Patent Number: 053848136
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1-5 show a storage rack 10 of the invention, which forms a close packed array 10, 3 rows by 5 columns of elongated cells C1-C15 in this embodiment, the odd numbered or primary cells C1, C3, C5, C7, C9, C11, C13, C15 are formed from rectangular cell housings 3 which extend along housing axes 3'. The even numbered or secondary cells C2, C4, C6, C8, C10, C12, C14 are formed by the walls of the surrounding cells. It is noted that the secondary cells along the perimeter of the array C2, C4, C6, C10, C12, C14 are not completely surrounded by primary cells. If it is necessary that one of these secondary cells is to be utilized, a stiffener wall 3A is inserted substantially flush with exterior walls of the adjacent primary cell housings to completely enclose the secondary cell as shown in FIG. 3. The individual cell housings 3 and the stiffener walls 3A are held in parallel alignment by upper and lower support bars 1, 7, and 8 which extend transverse to the longitudinal axis of the cell housings 3. The support bars 1, 7 and 8 are located between each of the rows of cells and along the perimeter of the array as shown in FIG. 5. Support bars 1, 7 and 8 are provided at both the top and bottom end portions of the rack. The cell housings are held in parallel alignment by welding the individual cell housings 3 to the upper and lower support bars 1, 7 and 8. The support bars also add strength to the upper and lower ends of the cell housings to resist damage during inserting and removal of the nuclear fuel rod assemblies. As shown in FIG. 2, a base plate 2 is welded to the bottom of the rack to close the bottom of the cells and support the nuclear fuel assemblies. The base plate 2 may also be provided with holes 12 at locations within each cell and pedestal feet 9 to facilitate the flow of water for enhanced cooling. Each cell housing 3 is an elongated tube having a rectangular cross section. The housing is constructed from suitable material, for example, .050 inch thick stainless steel tubing. Typically the tubes are square, approximately 81/2 inches along each side and 14 feet long. Each outer surface of the housing is planar, to which is applied, with a preload force, an elongated slab 4 constructed of a damping material. The damping material may also be a neutron absorbing material, such as borated stainless steel, borated aluminum, boral (such as manufactured by Brooks & Perkins, Minneapolis, Minnesota), or other neutron absorbing materials may be used. The damping material is preloaded against the outer surface by retainer clips 5, 5A, 5B which are welded to the outside of the housings along the perimeter of each surface. The retainer clips 5, 5A, 5B are composed from a flat plate of steel by forming an S-shaped bend which causes the plane of the raised edge portion 5C to be offset relative to the fixed edge portion 5D of the same surface. Preferably, the offset is the same size as the thickness of the slab 4. When retainer clips 5, 5A, 5B are plug or spot welded the housing 3, the weld shrinks and the clips are pulled tight against the housing thus preloading the elongated slab against the housing. The fixed edge portion 5D may be provided with holes to facilitate plug welding. Alternatively, the offset 5E may be less than the thickness of the damping material and therefore, when the fixed edge portion 5D is fixed to the housing 3, the raised edge portion 5C forces the damping material 4 against the outer surface of the housing. In this embodiment, the retainer clips may be fixed by welding as well as by rivets or threaded fasteners. As shown in FIG. 2, there are upper and lower horizontal retainer clips 5B attached at the upper and lower ends of each lateral surface of the cell housings. Also shown are vertical retainer clips 5 which are attached to the housings 3 along the vertical edges of the outer surfaces. As shown in FIG. 4, the vertical retainer clip 5 has a right angle bend 5' along its center and raised edge portions 5C on each side of the bend. This permits the vertical retainer clip 5 to preload the damping material on two adjacent surfaces of the housings 3. As shown in FIG. 4, the slabs 4 may be provided with recesses 4A along each edge. The depth of the recess 4A is preferably equal to the thickness of the retainer clip 5. The recess 4A permits the retainer clips 5 to be flush with the outer surface of the slab 4. This avoids damaging the retainer clips 5 during insertion and removal of the fuel assemblies. As shown in FIGS. 3 and 4, a stiffener wall 3A may be utilized to enclose the secondary cells (e.g., cell C4) along the perimeter of the array 10. The stiffener wall 3A is a U-shaped channel of the same material, length and thickness as the cell housing. It is of sufficient width to fill the space between two primary cells (e.g., cells C3 and C5). The outer surface of the stiffener wall 3A may have a damping slab 4 preloaded against it made of a material of a similar size and type of material preloaded against the walls of the cell housings 3. The slab 4 of damping material is preferably preloaded against the outer surface of the stiffener wall by horizontal retainer clips 5A along the upper and lower ends of the stiffener wall 3A and by vertical retainer clips 5B along the longitudinal edges of the stiffener wall 3A. In an alternate embodiment as shown in FIGS. 6 and 7, the retaining device is a cover plate 15 which extends over the entire housing surface. The cover plate 15 has a flange extending from each edge which is fixed to the housing 4. Each flange has a S-shaped bend which includes a sloped portion 15A and fixed portion 15B. After the fixed portion 15B is welded to the housing, the resulting weld shrinkage causes the sloped portion 15A to pull the cover plate 15 against the housing thus preloading the poison slab 4 against the outer surface. As shown in FIGS. 8-11, the invention may be embodied utilizing cells having different geometric cross-sections. By utilizing different cell geometries, the packing or spacing of nuclear fuel assemblies can be controlled to accommodate different system requirements. FIG. 8 shows an embodiment of the present invention utilizing cells of pentagonal cross-section. While the cells are shown in a circular array configuration, the cells may be arranged in other geometric or non-geometric configurations. FIGS. 9-11 show exemplary close packed arrays. FIG. 9 shows an embodiment of the present invention utilizing cells of triangular cross-section. In this embodiment, stiffener walls to enclose the outer cells 3A may also be provided. FIG. 10 shows an embodiment of the present invention utilizing cells of hexagonal cross-section. This configuration provides increased packing of the nuclear fuel assemblies and increased cell strength over rectangular configurations. FIG. 11 shows a modification of the embodiment of FIG. 10 wherein central cells A are formed by the walls of the adjacent surrounding cells B. The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of the equivalency of the claims are therefore intended to be embraced therein.