Event Notification Report for April 11, 2025

CONCURRENT REPORT FOR OFFSITE NOTIFICATION

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

"Notification per 10 CFR Part 70, Appendix A(c), NRC FCSS ISG-12, Rev 0 (Centrus ACO Procedure ACD2-RG-044, Appendix B, Section N):

"The licensee shall notify the NRC Operations Center of any event or situation: related to the health and safety of the public or onsite personnel, or protection of the environment, for which a news release is planned. Such an event may include an on-site fatality or inadvertent release of radioactively contaminated materials; if a notification to other government agencies has been or will be made, no matter the significance.

"The Ohio EPA [Environmental Protection Agency] will be notified by FBP [Fluor BWXT Portsmouth] Environmental that approximately 500 gallons of sewage had been released to the North Pond or Outfall 013.

"Recommended actions are to install straw bales in the discharge area, to contain and clean the area, and to monitor the North Pond for solids. Sandbags have been placed at the facility exit. Centrus Environmental has also notified Ohio EPA.

"The regulatory manager provided a courtesy notification of this concurrent Ohio EPA reporting to the NRC Region II Senior Inspector and the NRC HQ Senior Program Manager."

Condition Notification Number: 12535

AGREEMENT STATE REPORT - POTENTIAL OVEREXPOSURE

The following information was provided by the Texas Department of State Health Services (the Department) via phone and email:

"On April 4, 2025, the Department was notified by the licensee of a telephonic overexposure report they received from their dosimetry provider. The licensee radiation safety officer stated the report had one of their employees with an exposure of 7.7 rem for the month of February 2025. The licensee had other readings (pocket dosimeters) that did not match this level of exposure. The licensee removed the employee from the work environment until the dose can be confirmed. The employee affected is an assistant, and neither of the other two radiographers had any exposure near this level. The licensee is still investigating.

"More information will be made available according to SA-300 requirements."

Texas incident number: 10189
NMED number: TX250022

VALID ACTUATION OF EMERGENCY AC ELECTRICAL POWER SYSTEMS

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

"At 1924 MST on April 8, 2025, a loss of power (LOP) occurred to 'Train-A' 4.16 kV class 1E electrical bus while re-energizing 'Train-A' balance of plant (BOP) engineered safety features actuation system (ESFAS) from pre-planned maintenance. The LOP occurred when the circuit breaker supplying off-site power to the 'Train-A' 4.16 kV class 1E bus tripped when 'Train-A' BOP ESFAS system was re-energized. Operators restored power to 'Train-A' 4.16 kV class 1E bus with 'EDG-A' [emergency diesel generator for 'Train-A'] at 1934 MST. Operators restored all necessary plant loads which had lost power. Per the Palo Verde emergency plan, no emergency classification was required.

"At the time of the LOP, the reactor was defueled with the core offloaded to the spent fuel pool.

"Unit 2 and Unit 3 are not impacted by this event and remain in mode 1, 100 percent power.

"The cause of the circuit breaker supplying off-site power to the 'Train-A' 4.16 kV class 1E bus tripping is under investigation. NRC Resident Inspector has been notified.

"This event is being reported in accordance with 10 CFR 50.72(b)(3)(iv)(A) as an event that resulted in a valid actuation of emergency AC electrical power systems."

FAILED FITNESS FOR DUTY

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

"On April 8, 2025, at 1333 CDT, it was determined that a licensed operator violated the station's fitness-for-duty program. The employee's access to the plant has been terminated.

"This event is being reported under 10 CFR 26.719(b)(2)(ii)."

"The NRC Resident has been notified."

UNUSUAL EVENT - LOSS OF ALL BUT ONE AC POWER SOURCE TO EMERGENCY BUSES

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

"On 4/10/2025, Unit 1 was defueled at 0 percent power. The `A' train class bus was being powered by the `A' diesel generator (DG) and the `B' train bus was out of service for maintenance. Additionally, the `A' train offsite power transformer is currently out of service for maintenance. Abnormal indication was observed on the `A' DG with lowering voltage and the decision was made to manually trip the `A' DG.

