Universal fuel assembly construction for a nuclear reactor

摘要

The universal fuel assembly has a plurality of elongated corner posts extending longitudinally between and releasably and rigidly interconnecting top and bottom nozzles so as to form a rigid structural skeleton of the fuel assembly. Additionally, a plurality of transverse grids are supported at axially spaced locations along the corner posts and a plurality of fuel rods are supported by the grids. Certain groups of the fuel rods are spaced apart laterally from one another by a greater distance than the rest of the fuel rods so as to define a number of elongated channels extending between the top and bottom nozzles. A cluster assembly having a cluster plate with a plurality of elongated rods is adapted to be removably supported on the top nozzle with its rods extending through the channels. The rods can be a plurality of guide thimbles in the case of one cluster assembly, or a plurality of oversized fuel rods in the case of another cluster assembly. The provision of cluster assemblies allows a unique scheme for loading fuel in the reactor core. Cluster assemblies containing burnt fuel can be loaded into fuel assemblies containing fresh fuel and vice versa. Also, a guide fixture mounting guide rods and a pair of comb devices mounting locking bars are utilized to depress springs within the cells of the grids in order to load fuel rods into the grid cells without scratching their exterior surfaces.