A steam generator for a PWR comprise a pressure vessel having an upper portion forming a steam chamber and a bundle of U-shaped exchange tubes within the vessel. A feed-water ring header is located within the pressure vessel above the bundle, extends horizontally and is connected to a feed water inlet nozzle passing through the wall of the pressure vessel, said header having an approximately toridal shape. Feed water is discharged into the pressure vessel above the bundle by crook-shaped tubes each having an end opening into the upper portion of the header of and projecting upwardly from the header. The crook-shaped tubes are spaced apart at substantially equal angular intervals and have respective controlling cross-sectionam flow areas which differ depending on the angular position of the discharge tube on the header.