ML22332A549
| ML22332A549 | |
| Person / Time | |
|---|---|
| Site: | Quad Cities  |
| Issue date: | 12/21/2022 |
| From: | Nancy Salgado NRC/NRR/DORL/LPL3 |
| To: | Rhoades D Constellation Energy Generation, Constellation Nuclear |
| References | |
| EPID L-2022-LLR-0018 | |
| Download: ML22332A549 (1) | |
Text
December 21, 2022 Mr. David P. Rhoades Senior Vice President Constellation Energy Generation, LLC President and Chief Nuclear Officer Constellation Nuclear 4300 Winfield Road Warrenville, IL 60555
SUBJECT:
QUAD CITIES NUCLEAR POWER STATION, UNITS 1 AND 2 - PROPOSED ALTERNATIVE TO THE REQUIREMENTS OF THE ASME OM CODE (EPID L-2022-LLR-0018)
Dear Mr. Rhoades:
By letter dated February 17, 2022 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML22048B569), Constellation Energy Generation, LLC, (the licensee),
as supplemented by letter dated June 30, 2022 (ML22181B098), submitted an alternative request to the U.S. Nuclear Regulatory Commission (NRC) to the requirements of the American Society of Mechanical Engineers (ASME) Code for Operation and Maintenance of Nuclear Power Plants (OM Code), associated with valve inservice testing (IST) at Quad Cities Nuclear Power Station, Units 1 and 2 (Quad Cities).
Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR), part 50, section 55a, paragraph (z), subparagraph (1) (10 CFR 50.55a(z)(1)), to implement alternative request RV-09 for the frequency of the testing of certain main steam safety valves (MSSVs) at Quad Cities on the basis that the proposed alternative provides an acceptable level of quality and safety.
The NRC staff has reviewed the subject request and concludes, as set forth in the enclosed safety evaluation (SE), the proposal described in described in alternative request RV-09 to extend the required test interval for the MSSVs listed in table 1 of this SE from 6 years to 8 years from the date of the as-left set pressure test and to change the minimum number of MSSVs from each group to be tested from 20 percent within any 24-month interval to 40 percent within any 48-month interval will provide an acceptable level of quality and safety in achieving reasonable assurance of the operational readiness of the MSSVs within the scope of this request. Accordingly, the NRC staff concludes that the licensee has adequately addressed the regulatory requirements set forth in 10 CFR 50.55a(z)(1) for alternative request RV-09.
Therefore, the NRC staff authorizes the use of alternative request RV-09 for the sixth 10-year IST program interval at Quad Cities, which is scheduled to start on February18, 2023, and to end on February 17, 2033.
All other ASME OM Code requirements as incorporated by reference in 10 CFR 50.55a for which an alternative was not specifically requested, and authorized, in the subject request remain applicable.
If you have any questions, please contact the Project Manager, Robert Kuntz at 301-415-3733 or via e-mail at Robert.Kuntz@nrc.gov.
Sincerely, Nancy L. Salgado, Chief Plant Licensing Branch III Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-254 and 50-265
Enclosure:
Safety Evaluation cc: Listserv Nancy L.
Salgado Digitally signed by Nancy L. Salgado Date: 2022.12.21 10:47:12 -05'00'
Enclosure SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO ALTERNATIVE REQUEST RV-09 CONSTELLATION ENERGY GENERATION, LLC QUAD CITIES NUCLEAR POWER STATION, UNITS 1 AND 2 DOCKET NOS. 50-254 AND 50-265
1.0 INTRODUCTION
By a letter dated February 17, 2022 (Agencywide Documents and Access Management System (ADAMS) Accession No. ML22048B569) as supplemented by a letter dated June 30, 2022 (ML22181B098), Constellation Energy Generation LLC (CEG, the licensee) submitted Alternative Request RV-09 to the U.S. Nuclear Regulatory Commission (NRC) in lieu of specific inservice testing (IST) requirements in the 2017 Edition of the American Society of Mechanical Engineers (ASME) Operation and Maintenance of Nuclear Power Plants, Division 1, OM Code:
Section IST (OM Code) for implementation during the sixth 10-year IST program interval at Quad Cities Nuclear Power Station, Units 1 and 2 (Quad Cities).
