To prevent clogging of a pump suction strainer of an emergency core cooling system during a primary system piping rupture.

This reactor container has a dry well connected by a piping having a heat insulator and housing a nuclear reactor having a core, a suppression chamber 5 storing pool water 4, and a vent pipe 6 communicating the dry well with the pool water. A pump strainer 10 inlet part of the emergency core cooling system for feeding the pool water to the core in an emergency is positioned inside the pool water 4. A trapping means 20 trapping fragments 12 of the heat insulator when the heat insulator breaks and its fragments 12 enter the pool water 4 through the vent pipe 6 is position throughout a whole area of the suppression chamber 5 between a spouting part 7 of the vent pipe inside the pool water 4 and the pump strainer 10 inlet part.