Control method for BWR type power plant

Purpose: To continue the plant operation with no scram even if the system frequency is increased in a control system of a BWR type nuclear power plant. Method: In the case if disturbance is resulted in an electrical power system to such an extent as not to actuate a power load imbalance relay and the turbine load is abruptly decreased, a opening degree control signal for a turbine steam conditioning valve is limited such that the decrement in the flow rate of steams flowing the turbine steam control valve is less than the capacity of a bypass valve. Then, when the load continues to decrease for more than a predetermined of time, the restriction on the opening degree control signal is released to reduce the reactor power. The reactor operation is kept continued for the abrupt and short period increase in the frequency of the load, while avoiding the scram due to the increase in the reactor pressure by the restriction to the control valve opening degree and, while on the other hand, for the frequency increase in a long period while avoiding the scram by reducing the reactor power. (Kamimura, M.)