ML24100A804
| ML24100A804 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 04/24/2024 |
| From: | Jeffrey Whited Plant Licensing Branch III |
| To: | Conboy T Northern States Power Company, Minnesota |
| Ballard, Brent | |
| References | |
| EPID L-2024-LLR-0015 | |
| Download: ML24100A804 (1) | |
Text
April 24, 2024 Thomas A. Conboy Site Vice President Northern States Power Company - Minnesota Prairie Island Nuclear Generating Plant 1717 Wakonade Drive East Welch, MN 55089
SUBJECT:
PRAIRIE ISLAND NUCLEAR GENERATING PLANT, UNIT 2 - ALTERNATIVE REQUEST RR-09 FOR SAFETY INJECTION AND VOLUME CONTROL SYSTEM CATEGORY C CHECK VALVE INSERVICE TESTING (EPID L-2024-LLR-0015)
Dear Thomas Conboy:
By web-based submission dated February 11, 2024 (Agencywide Documents and Access Management System (ADAMS) Accession No. ML24042A001), as supplemented by letter dated February 13, 2024 (ML24044A103), Northern States Power Company, a Minnesota corporation, doing business as Xcel Energy (NSPM, the licensee) submitted a request 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 as incorporated by reference in Title 10 of the Code of Federal Regulations (10 CFR) 50.55a, Codes and standards, at Prairie Island Nuclear Generating Plant (Prairie Island), Unit 2.
Specifically, pursuant to 10 CFR 50.55a(z)(2), the licensee proposed to extend the inservice testing (IST) program requirement for testing specific check valves in the safety injection system and volume control system on the basis that compliance with the ASME OM Code requirements would result in hardship or unusual difficulty without a compensating increase in level of quality or safety.
The NRC staff provided verbal authorization of Alternative Request RR-09, as supplemented, on February 14, 2024 (ML24045A150), for the subject check valves until the end of the fifth 10-year IST program interval, or at the next opportunity that plant conditions support such testing prior to the end of the program interval at Prairie Island, Unit 2. The verbal authorization documentation provides a summary of the NRC staff evaluation for this proposed alternative. The enclosed safety evaluation provides the details of the NRC staffs review of Alternative Request RR-09 and concludes that NSPM has adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a(z)(2).
All other ASME OM Code requirements for which relief or an alternative was not specifically requested and granted or authorized (as appropriate) as part of this alternative request remain applicable.
T. Conboy 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. 50-306 cc: Listserv Jeffrey A.
Whited Digitally signed by Jeffrey A. Whited Date: 2024.04.24 10:18:09 -04'00'
Enclosure SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION ALTERNATIVE REQUEST RR-09 SAFETY INJECTION SYSTEM AND VOLUME CONTROL SYSTEM CATEGORY C CHECK VALVE INSERVICE TESTING NORTHERN STATES POWER COMPANY PRARIE ISLAND NUCLEAR GENERATING PLANT, UNIT 2 DOCKET NO. 50-306
1.0 INTRODUCTION
By web-based submission dated February 11, 2024 (Agencywide Documents and Access Management System (ADAMS) Accession No. ML24042A001), as supplemented by letter dated February 13, 2024 (ML24044A103), Northern States Power Company, a Minnesota corporation, doing business as Xcel Energy (NSPM, the licensee), submitted Alternative Request RR-09 to the U.S. Nuclear Regulatory Commission (NRC) proposing to extend the inservice testing (IST) program requirement for testing specific check valves in the safety injection (SI) system and volume control (VC) system at Prairie Island Nuclear Generating Plant (Prairie Island), Unit 2. In particular, the licensee proposes to defer certain inservice tests of the subject check valves required by the American Society of Mechanical Engineers (ASME) Code for Operation and Maintenance of Nuclear Power Plants (OM Code) as incorporated by reference in Title 10 of the Code of Federal Regulations, part 50, section 55a, Codes and standards, at Prairie Island, Unit 2.
Pursuant to 10 CFR 50.55a(z)(2), the licensee requested that the NRC authorize Alternative Request RR-09 for the subject check valves in the SI and VC systems at Prairie Island, Unit 2, on the basis that compliance with the ASME OM Code requirements would result in hardship or unusual difficulty without a compensating increase in level of quality or safety.
On February 14, 2004, the NRC provided a verbal authorization (ML24045A150) of proposed Alternative Request RR-09 for the subject check valves at Prairie Island, Unit 2. The verbal authorization documentation provides a summary of the NRC staff evaluation for this proposed alternative. This safety evaluation provides the details of the NRC staff review of proposed Alternative Request RR-09 for Prairie Island, Unit 2.
