Abstract: A grid structure is presented in which grid cells are formed by orthogonally intersecting straps prefitted in the longitudinal direction with a plurality of slitted spring frame members. Therefore, when the straps are assembled, the spring frame members are also orthogonally intersected. The spring frame members are made of Inconel and provided with welding tabs while the straps are made of zircalloy and provided with their own welding tabs. Therefore, welding can be performed to firmly join the spring frame members to each other while the straps can also be welded firmly to weld the like metals. The spring sections are thus firmly joined and attached to the straps which are firmly joined. The grid of this configuration thus provides an excellent service life without the losing The fuel rod retaining power, which would result from neutron radiation and thermal damages on holding devices made of zircalloy.

Abstract: There is disclosed a grid in a nuclear fuel assembly for supporting fuel rods and thimbles, which includes a plurality of elongated straps intersecting perpendicularly with each other to define a plurality of first grid cells for supporting the fuel rods and a plurality of second grid cells for supporting the thimbles. Each grid cell has a prescribed intervening distance defined between the opposed straps. A cylindrical sleeve is arranged on at least one of the opposite ends of the strap portions defining the second grid cell and has an inner diameter generally identical to the intervening distance. There is provided an engaging unit for securing each sleeve to the strap portions. The engaging unit includes at least one first engaging portion provided on the strap portions and at least one second engaging portion provided on the sleeve. The first and second engaging portions are held in resilient engagement with each other.