ENS 57659
ENS Event | |
|---|---|
14:11 Apr 10, 2025 | |
| Title | Unusual Event - Loss of All But One AC Power Source to Emergency Buses |
| Event Description | 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.
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).
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) |
| Where | |
|---|---|
Palo Verde  Arizona (NRC Region 4) | |
| Reporting | |
| Emergency class: | Unusual Event |
| 10 CFR 50.72(a) (1) (i), Emergency Class Declaration 10 CFR 50.72(b)(3)(iv)(A), System Actuation | |
| Time - Person (Reporting Time:+-3.7 h-0.154 days <br />-0.022 weeks <br />-0.00507 months <br />) | |
| Opened: | Tanner Goodman 10:29 Apr 10, 2025 |
| NRC Officer: | Tenisha Meadows |
| Last Updated: | Apr 10, 2025 |
| 57659 - NRC Website
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Palo Verde with 10 CFR 50.72(a)(1)(i), Emergency Class Declaration, 10 CFR 50.72(b)(3)(iv)(A), System Actuation | |
WEEKMONTHYEARENS 576592025-04-10T14:11:00010 April 2025 14:11:00
[Table view]10 CFR 50.72(a)(1)(i), Emergency Class Declaration, 10 CFR 50.72(b)(3)(iv)(A), System Actuation Unusual Event - Loss of All But One AC Power Source to Emergency Buses ENS 576562025-04-09T02:24:0009 April 2025 02:24:00 10 CFR 50.72(b)(3)(iv)(A), System Actuation Valid Actuation of Emergency AC Electrical Power Systems ENS 570662024-04-04T23:18:0004 April 2024 23:18:00 10 CFR 50.72(a)(1)(i), Emergency Class Declaration Notification of Unusual Event Due to Fire Alarm in the Vital Area ENS 570472024-03-24T23:34:00024 March 2024 23:34:00 10 CFR 50.72(b)(3)(iv)(A), System Actuation Valid Specified System Actuations of Unit 2 Train B Emergency Diesel Generator and Train B Auxiliary Feedwater ENS 565512023-06-02T11:05:0002 June 2023 11:05:00 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(b)(3)(iv)(A), System Actuation Automatic Reactor Trip ENS 564592023-04-09T04:44:0009 April 2023 04:44:00 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(b)(3)(iv)(A), System Actuation Automatic Reactor Trip Due to Loss of Reactor Coolant Pumps ENS 560442022-08-15T00:02:00015 August 2022 00:02:00 10 CFR 50.72(b)(3)(iv)(A), System Actuation Valid Actuations of Unit 1 and Unit 3 Emergency Diesel Generators and Unit 1 Auxiliary Feedwater Pump ENS 558782022-05-05T02:55:0005 May 2022 02:55:00 10 CFR 50.72(b)(3)(iv)(A), System Actuation Valid Actuation of Unit 2 and Unit 3 Emergency Diesel Generators and Unit 3 Auxiliary Feedwater Pump ENS 555342021-10-20T21:46:00020 October 2021 21:46:00 10 CFR 50.72(b)(3)(iv)(A), System Actuation Valid Specified System Actuations of Unit 1 and Unit 3 Emergency Diesel Generators ENS 542242019-08-16T15:21:00016 August 2019 15:21:00 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(b)(3)(iv)(A), System Actuation Automatic Reactor Trip Due to Turbine Trip ENS 534772018-06-27T07:00:00027 June 2018 07:00:00 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(b)(3)(iv)(A), System Actuation Automatic Reactor Trip on Low Steam Generator Water Level ENS 524352016-12-15T11:10:00015 December 2016 11:10:00 10 CFR 50.72(a)(1)(i), Emergency Class Declaration Alert Declared - Catastrophic Failure of an Emergency Diesel Generator ENS 515222015-11-09T12:47:0009 November 2015 12:47:00 10 CFR 50.72(a)(1)(i), Emergency Class Declaration Unusual Event Declared Due to Containment Fire Alarm ENS 514032015-09-17T06:01:00017 September 2015 06:01:00 10 CFR 50.72(a)(1)(i), Emergency Class Declaration Notification of Unusual Event Due to Rapid Combustion of a Load Center Breaker ENS 502372014-06-29T05:06:00029 June 2014 05:06:00 10 CFR 50.72(a)(1)(i), Emergency Class Declaration Unusual Event - Earthquake Felt on Site ENS 493172013-09-03T02:26:0003 September 2013 02:26:00 10 CFR 50.72(a)(1)(i), Emergency Class Declaration Unusual Event Declared Due to Fire in the Turbine Building ENS 491692013-07-03T07:00:0003 July 2013 07:00:00 10 CFR 50.72(a)(1)(i), Emergency