ML24222A182

– Proposed Alternative Request VR-09 to the Inservice Testing Requirements of the ASME OM Code for Main Steam Safety Relief Valves

ML24222A182
Person / Time
Site:	Monticello
Issue date:	08/27/2024
From:	Jeffrey Whited NRC/NRR/DORL/LPL3
To:	Hafen S Northern States Power Company, Minnesota
References
EPID L-2023-LLR-0064
Download: ML24222A182 (1)

Text

August 27, 2024 Shawn Hafen Site Vice President Northern States Power Company - Minnesota Monticello Nuclear Generating Plant 2807 West County Road 75 Monticello, MN 55362

SUBJECT:

MONTICELLO NUCLEAR GENERATING PLANT - PROPOSED ALTERNATIVE REQUEST VR-09 TO THE INSERVICE TESTING REQUIREMENTS OF THE ASME OM CODE FOR MAIN STEAM SAFETY RELIEF VALVES (EPID L-2023-LLR-0064)

Dear Shawn Hafen:

By letter dated November 13, 2023, as supplemented by letter dated May 16, 2024, Northern States Power Company, a Minnesota corporation, doing business as Xcel Energy (NSPM, the licensee) submitted alternative request VR-09 to the U.S. Nuclear Regulatory Commission (NRC) for the use of an alternative to certain American Society of Mechanical Engineers (ASME) Code for Operation and Maintenance of Nuclear Power Plants (OM Code) requirements at Monticello Nuclear Generating Plant (Monticello).

Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(z)(1), the licensee proposed to implement ASME Code Case OMN-17, Revision 1, for inservice testing of certain main steam safety relief valves, with two variations described in the enclosed safety evaluation, on the basis that the 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, that NSPM has adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a(z)(1) for alternative request VR-09 at Monticello. Therefore, the NRC staff authorizes the use of Alternative Request VR-09 for the sixth interval IST program at Monticello, which started on October 1, 2022, and is scheduled to end on May 31, 2032.

All other ASME BPV Code or ASME OM Code requirements for which relief or an alternative was not specifically requested and granted or authorized (as appropriate) remain applicable.

S. Hafen If you have any questions, please contact the Project Manager, Brent Ballard, at 301-415-0680 or by e-mail to Brent.Ballard@nrc.gov.

Sincerely, Jeffrey A. Whited, Chief Plant Licensing Branch III Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No(s). 50-263

Enclosure:

Safety Evaluation cc: ListServ Jeffrey A.

Whited Digitally signed by Jeffrey A. Whited Date: 2024.08.27 13:24:06 -04'00'

Enclosure SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION ALTERNATIVE REQUEST VR-09 SIXTH INTERVAL INSERVICE TESTING PROGRAM NORTHEN STATES POWER COMPANY MONTICELLO NUCLEAR GENERATING PLANT DOCKET NUMBER 50-263

1.0 INTRODUCTION

By a letter dated November 13, 2023 (Agencywide Documents and Access Management System (ADAMS) Accession No. ML23317A222) as supplemented by a letter dated May 16, 2024 (ML24137A235), Northern States Power Company, a Minnesota corporation, doing business as Xcel Energy (NSPM, the licensee), submitted Alternative Request VR-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 interval IST program at Monticello Nuclear Generating Plant (Monticello).

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 VR-09 for certain main steam safety relief valves (MSRVs) at Monticello on the basis that the proposed alternative will provide an acceptable level of quality and safety.

The licensee requested this alternative for the sixth interval IST program at Monticello, which started October 1, 2022, and is scheduled to end on May 31, 2032.

2.0 REGULATORY EVALUATION

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.

3.0 TECHNICAL EVALUATION

3.1 Licensees Alternative Request VR-09 Applicable Code Edition The applicable Code of Record for the sixth interval IST program at Monticello is the 2017 Edition of ASME OM Code as incorporated by reference in 10 CFR 50.55a.

ASME Code Components Affected In its submittal, the licensee proposed alternative testing for the main steam line safety/relief valves listed in Table 1:

Table 1 Component Description Class Category RV-2-71A Main Steam Line (MSL) Safety/Relief Valve on MSL A 1

BC RV-2-71B Main Steam Line Safety/Relief Valve on MSL B 1

BC RV-2-71C Main Steam Line Safety/Relief Valve on MSL C 1

BC RV-2-71D Main Steam Line Safety/Relief Valve on MSL D 1

BC RV-2-71E Main Steam Line Safety/Relief Valve on MSL A 1

BC RV-2-71F Main Steam Line Safety/Relief Valve on MSL D 1

BC RV-2-71G Main Steam Line Safety/Relief Valve on MSL B 1

BC RV-2-71H Main Steam Line Safety/Relief Valve on MSL C 1

BC

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Applicable Code Requirement===

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 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.

