A core energy plant with closed working gas circuit, in which within an or safety container there are arranged a reactor core of pre-stressed concrete for heating the working gas, a working gas driven turbo-set with generator, and other components of the working gas circuit such as heat exchanger and gas storage means. The reactor core is separated from the turbo-set and other components and is arranged in a separate reactor chamber with walls of pre-stressed concrete, while the other components are respectively arranged in separate chambers, within an inner concrete container which has chambers for receiving the turbo-set with generator and the remaining components of the working gas circuit and which has its outer wall arranged adjacent the vertical inner wall of the outer safety container there is provided a recess for a pre-stressed concrete container for receiving the reactor core.