Abstract: A nuclear fuel assembly skeleton having a top nozzle and a bottom nozzle (10) interconnected by guide tubes (16) designed to receive control cluster rods and each containing, at its bottom end, a tubular cartridge (20), each of said tubes being provided with a bottom plug (22) that bears against the bottom nozzle (10) and that is pierced by a hole for passing a fixing screw (26). The cartridge (20) includes a bottom plug (28) bearing against the guidetube plug (22) and in that the facing faces of the two plugs (22, 28) present axial projections that co-operate with one another to lock the two plugs against relative rotation once said screw (26) has been screwed into a tapped hole (32) in the cartridge plug (28).

Abstract: A control rod guide tube for a nuclear reactor fuel assembly consists of several mutually portions of zirconium-based alloy. They define a passage that is narrow in a bottom portion of the tube. The guide includes a top length extending over at least 70% of its total length, and a bottom length of thickness greater than that of the top length. The top of the bottom length is engaged in the top length and is welded to the top length along the terminal edge of the top length.