ML25336A006
| ML25336A006 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 12/02/2025 |
| From: | Wetzel B NRC/NRR/DORL/LPL3 |
| To: | Paulhardt W Northern States Power Company, Minnesota |
| Wetzel B, NRR/DORL/LPL3 | |
| References | |
| EPID L-2025-LLR-0041 | |
| Download: ML25336A006 (0) | |
Text
December 2, 2025 Mr. Werner Paulhardt 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, UNITS 1 AND 2 - RELIEF REQUESTS FOR INSERVICE TESTING PROGRAM INTERVAL (EPID L-2025-LLR-0041)
Dear Mr. Paulhardt:
By letter dated April 2, 2025 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML25093A006), as supplemented by \
letter dated November 20, 2025 (ML25324A243), Northern States Power Company, a Minnesota corporation, doing business as Xcel Energy (NSPM, the licensee) submitted to the U.S. Nuclear Regulatory Commission (NRC), Relief Request 6-IST-RR-01 with respect to specific inservice testing (IST) requirements in the 2020 Edition of the American Society of Mechanical Engineers (ASME) Operation and Maintenance of Nuclear Power Plants, Division 1, OM Code: Section IST (OM Code) as incorporated by reference in Title 10 of the Code of Federal Regulations (10 CFR), Section 50.55a, Codes and standards, for the IST Program at Prairie Island Nuclear Generating Plant (Prairie Island), Units 1 and 2.
Specifically, pursuant to 10 CFR Section 50.55a(f)(5)(iii), IST program update: Notification of impractical IST Code requirements. the licensee requested relief from certain IST requirements for pump vibration monitoring as impractical for the motor-driven cooling water (MDCL) pump and two diesel driven cooling water (DDCL) pumps at Prairie Island, Units 1 and 2.
The NRC staff has reviewed the subject request and concludes, as set forth in the enclosed safety evaluation, that Relief Request 6-IST-RR-01 is granted on the basis that compliance with the ASME OM Code requirements is impractical for the applicable pumps at Prairie Island, Units 1 and 2. The staff has determined that the proposed method in Relief Request 6-IST-RR-01 for vibration monitoring of the 12 DDCL pump, 22 DDCL pump, and 121 MDCL pump at Prairie Island, Units 1 and 2, provides reasonable assurance of their operational readiness. The staff further concludes that granting the relief will not endanger life or property or the common defense and security and is otherwise in the public interest, giving due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility.
Therefore, the NRC staff grants Relief Request 6-IST-RR-01 for the Code of Record interval that uses the 2020 Edition of the ASME OM Code at Prairie Island, Units 1 and 2. This request applies to the Code of Record interval, as defined in 10 CFR 50.55a(y), Definitions, that implements the 2020 Edition of the ASME OM Code. Use of this request with other codes of record is not authorized.
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) remain applicable.
If you have any questions, please contact me at 301-415-5223 or via email at Beth.Wetzel@nrc.gov.
Sincerely,
/RA/
Beth Wetzel, Project Manager Plant Licensing Branch III Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-282 and 50-306
Enclosure:
Safety Evaluation cc: Listserv
Enclosure SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELIEF REQUEST 6-IST-RR-01 ASME OM CODE, 2020 EDITION PRAIRIE ISLAND NUCLEAR GENERATING PLANT, UNITS 1 AND 2 NORTHERN STATES POWER COMPANY - MINNESOTA DOCKET NOS. 50-282 AND 50-306 EPID L-2025-LLR-0041 1.0 INTRODUCTION By letter dated April 2, 2025 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML25093A006), as supplemented by \
letter dated November 20, 2025 (ML25324A243), Northern States Power Company, a Minnesota corporation, doing business as Xcel Energy (NSPM or licensee), submitted to the U.S. Nuclear Regulatory Commission (NRC, the Commission) Relief Request 6-IST-RR-01 with respect to specific inservice testing (IST) requirements in the 2020 Edition of the American Society of Mechanical Engineers (ASME)
Operation and Maintenance of Nuclear Power Plants, Division 1, OM Code: Section IST (OM Code) as incorporated by reference in Title 10 of the Code of Federal Regulations (10 CFR),
Section 50.55a, Codes and standards, for the IST Program at Prairie Island Nuclear Generating Plant (Prairie Island), Units 1 and 2.