Specifically, pursuant to subparagraph (1) in paragraph (z), Alternatives to codes and standards requirements, of Section 55a, Codes and standards, in part 50, Domestic Licensing of Production and Utilization Facilities, to Title 10, Energy, of the Code of Federal Regulations (10 CFR 50.55a(z)(1)), the licensee requested to implement proposed alternative request RV-09 for certain main steam safety valves (MSSVs) at Quad Cities on the basis that the proposed alternative will provide an acceptable level of quality and safety.
The sixth 10-year IST program at Quad Cities is scheduled to start on February 18, 2023, and to end on February 17, 2033.
2.0 REGULATORY EVALUATION
2.1 Regulatory Requirements The NRC regulations in 10 CFR 50.55a(f)(4), Inservice testing standards requirement for operating units, 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 IST 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), Alternatives to codes and standards requirements, state that alternatives to the requirements of 10 CFR 50.55a(b) through (h) or portions thereof may be used when authorized by the Director, Office of Nuclear Reactor Regulation. A proposed alternative must be submitted and authorized prior to implementation. The applicant or licensee must demonstrate that:
(1) Acceptable level of quality and safety. The proposed alternative would provide an acceptable level of quality and safety; or (2) Hardship without a compensating increase in quality and safety. Compliance with the specified requirements of this section would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
2.2 ASME OM Code Requirements The applicable Code of Record for the sixth 10-year IST interval at Quad Cites is the 2017 Edition of ASME OM Code as incorporated by reference in 10 CFR 50.55a.
The IST requirements in the ASME OM Code, 2017 Edition, as incorporated by reference in 10 CFR 50.55a, related to this alternative request are as follows:
ASME OM Code, Division 1, Mandatory Appendix I, Inservice Testing of Pressure Relief Devices in Water-Cooled Reactor Nuclear Power Plants, paragraph I-1320, Test Frequencies, Class 1 Pressure Relief Valves, subparagraph (a), 5-Yr Test Interval, states:
Class 1 pressure relief valves shall be tested at least once every 5 yr [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-month 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 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, Revision 1, Alternative Rules for Testing ASME Class 1 Pressure Relief/Safety Valves, Section 1, Test Frequencies, Class 1 Pressure Relief Valves, paragraph (a), 72-Month Test Interval, states:
Class 1 pressure relief valves and PWR [pressurized-water reactor] Main Steam Safety Valves shall be tested at least once every 72 months (6 yr), 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.
3.0 TECHNICAL EVALUATION
3.1 Alternative Request RV-06 3.1.1 ASME Code Components Affected The submittal proposed alternative testing for the MSSVs listed in table 1:
Table 1 Component Description Class Category 1-0203-004A MS-4A Main Steam Safety Valve 1
C 1-0203-004B MS-4B Main Steam Safety Valve 1
C 1-0203-004C MS-4C Main Steam Safety Valve 1
C 1-0203-004D MS-4D Main Steam Safety Valve 1
C 1-0203-004E MS-4E Main Steam Safety Valve 1
C 1-0203-004F MS-4F Main Steam Safety Valve 1
C 1-0203-004G MS-4G Main Steam Safety Valve 1
C 1-0203-004H MS-4H Main Steam Safety Valve 1
C 2-0203-004A MS-4A Main Steam Safety Valve 1
C 2-0203-004B MS-4B Main Steam Safety Valve 1
C 2-0203-004C MS-4C Main Steam Safety Valve 1
C 2-0203-004D MS-4D Main Steam Safety Valve 1
C 2-0203-004E MS-4E Main Steam Safety Valve 1
C 2-0203-004F MS-4F Main Steam Safety Valve 1
C 2-0203-004G MS-4G Main Steam Safety Valve 1
C 2-0203-004H MS-4H Main Steam Safety Valve 1
C 3.1.2 Reason for Request At Quad Cities, there are eight Dresser Model 3777Q MSSVs installed on the main steam lines inside the drywell of each unit. These valves are all in the same IST program valve group. Subparagraph I-1320(a) of the ASME OM Code, appendix I, requires each installed MSSV to be pressure tested at least once every 5 years and a minimum of 20 percent of the MSSVs from each valve group shall be tested within any 24-month interval.