2.0 REGULATORY EVALUATION
The NRC regulations in 10 CFR 50.55a(f)(4), Inservice testing standards requirement for operating plants, state 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 IST requirements for pumps and valves that are within the scope of the ASME OM Code but are not classified as ASME Boiler and Pressure Vessel Code (BPV Code)
Class 1, Class 2, or Class 3 may be satisfied as an augmented IST program in accordance with 10 CFR 50.55a(f)(6)(ii) without requesting relief under 10 CFR 50.55a(f)(5) or alternatives under 10 CFR 50.55a(z). This use of an augmented IST program may be acceptable provided the basis for deviations from the ASME OM Code, as incorporated by reference in 10 CFR 50.55a, demonstrates an acceptable level of quality and safety, or that implementing the code provisions would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety, where documented and available for NRC review.
The NRC regulations in 10 CFR 50.55a(z), Alternatives to codes and standards requirements, state:
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
The information provided by the licensee in support of the request for an alternative to the ASME OM Code requirements as incorporated by reference in 10 CFR 50.55a has been evaluated and the bases for disposition are documented below.
3.1 Licensees Alternative Request Applicable Code Edition Prairie Island is currently implementing its fifth 10-year interval IST program with the 2004 Edition through the 2006 Addenda of the ASME OM Code as incorporated by reference in 10 CFR 50.55a as the IST Code of Record. The fifth 10-year IST program interval for Prairie Island began on December 21, 2014, and is currently scheduled to end on December 20, 2024.
ASME Code Components Affected Affected components in SI system:
Valve 2SI-7-1, FR REFUELING WTR STR TK TO RHR PUMP SUCT CHECK, Category C check valve.
Valve 2SI-7-2, FR REFUELING WTR STR TK TO RHR PUMP SUCT CHECK, Category C check valve.
Affected components in VC system:
Valve 2VC-8-2, 21 REGEN HX CHARGING OUTLET CHECK, Category C check valve.
Valve 2VC-8-3, 21 REGEN HX AUX SPRAY TO 21 PRZR CV-31421 OUTL CHK, Category C check valve.
Valve 2VC-17-1, 21 REGEN HX CHG LINE OUTL CV-31420 B-P CHK, Category C check valve.
Valve 2VC-8-1, 21 REGENERATIVE HT EXCH CHARGING INLET - CHK VLV, Category C check valve.
Valve 2VC-8-4, 22 RC PMP SEAL WTR INJECTION CHECK, Category C check valve.
Valve 2VC-8-5, 21 RC PMP SEAL WTR INJECTION CHECK VLV, Category C check valve.
These check valves are ASME OM Category C (self-actuating) valves without leakage limitation requirements (also referred to as Category B/C valves).
Applicable Code Requirements The IST requirements in the ASME OM Code, 2004 Edition through 2006 Addenda, as incorporated by reference in 10 CFR 50.55a, related to this alternative request are as follows:
ASME OM Code, Subsection ISTC, Inservice Testing of Valves in Light-Water Reactor Nuclear Power Plants, paragraph ISTC-3510, Exercising Test Frequency, states:
Active Category A, Category B, and Category C check valves shall be exercised nominally every 3 months, except as provided by ISTC-3520, ISTC-3540, ISTC-3550, ISTC-3570, ISTC-5221, and ISTC-5222. Power-operated relief valves shall be exercise tested once per fuel cycle.
ASME OM Code, subsection ISTC, paragraph ISTC-3522, Category C Check Valves, states in part:
Category C check valves shall be exercised as follows:
(a) During operation at power, each check valve shall be exercised or examined in a manner that verifies obturator travel by using the methods in ISTC-5221.
(c) If exercising is not practicable during operation at power and cold shutdowns, it shall be performed during refueling outages.
(f) All valve testing required to be performed during a refueling outage shall be completed before returning the plant to operation at power.
ASME OM Code, subsection ISTC, paragraph ISTC-3570, Valves in Systems Out of Service, states:
For a valve in a system declared inoperable or not required to be operable, the exercising test schedule need not be followed. Within 3 months before placing the system in an operable status, the valves shall be exercised and the schedule followed in accordance with requirements of this Subsection.
ASME OM Code, subsection ISTC, paragraph ISTC-5221, Valve Obturator Movement, states in part:
(a) The necessary valve obturator movement during exercise testing shall be demonstrated by performing both an open and a close test.
(3) Check valves that have a safety function in only the close direction shall be exercised by initiating flow and observing that the obturator has traveled [to] at least the partially open position,* and verify that on cessation or reversal of flow, the obturator has traveled to the seat. Observations shall be made by observing a direct indicator (e.g., a position-indicating device) or by other positive means (e.g., changes in system pressure, flow rate, level, temperature, seat leakage, testing, or nonintrusive testing results).
- The partially open position should correspond to the normal or expected system flow.
