Automatic Reactor Trip Due to Trip of Motor Control Center
On 1/20/2021 at 1822 EST, with Unit 2 in Mode 1 at 100 percent power, the reactor automatically tripped due to a loss of Motor Control Center 2B2. The trip was uncomplicated with all systems responding normally post trip. Operations stabilized the plant in Mode 3. Auxiliary feed-water automatically actuated on the 2A Steam Generator post trip. Current decay heat removal is the 2B main feedwater pump to both steam generators and the Steam Bypass Control System to the main condenser.
Unit 1 is not affected.
This event is being reported pursuant to 10 CFR 50.72(b)(2)(iv)(B).
Automatic Reactor Scram Due to High Reactor Pressure Signal
At 0245 EST on November 13, 2020, the Limerick Unit 1 reactor automatically scrammed on a valid Reactor High Pressure signal (1096psig). The Reactor High Pressure signal was caused by the closure of the 1B Inboard Main Steam Isolation Valve (MSIV), causing reactor pressure to rise, exceeding the Reactor Protection System (RPS) setpoint of 1096psig.
The shutdown was normal and the plant is stable in Hot Shutdown with normal pressure control via the Main Steam Bypass Valves to the Main Condenser and normal level control using the Feedwater System.
The closure of the 1B Inboard MSIV appears to have been caused by a loss of Primary Containment Instrument Gas (PCIG) pneumatic supply to the valve.
The licensee notified the NRC Resident Inspector, and will be notifying Berks, Chester, and Montgomery Counties, as well as the Pennsylvania Emergency Management Agency.
Manual Reactor Trip Due to an Un-Isolable Leak on the Turbine High Pressure Fluid System
On November 1, 2020, at 0534 CST the reactor was manually scrammed due to an un-isolable leak on the Turbine High Pressure Fluid System. Initial power level when the leak was identified was 100 percent. Power was lowered commencing at 0525 in accordance with shutdown procedures. The Reactor Operator scrammed the reactor at 0534 from approximately 75 percent power. Following the scram, Reactor vessel water level lowered to approximately -20 inches on the Wide Range Instruments, and was subsequently recovered to normal post scram range (approximately 36 inches) using the Reactor Feedwater system. Group 2 Isolation occurred due to Reactor vessel level reaching the isolation setpoint (3 inches). The plant is stable in MODE 3 and proceeding to cold shutdown. The Main Condenser remained available throughout the evolution and condenser vacuum is currently being maintained by the Mechanical Vacuum Pumps. Pressure is being controlled using the steam line drains to the main condenser.
All control rods fully inserted and there were no complications. All systems responded as designed. The Turbine High Pressure Fluid System has been secured.
This event is reportable under 10 CFR 50.72(b)(2)(iv)(B) due to RPS Actuation-Critical and 50.72(b)(3)(iv)(A) Valid Specified System Actuation.
The licensee has notified the NRC Resident Inspector.