At 2130 (EDT) on March 30, 2019, with Unit 2 in Mode 1 at 30 percent reactor power, the reactor was manually tripped due to a main steam isolation valve failing closed. The trip was not complex, with all systems responding normally. Operations stabilized the plant in Mode 3. Decay heat is being removed through the main steam lines through the steam dumps and into the condenser.
The expected actuation of the Auxiliary Feedwater System (an engineered safety feature) is being reported as an eight hour report under 10 CFR 50.72 (b)(3)(iv)(A).
Unit 1 was not affected.
There was no impact to the health and safety of the public or plant personnel.
Manual Reactor Scram and Specified System Actuation
At 17:47 Eastern Daylight Time (EDT) on March 30, 2019, with Unit 2 in Mode 1 at approximately 23 percent reactor power and main turbine startup in progress coming out of a refuel outage, a high temperature was sensed at main turbine bearing #9. As a result of and to arrest the high temperature condition, the main control room inserted a manual reactor scram.
All control rods inserted as expected during the scram. When the scram was inserted, reactor water level dropped below the Low Level 1 actuation setpoint. Per design, the Low Level 1 signal resulted in Group 2 (i.e., floor and equipment drain isolation valves), Group 6 (i.e., monitoring and sampling isolation valves) and Group 8 (i.e., shutdown cooling isolation valves) isolations.
The main control room manually closed all Main Steam Isolation Valves (MSIVs), in anticipation of a low vacuum prior to the Group 1 automatic closure signal being received. High Pressure Coolant Injection (HPCI) was aligned for pressure control and Reactor Coolant Isolation System (RCIC) was aligned for level control. The Reactor Coolant Sample Line Isolation valves closed as expected on low main condenser vacuum.
All systems responded as designed.
This event is being reported in accordance with 10 CFR 50.72(b)(2)(iv)(B) for RPS actuation and 10 CFR 50.72(b)(3)(iv)(A) as an event that results in valid actuations of the Primary Containment Isolation System.
There was no impact on the health and safety of the public or plant personnel.
The NRC Resident Inspector has been notified.
At the time of notification, decay heat was being removed by the condenser through one open MSIV and a feedwater pump running.
Automatic Actuation of the Primary Containment Isolation System and the Reactor Protecton System
At 1654 EDT on March 28, 2019, with Unit 1 in Mode 3 at 0 percent power, an actuation of the Primary Containment Isolation System occurred, closing the outboard Main Steam Isolation Valves (MSIVs) due to a low condenser vacuum signal. The MSIVs had been manually closed, per procedure, during the shutdown evolution to address drywell leakage. The inboard MSIVs had not been reopened when the isolation occurred.
Subsequently, at 1658 EDT a Reactor Protection System (RPS) actuation occurred due to reactor water level dropping below the actuation setpoint. All control rods were inserted at the time of the actuation.
This event is being reported in accordance with 10 CFR 50.72(b)(3)(iv)(A) as an event that results in valid actuations of the Primary Containment Isolation System and the Reactor Protection System.
There was no impact on the health and safety of the public or plant personnel. The safety function of both the MSIVs and the RPS had already been completed at the time of the event.