The licensee has implemented ASME OM Code Case OMN-17, which extends this 5-year test interval to 6 years, with the potential use of a 6-month grace period. The use of this code case allows the licensee to test all the MSSVs in table 1 of this safety evaluation (SE) over three refueling outages (RFOs), instead of two RFOs, which could reduce the number of MSSVs tested over three RFOs) by four MSSVs per unit.
The licensee conducted a performance assessment of the MSSVs listed in table 1 of this SE and asserts that these MSSVs will retain their set pressure within the required drift tolerances if the test interval is extended from the Code Case OMN-17 allowed interval of 6 years to 8 years. Also, extending the MSSV test interval will reduce the occupational radiological dose that is incurred during the removal, testing, and reinstallation of these valves.
3.1.3 Licensees Proposed Alternative and Basis for Use For the testing of the MSSVs listed in table 1 of this SE, the alternative proposes to use ASME OM Code Case OMN-17, with two modifications, as an alternative to the requirements in subparagraph I-1320(a) of the ASME OM Code, appendix I. The first modification to Code Case OMN-17 is to extend the test interval specified in the code case from 6 years to 8 years from the date of the as-left pressure test for each valve. With the 6-month grace period allowed by Code Case OMN-17, the test interval will not exceed 8.5 years. The second modification to Code Case OMN-17 is to change the minimum number of MSSVs 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 MSSVs which have not been tested during the previous 96-month interval, if they exist. All other provisions of Code Case OMN-17 will be retained and implemented, including the provision to disable and inspect all MSSVs prior to as-left testing and installation.
The licensee implemented a safety relief valve (SRV) best practices maintenance program at Quad Cities in 2010. The licensee made several enhancements to the program since its implementation to improve MSSV setpoint drift performance. The SRV best practices are developed from the application of the Electric Power Research Institute I Nuclear Maintenance Applications Center (EPRl/NMAC) Safety and Relief Valve Testing and Maintenance Guide and from Constellation (formerly Exelon) Operational Experience (OE). The SRV best practices have been implemented through the licensees oversight of the valve vendors test and rebuild processes. Major program elements include specific performance and inspection criteria and maintenance steps that exceed Original Equipment Manufacturer (OEM) specifications and/or industry established guidelines. The main program elements include: spring testing, lapping techniques and tools, set pressure adjustment methodology precision, average delay time (adt) trending, and internal component condition variations. The alternative requested described these elements in detail. For example, for the Dresser 3777Q MSSVs, tighter tolerances are applied to the spindle dimensions, replacement criteria for spindle runout, and disk to spindle movement (spindle tip rock), which reduce the likelihood of flow-induced vibration concerns.
Collectively, use of these elements has supported an improved setpoint retention in the MSSVs at Quad Cities.
In a letter dated June 30, 2022, the licensee stated that CEG Best Practices procedural guidance, ER-AA-400-1000, Safety & Relief Valve (SRV) Testing, Tracking, and Trending, assigns the corporate SRV program engineer the following responsibilities:
(1) Develop, implement, and update the SRV program (2) Maintain awareness of industry SRV issues (3) Identify and investigate opportunities for program improvements (4) Interface with EPRI, Safety Relief Valve Users Group (SRVUG) and Target Rock Users Group (TRUG)
Additionally, the applicable site SRV owner attends the annual SRVUG and TRUG meetings as a means of staying current with industry experience. These practices provide assurance that the latest industry experienced is identified, evaluated, and captured, as appropriate, in the best practices program.
The licensee recently performed an assessment pertaining to the performance of the Quad Cities Dresser MSSVs. The setpoint drift performance of the MSSVs at Quad Cities has steadily improved by implementation of the enhanced maintenance program. This assessment reviewed as-left/as-found set pressure data back to 1998 and evaluated: whether the valve set pressure drifted up or down, and the absolute set pressure change between tests. Based on the time between the as-left and as-found set pressure test of each MSSV, the set pressure drift was then linearly extrapolated to determine whether the MSSV set pressure would remain within the required +/- 3.0 percent tolerance following an 8-year period. This assessment concluded that the MSSVs will retain their set pressure within the required drift tolerances after extending the test interval from the 6-year interval to an 8-year interval.