Specifically, the licensee requested relief from certain IST requirements for pump vibration monitoring as impractical for the motor-driven cooling water (MDCL) pump and two diesel driven cooling water (DDCL) pumps at Prairie Island, Units 1 and 2, pursuant to 10 CFR 10.55a(f)(5)(iii). The NRC staff review of Relief Request 6-IST-RR-01 is described in this safety evaluation (SE).
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 inservice test requirements (except design and access provisions) set forth in the ASME OM Code and addenda that become effective subsequent to editions and addenda specified in [10 CFR 50.55a(f)(2) and (3)] and that are incorporated by reference in [10 CFR 50.55a(a)(1)(iv)], to the extent practical within the limitations of design, geometry, and materials of construction of the components.
The NRC regulations in 10 CFR 50.55a(f)(5), Requirements for updating IST programs, specify the following requirements in part:
(iii) IST program update: Notification of impractical IST Code requirements. If the licensee has determined that conformance with certain Code requirements is impractical for its facility, the licensee must notify the Commission and submit, as specified in § 50.4, information to support the determination.
(iv) IST program update: Schedule for completing impracticality determinations.
Where a pump or valve test requirement by the Code or addenda is determined to be impractical by the licensee and is not included in the revised inservice test program (as permitted by paragraph (f)(4) of this section), the basis for this determination must be submitted for NRC review and approval not later than 12 months after the expiration of the initial inservice examination and test interval from the start of facility commercial operation and each subsequent inservice examination and test interval during which the test is determined to be impractical.
The NRC regulations in 10 CFR 50.55a(f)(6), Actions by the Commission for evaluating impractical and augmented IST Code requirements, state:
(i) Impractical IST requirements: Granting of relief. The Commission will evaluate determinations under paragraph (f)(5) of this section that code requirements are impractical. The Commission may grant relief and may impose such alternative requirements as it determines are authorized by law, will not endanger life or property or the common defense and security, and are otherwise in the public interest, giving due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility.
(ii) Augmented IST requirements. The Commission may require the licensee to follow an augmented inservice test program for pumps and valves for which the Commission deems that added assurance of operational readiness is necessary.
3.0 TECHNICAL EVALUATION
3.1 Licensees Relief Request 6-IST-RR-01 Applicable ASME OM Code Edition The applicable OM Code of Record at Prairie Island, Units 1 and 2, is the 2020 Edition of ASME OM Code as incorporated by reference in 10 CFR 50.55a.
Applicable ASME OM Code Components In its submittal, the licensee requested relief from specific IST pump vibration monitoring requirements in the ASME OM Code for the following components:
Table 1: Applicable ASME OM Code Components for Relief Request 6-IST-RR-01 Pump ID Pump Description ASME Code Class ASME OM Code Category 045-091 121 MDCL Pump 3
Group A 145-392 12 DDCL Pump 3
Group B 245-392 22 DDCL Pump 3
Group B The 121 vertical MDCL pump serves as a diverse means of providing cooling water that is independent of the DDCL pumps. The Station Blackout / Electrical Safeguards Upgrade modification upgraded the 121 MDCL pump to safeguards status and changed the power supply to an essential safeguards diesel-backed power supply.
Each DDCL pump (the 12 DDCL pump and the 22 DDCL pump) is capable of supplying all essential cooling water loads during an accident. Only one cooling water pump is required for the safe shutdown of both units (accident in only one unit). The DDCL pumps are capable of providing safeguards water supply to the Auxiliary Feedwater Pumps. Each DDCL pump is capable of supplying sufficient cooling to the Unit 1 Emergency Diesel Generators, air compressors, Component Cooling heat exchangers, containment fan-coil units, and the auxiliary building unit coolers.
