Safety system of reactor container

The safety system of the present invention can shut down a BWR type reactor safely without operator's aid even upon occurrence of an abnormal state. Namely, a pressure/temperature measuring and controlling device is disposed to a dry well in the safety system of a reactor container incorporating a pressure vessel, a space between a dry wall and a wet well and a pressure suppression chamber. Operation signals sent from pipelines of an emergency reactor core cooling system delivered from the pressure vessel are inputted to the pressure/temperature measuring and controlling device. Output signals of the pressure/temperature measuring and controlling device are inputted to a spray device. With such procedures, when actuation of dry well spray is required upon loss of coolants accident, necessity for the actuation of the spray can be judged based on the pressure, temperature in the dry well, reactor water level and a state of operation and duration of abnormal state of other ECCS system using the pressure/temperature measuring and controlling device disposed in the dry well. If actuation of spray is required, the dry wall spray is automatically actuated to reduce pressure and temperature in the container. (I.S.)