Event Notification Report for April 11, 2023

AUTOMATIC REACTOR TRIP DUE TO LOSS OF REACTOR COOLANT PUMPS

The following information was provided by the licensee via 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 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 10 CFR 50.73.

"At 2144 MST on April 8, 2023, the Unit 1 reactor automatically tripped due to the loss of reactor coolant pumps stemming from the loss of 13.8 kV power to the pumps.

"Prior to the reactor trip, the main turbine tripped due to a loss of hydraulic pressure. The main generator output breakers did not automatically open on the turbine trip as expected so the control room operators opened the breakers per procedural guidance. Once the breakers were opened, the two 13.8 kV electrical distribution buses failed to complete a fast bus transfer, which resulted in the loss of power to the reactor coolant pumps, initiating the reactor trip. The control room operators manually actuated a main steam isolation signal per procedure, requiring use of the atmospheric dump valves.

"Following the reactor trip, all control element assemblies inserted fully into the core. No automatic specified system actuation was required or occurred. No emergency plan classification was required per the Emergency Plan. Safety related buses remained powered from offsite power during the event and the offsite power grid is stable. Unit 1 is stable and in Mode 3. Decay heat is being removed by the atmospheric dump valves and the class 1E powered motor driven auxiliary feedwater pump.

"The loss of hydraulic pressure, the main generator output breakers failing to automatically open and the fast bus transfer not actuating are being investigated.

"This event is being reported as a reactor protection system actuation in accordance with the reporting criteria of 10 CFR 50.72(b)(2)(iv)(B).

"The NRC Senior Resident Inspector has been informed.

"Unit 2 is in a refueling outage in Mode 5 and Unit 3 is in Mode 1 at 100 percent power."


* * * UPDATE ON 4/9/23 AT 0835 EDT FROM TANNER GOODMAN TO ADAM KOZIOL * * *

"This update is being made to report the manual actuation of the B-train auxiliary feedwater pump and manual main steam isolation signal (MSIS) actuation affecting multiple main steam isolation valves (MSIVs) following the reactor trip.

"This event is being reported as a reactor protection system actuation in accordance with the reporting criteria of 10 CFR 50.72(b)(2)(iv)(B) and a specified system actuation in accordance with 10 CFR 50.72(b)(3)(iv)(A).

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

AUTOMATIC REACTOR TRIP

The following information was provided by the licensee via email:

"At 0048 EDT on 4/10/2023, with Unit 3 in Mode 1 at 18 percent power, the reactor automatically tripped due to low reactor coolant flow due to voltage decaying to the reactor coolant pumps during main generator testing activities. The trip was not complex, with all safety-related systems responding normally post-trip.

"Operations responded and stabilized the plant. Decay heat is being removed by discharging steam via steam generator power operated relief valves to atmosphere. Units 1, 2, and 4 are not affected.

"Due to the Reactor Protection System actuation while critical, this event is being reported as a four-hour, non-emergency notification per 10 CFR 50.72(b)(2)(iv)(B).

"There was no impact on the health and safety of the public or plant personnel. The NRC Resident Inspector has been notified."