ML25099A288
| ML25099A288 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 04/10/2025 |
| From: | Ilka Berrios Plant Licensing Branch III |
| To: | Conboy T Northern States Power Co |
| Ballard, Brent | |
| References | |
| EPID L-2025-LLR-0036 | |
| Download: ML25099A288 (10) | |
Text
April 10, 2025 Thomas 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 - PROPOSED ALTERNATIVE RR-11 REGARDING COMPONENT COOLING WATER SYSTEM TESTING (EPID L-2025-LLR-0036)
Dear Thomas Conboy:
By letter dated March 11, 2025, as supplemented by letter dated April 2, 2025, Northern States Power Company, a Minnesota corporation (NSPM, the licensee), doing business as Xcel Energy, 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 at the Prairie Island Nuclear Generating Plant (Prairie Island), Unit 2.
Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(z)(2),
NSPM requested to defer certain testing requirements in the ASME OM Code as incorporated by reference in 10 CFR 50.55a for specified pumps and valves in the component cooling water (CC) system on the basis that complying with the specified requirements at this time would result in hardship or unusual difficulty without a compensating increase in the 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)(2) to demonstrate that performance of the specified ASME OM Code test requirements for the subject pumps and valves in the CC system at Prairie Island, Unit 2, at this time would result in a hardship or unusual difficulty without a compensating increase in the level of quality and safety. The NRC staff also has determined that the test and performance experience of the subject pumps and valves provides reasonable assurance that they will be operationally ready to perform their safety functions for the duration of the alternative request.
Therefore, the NRC staff authorizes Alternative Request RR-11 for the proposed extension of the inservice testing interval for the subject pumps and valves in the CC system at Prairie Island, Unit 2, until startup testing from the fall 2025 Unit 2 refueling outage is complete, which is scheduled to end November 9, 2025.
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.
If you have any questions, please contact the Project Manager, Beth Wetzel, at 301-415-5223 or by e-mail to Beth.Wetzel@nrc.gov.
Sincerely, Ilka Berrios, Chief Plant Licensing Branch III Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-306
Enclosure:
Safety Evaluation cc: Listserv ILKA BERRIOS Digitally signed by ILKA BERRIOS Date: 2025.04.10 11:54:50 -04'00'
Enclosure SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION PROPOSED ALTERNATIVE RR-11 REGARDING COMPONENT COOLING WATER SYSTEM TESTING NORTHERN STATES POWER COMPANY PRAIRIE ISLAND NUCLEAR GENERATING PLANT, UNIT 2 DOCKET NO. 50-306
1.0 INTRODUCTION
By letter dated March 11, 2025 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML25070A208) and supplemented by letter dated April 2, 2025 (ML25092A233), Northern States Power Company, a Minnesota corporation (NSPM, the licensee), doing business as Xcel Energy, submitted Alternative Request RR-11 to the U.S.
Nuclear Regulatory Commission (NRC) proposing an alternative to specific inservice testing (IST) requirements in the 2004 Edition through the 2006 Addenda of the American Society of Mechanical Engineers (ASME) Code for Operation and Maintenance of Nuclear Power Plants (OM Code) for specified pumps and valves in the component cooling water (CC) system at Prairie Island Nuclear Generating Plant (Prairie Island), Unit 2.
Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR)
Section 50.55a(z)(2), Hardship without a compensating increase in quality and safety, the licensee requested to defer certain testing requirements in the ASME OM Code as incorporated by reference in 10 CFR 50.55a for specified pumps and valves in the CC system on the basis that complying with the specified requirements at this time would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
The Fifth Interval IST program at Prairie Island, Unit 2, began on December 21, 2014, and is scheduled to end on December 20, 2025, using the 1-year extension allowed by the ASME OM Code as incorporated by reference in 10 CFR 50.55a.
2.0 REGULATORY EVALUATION
The NRC regulations in 10 CFR 50.55a(f)(4), Inservice testing standards requirement for operating plants, state in part:
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:
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 RR-11 Applicable ASME OM Code Edition The applicable Code of record for the Fifth IST Interval Program at Prairie Island, Unit 2, is the 2004 Edition through the 2006 Addenda of the ASME OM Code, as incorporated by reference in 10 CFR 50.55a.
