fleet Engineering Program will be established to define program elements and will specify fleetwide performance tracking and trending guidelines.
The licensees assessment reviewed the SRV as-left and as-found set pressure data since 2014. Based on the time between the as-left and as-found set pressure test for each SRV, the set pressure drift was linearly extrapolated to determine whether the SRV set pressure would still be within the +/-3 percent tolerance following an 8-year period. The licensee has removed and as-found tested 43 SRVs since 2014. Using the linear extrapolation method, which provided the best mathematical approach, the licensee projected that 39 of the 43 SRVs would have lift setpoints within the +/-3 percent tolerance following an 8-year period. The four SRVs that failed were out of tolerance.
The licensee stated that one SRV was disassembled, inspected, and tested before being reinstalled in 2012, and the second SRV was disassembled, inspected, and tested before being reinstalled in 2014. These two SRVs were then removed in 2017 and as-found tested.
The 2017 as-found test results were out of tolerance low with elevated seat leakage. These two SRVs were added to the Exelon SRV Best Practices Maintenance Program in 2014. The SRV maintenance and best practices were completed during the SRV refurbishment prior to reinstallation, and improved SRV performance is expected.
The licensee stated that the third and fourth SRVs were disassembled, inspected, and tested in 2014. The third SRV was recertified tested in 2015 before being reinstalled and then removed in 2019 and as-found tested. The 2014 maintenance and 2014 and 2015 testing occurred prior to the 2018 refinement of the seat leaktightness and SRV setpoint optimization techniques that were included in the Exelon SRV Best Practices Maintenance Program established in 2014.
After testing in 2014, the fourth SRV was reinstalled and then removed in 2019 and as-found tested. The refurbishment included a set pressure change from 1,170 pounds per square inch gage (psig) to 1,190 psig, but the post-adjustment set pressure testing did not include the multiple pressure test lifts that were added to the Exelon SRV Best Practices Maintenance Program after 2014. Consequently, the 2019 as-found test results were out of tolerance low with elevated seat leakage. The SRV maintenance and best practices will be completed during the SRV refurbishment prior to reinstallation, and improved SRV performance is expected.
The SRV Best Practices Maintenance Program requires all SRVs to be disassembled and inspected prior to as-left testing and installation. The program consists of methods and philosophies concerning maintenance, inspection, and techniques, which use the SRV manufacturers recommended maintenance practices and enhancements identified by the licensee.
The licensee will also continue to disassemble and inspect the SRVs after as-found set pressure testing. As stated above, each SRV will also be disassembled and inspected prior to as-left testing and installation, as well as other provisions specified in Code Case OMN-17.
NRC Staff Evaluation
The licensee plans to implement ASME OM Code Case OMN-17, if authorized, in response to alternative request 41-VRR-8 and is proposing two modifications to the provisions in the Code Case. The first modification is to extend the SRV test interval from 6 years to 8 years from the date of the as-left set pressure test and retain the allowed 6-month grace period. The second modification is to change the minimum number of SRVs to be tested from each group. Code Case OMN-17 specifies selecting 20 percent of the SRVs from each SRV group to be tested within any 24-month interval. The licensee is requesting to change this provision to 40 percent of the SRVs from each SRV group to be tested within any 48-month interval, with the 40 percent population consisting of SRVs that have not been tested during the previous 96-month interval, if they exist. This change will result in the same number of SRVs in each group tested during a 48-month interval as would be tested during two 24-month intervals.
In its alternative request, the licensee stated that an SRV Best Practices Maintenance Program has been in place since 2010. The elements of the program include spring testing, lapping techniques and tools, set pressure adjustment methodology precision, average delay trending, and internal component condition variations. For the SRVs listed in Table 2 of this SE, the licensee applies tighter tolerances to the pilot abutment and preload gaps, which reduce the likelihood of vibration-induced seat leakage caused by pressure transients. These licensee activities reduce the probability of flow-induced vibration issues caused by pressure transients.
The licensee also disassembles and inspects the SRVs after as-found set pressure testing and before as-left set pressure testing. If any internal parts are found damaged, they are replaced.