Licensees Proposed Alternative The 2017 Edition of the ASME OM Code, subsection ISTC, paragraph ISTC-5240, requires that safety relief valves (SRVs) shall meet the IST requirements of Mandatory Appendix I of the ASME OM Code. 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. In alternative request VR-09 for Monticello, the licensee proposes the use of ASME OM Code Case OMN-17 in lieu of ASME OM Code, Appendix I, paragraph I-1320(a),

with two modifications for testing of the MSRVs listed in Table 1 of this SE. The first proposed modification is to extend the test interval from 6 years to 8 years from the date of the as-left pressure test for each valve, while retaining the allowed 6-month grace period. The second proposed modification is to change the minimum number of MSRVs from each group to be tested. Code Case OMN-17, Revision 1, specifies selecting 20 percent of the valves from each valve group to be tested within any 24-month interval. The licensee is requesting to change this provision to allow it to select 40 percent of the valves from each valve group to be tested within any 48-month interval, with the 40 percent population consisting of MSRVs which have not been tested during the previous 96-month interval, if they exist. Although the number of MSRVs tested in any 24-month interval could be reduced, the number of MSRVs tested over any 48-month interval would not change with this proposed alternative. All other provisions of Code Case OMN-17 will be retained and implemented.

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Reason for Request===

At Monticello, there are eight Target Rock, 3-stage, base Model 67F (Model Nos.73-67F and 74-67F) MSRVs installed on the MSLs inside the drywell. All of these MSRVs have a nominal 1109 pounds per square inch gage (psig) setpoint. These MSRVs are included in the same IST program valve group. Paragraph I-1320(a) of the ASME OM Code, appendix I, requires each installed MSRVs to be pressure tested at least once every 5 years, and a minimum of 20 percent of the MSRVs from each valve group to be tested within any 24-month interval. The licensee has implemented ASME OM Code Case OMN-17, Revision 1, 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 MSRVs in Table 1 of this SE over three refueling outages (RFOs), instead of two RFOs, which could reduce the number of MSRVs tested over three RFOs by two MSRVs.

The licensee states that the Monticello MSRVs have had historically good set-pressure performance. The licensee asserts that these MSRVs will retain their set pressure within the required drift tolerances if the test interval is extended from the Code Case OMN-17 allowed interval from 6 years to 8 years. Also, the licensee indicates that extending the MSRV test interval will reduce the occupational radiological dose that occurs during the removal, testing, and reinstallation, of these valves.

Licensees Basis for Use The licensee has incorporated the guidance of 2015 Electric Power Research Institute (EPRI)

Technical Report (TR), Nuclear Maintenance Applications Center: Safety and Relief Valve Testing and Maintenance Guide, revision of TR 105872, TR 3002005362, into the procedures for receipt inspection requirements, predictive maintenance, and inspection of the MSRVs. In its letter dated May 16, 2024, the licensee specified that these procedures are referred to as the SRV precision/critical maintenance practices.

NSPM recently performed an evaluation of the performance of the Target Rock MSRVs. The licensee asserts that there was reasonable assurance that the required setpoint drift tolerance of

+/-3 percent would be met after extending the test interval from the current 6-year interval to the proposed 8-year interval.

The licensee states that this assessment reviewed as-left/as-found set pressure data back to 2017 and identified; (1) Whether the valve set pressure drifted up or down, and (2) the absolute set pressure change between tests. Based on the time between the as-left and as-found set pressure test of each MSRV, the set pressure drift was then linearly extrapolated to determine whether the MSRVs set pressure would still be within the sites required three percent tolerance band following an 8-year period. In Table 2 of Alternative Request VR-09 the licensee summarizes the setpoint drift projection, in years of service, predicting when each MSRV would exceed the +/-3 percent set pressure tolerance band for MSRVs removed and tested since 2017.

Table 2 of Alternative Request VR-09 includes as-left testing for the setpoint for each MSRV.

The NSPM MSRV Precision/Critical Maintenance practices are developed from the application of the EPRI/NMAC Safety and Relief Valve Testing and Maintenance Guide and from NSPM Operational Experience (OE). The NSPM MSRV Precision/Critical Maintenance has been implemented through NSPMs oversight of the valve vendors test and rebuild processes.

The licensee states that extending the test interval from 6 to 8 years and revising the intervening outage testing sample size and frequency are acceptable based upon past MSRV performance.

The ASME OM Code requires additional valves to be tested if as-found values are outside the acceptable range. For each MSRV tested at Monticello for which the as-found set pressure exceeds the greater of either the plus/minus tolerance limit of the established set-pressure acceptance criteria or +/-3 percent of MSRV nameplate set-pressure, two additional MSRVs are tested from the same valve group. If the as-found set-pressure of any of the additional MSRVs tested exceeds the criteria, then all the remaining valves of that same group will be tested.

