Cooling systems upon isolation of nuclear reactors

Purpose: To moderate thermal shocks to structures in nuclear reactors upon cooling water spray. Constitution: In a cooling system adapted to cool the inside of the reactor using cooling water to thereby keep the pressure in the reactor within a predetermined level upon isolation of the reactor from a main steam turbine, a heating mechanism using reactor steams in provided to the feed channel of cooling water sprayed to the reactor core for increasing the temperature of the cooling water. The cooling water thus warmed is controlled its temperature by the signal from a thermometer and poured through the reactor head spray into the reactor. Since the temperature difference between the inside of the reactor and the sprayd cooling water is reduced, thermal shocks applied to the structures in the core can be moderated, whereby the reliability and the safety for the structures in the reactor core can be improved. (Furukawa, Y.)