Proposed Alternative Alternative Request RR-09 proposes to extend the test intervals required in ASME OM Code, subsection ISTC, paragraphs ISTC-3510, ISTC-3522(f), and ISTC 3570, for the subject valves until the next Unit 2 refueling outage (RFO) or the end of the 5th interval whichever comes first.
Check valve 2VC-8-3 will be tested in accordance with ISTC-5221(a)(3) at that time.
Reason for Request
The licensee tests the subject SI check valves in accordance with ASME OM Code, subsection ISTC, paragraph ISTC-3510, on an RFO interval because these tests can only be performed when the refueling cavity is being flooded via the open reactor vessel using the residual heat removal pumps taking suction from the refueling water storage tank. The licensee tests the subject VC check valves in accordance with ASME OM Code, subsection ISTC, paragraph ISTC-3510, on an RFO interval because testing requires a specific alignment of the system that is only practicable with refueling cavity filled. In addition, the licensee notes that check valve 2VC-8-3 lacks documented evidence of forward flow prior to closure test as required by ASME OM Code, subsection ISTC, paragraph ISTC-5221(a)(3). Following completion of core refueling, Prairie Island, Unit 2 was transitioned to cold shutdown. While heating up in technical specification (TS) MODE 4 in preparation for startup, the licensee reports that an issue occurred that required Unit 2 to be returned to TS MODE 6 for resolution. As a result, Unit 2 did not return to operation at power prior to exceeding the 92-day test frequency required by ASME OM Code, subsection ISTC, paragraph ISTC-3510. The licensee states that realigning Unit 2 to flood the refueling cavity in order to test the subject valves represents a hardship.
Basis for Use of Request The licensee states that compliance with the specified ASME OM Code requirements for the affected components would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety. The licensee reviewed the maintenance and testing history of the subject check valves since 2019 (3 RFOs including 2R33 in 2023) and found the following:
For the SI check valves, all testing has been satisfactory since 2019. In 2021, the licensee conducted routine preventive maintenance of check valve 2SI-7-1 that included as-found freedom of movement check and inspection of valve internals, both of which were satisfactory.
For the VC check valves, all testing, with the exception of 2VC-8-3, has been satisfactory since 2019. In 2021, the licensee disassembled 2VC-8-1 and 2VC-8-4 to investigate failure of 10 CFR Part 50, Appendix J, local leak rate testing of the valves. The valves were determined to be acceptable from an IST perspective. The licensee subsequently evaluated the check valves and determined they were not required to be within the scope of the Prairie Island Appendix J program.
The licensee reported that the current IST program plan contains a known issue with respect to the test interval listed for check valves 2VC-8-1, 2VC-8-4, and 2VC-8-5 in that the valves are shown as having a 92-day test interval. However, these valves should have an RFO test interval and should be included in the same RFO justification as check valves 2VC-8-2, 2VC-8-3, and 2VC-17-1. The licensee noted that this documentation discrepancy had been entered into the corrective action program for resolution.
The licensee reported that the closure test process for check valve 2VC-8-3 does not validate forward flow was achieved prior to the closure test. The test demonstrates the check valve is closed. The licensee stated that the check valve has met the differential pressure criteria to validate closure in each of the last three RFOs with no adverse trends identified. The licensee indicated that this issue with the test process had been entered into the corrective action program for resolution.
The licensee described that the 2R33 RFO duration had been extended and that Unit 2 was brought from Mode 4 to Mode 6 due to unforeseen circumstances. The licensee stated that testing of the subject check valves would require flooding the cavity by overflowing the reactor vessel flange. The licensee reported that flooding the refueling cavity posed several potential hardships, including:
- Increased radiation dose as a result of the need for additional decontamination activities.
Flooding the reactor cavity in order to complete the required testing would add approximately 500 millirem in radiation dose to workers.
- Extended time in the outage including additional time at lowered inventory.
3.2
NRC Staff Evaluation
In Alternative Request RR-09 as supplemented by letter dated February 13, 2024, the licensee proposed to extend the test intervals required in the ASME OM Code as incorporated by reference in 10 CFR 50.55a for the subject check valves at Prairie Island, Unit 2. The IST program requirements applicable to Alternative Request RR-09 include ASME OM Code, subsection ISTC, paragraphs ISTC-3510, ISTC-3522, ISTC-3570, and ISTC-5221. The licensee proposed that the specified test intervals for the subject check valves be extended until the end of the fifth 10-year IST program interval at Prairie Island.
