Method of depressurizing and cooling reactors

Purpose: To automatically and effectively perform depressurization cooling operation for a nuclear reactor while keeping the restricted condition of temperature decreasing rate. Method: In carrying out the depressurization cooling for a nuclear reactor by calculating the deviation between a main steam pressure and an aimed pressure, calculating the operation amount for the opening degree of a bypass valve and controlling a turbine bypass valve at the opening of a main steam isolation valve based on the signal indicating the higher value of the operation amount and the set value for the opening degree of the bypass valve, a deviation between an aimed reactor water temperature and an actual reactor water temperature is calculated and the operation amount for the opening degree of the turbine bypass valve is determined based on the calculated deviation. This enables to perform stable bypass valve control for the depressurization cooling operation for the nuclear reactor by always controlling the bypass valve directly. (Horiuchi, T.)