The licensee asserts that the proposed Alternative Request will align with the principles of maintaining radiation dose As Low As Reasonably Achievable (ALARA). Using recent dose measurements over the past four RFOs, the average radiological exposure incurred per MSRV removal and replacement is reported to have been approximately 1.375 rem (roentgen equivalent man) of radiological dose. Extending the testing interval from 6 years using OMN-17, Revision 1, to 8 years would allow extending the testing of the eight MSRVs from three to four RFOs, potentially providing a reduction of four MSRV tests over a 10-year interval. The licensee states that this would lower overall radiological exposure and optimize the testing sequence to support plant configuration.

The NRC staff requested NSPM provide additional information to support Alternative Request VR-09. In its May 16, 2024, supplement, the licensee stated:

Performance information over the proposed test intervals for the applicable SRVs will continue to be obtained for NSPMs population of SRVs. NSPM plans to continue its current practice of refurbishment, assembly, and testing of assembled SRV bodies and topworks at an off-site facility. Each tested SRV assembly is installed for a duration permitted by the Code Case OMN-17. In accordance with the technical specifications (TS) and the IST program, performance information from the valve population is taken and trended.

NSPM plans to create an SRV program document providing guidance for determining maximum allowed in service time. The maximum in service time for each valve is considered dependent upon the following factors: Code Case OMN-17 allowed test interval, set pressure drift history, pilot and main seat leak tightness, and the number of test and operating lifts. The data from all valves is used and will continue to be used to monitor the performance of each SRV over their proposed extended test interval. Test results are analyzed for acceptability. Common cause issues are identified through trending and through code-required testing scope expansion and evaluation for any unsatisfactory SRV test results.

The NSPM SRV precision/critical maintenance practices are comprised of guidelines from EPRI/NMAC TR 3002005362, vendor procedures, lessons learned from operating experience (OE), and specific testing, maintenance, inspection, and repair, criteria that are approved by NSPM (incorporated into vendor test/maintenance procedures through procurement documents). Maintenance practices include specific performance and inspection criteria and certain maintenance steps that exceed original equipment manufacturer (OEM) specifications and/or industry established guidelines.

Procedures for these elements include receipt inspection, predictive maintenance, SRV inspection, test system design, test sequence, test procedures, environmental conditions, spring assembly removal and inspection, cold bar seat tightness test, and set pressure test used at Monticello and at the vendor facility which align with the EPRI TR 3002005362. Testing is performed in accordance with 2017 ASME Code and Code Case OMN-17 for the Monticello sixth IST interval.

NSPM is in the process of enhancing the NSPM SRV precision/critical maintenance practices to improve the SRV best practice elements and process described above.

New techniques and technology for SRV testing and maintenance continue to be evaluated for implementation.

In addition, the licensee specified that Monticello conducts the following SRV activities which are aligned with elements of the EPRI Report (shown in parentheses):

SRV receipt inspection performed in accordance with NSPM quality assurance program (EPRI Report Section 5.2.2.2, PRV Receipt Inspection)

Predictive maintenance (EPRI Report, Section 6.1, Predictive Maintenance, and Inspection)

Inspection (EPRI Report, Section 6.3, Preventive Maintenance).

Test System Design (EPRI Report, Appendix E, Test Benches and Test Systems.

Test Sequence (EPRI Report, Section 4.2.1, Test Sequence)

Testing Procedures (EPRI Report, Section 4.2.2, Test Repeatability)

Environmental Conditions (EPRI Report, Section 4.2.2.1, Environmental Conditions)

Spring Assembly Removal and Inspection (EPRI Report, Section 6.3.2.9, Spring Assembly (Spring and Washer) Removal and Inspection)

Cold Bar Seat Tightness Test (EPRI Report, Table C-3. Seat Tightness Testing Methods for Pressure Relief Devices)

Set Pressure Test performed in conformance with ASME OM Code, OMN-17, and EPRI Report Guidance Further, the licensee states that the current elements from the NSPM SRV precision/critical maintenance practices that have driven satisfactory set pressure performance are:

Spring Measurements Lapping Techniques Internal Component Condition Control The licensee states that at the off-site vendor facility, detailed NSPM-approved vendor procedures are followed for maintenance and provide the required steps for disassembly, inspection, repair, replacement of components, and reassembly of the SRV. Trained vendor personnel perform disassembly, inspection, repair or refurbishment and reassembly. Vendor quality assurance and quality control inspectors monitor work activities per the vendor quality assurance program. Following testing and refurbishment, the valve is inspected for cleanliness and sealed prior to shipping. The licensee provided a brief description of the process for the following activities:

Pilot Stage Disassembly, Inspection, and Testing Second Stage Disassembly, Inspection, and Testing Main Body Disassembly, Inspection, and Testing The licensee stated NSPM SRV precision/critical maintenance practices incorporate learnings from the NSPM OE program, which provides guidance and requirements for sharing, evaluating, translating OE into station processes. The corrective action program is also used to document and evaluate applicable and significant operating experience. Other elements include the OE from the OEM specifications and/or industry established guidelines.

