Abstract: The apparatus is intended for rebuilding an assembly comprising a skeleton formed by two end members connected by tie rods attached to the end members and grids distributed between the end members along the tie rods and adapted to retain a cluster of fuel rods trapped between the end members. The apparatus comprises a first chamber (AI) for receiving a fuel assembly, a second chamber (AS) for receiving a new skeleton, a repair station comprising a lift adapted to receive the two vertically disposed aligned chambers and to bring the chambers to a level such that there subsists a layer of protective water above the rods, a transfer tool (106) to draw one fuel rod at a time into the skeleton from the assembly contained in the first chamber, and means for mounting the end members on the skeleton.