Importance

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Abstract

A BWR fuel assembly has a bundle 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 with a lower flow inlet end, an opposite upper flow outlet end and an open inner cruciform flow channel for subcooled moderator fluid flow through the fuel assembly. The water cross extends through the outer flow channel and is interconnected with the outer channel so as to divide it into separate compartments and the bundle of fuel rods into a plurality of mini-bundles thereof. Also, a pair of upper and lower tie plates are connected to the opposite ends of the fuel rods in each mini-bundle thereof so as to provide a separate fuel rod subassembly in each of the compartments. The tie plates have flow openings defined therethrough for allowing the flow of the coolant/moderator fluid into and from the separate fuel rod subassembly. The BWR includes an improvement which allows free cross flow of fluid between the lower ends of the respective fuel rod mini-bundles of the separate fuel rod subassemblies and in such manner minimizes maldistribution of flow between the mini-bundles. The improvement takes the form of a lower cross-shaped flow mixing chamber located between and extending upwardly from the lower tie plates of the mini-bundles and extending downwardly from the lower end of the water cross. Also, a plurality of axially spaced grids in each fuel rod subassembly maintain the fuel rods of its mini-bundle thereof in side-by-side spaced relationship, and the lower flow mixing chamber has an axial height less than the axial distance from the lower tie plate to the lowermost one of the axially spaced grids of each fuel rod subassembly.

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First Claim