Event Notification Report for November 14, 2025

UNUSUAL EVENT - LOSS OF ALL OFFSITE POWER TO VITAL BUSSES

The following information was provided by the licensee via phone:

On November 14, 2025, at 1351 CST, while in a system outage window, for the reserve auxiliary transformer 'B' bus work inspections, the emergency reserve auxiliary transformer tripped. This resulted in the loss of offsite power to all vital busses.
At 1402 CST, a notice of unusual event was declared (MU.1) due to the loss of all offsite power to vital busses.
All three emergency diesel generators actuated and energized the vital busses.

Notified DHS SWO, DOE Ops Center, FEMA Operations Center, FEMA NWC, CWMD Watch Desk, HHS Ops Center, CISA Central Watch Officer, USDA Ops Center, EPA EOC, FDA EOC (email), DHS Nuclear SSA (email), DHS NRCC THD Desk (email), FEMA NRCC SASC (email), and FERC Reliability Monitoring Center (email).

* * * UPDATE ON 11/16/2025 AT 0647 EST FROM JASON VINCENT TO KERBY SCALES * * *

The following update is a summary of information provided by the licensee via phone and email:

On November 16, 2025, at 0500 CST, the Unusual Event was terminated. All offsite electrical power has been restored, and the plant is in a normal electrical lineup.

The NRC Resident Inspector was notified.

Notified R3RA (Geissner), NRR (Groom), NSIR (Williams), R3DO (Ziolkowski), NRR EO (Mckenna), IR MOC (Grant), R3PAO (Mitlyng), R3DRSS (Heck).

Notified DHS SWO, DOE Ops Center, FEMA Operations Center, FEMA NWC, CWMD Watch Desk, HHS Ops Center, CISA Central Watch Officer, USDA Ops Center, EPA EOC, FDA EOC (email), DHS Nuclear SSA (email), DHS NRCC THD Desk (email), FEMA NRCC SASC (email), and FERC Reliability Monitoring Center (email).

AUTOMATIC ACTUATION OF EMERGENCY DIESEL GENERATORS

The following information was provided by the licensee via phone and email:

"At 1351 CST on 11/14/25, with the unit in mode 1 at 99 percent power, an actuation of the division 1, 2, and 3 emergency diesel generators (EDGs) occurred when a fault occurred on the emergency reserve auxiliary transformer (ERAT). The reserve auxiliary transformer `B' was de-energized and isolated for maintenance. The cause of the division 1, 2, and 3 EDGs auto-start was an actuation of the loss of voltage function undervoltage relays for each respective bus. The division 1, 2, and 3 EDGs automatically started as designed when the applicable loss of voltage signals were received.
"This event is being reported in accordance with 10 CFR 50.72(b)(3)(iv)(A) as an event that results in a valid actuation of the division 1, 2, and 3 EDGs.
"The NRC Resident Inspector has been notified."

AUTOMATIC ACTUATION OF EMERGENCY AC POWER SYSTEM

The following information was provided by the licensee via phone and email:

"At 2254 EST, on November 14, 2025, with Unit 2 in no mode at zero percent power, an actuation of the emergency AC power system occurred during verification of electrical system alignment. The reason for the Keowee Hydro units actuating was due to loss of power to the Unit 2 main feeder busses when a potential transformer drawer for the Unit 2 main feeder busses was opened, resulting in breakers supplying power to the Unit 2 main feeder busses opening. The Keowee Hydro Units 1 and 2 automatically started as designed when a main feeder bus undervoltage signal was received. There was no impact to Unit 1 or Unit 3.

"This event is being reported in accordance with 10CFR50.72(b)(3)(iv)(A) as an event that results in a valid actuation of the emergency AC power system. There was no impact on the health and safety of the public or plant personnel. The NRC Resident Inspector has been notified."

AGREEMENT STATE REPORT - LOST EXIT SIGNS

The following is a summary of information provided by the Colorado Department of Public Health and Environment via email:

The licensee reported three exit signs, each containing 17.51 Ci of tritium, were lost in Longmont, Colorado.

Manufacturer: SRB Technologies
Model number: BXU20GS

Colorado event number: CO250043

THIS MATERIAL EVENT CONTAINS A 'Less than Cat 3' LEVEL OF RADIOACTIVE MATERIAL

Sources that are "Less than IAEA Category 3 sources," are either sources that are very unlikely to cause permanent injury to individuals or contain a very small amount of radioactive material that would not cause any permanent injury. Some of these sources, such as moisture density gauges or thickness gauges that are Category 4, the amount of unshielded radioactive material, if not safely managed or securely protected, could possibly - although it is unlikely - temporarily injure someone who handled it or were otherwise in contact with it, or who were close to it for a period of many weeks. For additional information go to http://www-pub.iaea.org/MTCD/publications/PDF/Pub1227_web.pdf