Patent Number: 047388196
Section: abstract

A BWR fuel assembly having an array of spaced fuel rods, an outer tubular flow channel surrounding the fuel rods so as to direct flow of coolant/moderator fluid along the fuel rods, and a hollow central water cross extending through the channel and composed of radially extending members dividing the fuel rods into separate fuel rod mini-bundle subassemblies, includes features which eliminate or at least minimize degradation of CHF performance and the penalties and uncertainties associated therewith. Each subassembly has spacers which surround its fuel rods and maintain them in side-by-side spaced relationship. The spacers are axially displaced apart between the bottom and top of the subassembly. Each radial member of the water cross is connected at multiple segments along its outer longitudinal edge to the channel so as to define a series of spaced apart openings between the members and channel which allow cross-flow communication of coolant/moderator fluid between the adjacent ones of the mini-bundle subassemblies for pressure equalization therebetween. The features of the present invention incorporated in the BWR fuel assembly, which eliminate or at least minimize degradation of CHF performance, are solid continuous ribs, welds or bars extending between and interconnecting the channel and water cross radial members at the locations of the upper ones of the spacers for blocking portions of the coolant/moderator fluid cross-flow between the separated mini-bundles at such locations.