Patent Number: 050842374
Section: description

DETAILED DESCRIPTION Referring to FIG. 1, the assembly includes a bottom tie plate 2 and fuel rods 4. As will be understood, fuel rods actually occupy the entire area of the tie plate; for convenience, only a few are shown. Our spacer includes a lower comb 6 and an upper comb 8. The two combs are essentially identical so the description will be made in connection with the lower comb. The comb includes a single end strip 10 which corresponds in length to the width of the assembly. This in turn is determined by the width of the tie plate 2. Extending at right angles to the end strip 10 are a plurality of grid strips 12. In the particular embodiment shown, these grid strips are made double and of spring material. They are also provided with inclined channels 14 for directing streams of cooling water in such a manner as to produce swirling about the fuel rods. These inclined channels engage the fuel rods and when they do so, the spring strips are pressed together thereby exerting a spring action on the fuel rods. The condition of the strips in the unloaded and loaded positions are indicated by the respective legends. The ends of strips 12 remote from strip 10 are free. As is well known, fuel assemblies for boiling water reactors are enclosed by a flow channel. We provide a bracket 16 having a protrusion 18 which engages this flow channel and holds the combs firmly within the assembly. Optionally, the bracket 18 may include a hook (not shown) extending under the tie plate 2 and holding the comb against vertical movement along the fuel rods due to water pressure. Since the strips 12 engage the fuel rods with a spring action, this feature is not essential. As is apparent from FIG. 1, the grid strips of the combs 6 and 8 extend at right angles to each other in this embodiment. Sometimes fuel assemblies are made hexagonal, in which case they would be at an angle of 60.degree. to each other. Other angles would be possible, but are not ordinarily utilized. In FIG. 2, we show a partial plan view of a comb adapted for use in a pressurized water reactor. The structure is essentially the same as that shown in FIG. 1 with only such differences as are necessitated by the difference in structure of assemblies for pressurized water reactors as compared to those for reactors of the boiling water type. It includes an end strip 30 and grid strips 32, the latter being shown in their unloaded condition in FIG. 2. Since pressurized water reactor assemblies do not usually include the flow channel characteristic of boiling water reactors, it is necessary to provide different means to hold the combs firmly within the assembly. To this end, we provide spring clips 34, 34' which extend around the terminal fuel rods of the row, and so hold the comb against outward movement. FIG. 3 shows an end view of this comb. While we have described two embodiments of our invention, it will be understood that various changes are possible. For example, the water channels 14 may be made vertical instead of inclined if the swirling of the water is not necessary. Furthermore, other spring arrangements may be substituted. The essential features are that the grid strips are fastened at one end only to an end strip so as to form combs which can be inserted into the fuel rod without disassembly and that the grid strips extending in different directions are on different combs which are superposed on one another.