Applicable ASME OM Code Requirements ASME OM Code, Subsection ISTB, Inservice Testing of Pumps in Water-Cooled Reactor Nuclear Power Plants - Pre-2000 Plants, paragraph ISTB-3540, Vibration, subparagraph (b) states: On vertical line shaft pumps, measurements shall be taken on the upper motor-bearing housing in three approximately orthogonal directions, one of which is the axial direction.
Licensees Proposal and Basis In Relief Request 6-IST-RR-01, the licensee proposed to measure vibration for the 12 DDCL pump and the 22 DDCL pump on the right-angle drive. The thrust from the pump and driver would be transmitted to the right-angle drive; thus, monitoring vibration at this location will give an acceptable indication of pump degradation. Vibration measurements will be taken in three orthogonal directions, one of which is the axial direction. An additional vibration measurement will be taken on each of the diesel engines.
Vibration measurements for the 121 MDCL pump will be taken on the motor housing in three orthogonal directions, one of which is the axial direction. Vibration readings on the motor housing will give an acceptable indication of pump degradation. The axial reading will be taken on the side of the motor housing, midway between the upper and lower bearing.
Licensees Reason for Request The motor-bearings are inaccessible due to the design of the 121 MDCL pump and the 12 and 22 DDCL pumps.
The drivers for the 12 and 22 DDCL pumps are diesel engines coupled to a right-angle drive.
The pump bearings are inaccessible for vibration measurements.
The design of the MDCL pump limits access to the upper thrust bearing housing of the motor to take vibration readings with a portable instrument while the pump is running. The licensee stated that climbing on top of the motor while it is running is a potential personnel hazard. The licensee also stated that to remove the bearing housing cover is a potential personnel hazard while the pump is running and thus taking direct readings is not practical.
3.2
NRC Staff Evaluation
ASME OM Code, Subsection ISTB, paragraph ISTB-3540(b), requires that for vertical line shaft pumps, measurements shall be taken on the upper motor bearing housing in three approximately orthogonal directions, one of which is the axial direction. In Relief Request 6-IST-RR-01, the licensee notified the NRC staff that these ASME OM Code requirements for pump vibration measurement are not practical for the 12 DDCL pump, 22 DDCL pump, and 121 MDCL pump in accordance with 10 CFR 50.55a(f)(5)(iii).
In 10 CFR 50.55a(f)(6)(i), the NRC regulations state that the Commission will evaluate determinations under 10 CFR 50.55a(f)(5) that Code requirements are impractical. The NRC staff has determined that the inaccessibility due to pump design precludes the taking of the required vibration measurements at the ASME OM Code-specified locations on the subject pumps. Therefore, it is impractical to meet the ASME OM Code requirements. The pumps would have to be redesigned or replaced to accommodate compliance with the ASME OM Code requirements.
In 10 CFR 50.55a(f)(6)(i), the NRC regulations state that the Commission may grant relief and may impose such alternative requirements as it determines are authorized by law, will not endanger life or property or the common defense and security, and are otherwise in the public interest, giving due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility.
In Relief Request 6-IST-RR-01, the licensee states that vibration for the 12 DDCL pump and the 22 DDCL pump will be measured on the right-angle drive for these vertical line shaft centrifugal pumps. Vibration measurements will be taken in three orthogonal directions, one of which is the axial direction. An additional vibration measurement will be taken on each of the diesel engines.
In that the thrust from the pump and driver in the case of the DDCL pumps would be transmitted to the right-angle drive, the NRC staff finds that monitoring vibration at these locations will provide an acceptable indication of potential degradation of the 12 DDCL pump and 22 DDCL pump.
In Relief Request 6-IST-RR-01, the licensee states that vibration measurements for the 121 MDCL pump will be taken on the motor housing of this vertical line shaft centrifugal pump in three orthogonal directions, one of which is the axial direction. The axial reading will be taken on the side of the motor housing, midway between the upper and lower bearing. The NRC staff finds that the axial vibration from the upper motor thrust bearing of the MDCL pump will be transmitted to the motor housing, and vibration measurements taken on the motor housing in three orthogonal directions (including axial) will provide an acceptable indication of potential degradation of the 121 MDCL pump.