"Power was restored to the `A' class bus by crosstieing `B' train offsite power via engineering safety feature transformer NBN-X04. This resulted in a loss of all but one AC power source to emergency buses for 15 minutes or longer which is an Unusual Event (UE) CU2.1. It is currently not known at this time what caused the abnormal voltage indications on the `A' DG."

State and local agencies were notified. 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).

The following additional information was obtained from the licensee in accordance with Headquarters Operations Officers Report Guidance:

Palo Verde Units 2 and 3 were not affected by this event. The licensee restored spent fuel pool cooling.

* * * UPDATE ON 4/10/2025 AT 1701 EDT FROM TANNER GOODMAN TO SAMUEL COLVARD * * *

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

"The following event description is based on information currently available. If through subsequent reviews of this event additional information is identified that is pertinent to the event or alters the information being provided at this time, a follow up notification will be made via the ENS or under the reporting requirements of 10 CFR 50.73.

"Train `A' emergency diesel generator (DG) was supplying power to PBA-S03 bus. At 0658 MST on April 10th, 2025, train `A' DG was exhibiting erratic and degraded voltage and was placed in emergency stop, which caused a loss of power to PBA-S03.

"When the `A' DG was stopped, train `A' balance of plant engineered safety features actuation system (BOP ESFAS) detected the loss of power condition on PBA-S03, and sent an emergency start signal to the train `A' DG. Train `A' DG did not respond as it was placed in emergency stop. Operators restored power to PBA-S03 at 0703 MST. At the time of the [loss of power], the reactor was defueled with the core offloaded to the spent fuel pool. Unit 2 and Unit 3 are not impacted by this event and remain in Mode 1, 100 percent power. Unit 1 is still currently in Unusual Event, CU2.1

"This [update] is in addition to the event reported at 1029 EDT EN 57659. The original EN reported an Emergency Classification definition as a loss of all but 1 AC power source to emergency buses for 45 minutes. The correct time is 15 minutes.

"The NRC Senior Resident Inspector has been notified of the update."

[This update is an 8-hour, non-emergency, 10 CFR 50.72(b)(3)(iv)(A) report of a valid specified system actuation due to the BOP ESFAS attempting to start 'A' DG upon loss of the PBA-SO3 bus during the initial event.]

Notified R4DO (Vossmar).

* * * UPDATE ON 4/10/2025 AT 2245 EDT FROM NGOC NGUYEN TO SAMUEL COLVARD * * *

The following information was provided by the licensee via phone:

On 4/10/2025, at 2224 EDT, Palo Verde Unit 1 terminated the Unusual Event. Restoration of 'A' DG was made by swapping to its redundant automatic voltage regulator and performance of a functional startup. This restores two sources of power to the class 1E bus: offsite power and 'A' DG in a standby configuration. The redundant automatic voltage regulator was tested in surveillance in the previous cycle and remains operable. The issues that led to the declaration of Unusual Event with 'A' DG have been entered into the corrective action program.

State and local authorities have been notified. The NRC Resident Inspector has been notified.

Internal notifications: R4DO (Vossmar), NRR EO (Felts), IR MOC (Crouch), R4 RA (Monninger), NRR (King), R4 PAO (Dricks), and NSIR (Erlanger)
External notifications: DHS SWO, FEMA Operations Center, CISA Central Watch Officer, FEMA NWC, DHS Nuclear SSA (email), CWMD Watch Desk (email)

FITNESS FOR DUTY

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

"On April 10, 2025, at 1124 CDT, a licensed operator at Arkansas Nuclear One, Unit 1, had a confirmed positive result for alcohol during random testing per the Entergy fitness for duty (FFD) program. The individual's unescorted access has been terminated. This event is being reported under 10 CFR 26.719(b)(2)(ii).

"The NRC Resident Inspector has been informed."