Patent Number: 041750039
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawing wherein like reference characters designate like or corresponding parts throughout the several views, there is shown in FIG. 1, a grid 10 for a nuclear reactor fuel assembly. The grid consists of interleaved straps 12, 14 enclosed in a peripheral frame 15 which form openings or cells 16 of egg-crate configuration. Such cells are designed to accept fuel rods 18 (only a few shown) and control rod guide tubes 20 which serve to accommodate control rods during reactor operation. As indicated above, previous grids use a combination of dimples and springs for holding fuel rods in position in a grid. The improved grid of this invention uses interleaved straps as in the old designs but the dimples have been replaced by springs so that each fuel rod accordingly is held in position in each cell by a six point spring supporting arrangement. As shown in FIG. 2, each of the springs 22, 24, 26, 28 are spaced at 90.degree. intervals and may take a generally sinuous form along the length or be of the design illustrated in U.S. Pat. No. Re. 28,079, for example. The FIG. 2 springs 22, 24 are integrally formed with and merge directly into the strap material at both the top and bottom portions 30, 32. The spring sections 34, 36 intermediate the top and bottom portions of each of springs 22, 24 project inwardly into one cell to engage two sides of a fuel rod while the spring section 38 on these two springs project outwardly into the next adjacent cell. The remaining two springs 26, 28 in the adjacent straps which form the cell, each have the middle section 40, (only one spring shown in FIG. 2) projecting into the cell to engage a fuel rod on the other two sides. The spring sections 44, 46 of springs 26, 28 each project into the next cells to help support fuel rods adapted for positioning therein. The complete grid arrangement therefore includes the sections of four springs which project into each cell for fuel rod supporting purposes. Since both sections 34, 36 of each spring 22, 24 contact the fuel rod along its length, it will be apparent the fuel rod is supported by a total of four contact points on the two springs. The other two springs 26, 28 formed in the other two straps have sections 38 which project into the same cell and these two spring sections contact the fuel rod on its other two sides but at only a total of two points of contact, because only one section of each spring is directed inwardly. It therefore is apparent the fuel rod will be supported by a total of six spring contacts on four sides. Since each cell includes the same arrangement of springs, except those cells containing control rod guide tubes, instrumentation probes, or the like, all fuel rods passing through a grid will be held in spaced relationship with other fuel rods in the grid. The above described grid design obviously eliminates the grid strap dimples of the prior art and will therefore improve the fuel rod loading capability since possible tearing or deformation of dimples will no longer occur. According to present practices, the fuel rods are pulled into each grid cell and if too much force is exerted by the fuel rod against one or both dimples in the cell as the fuel rod is actually pulled therethrough, the material of the strap material may actually tear or deform during the loading process. The tolerances are so close that if cracks appear near the dimples, or if other deformation of a dimple material of the strap takes place, it is necessary to discard the particular grid in question and this action obviously involves substantial expense to the manufacturer. The resilient nature of the springs is such that they will permit each fuel rod to assume a set position in each grid cell, thus relieving stresses throughout each fuel assembly structure while simultaneously providing uniform rod-to-rod spacing throughout the assembly. The use of springs will further permit thermal expansion and contraction in both axial and radial directions of the fuel rods, and vibration of each rod will be minimized because of the flexibility characteristics of the spring supports. It will be apparent that many modifications and variations are possible in light of the above teachings. It therefore is to be understood that within the scope of the appended claims, the invention may be practiced other than as specifically described.