Patent Number: 048030449
Section: abstract

A fuel assembly for boiling water reactors includes, in addition to the usual outer flow channel which surrounds the fuel rods, an inner flow channel having rectilinear sides disposed within the fuel assembly, extending vertically therethrough, and arranged to receive cooling water at or below the bottom of the assembly. The channel is of such size as to span several cooling rods in each direction. A closure is provided in the channel within the critical heat flux zone of the assembly. At least one inner tube extends through the closure. The channel is closed at its upper end, and the inner tube is open at its upper end, which is located near the upper end of the channel. Egress openings are provided in the walls of the channel just above the closure. These openings are so positioned relative to the fuel tubes that jets of water emitted from them do not impinge directly on the fuel tubes, but rather enter the flow spaces between them. Other egress openings are provided in the walls of the channel below the closure.