Abstract: A reactor container is composed of a dry well and a wet well and, in the reactor container, there is provided with a dry well cooling system, the dry well cooling system including, in one aspect, an in-dry-well heat exchanger disposed in the dry well of the reactor container, an in-dry-well blower connected to a primary side of the in-dry-well heat exchanger, a circulation pipe connected to a secondary side of the in-dry-well heat exchanger, a normal cooling system connected to the secondary side of the in-dry-well heat exchanger through the circulation pipe and including an equipment cooling pump, an equipment cooling heat exchanger and a seawater pump, and a standby cooling system connected to and branched from the circulation pipe.