Event Notification Report for April 10, 2025
U.S. Nuclear Regulatory Commission
Operations Center
EVENT REPORTS FOR
04/09/2025 - 04/10/2025
Power Reactor
Event Number: 57659
Facility: Palo Verde
Region: 4 State: AZ
Unit: [1] [] []
RX Type: [1] CE,[2] CE,[3] CE
NRC Notified By: Tanner Goodman
HQ OPS Officer: Tenisha Meadows
Region: 4 State: AZ
Unit: [1] [] []
RX Type: [1] CE,[2] CE,[3] CE
NRC Notified By: Tanner Goodman
HQ OPS Officer: Tenisha Meadows
Notification Date: 04/10/2025
Notification Time: 10:29 [ET]
Event Date: 04/10/2025
Event Time: 07:11 [MST]
Last Update Date: 04/10/2025
Notification Time: 10:29 [ET]
Event Date: 04/10/2025
Event Time: 07:11 [MST]
Last Update Date: 04/10/2025
Emergency Class: Unusual Event
10 CFR Section:
50.72(a) (1) (i) - Emergency Declared 50.72(b)(3)(iv)(A) - Valid Specif Sys Actuation
10 CFR Section:
50.72(a) (1) (i) - Emergency Declared 50.72(b)(3)(iv)(A) - Valid Specif Sys Actuation
Person (Organization):
Vossmar, Patricia (R4DO)
Monninger, John (R4RA)
King, Michael (NRR)
Erlanger, Craig (NSIR)
Crouch, Howard (IR)
Vossmar, Patricia (R4DO)
Monninger, John (R4RA)
King, Michael (NRR)
Erlanger, Craig (NSIR)
Crouch, Howard (IR)
| Unit | SCRAM Code | RX Crit | Initial PWR | Initial RX Mode | Current PWR | Current RX Mode |
|---|---|---|---|---|---|---|
| 1 | N | N | 0 | Defueled | 0 | Defueled |
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)
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)
Power Reactor
Event Number: 57661
Facility: Arkansas Nuclear
Region: 4 State: AR
Unit: [1] [] []
RX Type: [1] B&W-L-LP,[2] CE
NRC Notified By: Shannon Mosby
HQ OPS Officer: Sam Colvard
Region: 4 State: AR
Unit: [1] [] []
RX Type: [1] B&W-L-LP,[2] CE
NRC Notified By: Shannon Mosby
HQ OPS Officer: Sam Colvard
Notification Date: 04/10/2025
Notification Time: 17:39 [ET]
Event Date: 04/10/2025
Event Time: 11:24 [CDT]
Last Update Date: 04/10/2025
Notification Time: 17:39 [ET]
Event Date: 04/10/2025
Event Time: 11:24 [CDT]
Last Update Date: 04/10/2025
Emergency Class: Non Emergency
10 CFR Section:
26.719 - Fitness For Duty
10 CFR Section:
26.719 - Fitness For Duty
Person (Organization):
Vossmar, Patricia (R4DO)
FFD Group, (EMAIL)
Vossmar, Patricia (R4DO)
FFD Group, (EMAIL)
| Unit | SCRAM Code | RX Crit | Initial PWR | Initial RX Mode | Current PWR | Current RX Mode |
|---|---|---|---|---|---|---|
| 1 | N | Y | 100 | Power Operation | 100 | Power Operation |
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."
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."