Reactor coolant cleanup system and operation method therefor

During normal operation of a nuclear reactor, reactor coolants at a flow rate of not more than a predetermined level are taken by a coolant feeding means, and first and second control valves are always closed by first and second control means, to ensure the same cleanup performance as usual. On the other hand, in a reactor shutdown process, heat removal by the coolant cleanup system is started before the completion of heat removal by a condensate feeding system and the start of the heat removal by a remaining heat removing system, to cool the reactor water while cleaning reactor water. Namely, the flow rate in a cleaning means is maintained to a constant level by the first control means, and the flow rate of a heated portion is maintained to a predetermined level by the second control means. The cleaning performance of reactor water can be remarkably improved, and heat is removed in the condensate feeding system, and after cooling the reactor water to a relatively low temperature, the heat removal is performed switchingly in the remaining heat removing system. Accordingly, deposition of radioactive corrosion products in the remaining heat removing system can be suppressed and dose rate can be reduced. (N.H.)