Nuclear fuel assemblies

A nuclear fuel assembly for a nuclear reactor comprises a plurality of vertically extending fuel elements and control rod guide tubes and a plurality of spacer assemblies, each comprising a plurality of rectangular slotted grid plates intersecting and interlocking in egg-crate fashion, which laterally maintain the fuel elements and guide tubes in a spaced array. Spacer assembly movement is restrained, to maintain structural integrity of the nuclear fuel assembly during all phases of reactor operation, by collars welded to guide tubes and mechanically fixed to guide tube sleeves circumscribing the guide tubes at each spacer assembly location by virtue of each collar being crimped to extend into an aperture in a sleeve. Each collar is interlocked to a spacer assembly by a said grid plate thereof passing through a slot in the collar so that the collar is interlocked with the grid plate. (UK)