Applicable ASME OM Code Components Table 1 of this safety evaluation (SE) lists the pumps and valves at Prairie Island, Unit 2, for which this alternative is being requested:
Table 1 Component Description Category/
Group Type PI:2:_CC:245-121 21 CC Pump Group A Centrifugal Pump -
Horizontal PI:2:_CC:245-122 22 CC Pump Group A Centrifugal Pump -
Horizontal PI:2:_CC:CV-31253 21 Excess Letdown Heat Exchanger CC Outlet Control Valve Category B Air-Operated Valve PI:2:_CL:CV-31383 21 CC Heat Exchanger Cooling Water Outlet Control Valve Category B Air-Operated Valve PI:2:_CL:CV31384 22 CC Heat Exchanger Cooling Water Outlet Control Valve Category B Air-Operated Valve PI:2:_CC:MV-32117 121 Spent Fuel Pool Heat Exchange Inlet Header Motor Valve A Category B Motor-Operated Valve PI:2:_CC:MV-32122 21 CC Heat Exchanger Outlet Motor Valve Category B Motor-Operated Valve PI:2:_CC:MV-32123 22 CC Heat Exchanger Outlet Motor Valve Category B Motor-Operated Valve PI:2:_CC:MV-32128 21 Residual Heat Removal (RHR) Heat Exchanger CC Inlet Motor Valve Category B Motor-Operated Valve PI:2:_CC:MV-32129 22 RHR Heat Exchanger CC Inlet Motor Valve Category B Motor-Operated Valve PI:2:_CC:MV-32130 21 Excess Letdown Heat Exchanger CC Inlet Motor Valve Category B Motor-Operated Valve PI:2:_CC:MV-32211 21 CC Pump Suction Motor Valve Category B Motor-Operated Valve PI:2:_CC:MV-32212 22 CC Pump Suction Motor Valve Category B Motor-Operated Valve PI:2:_CC:2CC-3-1 21 CC Pump Discharge Category C Check Valve PI:2:_CC:2CC-3-2 22 CC Pump Discharge Category C Check Valve PI:2:_CC:2CC-3-3 21 CC Pump CC Return Category C Check Valve PI:2:_CC:2CC-3-4 22 CC Pump CC Return Category C Check Valve PI:2:_CC:2CC-5-1 21 CC Pump CC Return Category C Check Valve PI:2:_CC:2CC-5-2 22 CC Pump CC Return Category C Check Valve Applicable ASME OM Code Requirements The IST requirements in the ASME OM Code, 2004 Edition through the 2006 Addenda, as incorporated by reference in 10 CFR 50.55a, related to this alternative request are as follows:
ASME OM Code, Subsection ISTB, Inservice Testing of Pumps in Light-Water Reactor Nuclear Power Plants, paragraph ISTB-3400, Frequency of Inservice Tests, states that an inservice test shall be run on each pump as specified in Table ISTB-3400-1.
ASME OM Code, Subsection ISTC, Inservice Testing of Valves in Water-Cooled Reactor Nuclear Power Plants, paragraph ISTC-3510, Exercising Test Frequency, states that 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-3521, Category A and Category B Valves, states, in part:
(a) Full-stroke exercising of Category A and Category B valves during operation at power to the position(s) required to fulfill its function(s), and exercising or examining check valves during plant operation in a manner that verifies obturator travel to the closed, full-open, or partially open position required to fulfill its function(s).
ASME OM Code, Subsection ISTC, paragraph ISTC-3522, Category C Check Valves, states, in part, that 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.
ASME OM Code, Subsection ISTC, paragraph ISTC-3560, Fail-Safe Valves, states that valves with fail-safe actuators shall be tested by observing the operation of the actuator upon loss of valve actuating power in accordance with the exercising frequency of ISTC-3510.
ASME OM Code, Subsection ISTC, paragraph ISTC-5120, Motor Operated Valves, subparagraph ISTC-5121, Valve Stroke Testing, states, in part, that active valves shall have their stroke times measured when exercised in accordance with ISTC-3500.
ASME OM Code, Subsection ISTC, paragraph ISTC-5130, Pneumatically Operated Valves, subparagraph ISTC-5131, Valve Stroke Testing, states, in part, that active valves shall have their stroke times measured when exercised in accordance with ISTC-3500.
