Method of controlling the recycling flow rate of a nuclear reactor

A recycling pump connected to a BWR reactor is controlled by a recycling flow rate control system comprising a secondary resistor control system and an induction motor for driving the recycling pump. The reactor power is converted into steam and fed to a steam turbine to drive a power generator. The frequency of the power generator is detected through a governor and fed to the flow rate control system. If the frequency exceeds a predetermined value, the resistor control system is operated by this signal to insert a resistor into the secondary of the induction motor to suppress a temporary increase of the motor rotation speed, i.e., the pump operation speed. The peak power of the neutron flux in the reactor is accordingly lowered to a level below the scram level. In so far as the reactor scram is caused by the frequency increase of the generator due to an abrupt interruption of the reactor system load, reactor shut-down is avoided without having any adverse effect on the other control system. (Ohno, Y.)