Control device for control rod drives

Purpose: To avoid contact between the piston shaft for control rod drives and collect fingers upon extraction of control rods in BWR type reactors. Constitution: Four solenoid valves are provided for the control of hydraulic pressures applied to the piston of control rod drives. Upon extraction of the control rods, the four solenoid valves are actuated at delayed timings by the use of timers and electronic circuits. Specifically, the solenoid valves are actuated at first so that the piston is raised, whereby the force applied so far to the collect fingers are released. Then, the solenoid valves are actuated so that the piston may be lowered slowly, where at the collect fingers move rapidly to be apart from the piston. Then, the solenoid valves are actuated so that the piston may be lowered at a predetermined speed. (Ikeda, J.)