05000263/LER-2025-001-01, Automatic Reactor Scrap on Low Water Level
| ML25274A095 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 09/24/2025 |
| From: | Neal M Northern States Power Co, Xcel Energy |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| L-MT-25-034 LER 2025-001-01 | |
| Download: ML25274A095 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 2632025001R01 - NRC Website | |
text
2807 West County Road 75 Monticello, MN 55362 L-MT-25-034 10 CFR 50.73
(! Xcel Energy*
September 24, 2025 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 (MNGP) Licensee Event Report 2025-001-01 Northern States Power Company, a Minnesota corporation, doing business as Xcel Energy (hereafter "NSPM"), hereby submits a supplement to MNGP Licensee Event Report (LER) 2025-001-00 in accordance with 10 CFR 50.73(a)(2)(iv)(A).
If you have any questions about this submittal, please contact Rick Loeffler, Senior Nuclear Regulatory Engineer, by email at rick.a.loeffler@xcelenergy.com, or by phone at 612-539-3370.
Summary of Commitments This letter makes no new commitments and no revisions to existing commitments.
Michelle Neal Plant Manager, Monticello Nuclear Generating Plant Northern States Power Company - Minnesota Enclosure cc:
Administrator, Region 111, USNRC Project Manager, Monticello, USNRC Resident Inspector, Monticello, USNRC State of Minnesota Connected
- Committed
- Trustworthy
- Safe
ENCLOSURE MONTICELLO NUCLEAR GENERATING PLANT LICENSEE EVENT REPORT 2025-001-01 5 pages follow
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G. The failure mode, mechanism, and effect of each failed component
The 11 RFP tripped on low suction pressure due to low water level within the Condenser Hotwell.
Stuck/degraded (partially filled) vacuum air release valves on the Condenser reduced the scavenging system capability to remove air from the inner loop water boxes.
Condenser Hotwell level control was challenged due to issues with the level controller.
H. Operator actions
Operations personnel stabilized the plant in Mode 3 following the reactor scram.
I. Automatically and manually initiated safety system responses
RPS actuation and PCIS Group 2 isolation signals received, and the components actuated as required.
Ill. Cause of the Event A Cause of each component or system failure or personnel error.
The cause of the scram was low RPV water level due to a trip of the 11 RFP. The 11 RFP tripped on low suction pressure due to low water level within the Condenser Hotwell and air binding in the Circulating Water System.
Several different issues resulted in air binding of the Condenser. Condenser tube sheet fouling caused air binding to occur in the condenser outlet piping. Stuck/degraded vacuum air release valves reduced the scavenging system capability to remove air from the inner loop water boxes. Hotwell level control issues challenged and increased the impact of the air binding within the Condenser and Circulating Water System.
No human performance errors were identified during the investigation.
Following the repairs and cleaning of the Condenser the reactor was restarted and synced to the electrical grid on March 22, 2025.
B. Corrective Actions to Prevent Recurrence or to reduce the probability of similar events occurring in the future
The following procedural and/or scheduling activities have been put in place:
1)
Vacuum air release valves are scheduled to be replaced each refueling outage.
2)
Clean Condenser each fall and spring, as required, based on evaluation of plant parameters.
3)
Procedural changes to modify dredging activities to record and trend silt accumulations and clarify the acceptance criteria for dredging.
4)
Procedural changes to strengthen the guidance for identification and mitigation of reduced Condenser and CWS margin.
VII. Previous Similar Events at the Same Site
A search of LERs for the MNGP identified no previous similar events in the past three years.
VIII. Additional Information
There is no additional information.
Energy Industry Identification System (EIIS) codes are identified in the text as [XX]. Page 5
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