PROBLEM TO BE SOLVED: To completely cool a reactor containment vessel even when a transient phenomenon such as a loss of total AC current source occurs, and further even if a core damage occurs, to completely cool the reactor containment vessel without operation of a filter vent device, in other words, even if a severe accident happens, to completely cool the reactor containment vessel with no venting.SOLUTION: A nuclear power plant according to an embodiment comprises: a nuclear containment vessel 3 including a dry well 4, a wet well 5, and a LOCA vent pipe 8; a cooling pool 13; a heat exchanger 16 including an inlet plenum 17, an outlet plenum 18, and a heat-transfer pipe 19; a gas supply pipe 20 for supplying gas from the wet well 5 to the inlet plenum 17; a condensed water return pipe 21 for guiding condensed water in the heat exchanger 16 from the outlet plenum 18 to the nuclear containment vessel 3; and a gas vent pipe 22 for venting gas from the outlet plenum 18 to the dry well 4.
