Integral reusable locking arrangement for a removable top nozzle subassembly of a reconstitutable nuclear fuel assembly

In a reconstitutable fuel assembly having at least one control rod guide thimble and a top nozzle, the guide thimble is described including an upper end portion having an annular externally threaded section. The top nozzle includes at least one tubular alignment sleeve having a lower annular internally threaded section and being rotatably movable relative to the guide thimble upper end portion between lowered and raised positions for threading and unthreading its internally threaded section comprising: (a) inner means mounted on the guide thimble upper end portion above the externally threaded section thereon; and (b) outer means mounted on the alignment sleeve above the internally threaded section thereon; (c) the inner and outer means being configured to coact with one another as the internally threaded section of the alignment sleeve is threaded on the externally threaded section of the guide thimble upper end portion