Composite spacer with Inconel grid and Zircaloy band

摘要

An improved spacer is disclosed which contains an Inconel grid and a Zircaloy surrounding band. The Inconel grid can be fabricated from the extremely thin and highly elastic spring metal utilizing a modification of a prior art cell construction that includes paired inwardly bent vertical spring legs with cantilevered and rod encircling upper and lower arm pairs. The spring legs extend at spaced apart locations between the upper and lower arm pairs and have a medial spring rod contacting portion for biasing the rods into stops on the rod encircling arm pairs. The springs at the upper and lower ends are provided with spring dimple stops to prevent over stressing of the spring during assembly or handling of the fuel bundle into which the spacer is incorporated. The rod encircling arm pairs have an offset from center where the two arms meet at their distal ends to complete encirclement of the rods. This offset from center enables the cells to be fastened in cell pairs at their respective embracing arms. The cell pairs can in turn be manipulated as a unit to define the necessary types of spacer grids required for any particular grid construction. A preferred grid construction for a ten by ten fuel rod matrix is disclosed including a grid filling all rod lattice positions for the bottom of a fuel bundle, a grid enabling the placement of a water rod of varying diameter, and finally a grid defining missing lattice positions for overlying partial length rods and permitting upward venting of steam with minimum pressure drop. An all Zircaloy band is disclosed for surrounding containment of the Inconel grid. The band consists of two or four segments. Apertures are provided in the band at the corners, and portions of the corner Inconel cells project into these apertures, keying the Inconel grid to the Zircaloy band. The band is welded into continuous encircling relation. There results a spacer with an Inconel grid and surrounding Zircaloy band having minimum pressure drop and minimum neutron absorption useful with a high density fuel rod matrix required in modern fuel bundle design.