A reactor containment vessel comprising an internal structural wall provided within said reactor containment vessel, said internal structural wall constituting a dry well portion for containing a reactor pressure vessel, and an inner peripheral portion of a pressure control chamber for condensing steam in said dry well portion, said internal structure wall being surrounded by said reactor containment vessel of steel in such a manner that said internal structural wall is spaced from a reactor containment vessel wall to form an outer peripheral portion of said pressure control chamber, said reactor containment vessel being disposed in an outer peripheral pool, said inner and outer peripheral portions having respective pressure control pool portions and respective wet well portions disposed above said pressure control pool portions, said pressure control pool portions of said inner and outer peripheral portions being communicated with each other, said wet well portions of said inner and outer peripheral portions being separated from each other, said reactor containment vessel surrounding an operation floor, said operation floor being communicatable with a space in said wet well portion of said outer peripheral portion via a pressure release valve, that portion of said reactor containment vessel which surrounds said operation floor being covered with a wall having a gas inlet at its lower portion and a gas outlet at its upper portion, and a radiator plate being provided in a space between said wall and said that portion of said reactor containment vessel surrounding said operation floor.