Method of removing decay heat

Purpose: To carry out the removal of decay heat, at the time decay heat has decreased further after using a secondary coolant system, by employing a cooling system of a coolant purification system, thereby to remove decay heat stably by a simple operation. Method: At the time decay heat has become miniscule, the secondary coolant system is stopped, and the removal of decay heat is carried out by using the cooling system of a coolant purification system provided in the overflow system connected to the reactor container, that is, a sodium cooler. The switching operation at this time is carried out in such a manner that the inlet valve of a cold trap is closed, a flash line check valve used when the system is periodically flashed is opened, and sodium which has been cooled by the sodium cooler is directly returned to an overflow tank. (Yoshino, Y.)