Event Notification Report for September 10, 2025

UNUSUAL EVENT - RCS IDENTIFIED LEAKAGE GREATER THAN 25 GPM FOR GREATER THAN 15 MINUTES

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

At 1207 EDT on September 10, 2025, Oconee Nuclear Station Unit 1 declared an Unusual Event (SU5.1) due to identified reactor coolant system (RCS) leakage from Unit 1 for greater than 15 minutes. The calculated leak rate was 26 gallons per minute (gpm).
The leakage was identified to be from letdown filter 1A, which was subsequently isolated.
Units 2 and 3 remain at 100 percent power and are unaffected by this event.
This event was terminated at 1353 after isolating the source of the leak.

The NRC Resident Inspector has been notified.

Notified DHS SWO, FEMA Operations Center, CISA Central Watch Officer, FEMA NWC, DHS Nuclear SSA (email), CWMD Watch Desk (email).

OFFSITE NOTIFICATION

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

"At 1207 EDT on September 10, 2025, Oconee Nuclear Station Unit 1 declared an unusual event (Event number 57914). A small reactor coolant system (RCS) leak occurred during routine RCS letdown filter maintenance. The letdown filters were bypassed, and the leak was isolated. The unusual event was terminated at 1353 EDT.
"This notification is being made solely as a four-hour, non-emergency notification for a news release. This event is reportable in accordance with 10 CFR 50.72(b)(2)(xi).
"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 - DAMAGED PORTABLE MOISTURE DENSITY GAUGE

The following information was provided by the Virginia Department of Health, Office of Radiologic Health (RMP) via email:

"On September 10, 2025, at approximately 1500 EDT, RMP was notified of an incident involving damage to a portable nuclear gauge.

"Earlier, at approximately 1230, a Troxler Model 4640 B portable nuclear moisture density gauge, containing 9 mCi Cs-137, (SN #2256) was struck by a roller on a paving site at Westmoreland, VA. The authorized user notified the radiation safety officer (RSO) who went to the site to evaluate the gauge condition, and he notified RMP.

"Per the RSO, the gauge was clipped on the side by a CB-13 roller during the construction of a roller pattern and control strip. There was damage to the gauge cover and one battery pack. The source rod was not out when it was struck. There is no apparent [damage] to the source or the capsule. The gauge was surveyed onsite using with a TroxAlert 3105 (#64502) [meter] and readings were within acceptable ranges. The gauge was placed in its transport case and returned to the licensee's storage facility to be leak tested. Then the gauge will be sent to Troxler for evaluation.

"The Radioactive Materials Program will follow up with an investigation."

Event Report ID No.: VA250003

TECHNICAL SPECIFICATION REQUIRED REPORT

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

"A reportable occurrence [was] identified on September 15, 2025, for a failure to implement administrative controls. Per technical specification 6.2(b).4, the facility reactor safeguards committee (RSC) shall determine whether changes in the facility as described in the safety analysis report (SAR) may be accomplished in accordance with 10 CFR 50.59, without obtaining prior NRC approval via license amendment pursuant to 10 CFR 50.90. On September 10, 2025, changes to the normal and emergency electrical power systems described in the SAR were made without completing a review and acquiring RSC approval for the change.

"The reactor is and will remain shutdown until review and approval by the RSC of corrective actions is completed in accordance with Technical Specifications.

"A written report will be submitted within ten days summarizing the reportable occurrence."