Lateral support for nuclear fuel assemblies

Nuclear fuel assemblies are described which have square cross-sections mount tubes at each corner, the tubes containing springs which are extended through apertures in the tube walls when actuated by solid rods extended down into the tubes by the weight of the upper guide structure of the nuclear vessel in which the fuel assemblies are mounted. The springs, extended from strategically located positions along the length of the tubes, engage the surface of adjacent fuel assemblies to dimensionally stabilize the fuel assemblies relative to each other and the vessel in which they are mounted