Abstract: In the casing of a steam generator there are provided a vertically extending manifold having a first chamber for admitting a heat carrier of the primary circuit and a second chamber for removing the heat carrier of the primary circuit, said chambers being isolated from one another, bundles of tubes for conveying the heat carrier of the primary circuit, said tubes defining a heat dispersing surface, a horizontally extending annular manifold for admitting feed water to the intertube space, a steam separator provided upstream the heat dispersing surface in the steam flow direction, the steam separator being secured to the casing, and a means for returning recirculation water back to the intertube space, said means being connected to the steam separator. The annular manifold extends concentrically with the vertically extending manifold and communicates with a pipe for supplying feed water.