The alternative request states that the improved SRV performance can be attributed to both use of ASME OM Code Case OMN-17, which specifies that all valves be disassembled and inspected prior to as-left testing and installation, and the implementation of the SRV best practices program. The licensee will 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 MSSV will be disassembled and inspected prior to as-left testing and installation in accordance with the SRV best practices.
The licensee considers that extending the test interval from 6 to 8 years and revising the intervening outage testing sample size and frequency, are supported based upon past performance, and its evaluation that the Quad Cities Dresser MSSVs are capable of maintaining their setpoint within tolerance over an 8-year period. The proposed alternative asserts that the MSSV testing requirements will also contribute to the principal of maintaining radiation dose as low as reasonably achievable (ALARA).
The alternative request reports that using recent dose measurements associated with MSSV removal and replacement at Quad Cities the average radiological exposure incurred per MSSV has been 0.54 rem. The alternative request states that extending the Code Case OMN-17 testing interval of MSSVs interval from 6 to 8 years would allow extending the schedule of testing of the eight MSSVs on each Quad Cities unit from three to four RFOs, potentially providing a reduction of two MSSVs tested every 10 years per unit. The licensee calculates that this would amount to a potential radiological exposure savings of approximately 2 rem (roentgen equivalent man) for Quad Cities over a 10-year IST interval.
ASME OM Code Case OMN-17 includes a provision that at least 20 percent of the MSSVs be tested every 24 months, with these 20 percent made up of MSSVs which have not been tested during the current 72-month interval, if they exist. The alternative request proposes to revise the 20 percent and 24-month testing provisions to a 48-month interval with at least a minimum of 40 percent of the MSSVs to be tested every 48 months, with these 40 percent made up of MSSVs which have not been tested during the current 96-month interval, if they exist.
The alternative request states that Quad Cities will continue to implement all other provisions within ASME OM Code Case OMN-17. During outages when there is only a partial complement of MSSVs replaced, those MSSVs removed shall be as-found tested prior to resumption of electrical generation. For each MSSV that fails to meet the Quad Cities set pressure acceptance criteria tolerance, two additional MSSVs shall be tested. If either of these two additional MSSVs are found to not meet their Quad Cities set pressure acceptance criteria, then all remaining MSSVs within the same group shall be tested.
The alternative request states that Quad Cities shall also continue to disassemble and inspect each subject MSSV 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 be disassembled and inspected prior to as-left testing and installation to the provisions specified above as well as all other provisions in Code Case OMN-17.
Since 2014, Constellation has been collecting, trending, and analyzing SRV test, maintenance, inspection, and performance data across its fleet of nuclear power plants. Trending and analyzing data between the nuclear power plants, which have the same SRV model, reduces the effective maximum elapsed time between the same model SRV tests.
The alternative request states that 32 MSSVs at Quad Cities have been removed since 2014 and as-found tested. Using a linear extrapolation method, 29 MSSVs were projected to have lift set points within the +/- 3 percent set pressure tolerance for more than 8 years. An evaluation of the three MSSVs that did not meet the 8-year setpoint tolerance criteria was performed by use of the Constellation SRV best practices program to address the cause and corrective actions.
Details of the evaluation are provided in the submittal dated February 17, 2022. This improved performance can be attributed to both use of the ASME OM Code Case OMN-17 which requires that all valves be disassembled and inspected prior to as-left testing and installation, and implementation of the SRV best practices.
3.2
NRC Staff Evaluation
ASME OM Code Case OMN-17, listed in ASME OM Code, 2017 Edition, is only applicable from the 2001 Edition through the 2006 Addenda of the OM Code. Whereas the applicable ASME OM Code Case OMN-17, Revision 1, is approved for use in Regulatory Guide (RG) 1.192, Operation and Maintenance Code Case Acceptability, ASME OM Code, Revision 4 (ML21181A223), which was incorporated by reference in 10 CFR 50.55a on March 3, 2022, and effective on April 4, 2022. In Code Case OMN-17, Revision 1, the only change is the code case acceptability from 2001 Edition through the 2020 Edition of the ASME OM Code.