3.2

NRC Staff Evaluation

The NRC approved the use of ASME OM Code Case OMN-17, Revision 1, in Regulatory Guide (RG) 1.192, Operation and Maintenance Code Case Acceptability, ASME OM Code, Revision 5 (ML23291A006), which is incorporated by reference in 10 CFR 50.55a. 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 MSRVs 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 Alternative Request VR-09 for Monticello focused on the proposed modifications to ASME OM Code Case OMN-17.

In its Alternative Request VR-09 as supplemented, the licensee states that NSPM developed the MSRV Precision and Critical Maintenance practices from the application of the EPRI/NMAC SRV Testing and Maintenance Guide, EPRI TR 105872, and OE for receipt inspection requirements, preventive maintenance and inspection of the MSRVs. NSPM recently performed an evaluation of performance of the Target Rock MSRVs demonstrating that there is reasonable assurance that the required setpoint drift tolerance of +/-3 percent would be met after extending the test interval from the current 6-year interval to a proposed 8-year interval. Table 2 in Alternative Request VR-09 summarizes the setpoint drift projection, in years of service, predicting when each MSRV would exceed the +/-3 percent set pressure tolerance band for MSRVs removed and tested since 2017.

As described above, NSPMs SRV precision/critical maintenance practices includes SRV Receipt Inspection, Preventive Maintenance, spring measurement testing, set pressure adjustment methodology, lapping techniques, and internal component condition variations. For the MSRVs in Table 1 of this SE, the licensee also disassembles and inspects the MSRVs 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.

Based on its review of the licensees submittal, as supplemented, the NRC staff finds that the Alternative Request VR-09 for Monticello provides an acceptable level of quality and safety, because:

1. With the exception of the two modifications discussed in this SE, Monticello will continue to meet the provisions of the NRC-approved ASME OM Code Case OMN-17, Revision 1, including the provision to disassemble and inspect all valves prior to as-left testing and installation.

2. NSPM MSRV Precision and Critical Maintenance practices program has been implemented for the MSRVs within the scope of this proposed Alternative Request.

3. NSPM MSRV Precision and Critical Maintenance practices program includes the sharing of applicable test data between various MSRVs.

4. The results of the as-left and as-found set pressure test data for the Monticello MSRVs indicate that the MSRV set pressures will remain within acceptable tolerance levels for at least 8 years.

The NRC staff notes that in its letter dated May 16, 2024, the licensee clarifies that there is an error in the Monticello IST program sixth interval plan (ML22249A234), which incorrectly specified VR-05 on page 27, where it should be specified as Code Case OMN-17. The licensee stated that VR-05 is not related to VR-09, and this error has been entered in the Monticello Corrective Active Program.

Based on the licensees MSRV Precision and Critical Maintenance practices program, the implementation of an engineering program to share applicable test data, and the results of the MSRV as-left and as-found set pressure testing, the NRC staff finds that the proposal in Alternative Request VR-09 to extend the required test interval for the MSRVs 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 MSRVs 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 MSRVs within the scope of this request in accordance with 10 CFR 50.55a(z)(1) for the sixth interval IST program at Monticello.

4.0 CONCLUSION

As described above, the NRC staff finds that the licensees proposal described in Alternative Request VR-09 to extend the required test interval for the MSRVs 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 MSRVs 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 MSRVs 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 VR-09 at Monticello. Therefore, the NRC staff authorizes the use of Alternative Request VR-09 for the sixth interval IST program at Monticello, which started on October 1, 2022, and is scheduled to end on May 31, 2032.

All other ASME OM Code requirements as incorporated by reference in 10 CFR 50.55a for which relief or an alternative was not specifically requested, and granted or authorized (as appropriate), in the subject request remain applicable.

Principal Contributors:

Gurjendra Bedi, NRR/DEX/EMIB Thomas Scarbrough, NRR/DEX/EMIB Dated: August 27, 2024

ML24222A182 OFFICE NRR/DORL/LPL3/PM NRR/DORL/LPL3/LA NRR/DEX/EMIB/BC NRR/DORL/LPL3/BC NAME BBallard SRohrer SBailey JWhited DATE 8/8/2024 8/14/24 8/7/2024 8/27/2024