Automatic depressurization device in nuclear reactors

Purpose: To enable to surely maintain the reactor core integrity in nuclear reactors. Constitution: A control circuit is disposed such that a reactor high water level signal outputted when the water level in the reactor pressure vessel is reduced to an alarm level and a containing vessel high signal outputted when the pressure inside the reactor container vessel increase to an alarming pressure are at least inputted simultaneously, and the reactor pressure is maintained to a predetermined range by the ON-OFF of a safety valve in case if the reactor pressure is reduced to less than a predetermined level after a valve opening signal for opening the safety valve is outputted when the reactor power is maintained higher than a critical power. Then, the device is effectuated in the same manner as the conventional device against loss of coolants accidents, while only the low pressure ECCS is set to stand-by state necessary and sufficient for insuring the water level even in a state where the actuation of the automatic depressurization device is not desired, thereby surely maintaining the integrity of the reactor core even if the automatic depressurization device is actuated. (Yoshihara, H.)