APPARATUS AND METHOD FOR PREASSEMBLING A TOP NOZZLE SUBASSEMBLY FOR A NUCLEAR FUEL ASSEMBLY

The invention relates to an apparatus for preassembling components of a top nozzle as a subassembly for subsequent mounting thereof on the skeleton of a nuclear fuel assembly, the components comprising a lower adapter plate (30), guide-thimble extensions (26) extending through holes in the adapter plate, an upper bearing plate (34) with passageways (38) for receiving upper end portions of the extensions (26), hold-down springs (46) between the adaptor and bearing plates, and lower and upper retainers (48, 50) cooperable in the finished sub-assembly with the adaptor and bearing plates for maintaining the hold-down springs partially compressed therebetween. The preassembling apparatus comprises a base (70) with compliant means (74, 76) for yieldingly supporting the lower ends of the guide-thimble extensions and biasing the lower retainers (48) thereon against the adaptor plate; locating pins (78) insertable through the passageways of the bearing plate and into the upper end portions of the extensions to provide axial alignment and guidance for the latter with respect to the passageways; and loading means (80, 86) operable to move the bearing plate toward adapter plate, thereby to compress the hold-down springs between the plates and, at the same time, guidedly insert the upper end portions of the extensions into said passageways for connection of said end portions to the upper retainers (50). An orientation plate (88) has alignment pins (90) which cooperate with scallops (56) in the lower retainers (48) to assure proper alignment of the scallops with fuel rods upon mounting of the subassembly on the fuel assembly skeleton.