Abstract: A steam-generator, particularly to be used in nuclear power stations, with easily detachable parts, especially for the substitution of the tube bundle or a part thereof, comprises five separate portions fastened one to another by means of connections or merely abutting with intermediate sealings. In a substantially cylindrical vessel or housing, defined at the lower end by a distributor chest and at the upper end by a top cover, there are disposed, respectively from the bottom upwards: a heat-exchanger with a bundle of tubes on a common tubeplate, a steam-separator, and a drier unit, which are so supported within the vessel to be readily separable from one another and the vessel by relative vertical displacement therebetween with no interference with the inner wall of the vessel itself. In two alternative embodiments, the distributor chest, i.e. the manifold of the heat-carrier primary medium, is integral either to the heat-exchanger or to the housing.