At 0925 EDT, on September 8, 2020, with Unit 1 in Mode 1 at 100 percent power, the reactor automatically tripped on Overpower Delta Temperature. Unit 1 Channel 1 Overpower Delta Temperature was tripped as a planned evolution when an inadvertent Unit 1 Channel 2 Overpower Delta Temperature signal was received. This resulted in an
automatic reactor trip. The trip was not complex, with all systems responding normally. Because of the reactor trip, the
Auxiliary Feedwater (
AFW) System actuated as expected due to on
ATWS Mitigation System Actuation Circuitry (
AMSAC) signal. Unit 2 is not affected.
Operations responded and stabilized the plant. Decay heat is being removed by discharging steam to the main condenser using the condenser steam dump valves.
Due to the Reactor Protection System (RPS) actuation while critical, this event is being reported as a 4-hour, non-emergency notification per 10 CFR 50.72(b)(2)(iv)(B). This event is also being reported as an 8-hour non-emergency notification per 10 CFR 50.72(b)(3)(iv)(A) as an event that results in a valid actuation of the AFW system.
There was no impact on the health and safety of the public or plant personnel. The NRC Resident Inspector has been notified.
