JPH0631812B

PURPOSE:To prevent damage to a recirculation pump of a boiling water reactor, by making other pumps to be run back automatically in case one recirculation pump trips down. CONSTITUTION:A tripping of a recirculation pump 5a driven by a motor 4a is detected from an on-off situation of an input breaker 13a of a variable cycled power supply 9a. A monitoring circuit 1 memories a reactor output and a core flow characteristics of each pump and monitors whether an operation point of the recirculation pump 5 reaches a cavitation zone or not, based on a feed water signal 22, a core flow signal 23 and a trip signal 12a from a trip detection circuit 12. An interlock circuit 20, based upon an output of the monitoring circuit 19, put out a runback direction signal, switches a manual/auto switching contact 10 of a speed governor 31 to a manual side (b) and controls a speed of another recirculating pump 5b by a directing signal 39 of speed setting from a runback setter 31.