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| Entered date | Event description | |
|---|---|---|
| ENS 56044 | 15 August 2022 01:18:00 | The following information was provided by the licensee via phone and email: At 1702 MST on August 14, 2022, a start-up transformer de-energized, resulting in a loss of power to the Unit 1 Train B 4.16 kV Class 1E Bus and the Unit 3 Train A 4.16 kV Class 1E Bus. The Unit 1 Train B Emergency Diesel Generator (EDG) and Unit 3 Train A EDG automatically started and energized their respective 4.16 kV Class 1E Buses. As a result of the loss of power on the Unit 1 Train B 4.16 kV Class 1E Bus, the B Auxiliary Feedwater Pump automatically started, as expected. The B Auxiliary Feedwater Pump was not needed for steam generator level control and no auxiliary feedwater valves repositioned. The B Auxiliary Feedwater Pump did not supply feedwater to the steam generators. 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 emergency AC electrical power systems and an auxiliary feedwater system. All systems operated as expected. Per the Emergency Plan, no classification was required due to the event. The 4.16 kV Class 1E Buses in Unit 2 were not affected by the de-energization of the start-up transformer since it was not aligned as normal power for Unit 2. Units 1, 2 and 3 remain in Mode 1 at 100% power. The cause of the start-up transformer being de-energized is under investigation. No plant transient occurred as a result of this failure. The NRC Resident Inspectors have been informed. |
| ENS 55878 | 5 May 2022 04:30:00 | The following information was provided by the licensee via email: At 1955 on May 4, 2022, a start-up transformer de-energized, resulting in a loss of power to the Unit 2 Train A 4.16 kV Class 1E Bus and the Unit 3 Train B 4.16 kV Class 1E Bus. The Unit 2 Train A Emergency Diesel Generator (EDG) and Unit 3 Train B EDG automatically started and energized their respective 4.16 kV Class 1E Buses. As a result of the Loss of Power on the Unit 3 Train B 4.16 kV Class 1E Bus, the B Auxiliary Feedwater Pump automatically started, as expected. The B Auxiliary Feedwater Pump was not needed for steam generator level control and no auxiliary feedwater valves repositioned. The B Auxiliary Feedwater Pump did not supply feedwater to the steam generators. 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 emergency AC electrical power systems and an auxiliary feedwater system. |
| ENS 55626 | 6 December 2021 17:17:00 | 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 this 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 10CFR50.73. At 1203 MST on December 6, 2021, the Unit 3 reactor automatically tripped on low departure from nucleate boiling ratio. A part-strength control element assembly was being moved at the time of the trip. Unit 3 is stable and in Mode 3. In response to the reactor trip, all control element assemblies inserted fully into the core. Safety-related electrical power remains energized from off-site power sources and reactor coolant pumps continue to provide forced circulation through the reactor. Decay heat is being removed by the steam bypass control system and main feedwater system. Required systems operated as expected. No emergency classification was required per the Emergency Plan. The NRC Senior Resident Inspector has been informed. Units 1 and 2 were unaffected by this transient. |