The licensee reported that the setpoint drift of the SRVs has improved since implementing the SRV Best Practices Maintenance Program. The licensee reviewed the as-left and as-found set pressure test data for the SRVs since 2014 and then linearly extrapolated the set pressure drift to determine that the SRV set pressure would still be within the acceptable +/-3 percent tolerance after 8 years of service. The licensee has removed 43 SRVs since 2014 and performed as-found set pressure tests. Using the linear extrapolation method, the licensee determined that 39 of the SRVs would have a set pressure within the +/-3 percent tolerance for more than 8 years. The four SRVs that failed were out of tolerance low and were maintained and tested prior to the refinement of the upgraded lapping, pilot abutment, and preload gap settings optimization techniques that were added to the SRV Best Practices Maintenance Program in 2014. The SRV maintenance and best practices will be completed during the SRV refurbishment prior to reinstallation, and improved SRV performance is expected.
During its review of proposed alternative 41-VRR-7, the NRC staff requested the licensee to describe any measures to obtain information on the performance of the SRVs at intervals more frequently than once every 48 months, such as staggering the testing at different reactor units that have the same SRV model. In its letter dated June 26, 2020, the licensee stated that the maximum time elapsed between SRV tests would be 36 months at Limerick, Units 1 and 2. The licensee indicated that since 2014, it has been collecting, trending, and analyzing SRV test, maintenance, inspection, and performance data for each Exelon nuclear power plant unit listed in its letter. In particular, the licensee noted that Dresden, Units 2 and 3; Quad Cities, Units 1 and 2; and Peach Bottom, Units 2 and 3 use the same SRV base model as Limerick, Units 1 and 2. The licensee stated that trending and analyzing test data between the stations that have the same SRV model reduce the effective maximum elapsed time between same model SRV tests. Prior to implementing this alternative request, the licensee will establish an SRV Best Practices Fleet Engineering Program to define program elements and will specify fleetwide
performance tracking and trending guidelines. This program will allow the licensee to detect negative trends and maintain SRV set pressures within the +/-3 percent tolerance.
Based on the licensees SRV Best Practices Maintenance Program that has been implemented for these SRVs, the implementation of an SRV Best Practices Fleet Engineering Program prior to implementing this alternative request to share applicable SRV test data between Exelon nuclear power plant units and the results of the SRV as-left and as-found set pressure test data, the NRC staff finds that the proposed alternative 41-VRR-7 to extend the SRV test interval from 6 years to 8 years from the date of the as-left set pressure test provides an acceptable level of quality and safety for the testing of the SRVs. Based on this evaluation, the NRC staff has determined that the licensees proposed alternative 41-VRR-7 provides an acceptable level of quality and safety for the testing of the SRVs as listed in Table 2 of this SE for the duration of the current IST Program interval at Limerick, Units 1 and 2. Therefore, the NRC staff concludes that the licensee has adequately addressed the regulatory requirements set forth in 10 CFR 50.55a(z)(1) for 41-VRR-7.
4.0 CONCLUSION
As set forth above, the NRC staff has determined that proposed alternative requests 41-VRR-8 and 41-VRR-7 provide an acceptable level of quality and safety for the testing of the SRVs listed in Tables 1 and 2 of this SE. Accordingly, the NRC staff concludes that the licensee has adequately addressed the regulatory requirements set forth in 10 CFR 50.55a(z)(1) for 41-VRR-8 and 41-VRR-7. Therefore, the NRC staff authorizes the use of alternative requests 41-VRR-8 and 41-VRR-7 for the remainder of fourth 10-year IST Program interval at Limerick, Units 1 and 2, which began on January 8, 2020, and is scheduled to end on January 7, 2030.
All other ASME OM Code requirements for which relief or an alternative was not specifically requested and approved as part of this request remain applicable.
Principal Contributor: G Bedi Date: December 10, 2020
- by e-mail OFFICE NRR/DORL/LPL1/PM* NRR/DORL/LPL1/LA* NRR/DEX/EMIB/BC* NRR/DORL/LPL1/BC*
NAME VSreenivas LRonewicz ABuford JDanna DATE 11/19/2020 11/19/2020 09/24/2020 12/10/2020