Nuclear power plants

Purpose: To improve the reactor safety by stopping a plurality of recycling pumps stepwise with a predetermined time difference upon generation of reactor scram signals to thereby suppress various transient phenomena due to the stopping of the pumps within a low level. Constitution: A plurality of nuclear reactor scram signals are inputted into a recycling pump trip logic circuit constituted with a logical circuit and then outputted to recycling pumps A and B in a dual system. Further, a timer is connected to the midway of a signal line connecting the input of the recycling pump in the system B with the output of the recycling pump trip logic circuit, so that the recycling pump in the system B is stopped with a delay set by the timer after the stopping of the operation for the recycling pump in the system A. It is thus possible to avoid the transient phenomena in the reactor operation caused by the simultaneous stopping for the operation of the two recycling pumps in the systems A and B. (Kawakami, Y.)