Nuclear fuel assembly debris resistant bottom nozzle

Abstract

A debris resistant bottom nozzle in a fuel assembly has a support structure in the form of four legs adapted to rest on a lower core plate of a nuclear reactor and a top flat plate fixed on one side of the four legs facing upwardly toward a lowermost grid of the fuel assembly. The flat plate is of a substantially solid configuration with a plurality of spaced cut-out regions defined therethrough in alignment with and directly above a plurality of inlet liquid coolant flow holes in the lower core plate. A plurality of open separate criss-cross structures are provided, each being fixed to the plate and extending across one of the cut-out regions therein within the plane of the plate. The criss-cross structures define individual openings small enough in cross-sectional size to filter debris of damage-inducing size which otherwise collects in unoccupied spaces of the lowermost grid of the fuel assembly, but large enough in size to let pass debris of nondamage-inducing size which otherwise passes through the unoccupied spaces of the lowermost grid. The criss-cross structure in one embodiment is in the form of a plurality of interleaved straps forming an open grid structure, and in another embodiment is in the form of a plurality of interconnected crossed wires forming an open mesh structure. Also, at least one pressure drop reducing flow hole is defined in the plate at a location spaced from the cut-out regions.