Patent Number: 054385989
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, it is seen in FIG. 1 that the invention is generally indicated by the numeral 10. Combined lower end fitting and debris filter 10 is a lower end fitting 12 for a nuclear fuel assembly that is formed from a single cast piece. Lower end fitting 12 is provided with an anti-straddle bar 14 at each corner that serve to indicate whether the fuel assembly is properly installed in the reactor. Lower end fitting 12 also contains a plurality of bores 16 therethrough for guide tubes and a central bore 18 therethrough for an instrument tube. Lower end fitting 12 is a single cast piece having a plurality of interconnected ribs 20(best seen in FIG. 2) at least five-eighth inch thick and a plurality of membranes 22 between ribs 20 that have a thickness of approximately 0.080 inch. The ribs provide the necessary structural integrity during a loss of coolant accident. Coolant flow holes 24 are cast in membranes 22 during the casting of lower end fitting 12. Coolant flow holes 24 are sized to act as a filter in the coolant stream to prevent potentially damaging debris from flowing past lower end fitting 12 to the fuel rods. For ease of illustration, and because the size and arrangement of flow holes 24 will be dependent upon the fuel assembly in which lower end fitting 12 and debris filter 10 is used, only a sampling of flow holes 24 are shown in FIG. 1. It should be understood that membranes 22 and flow holes 24 are spaced across the entire surface of lower end fitting 12 and that the partial cut away view is for the purpose of illustrating the single piece nature of lower end fitting 12 and debris filter 10. As seen in the side sectional view of FIG. 2, flow holes 24 are preferably larger at their lower end and are tapered inwardly in the direction of coolant flow through flow holes 24. This reduces pressure drop of coolant flow across flow holes 24 while maintaining acceptable filtration characteristics. The cast one-piece lower end fitting and debris filter provides for a simpler and less expensive structure than the multi-piece debris filters and end fittings currently in use. Because many varying and differing embodiments may be made within the scope of the inventive concept herein taught and because many modifications may be made in the embodiment herein detailed in accordance with the descriptive requirement of the law, it is to be understood that the details herein are to be interpreted as illustrative and not in a limiting sense.