Therefore, the use of ASME OM Code Case OMN-17, Revision 1, is acceptable. As an alternative to the requirements in Appendix I, paragraph I-1320, of the ASME OM Code (2017 Edition), Code Case OMN-17 allows licensees to extend the test interval for SRVs to 6 years, with the potential use of a 6-month grace period, provided that additional maintenance requirements are met. The NRC staffs review of this application focused on the proposed modifications to ASME OM Code Case OMN-17.
The alternative request states that an SRV best practices maintenance program had 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 MSSVs in table 1 of this SE, the licensee applies tighter tolerances to the spindle dimensions, replacement criteria for spindle runout, and disk to spindle movement (spindle tip rock), which reduces the likelihood of flow-induced vibration concerns.
The licensee also disassembles and inspects the MSSVs after as-found set pressure testing and before as-left set pressure testing. If any internal parts are found damaged, the licensee will replace those parts.
The alternative request states that an assessment of the MSSVs at Quad Cities was performed. The results of this assessment are described in section 3.1 of this SE.
Based on its review of alternative request RV-09, as supplemented, the NRC staff finds that the proposed alternative request for Quad Cities provides an acceptable level of quality and safety, because:
- 1. With the exception of the two modifications discussed in this SE, the licensee will continue to meet the provisions of ASME OM Code Case OMN-17, including the provision to disassemble and inspect all valves prior to as-left testing and installation;
- 2. Constellations SRV best practices maintenance program has been implemented for the MSSVs within the scope of this proposed alternative;
- 3. Constellations SRV best practices fleet engineering program, which includes the sharing of applicable SRV test data between Constellation nuclear power plant units, will be established prior to implementation of this proposed alternative; and
- 4. The results of the as-left and as-found set pressure test data for the Quad Cities MSSVs indicate that the MSSV set pressures will remain within acceptable tolerance levels for at least 8 years.
Based on the licensees SRV best practices maintenance program, the implementation of an SRV best practices fleet engineering program to share applicable SRV test data between the licensees nuclear power plants, and the results of the MSSV as-left and as-found set pressure testing, the NRC staff finds that the proposal in alternative request RV-09 to extend the required test interval for the MSSVs listed in table 1 of this SE from 6 years to 8 years from the date of the as-left set pressure test and to change the minimum number of MSSVs from each group to be tested from 20 percent within any 24-month interval to 40 percent within any 48-month interval, provides an acceptable level of quality and safety in providing reasonable assurance of the operational readiness of the MSSVs within the scope of this request in accordance with 10 CFR 50.55a(z)(1) for the sixth 10-year IST interval at Quad Cities.
4.0 CONCLUSION
As described above, the NRC staff finds that the licensees proposal described in alternative request RV-09 to extend the required test interval for the MSSVs listed in table 1 of this SE from 6 years to 8 years from the date of the as-left set pressure test and to change the minimum number of MSSVs from each group to be tested from 20 percent within any 24-month interval to 40 percent within any 48-month interval will provide an acceptable level of quality and safety in achieving reasonable assurance of the operational readiness of the MSSVs within the scope of this request. Accordingly, the NRC staff concludes that the licensee has adequately addressed the regulatory requirements set forth in 10 CFR 50.55a(z)(1) for alternative request RV-09.
Therefore, the NRC staff authorizes the use of alternative request RV-09 for the sixth 10-year IST interval at Quad Cities, which is scheduled to start on February 18, 2023, and to end on February 17, 2033.
All other ASME OM Code requirements as incorporated by reference in 10 CFR 50.55a for which an alternative was not specifically requested, and authorized, in the subject request remain applicable.
Principal Contributors: Gurjendra Bedi, NRR Thomas Scarbrough, NRR Date: December 21, 2022
ML22332A549 OFFICE NRR/DORL/LPL3/PM NRR/DORL/LPL3/LA NRR/DEX/EMIB/BC NRR/DORL/LPL3/BC NAME RKuntz SRohrer SBailey NSalgado DATE 11/25/22 11/29/22 11/15/2022 12/21/2022