05000263/LER-2024-002-01, Low Pressure Coolant Injection Inoperable Due to Motor Valve Failure
| ML25150A333 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 05/30/2025 |
| From: | Brown G Northern States Power Company, Minnesota, Xcel Energy |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| L-MT-25-022 LER 2024-002-01 | |
| Download: ML25150A333 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 2632024002R01 - NRC Website | |
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Xcel Energy*
2807 West County Road 75 Monticello, MN 55362 May 30, 2025 L-MT-25-022 10 CFR 50.73 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 Monticello Nuclear Generating Plant Docket No. 50-263 Subsequent Renewed Facility Operating License No. DPR-22 Monticello Nuclear Generating Plant Licensee Event Report 2024-002-01 Northern States Power Company, a Minnesota corporation, doing business as Xcel Energy (hereafter "NSPM"), hereby submits Licensee Event Report (LER) 50-263/2024-002-01 per 10 CFR 50.73(a)(2)(i)(B), 10 CFR 50.73(a)(2)(v)(B), and 10 CFR 50.73(a)(2)(v)(D). This report is a supplement to LER 50-263/2024-002-00 which was submitted on August 27, 2024 (ADAMS accession number ML24240A166).
If you have any questions about this submittal, please contact Carrie Seipp, Senior Regulatory Engineer, at 612-330-5576.
Summary of Commitments This letter makes no new commitments and no revisions to existing commitments.
Greg D. Brown Plant Manager, Monticello Nuclear Generating Plant Northern States Power Company - Minnesota Enclosure cc: Administrator, Region III, USNRC Project Manager, Monticello, USNRC Resident Inspector, Monticello, USNRC State of Minnesota
ENCLOSURE MONTICELLO NUCLEAR GENERATING PLANT LICENSEE EVENT REPORT 50-263/2024-002-01 4 pages follow
Abstract
On June 28, 2024 at 0110 CDT, Monticello Nuclear Generating Plant was in Mode 1 at 100 percent power and performing OSP-RHR-0556 Residual Heat Removal (RHR) Water Fill Verification Technical Specification Surveillance Procedure. When the RHR Low Pressure Coolant Injection (LPCI) Motor Valve MO-2012 "RHR Division 1 LPCI Injection Outboard Valve" was attempted to be cycled, the Outboard Motor Valve opened approximately one inch then stopped. With the Outboard Motor Valve incapable of opening, the A LPCI injection path was inoperable for injection as an Emergency Core Cooling system; and due to the plant design of the LPCI Loop Select Logic, this rendered both subsystems of LPCI inoperable. Subsequent evaluation determined that the Outboard Motor Valve was considered inoperable when it was configured closed based on the potential to have Reactor pressure on the inboard side of the valve due to leakage past the associated RHR Division 1 LCPI Injection Inboard Motor Valve.
The cause of the event was that the Outboard Motor Valve's motor pinion was not secured to the motor shaft because an incorrect-sized set screw was installed. The shorter motor pinion set screw relaxed, allowing the motor pinion to move axially along the motor shaft until it no longer engaged the worm shaft clutch gear.
On June 29, 2024, the Outboard Motor Valve's motor pinion was adjusted back into position on the motor shaft. On August 7, 2024, the incorrect motor pinion set screw on the Outboard Motor Valve was replaced with the correct set screw.
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- 3. LER NUMBER YEAR SEQUENTIAL NUMBER REV NO.
052 050 4
4 Monticello Nuclear Generating Plant 263 2024 002 01
ASSESSMENT OF SAFETY CONSEQUENCES
Actual safety consequences of the event were very low for both normal operation and design basis event operation.
High Pressure Emergency Core Cooling System (ECCS), the Low Pressure ECCS subsystem of Core Spray, and the remaining functions of RHR including Drywell Spray and Suppression Pool Cooling were not affected. A probabilistic risk assessment was performed to estimate the impact of the unavailability of the Outboard Motor Valve on Core Damage Frequency and Large Early Release Frequency. The results were within the bounds of "Very Low Safety Significance" described in NRC Inspection Manual Chapter 0609. There were no radiological or industrial impacts associated with this event. The health and safety of the public and site personnel were not impacted during this event.
CAUSE OF THE EVENT
The Outboard Motor Valve failed to operate because the motor pinion was not secured to the motor shaft because an incorrect-sized set screw was installed. The shorter motor pinion set screw relaxed, allowing the motor pinion to move axially along the motor shaft until it no longer engaged the worm shaft clutch gear.
CORRECTIVE ACTIONS
On June 29, 2024, the Outboard Motor Valves motor pinion was adjusted back into position on the motor shaft. On August 7, 2024, the incorrect motor pinion set screw on the Outboard Motor Valve was replaced with the correct set screw.
PREVIOUS SIMILAR EVENTS
There were no previous similar events in the past three years.
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