The invention relates to the electric power industry, and more particularly to horizontal steam generators for nuclear power stations and to a reactor plant with a water-cooled, water-moderated reactor and a horizontal steam generator. The present reactor plant comprises: a nuclear reactor with four circulation loops, each of which comprises a steam generator with a horizontal bundle of heat exchange tubes, said tubes being divided into banks by intertube passages and being connected to primary coolant collectors inside a cylindrical housing with ellipsoidal ends; a main circulation pump; and also a main primary coolant circulation pipe. The inside diameter of the housing, the transverse distance between the axes of the primary coolant collectors, and the length of the steam generator along the inside surfaces of the ellipsoidal ends are selected from defined relationships. The invention improves the heat transfer performance as well as the reliability and lifespan of the steam generator.