ASME OM Code, Subsection ISTC, paragraph ISTC-5221, Valve Obturator Movement, states in part, that the necessary valve obturator movement during exercise testing shall be demonstrated by performing both an open and a close test.
Proposed Alternative and Basis for Use:
In Section 5 of the enclosure to its submittal dated March 11, 2025, the licensee stated:
For the components listed in the above table, relief from ASME OM Code required Testing under the PINGP IST Program is requested to minimize additional perturbations on the 22 RCP seal. This is requested for both trains of Unit 2 CC and includes the respective IST Program testing of pumps and valves listed above. Testing is requested to be postponed until the end of the upcoming Refueling Outage (expected end date November 2025) when the 22 RCP seal will be repaired.
The request is made in accordance with 10 CFR 50.55a(z)(2), 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. Testing the affected components per the ASME OM Code for the duration of the proposed alternative would result in a hardship imposed by an extended forced outage in response to a potential RCP seal failure. The proposed alternative provides an acceptable level of quality and safety as the performance of the included components has been acceptable with stable trends, and their performance is expected to remain acceptable for the duration of the proposed alternative. None of the components are near alert or action levels as specified in the ASME OM Code as shown in Attachment 1.
=
Reason for Request===
In Section 4 of the enclosure to its submittal dated March 11, 2025, the licensee stated:
The 22 Reactor Coolant Pump (RCP) seal has been experiencing degrading performance of two of three stages. Seal leakoff is within limits, but a Unit 1 RCP seal failed unexpectedly last year, which resulted in PINGP not having the necessary spare parts in the event of a Unit 2 RCP seal failure. As such, a failure of 22 RCP seal would result in an unplanned Unit 2 shutdown that would extend until either the existing seal was refurbished or a new seal could be procured. To avoid this hardship, NSPM is proposing the alternative test frequency for Unit 2 CC.
CC is used to cool the RCP seals and CC system changes cause perturbations of the RCP seals. While testing per the OM Code has not been shown to increase the rate of degradation of the RCP seal performance, trending shows measurable impact on system flow rates and pressures during testing. Eliminating the changes in system alignments that are required for testing the affected components will minimize perturbations on the RCP seal and reduce the likelihood of an extended forced shutdown.
3.2
NRC Staff Evaluation
In Alternative Request RR-11, submitted on March 11, 2025, and supplemented by letter dated April 2, 2025, the licensee proposed an extension of the ASME OM Code test schedule for specified pumps and valves in the CC system at Prairie Island, Unit 2. The licensee stated that performance of the IST tests for these pumps and valves at this time might result in failure of the 22 RCP seal and cause an extended forced shutdown of Prairie Island, Unit 2. As a result, the licensee submitted the proposed alternative under the hardship provisions of 10 CFR 50.55a(z)(2).
The licensee is required to test the subject pumps and valves every 3 months per the requirements of the ASME OM Code as incorporated by reference in 10 CFR 50.55a. The licensee reports that the performance of the next required IST test for components within the scope of Alternative Request RR-11 at Prairie Island, Unit 2, is due on April 13, 2025. The licensee proposed to extend the IST testing schedule for these pumps and valves until the end of the upcoming refueling outage in the fall of 2025 at Prairie Island, Unit 2, when the 22 RCP seal will be repaired.
In its submittal dated March 11, 2025, the licensee reported that the 22 RCP seal at Prairie Island, Unit 2, has been experiencing degrading performance in two of its three stages.
Additionally, a Unit 1 RCP seal failed unexpectedly last year, resulting in a lack of necessary spare parts in the event of a Unit 2 RCP seal failure. The licensee reported that a failure of the 22 RCP seal would result in an unplanned Unit 2 shutdown that would extend until either the existing seal was refurbished or a new seal could be procured. The licensee reported that the CC system is used to cool the RCP seals, and CC system changes cause perturbations of the RCP seals. As such, the licensee states that minimizing perturbations on the RCP seal would reduce the likelihood of an extended forced shutdown. Based on this information, the NRC staff agrees that testing these components before repair of the 22 RCP seal would cause stress to the seal and result in further degradation and challenge plant safety.
