[en] The described steam generator for nuclear power plants with light water cooled and moderated reactors increases operating safety with regard to tube corrosion, is highly variable and is easily assembled. Heat exchange tubes are inserted by one end to the inlet chamber and by the other end in the outlet chamber of the primary medium where in the space between the tubes steam is generated by extrusion or by natural circulation. The inside walls of the inlet and outlet chambers are formed by the pressure jacket of the steam generator and their outer walls by the torus jacket. In the centre of the pressure jacket of the steam generator is coaxially placed a pressure-free jacket which forms the flooding space of the natural circulation circuit. (M.D.)