At 0026 (EDT) on October 12, 2020, D.C. Cook Unit 2 tripped automatically on low-low level of #24 steam generator which occurred after a lowering of main condenser vacuum.
The reason for the lowering main condenser vacuum and the reason for the low steam generator #24 level is under investigation.
This notification is being made in accordance with 10 CFR 50.72(b)(2)(iv)(B), Reactor Protection System (RPS) actuation as a four (4) hour report. Notification is also being made as an eight (8) hour report under 10 CFR 50.72(b)(3)(iv)(A) due to actuation of the Auxiliary Feedwater System (AFW).
The D.C. Cook Resident NRC Inspector has been notified.
Unit 2 is being supplied by offsite power. All control rods fully inserted. Auxiliary Feedwater Pumps started as required and are operating properly. Decay heat is being removed via steam generator power operated relief valves (PORVs) due to condenser steam dump unavailability from low main condenser vacuum. All four Reactor Coolant Pumps remain running. Preliminary evaluation indicates all plant systems functioned normally following the reactor trip. D.C. Cook Unit 2 remains stable in Mode 3. No radioactive release is in progress as a result of this event.
Automatic Reactor Trip on Over Power Delta Temperature
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.
Tennessee Valley Authority, Application to Modify the Watts Bar Nuclear Plant Unit 1 and Unit 2 Technical Specifications for Function 6.e of Table 3.3.2-1, Engineered Safety Feature Actuation System Instrumentation (WBN-TS-19-27)
Reactor Scram After Loss of Feedwater - Grand Gulf
On August 24, 2020 at 2305 CT at Grand Gulf Nuclear Station (GGNS) an Automatic Reactor Scram occurred after a trip of the Reactor Feed Pump B and subsequent lowering of reactor water level to 11.4 inches Narrow Range. The scram occurred with Reactor Power at 14% and the main generator offline.
All control rods fully inserted and there were no complications. All systems responded as designed.
Main Steam Isolation Valves were manually closed to control reactor cooldown, Currently GGNS reactor pressure is being maintained at 450-600psig. Reactor water level is being maintained with condensate through startup level control.
No radiological releases have occurred due to this event from the unit.
The NRC Resident has been notified.
Decay heat is being removed via the main condenser.