In Attachment 1 to Alternative Request RR-11, the licensee provided plots of test data for most of the pumps and valves within the scope of Alternative Request R-11 that indicated successful test history for those components. The NRC staff reviewed this information and issued a request for additional information (RAI) to the licensee for additional details regarding the performance of certain components within the scope of the proposed alternative. Specifically, the licensee did not provide information regarding (1) the performance of check valves within the scope of the proposed alternative, (2) motor-operated valve (MOV) testing results conducted as part of the diagnostic testing required by 10 CFR 50.55a(b)(3)(ii), or (3) the cause of certain performance trend data included in Attachment 1 of the submittal dated March 11, 2025. The licensee also had not discussed the potential for repair of the 22 RCP seal if a forced outage of sufficient duration were to occur prior to the upcoming refueling outage.
In its RAI response dated April 2, 2025, the licensee provided performance history for the check valves within the scope of the alternative request. In particular, the licensee reported that the check valves passed their tests over the reviewed time frame. In addition, the licensee provided MOV diagnostic testing results demonstrating acceptable margin for the MOV testing program under 10 CFR 50.55a(b)(3)(ii). The licensee explained the performance trend data, annotated the data plots with specific details, and provided additional data to demonstrate that component performance was within the allowed margin with no identified deficiencies. At this time, the licensee reported that it does not have the capability to perform the necessary repairs on the 22 RCP seal prior to the upcoming refueling outage, because of the long lead time to receive the necessary parts. However, the licensee stated that consideration would be given to adding the seal replacement to the Unit 2 forced outage list if replacement parts arrive prior to the upcoming refueling outage.
In its submittal dated March 11, 2025, as supplemented by the letter dated April 2, 2025, the licensee provided performance history for all components within the scope of this proposed alternative. The components have performed satisfactorily and do not show adverse trends or significant degradation of margin over their performance history. Test results for the applicable components have been within the ASME OM Code limits such that their performance is expected to remain acceptable for the duration of the proposed alternative.
Based on its independent review of the test and performance history of the pumps and valves within the scope of Alternative Request RR-11, the NRC staff determined that there is reasonable assurance of the operational readiness of the components listed in table 1 of this SE at Prairie Island, Unit 2, to be capable of performing their design functions during the proposed IST test interval extension. The NRC staff found that compliance with the specified IST requirements for the subject pumps and valves during the short duration of the requested alternative would result in a hardship or unusual difficulty without a compensating increase in the level of quality and safety. Therefore, the NRC staff determined that the proposed alternative meets the requirements of 10 CFR 50.55a(z)(2). As a result, the NRC staff finds that Alternative Request RR-11 may be authorized for an extension of the specified test intervals for the components listed in table 1 of this SE at Prairie Island, Unit 2, until the end of the upcoming refueling outage in the fall of 2025, when the 22 RCP seal will be repaired.
4.0 CONCLUSION
As set forth above, the NRC staff has determined that NSPM has justified in Alternative Request RR-11 that performance of the specified ASME OM Code test requirements for the subject pumps and valves in the CC system at Prairie Island, Unit 2, at this time would result in a hardship or unusual difficulty without a compensating increase in the level of quality and safety.
The NRC staff also has determined that the test and performance experience of the subject pumps and valves provides reasonable assurance that they will be operationally ready to perform their safety functions for the duration of the alternative request. Accordingly, the NRC staff concludes that the licensee has adequately addressed the regulatory requirements in 10 CFR 50.55a(z)(2). Therefore, the NRC staff authorizes Alternative Request RR-11 for the proposed extension of the IST test interval for the subject pumps and valves in the CC system at Prairie Island, Unit 2, until startup testing from the fall 2025 Unit 2 refueling outage is complete, which is scheduled to end November 9, 2025.
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: Nicholas Hansing, NRR/DEX/EMIB Thomas G. Scarbrough, NRR/DEX/EMIB Date: April 10, 2025
ML25099A288 OFFICE NRR/DORL/LPL3/PM NRR/DORL/LPL3/LA NRR/DEX/EMIB/BC NRR/DORL/LPL3/BC NAME BWetzel (BBallard for) SRohrer SBailey IBerrios DATE 4/8/2025 4/10/2025 4/8/2025 4/10/2025