Patent Number: 055662170
Section: description

BEST MODE FOR CARRYING OUT THE INVENTION Referring now to FIG. 1, there is illustrated a nuclear fuel assembly, generally designated 10, including a plurality of fuel elements or rods 12 supported between an upper tie plate 14 and a lower tie plate 16. Fuel rods 12 pass through a plurality of fuel rod spacers 18 at vertically spaced positions along the fuel bundle. The spacers 18 provide intermediate support to retain the elongated fuel rods 12 in spaced relation relative to one another and to restrain the fuel rods from lateral vibration. With reference to FIGS. 1 and 2, a 10.times.10 array of fuel rods is disclosed. It will be appreciated, however, that the invention hereof is applicable to arrays of fuel rods of different numbers, for example, 8.times.8 arrays. Each fuel rod 18 is formed of an elongated tubular cladding material, with the nuclear fuel and other materials sealed in the tube by end plugs. The lower end plugs register in bores formed in the lower tie plate 16, while the upper end plugs are disposed in cavities in the upper tie plate 14. Additionally, the fuel rod assembly includes a channel 20 of substantially square cross-section sized to form a sliding fit over the upper and lower tie plates and the spacers so that the nuclear fuel bundle, including the channel, tie plates, rods and spacers can be removed. Turning now to FIG. 2, there is illustrated a spacer 18 constructed in accordance with the present invention and having a plurality of individual ferrules 22 and springs 24, each ferrule having an associated spring. The ferrules 22 are arranged in a square matrix in which each ferrule receives a fuel rod and maintains the fuel rod spaced and restrained relative to adjoining fuel rods. The spring assembly 24 is provided each ferrule for purposes of biasing the fuel rod in a lateral direction against stops 26 opposite the springs whereby the fuel rods are maintained in a predetermined position relative to one another and in the spacer 18. Each spacer 18 also includes a marginal band 28 with inwardly directed upper flow tabs 30. Referring now to FIGS. 4 and 5, each spacer ferrule 22 has a generally cylindrical configuration. The wall of each cylindrical ferrule is indented at circumferentially spaced locations along one side of the ferrule to form the inwardly directed stops 26. It will be appreciated that the stops 26 extend the full height of the ferrule, although the stops could be provided at axially spaced locations along the height of the ferrule. As best illustrated in FIGS. 10-12, each ferrule 22 includes a central opening 30 opposite the stops 26. Opening 30 is straddled by band portions 32 above and below the opening. As indicated previously, the ferrules are symmetrically disposed within the spacer 18 with the side portion 34 of each spacer engaging the band portions 32 of the next-adjacent spacer. Also, the opposite sides of the ferrules (the sides of the ferrule 90.degree. from side portion 34 and band portions 32) engage one another. Preferably, the ferrules are welded one to the other in the spacer 18 at their areas of engagement. Referring now to FIGS. 6-9, there is illustrated a spring 40 for use with each of the ferrules 22. Spring 40 includes a flat leaf spring body 41 having sides 42 defining and lying in a plane. Opposite spring end portions 44 extend across the spring coupling between the opposite sides 42 and projecting to one side of the plane at opposite ends of the spring 40. An outwardly projecting convex dimple 46 is provided in each of the end portions 44 for engagement with the fuel rod in the associated ferrule 22. Substantially medially of the length of the spring 40, there is provided an intermediate cross-piece or central portion 48 which projects to the opposite side of the plane containing the spring 40. The cross-piece 48 has a convexly-shaped dimple 50 projecting toward the plane. Adjacent opposite sides of the cross-piece 48, there is provided a pair of projections or protuberances 52 which project from the plane on the same side thereof as the end pieces 44. From a review of FIG. 8, it will be appreciated that the cross-piece 48 and the end pieces 44 are spaced from one another to define a pair of openings 54 on opposite sides of the cross-piece 48 and bounded by the cross-piece 48, end pieces 44 and sides 42. The cross-piece 48 has a height dimension enabling it to be received within the opening 30 of the ferrule. Additionally, the protuberances 52 lie along opposite sides of the spring a distance from one another such that they engage the outer surface of the ferrule 22 adjacent opposite side edges of opening 30, as illustrated in FIG. 4. It will also be appreciated that the openings 54 in the spring 40 are sized to receive the ferrule band portions 32 above and below the ferrule opening 30. In the spacer and as indicated previously, the ferrules 22 are welded one to the other to afford structural integrity within the spacer. The adjacent ferrules are secured one to the other with the springs in place. That is, the springs are located prior to assembly with the sides 42 straddling the opening 30 and the cross-piece 48 disposed within the opening 30. The sides 42 lie external to both ferrules, with the projections 52 engaging the outer surface of one ferrule adjacent opposite sides of opening 30. It will be appreciated that in this configuration, and as illustrated in FIG. 5, the end portions 44 lie above and below the upper and lower edges of the ferrules 22, respectively. Thus, the protuberances 46 engage the fuel rods above and below the ferrule and bias the fuel rods against the opposing stops 26. The cross-piece 48 of the spring bears against the portion 34 of the adjacent ferrule 22 between its stops 26 and thus provides a reaction force for the spring 40 bearing against the fuel rod of the one ferrule 22. Consequently, it will be seen that the individual ferrules are reduced in height minimizing the magnitude of the ferrule material, yet maintain their structural integrity surrounding and positioning the fuel rods. In a typical spacer, the ferrules have a height-to-diameter ratio within a range of 0.8 to 0.4 and preferably the height-to-diameter ratio is about 0.6. The height H and diameter D dimensions are illustrated in FIG. 11. While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.