Event Description:
Reactor scram (4 hr notification) automatic scram
Primary containment isolation of Groups 2,3,4, and 5 due to RPV Level < low level setpoint (<127") due to reactor scram. (8 hr notification).
Actions Taken (reference applicable Technical Specifications):
Implemented OT 3100 (Reactor Scram Procedure) EOP-1 (RPV Control). Placed the plant in a stable condition and implemented OP 0109, Plant Restoration.
The NRC Resident Inspector was notified of this event by the licensee.
Reactor was initially at approximately 63% power due to
cooling tower damage which occurred more than a week ago. License was performing a surveillance test of the # 2 turbine stop valve. The valve was shut per the surveillance test procedure but they were unable to open the valve. Personnel were in the heater bay and mechanical assistance was applied to open the valve. The valve opened quickly at which point the licensee received a turbine stop valve closure signal which generated an
automatic reactor scram. All rods fully inserted into the core.
Reactor vessel water level decreased below 127 inches, due to the reactor
scram, which caused
primary containment isolation of groups 2,3,4 and 5. Reactor vessel water began to increase because Reactor
feedwater pumps "A" & "B" were still operating. Reactor
feedwater pump "B" was secured. When reactor vessel water increased to 173 inches, high level alarm, reactor
feedwater pump "A" automatically tripped. Highest
reactor vessel water level increased to was approximately 179 inches. No
SRV's opened. All
Emergency Core Cooling Systems,
EDGs are fully operable if needed and the electrical grid is stable.
Reactor vessel water level is being maintained using a reactor
feedwater pump. Only other anomaly was that for some unknown reason automatic pressure control went to mechanical pressure control during the
transient. Licensee is investigating the event.