The licensee plans to apply the provision allowed with conditions in the ASME OM Code, subsection ISTA, General Requirements, paragraph ISTA-3120, Inservice Test Interval, subparagraph (d), to extend the fifth 10-year IST program interval for 1 year to a new end date of December 20, 2025, which will encompass the next RFO for Prairie Island, Unit 2, scheduled for the fall of 2025. If the fifth 10-year IST program interval is not extended, the licensee will need to conduct the required OM Code testing of the subject check valves by the current interval end date or submit a request under 10 CFR 50.55a(z) for an alternative approach applicable to the sixth IST program interval in a timely manner. In addition to the provision for testing the subject check valves by the end of the fifth 10-year IST program interval, Alternative Request RR-09, as supplemented by the licensees letter dated February 13, 2024, indicates that the subject check valves will undergo the required OM Code testing the next time that plant conditions support conducting the tests.
The licensee submitted Alternative Request RR-09 in accordance with 10 CFR 50.55a(z)(2),
which allows a licensee to propose an alternative to specific ASME OM Code requirements where justifying that compliance with those requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety. In this case, the licensee stated that the ASME OM Code testing of the subject check valves would require flooding the refueling cavity by overflowing the reactor vessel flange. The licensee reported that flooding the refueling cavity would result in increased radioactive exposure to plant workers with the subsequent need for decontamination activities. The licensee also noted that the completion of the testing of the subject check valves would result in further outage time for Prairie Island, Unit 2.
In Alternative Request RR-09, the licensee provided the results of its review of the maintenance and testing history of the subject check valves since 2019. For example, the licensee reported that all testing of the subject SI check valves has been satisfactory. Further, the licensee conducted successful preventive maintenance of SI check valve 2SI-7-1, including an internal inspection, in 2021. The licensee also conducted an internal inspection of VC check valves 2VC-8-1 and 2VC-8-4 in 2021. The licensee reported that all testing of the subject VC check valves (with the exception of check valve 2VC-8-3) has been satisfactory. The licensee found that the closure test process for check valve 2VC-8-3 had not been validating forward flow prior to the closure test in accordance with the ASME OM Code. However, the licensee reported that check valve 2VC-8-3 met the differential pressure criteria to validate closure in each of the previous three RFOs with no adverse trends.
In addition to the closure test process for check valve 2VC-8-3, the licensee identified discrepancies related to the accuracy of its current IST Program Plan for the test intervals for certain check valves during its preparation of the alternative request. The licensee stated that these discrepancies have been entered into its correction action program for resolution. The NRC staff notes that this authorization relates to future activities and does not address the review of OM Code compliance for previous test activities.
Based on the information provided by the licensee, the NRC staff finds that a hardship exists without a compensating increase in the level of quality and safety, in accordance with 10 CFR 50.55a(z)(2), for the performance of specific inservice tests as scheduled in the ASME OM Code for the subject check valves as described in Alternative Request RR-09, as supplemented, at Prairie Island, Unit 2. Based on the maintenance and testing history of the subject check valves, the NRC staff finds that the licensee has provided reasonable assurance that the subject check valves will be operationally ready to perform their safety functions until the next scheduled tests. Therefore, the NRC staff finds that the licensees proposed alternative to defer the OM Code tests for the subject check valves until the end of the fifth 10-year IST program interval, or at the next opportunity that plant conditions support such testing prior to the end of the program interval, will not adversely impact the reasonable assurance that those components will be operationally ready to perform their safety functions.
4.0 CONCLUSION
As set forth above, the NRC staff has determined that Alternative Request RR-09 as described in the licensees submittals dated February 11, 2024, and February 13, 2024, provides reasonable assurance of the operational readiness of the applicable check valves until the next scheduled test activities, in light of the hardship caused by implementation of the applicable ASME OM Code requirements without a compensating increase in the level of quality and safety. Accordingly, the NRC staff concludes that the licensee has adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a(z)(2) for Alternative Request RR-09.
Therefore, the NRC staff authorizes Alternative Request RR-09 to defer the specified inservice tests for the subject check valves until the end of the fifth 10-year IST program interval, or at the next opportunity that plant conditions support such testing prior to the end of the program interval at Prairie Island, Unit 2. The NRC staff does not authorize Alternative Request RR-09 beyond the end of the fifth 10-year IST program interval, or the next opportunity that plant conditions support the OM Code testing of the subject check valves prior to the end of the program interval at Prairie Island, Unit 2.
All other ASME OM Code requirements for which relief or an alternative was not specifically requested and granted or authorized (as appropriate) as part of this alternative request remain applicable. If the licensee identifies a performance issue with any of the SI system or VC system components, the licensee will be expected to take action to implement the requirements of its TSs.
Principal Contributor: Thomas G. Scarbrough, NRR/DEX/EMIB Dated: April 24, 2024
ML24100A804 OFFICE NRR/DORL/LPL3/PM NRR/DORL/LPL3/LA NRR/DEX/EMIB/BC NAME BBallard SRohrer SBailey DATE 4/9/2024 4/10/2024 4/4/2024 OFFICE NRR/DORL/LPL3/BC NAME JWhited DATE 4/24/2024