JPH068881B

PURPOSE:To prevent the damage of a recirculating pump and the like by automatically running back the speed of rotation of the other recirculating pumps in operation up to a prescribed limit for avoiding cavitation area in the case where the recirculating pump trips. CONSTITUTION:Detectors 10a, 10b detect closing conditions of input breakers 15a, 15b of variable frequency power sources 9a, 9b which are drive sources of each recirculating pump and catch trips of recirculating pumps 5a, 5b... A logic circuit 11 detects that reactor core flow distribution of coolant is not uniform with signals from the detectors 10a, 10b and outputs a signal. A timer 12 is connected to the secondary side of the circuit 11, delays the output signals of the circuit 11 up to a prescribed time and outputs a signal to a overspeed limiter 13 and a rate-of-change limiter 14. The limiter 13 limits the speed of rotation of the other recirculating pumps in operation in accordance with a set signal from a speed setter 6, outputs a speed limit signal 16 for decreasing up to memories limit speed. The limiter 14 receives the signal 16, rate-of-change of speed of rotation is held memorized limit value and a decreasing signal is output in the power source 9a.