Coolant flow rate control device in bwr type reactors

Purpose: To improve the safety of reactor operation with no abnormal decrease in the thermal allowance of fuels. Constitution: A low level preference circuit for automatically controlling the variations in the coolant flow rate is provided in the preceeding stage to a control operator of a coolant flow rate control device in a bwr type reactor. The upper limit of a signal for coolant flow rate changes, which is obtained from the deviation between the output signal from a neutron flux control device that issues a coolant flow rate demand signal as a function of the deviation between the output signals from a main control device and neutron flux instruments and the output signal from a recycle flow rate instruments, is restricted by a value obtained from the output signal of the neutron flux instruments and converted into a restrictive value for the variations in the coolant flow rate, so that an output signal corresponding to a value greater than the above restrictive value may not be sent out. (Furukawa, Y.)