After-heat removal system in nuclear power plant

The object of the present invention is to delay the time as much as possible for a reactor container to be broken, to thereby decrease the extent of effect given to circumstances in a case of failing to attain reactor sub-criticality after the occurrence of a first event upon reactor accident. That is, in a power plant in which a reactor core is cooled by an remaining heat removing system having a suppression pool as a water source, a condensate tank disposed outside of the reactor container is also used as the water source for the remaining heat removing system. The reactor water level is ensured by a pump system other than an after-heat removing system, and a logic circuit is so constituted to be automatically actuated in a reactor container spray cooling mode on the condition of abnormal high pressure in a reactor container. With such a constitution, even if the reactor sub-criticality is failed to attain upon occurrence of an accident, the time for the reactor container to be broken due to excess pressure can be delayed. Accordingly, the possibility of conducting trouble-shooting operation and settling down the accident during this period is increased. Further, if a risk reducing countermeasure such as a filter bent is adopted, the main effect due to rare gases to circumstances can be reduced. (I.S.)