Steam-water separating system for boiling water nuclear reactors

A boiling water nuclear fission reactor having an improved steam-water separating system, comprising the combination of a cylindrical reactor pressure vessel having an inlet for supplying feedwater and a steam outlet and containing a core of fissionable fuel for producing heat to generate steam, said fuel core being mounted between a discontinuous core support plate and a top spacing grid plate and surrounded by a shroud which is spaced inward among from the wall of the pressure vessel to provide an annular flow path outside the fuel core whereby supplied feedwater together with recirculated liquid coolant can flow downward around the exterior of the fuel core and then back upward through the fuel core for the transfer of thermal energy from the fuel of the core to the water and generation of steam, a core upper plenum superimposed above the fuel core defined by a peripheral shroud covered with a top plate for receiving hot water and steam produced from recirculated liquid coolant passing up through the heat producing fuel core, a wet steam plenum defined by a peripheral shroud covered with a top plate positioned an extended distance above the core upper plenum, a multiplicity of mechanical steam separators each comprising a standpipe with an end in fluid contact with the core upper plenum and extending up from said core upper plenum top plate to the wet steam plenum and having a steam separating assembly mounted on its upper end within the wet steam plenum, and a plurality of steam collecting an transferring units positioned within the core upper plenum comprising an open bottom steam collecting chamber having a side wall with a domed top and a vent pipe extending up from the top of said chamber and passing through the core upper plenum top plate to the wet steam plenum for collecting steam from the core upper plenum in the chamber and venting the steam into the wet steam plenum among the mechanical steam separators.