In the licensee submittal dated April 2, 2025, it was not clear as to whether the licensee proposed that its request be evaluated as relief under 10 CFR 50.55a(f) or an alternative under 10 CFR 50.55a(z). In its supplement dated November 20, 2025, the licensee confirmed that its submittal could be evaluated as a relief request under 10 CFR 50.55a(f). Therefore, the NRC staff evaluated this request under the relief process specified in 10 CFR 50.55a(f).
Based on its review, the NRC staff has determined that the licensee has justified in Relief Request 6-IST-RR-01 that the pump vibration monitoring requirements in the ASME OM Code are impractical for the 12 DDCL pump, 22 DDCL pump, and 121 MDCL pump at Prairie Island, Units 1 and 2, in accordance with 10 CFR 50.55a(f)(5)(iii). Further, the staff finds that the licensee has proposed an acceptable approach for monitoring the vibration of the 12 DDCL pump, 22 DDCL pump, and 121 MDCL pump in lieu of the applicable ASME OM Code requirements. The staff finds that the monitoring of pump vibration as described in Relief Request 6-IST-RR-01 and the implementation of the other IST requirements for these pumps provide reasonable assurance of the operational readiness of these pumps to perform their safety functions.
The NRC staff notes that the applicable OM Code of Record for Prairie Island, Units 1 and 2, is the 2020 Edition of the ASME OM Code, as incorporated by reference in 10 CFR 50.55a. The ASME OM Code (2020 Edition), Subsection ISTA, General Requirements, paragraph ISTA-3120, Inservice Examination and Test Interval, as incorporated by reference in 10 CFR 50.55a, requires that licensees implement 10-year intervals for their IST programs. The NRC regulations in 10 CFR 50.55a allow licensees to implement the same ASME OM Code as their Code of Record for two successive IST program intervals. Therefore, the licensee of Prairie Island, Units 1 and 2, could implement the 2020 Edition of the ASME OM Code, as incorporated by reference in 10 CFR 50.55a, for two successive IST intervals required by the ASME OM Code, Subsection ISTA, paragraph ISTA-3120.
4.0 CONCLUSION
Based on the above evaluation, the NRC staff grants Relief Request 6-IST-RR-01 pursuant to 10 CFR 50.55a(f)(6)(i) on the basis that compliance with the ASME OM Code requirements is impractical for the applicable pumps at Prairie Island, Units 1 and 2. The staff has determined that the proposed method in Relief Request 6-IST-RR-01 for vibration monitoring of the 12 DDCL pump, 22 DDCL pump, and 121 MDCL pump at Prairie Island, Units 1 and 2, provides reasonable assurance of their operational readiness. The staff further concludes that granting the relief will not endanger life or property or the common defense and security and is otherwise in the public interest, giving due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility. Therefore, the NRC staff grants Relief Request 6-IST-RR-01 for the Code of Record interval that uses the 2020 Edition of the ASME OM Code at Prairie Island, Units 1 and 2. This request applies to the Code of Record interval, as defined in 10 CFR 50.55a(y), Definitions, that implements the 2020 Edition of the ASME OM Code.
Use of this request with other codes of record is not authorized.
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) remain applicable.
Principal Contributors: Yuken Wong, NRR/DEX/EMIB Thomas G. Scarbrough, NRR/DEX/EMIB Date: December 2, 2025
ML25336A006 NRR-028 OFFICE NRR/DORL/LPL3/PM NRR/DORL/LPL3/LA NRR/DEX/EMIB NAME BWetzel SLent SBailey DATE 12/2/2025 12/2/2025 11/25/2025 OFFICE NRR/DORL/LPL3/BC (A)
NRR/DORL/LPL3/PM NAME IBerrios BWetzel DATE 12/2/2025 12/2/2025