Class Declaration Notice of Unusual Event Due to Explosion in a Non-Safety Related Load Center ENS 473332011-10-08T23:19:0008 October 2011 23:19:00 10 CFR 50.72(b)(2)(xi), Notification to Government Agency or News Release, 10 CFR 50.72(a)(1)(i), Emergency Class Declaration Notification of Unusual Event Due to Severe Electrical Fault in Rcp Junction Box ENS 466332011-02-22T03:01:00022 February 2011 03:01:00 10 CFR 50.72(b)(3)(iv)(A), System Actuation Auto Start and Load of Edgs on Units 1&3 Following Loss of Start-Up Transformer ENS 465562011-01-20T01:41:00020 January 2011 01:41:00 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(b)(3)(iv)(A), System Actuation Reactor Trip Due to Main Feedwater Pump Trip ENS 460252010-06-18T15:08:00018 June 2010 15:08:00 10 CFR 50.72(a)(1)(i), Emergency Class Declaration Unusual Event Declared Due to Damaged Energized Equipment ENS 458232010-04-08T17:15:0008 April 2010 17:15:00 10 CFR 50.72(a)(1)(i), Emergency Class Declaration Earthquake ENS 458112010-04-04T22:42:0004 April 2010 22:42:00 10 CFR 50.72(a)(1)(i), Emergency Class Declaration Unusual Event Declared Due to an Earthquake ENS 457842010-03-23T01:11:00023 March 2010 01:11:00 10 CFR 50.72(a)(1)(i), Emergency Class Declaration Notification of Unusual Event Due to Unidentified Leakage Greater than 10 Gpm ENS 457482010-03-07T18:24:0007 March 2010 18:24:00 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(a)(1)(i), Emergency Class Declaration Notification of Unusual Event Due to Electrical Fault Causing Damage to Equipment ENS 437642007-11-02T14:44:0002 November 2007 14:44:00 10 CFR 50.72(b)(2)(xi), Notification to Government Agency or News Release, 10 CFR 50.72(a)(1)(i), Emergency Class Declaration Suspicious Explosive Device Discovered in Vehicle at Oca Access Checkpoint ENS 429382006-10-27T06:53:00027 October 2006 06:53:00 10 CFR 50.72(b)(3)(iv)(A), System Actuation Loss of Power to the Unit 1 and Unit 3 Train B Safety Buses with Emergency Diesel Generator Actuation ENS 426092006-05-30T15:13:00030 May 2006 15:13:00 10 CFR 50.72(b)(3)(iv)(A), System Actuation Loss of Power to Train "a" 4 Kv Safety Bus ENS 425592006-05-06T23:35:0006 May 2006 23:35:00 10 CFR 50.72(b)(3)(iv)(A), System Actuation Valid Actuation of Emergency Diesel Generator Due to Low Voltage Condition ENS 424682006-04-03T03:54:0003 April 2006 03:54:00 10 CFR 50.72(b)(3)(iv)(A), System Actuation Emergency Diesel Trip During Testing ENS 413792005-02-07T05:19:0007 February 2005 05:19:00 10 CFR 50.72(b)(3)(iv)(A), System Actuation Emergency Diesel Start Due to Bus Deenergization ENS 413042004-12-31T17:42:00031 December 2004 17:42:00 10 CFR 50.72(b)(3)(iv)(A), System Actuation Plant Had Auto Start and Loading of Two Emergency Diesel Gererators ENS 408152004-06-14T14:44:00014 June 2004 14:44:00 10 CFR 50.72(b)(2)(xi), Notification to Government Agency or News Release, 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(a)(1)(i), Emergency Class Declaration, 10 CFR 50.72(b)(3)(iv)(A), System Actuation Unusual Event Declared Due to Reactor Trip Due to Loss of Off Site Power ENS 408162004-06-14T14:44:00014 June 2004 14:44:00 10 CFR 50.72(b)(2)(xi), Notification to Government Agency or News Release, 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(a)(1)(i), Emergency Class Declaration, 10 CFR 50.72(b)(3)(iv)(A), System Actuation Unusual Event Due to Reactor Trip Due to Loss of Off Site Power ENS 408142004-06-14T14:44:00014 June 2004 14:44:00 10 CFR 50.72(b)(2)(xi), Notification to Government Agency or News Release, 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(a)(1)(i), Emergency Class Declaration, 10 CFR 50.72(b)(3)(iv)(A), System Actuation Alert Declared - Reactor Trip Due to Loss of Off Site Power ENS 403492003-11-22T05:53:00022 November 2003 05:53:00 10 CFR 50.72(b)(3)(iv)(A), System Actuation Valid Actuation of the "a" Emergency Diesel Generator During Testing 2025-04-09T02:24:00 | |