Patent Number: 055263887
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, it is seen in FIG. 2 that the invention is generally indicated by the numeral 10. The invention is generally comprised of a sleeve 12 sized to fit over a fuel rod in a nuclear fuel assembly. For ease of illustration, FIG. 1 illustrates only the relevant portion of a nuclear fuel assembly. Fuel rod 14 is received in one of the cells defined by lowermost spacer grid 16. Although only one spacer grid is shown, it should be understood that a plurality of spacer grids are normally spaced apart along the length of the fuel rods. Each cell of spacer grid 16 is provided with one or more hard stops 18 and one or more soft stops 20 that position fuel rod 14 in the cell for minimal contact with the spacer grid and maximum coolant flow contact across the fuel rod. As indicated by numeral 22, lower end cap 24 is welded to the lower end of fuel rod 14. Lower end cap 24 may rest upon lower end fitting 26. Sleeve 12 is shown in FIG. 1 installed on a nuclear fuel rod 14 of a nuclear fuel assembly. Sleeve 12 is provided with a plurality of openings 28 therethrough spaced around the circumference of sleeve 12 that correspond to the location of hardstops 18 in the cells in spacer grid 16. Openings 28 are sized to receive hardstops 18 such that they bear against fuel rod 14 and, in addition to retaining fuel rod 14 in position, also retain sleeve 12 in its installed position on fuel rod 14. As seen in FIG. 2, for sleeves 12 that are used in the outboard cells of spacer grid 16, a portion of the circumference of either or both ends of sleeve 12 may be tapered inwardly toward the longitudinal center of sleeve 12 as indicated by numeral 30. Only the portion of sleeve 12 that faces the outboard portion of spacer grid 16 need be provided with tapered portion 30. This serves as a lead-in feature to prevent the fuel rod 14 and sleeve 12 from hanging up during insertion of the fuel assembly into the reactor core. As illustrated in FIG. 3, sleeve 12 may be of any suitable shape such as circular, square, or octagonal. The walls of sleeve 12 may be rigid or flexible. In the preferred embodiment, sleeve 12 is sized such that its upper end extends at least to the upper surface of lowermost spacer grid 16 or higher and has a lower end which at least substantially coincides with the joint between lower end cap 24 and fuel rod 14 and may extend down to lower end fitting 26. It is important that the lower end of sleeve 12 coincide with lower end cap 24 so that any debris captured therebetween will contact lower end cap 24 and not the cladding on the fuel rod. Sleeve 12 is preferably very thin so as to have minimal effect on coolant flow and is also made from a wear resistant material suitable for the operating conditions that are encountered in a nuclear reactor. 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.