A reactor containment vessel comprising: a reactor pressure vessel that accommodates a core; a reactor shielding wall provided to surround an outer circumferential surface of the reactor pressure vessel; a dry well that forms a space that accommodates the reactor pressure vessel; a suppression chamber for controlling an internal pressure in the reactor containment vessel; and a reactor containment vessel cooling system for cooling the reactor containment vessel by acquiring the water vapor in the reactor containment vessel and by using water vapor pressure in the vessel as a drive force to thereby condense the acquired water vapor into condensate and cool the reactor containment vessel with the condensate, the cooling system comprising: a heat exchange pool that is arranged apart from the dry well (15a, 15b) and the suppression chamber in the reactor containment vessel and stores a medium for cooling acquired water vapor; a heat exchanger that is immersed in the heat exchange pool, is configured to acquire water vapor from the dry well in the reactor containment vessel, and is configured to perform heat exchange between the water vapor and the cooling medium in the heat exchange pool so as to convert the water vapor into condensate; a water vapor sucking tube extending from the heat exchanger; and a condensate drain pipe that is further provided for the heat exchanger so as to extract the condensate from the heat exchanger, characterized in that the condensate drain pipe is either configured to guide and discharge the condensate at the side surface or at the top of a reactor pressure vessel, or configured to discharge the condensate at the side surface or at the top of a thermally insulating member that surrounds the reactor pressure vessel. a reactor pressure vessel that accommodates a core; a reactor shielding wall provided to surround an outer circumferential surface of the reactor pressure vessel; a dry well that forms a space that accommodates the reactor pressure vessel; a suppression chamber for controlling an internal pressure in the reactor containment vessel; and a reactor containment vessel cooling system for cooling the reactor containment vessel by acquiring the water vapor in the reactor containment vessel and by using water vapor pressure in the vessel as a drive force to thereby condense the acquired water vapor into condensate and cool the reactor containment vessel with the condensate, the cooling system comprising: a heat exchange pool that is arranged apart from the dry well (15a, 15b) and the suppression chamber in the reactor containment vessel and stores a medium for cooling acquired water vapor; a heat exchanger that is immersed in the heat exchange pool, is configured to acquire water vapor from the dry well in the reactor containment vessel, and is configured to perform heat exchange between the water vapor and the cooling medium in the heat exchange pool so as to convert the water vapor into condensate; a water vapor sucking tube extending from the heat exchanger; and a condensate drain pipe that is further provided for the heat exchanger so as to extract the condensate from the heat exchanger, characterized in that the condensate drain pipe is either configured to guide and discharge the condensate at the side surface or at the top of a reactor pressure vessel, or configured to discharge the condensate at the side surface or at the top of a thermally insulating member that surrounds the reactor pressure vessel. a heat exchange pool that is arranged apart from the dry well (15a, 15b) and the suppression chamber in the reactor containment vessel and stores a medium for cooling acquired water vapor; a heat exchanger that is immersed in the heat exchange pool, is configured to acquire water vapor from the dry well in the reactor containment vessel, and is configured to perform heat exchange between the water vapor and the cooling medium in the heat exchange pool so as to convert the water vapor into condensate; a water vapor sucking tube extending from the heat exchanger; and a condensate drain pipe that is further provided for the heat exchanger so as to extract the condensate from the heat exchanger, characterized in that the condensate drain pipe is either configured to guide and discharge the condensate at the side surface or at the top of a reactor pressure vessel, or configured to discharge the condensate at the side surface or at the top of a thermally insulating member that surrounds the reactor pressure vessel.