Patent Number: 052895157
Section: claims

1. In a combination of a grid for a nuclear fuel assembly and a plurality of elongated key members, said grid comprising a plurality of elongated straps intersected with each other to define a plurality of grid cells therein, a plurality of pairs of dimples and springs formed on said straps for supporting a plurality of fuel rods, and a plurality of openings which are defined at intersections among said straps, each pair of dimples and springs being disposed in facing relation to each other, on wall sections of said straps, which cooperate with each other to define one of said grid cells, the pair of dimples and springs projecting into the grid cell, and  each of said elongated key members being provided for maintaining the springs deflected respectively away from the dimples, the key member being capable of being inserted into said grid cells through said openings along a longitudinal direction of a corresponding one of said straps;  the combination further comprising:  a deflecting jig capable of being inserted into one of said grid cells, said deflecting jig being in the form of a rod having a diameter capable of being enlarged to urge the spring associated therewith against resilient force of the spring to deflect the spring away from the dimple associated therewith;  each of said elongated key members being formed with a plurality of hooks which are spaced a predetermined spacing from each other along a longitudinal direction of the key member, and being rotatable about its axis to cause the hooks of the key member to project from a wall surface of the strap associated with the key member, through the openings, in a direction opposite to the projecting direction of the spring formed on the strap, said key member being movable forwardly in a longitudinal direction of the strap to engage the hooks of the key member with the wall surface of the strap, thereby fixedly mounting the key member to the strap to maintain the spring deflected, and being formed such that when the urging of the spring due to said deflecting jig is released to allow the same to be withdrawn from the grid cell and, subsequently, said fuel rods are inserted respectively into said grid cells, said key member is movable rearwardly to release retention of the springs due to the hooks of the key member thereby bringing the springs into pressure contact with the fuel rods, respectively, and allow said key members to be withdrawn from said grid cells. 2. A combination according to claim 1, wherein the pair of dimples and springs are disposed so as to have a distance therebetween which is larger than a diameter of the fuel rod when the respective springs are maintained deflected by the hooks of the key member. 3. A combination according to claim 1, wherein each of said straps includes a plurality of ribs associated respectively with the springs formed on the strap, each of the hooks on the key member being able to be engaged with a corresponding one of the ribs. 4. A combination according to claim 3, wherein each of the ribs is spaced from a corresponding one of the springs in a direction away from the grid cell associated with the spring. 5. A combination according to claim 4, wherein each of the straps includes a plurality of pairs of ribs, and wherein each spring is located between a corresponding pair of ribs. 6. A combination according to claim 1, wherein said deflecting jig comprises a sleeve divided into a plurality of sleeve pieces and a tapered pin inserted into said sleeve for axial sliding movement along the same.