Patent Number: 046997598
Section: abstract

A double lock joint structure is used in a reconstitutable fuel assembly for attaching the adapter plate of the assembly top nozzle in releasable locking engagement upon the upper end portions of the assembly guide thimbles. The joint structure includes axially extending slots defined in each guide thimble upper end portion permitting inward elastic collapse thereof to a compressed position and outward elastic return thereof to an expanded position. The joint structure also includes axially spaced upper and lower annular bulges formed in the upper end portion. The upper annular bulge has an outside diametric size greater than the inside diametric size of the adapter plate passageway when the guide thimble upper end portion is at its expanded position and less than the inside diametric size of the adapter plate passageway when the upper end portion is collapsed to its compressed position allowing insertion and withdrawal of the upper end portion into and from the adapter plate passageway. The lower annular bulge has an outside diametric size greater than the inside diametric size of the adapter plate passageway when the guide thimble upper end portion is at either one of its expanded and collapsed positions. The upper annular bulge is axially displaced from the lower annular bulge through a distance approximately equal to that between the top and bottom surfaces of the adapter plate such that after insertion of the upper end portion of the guide thimble through the adapter plate passageway the adapter plate is placed in a captured position between the upper and lower annular bulges. Furthermore, the joint structure includes a locking tube insertable into and removable from each guide thimble upper end portion between a locking position which maintains the upper end portion in the expanded position and the adapter plate in the captured position between the upper and lower annular bulges and an unlocking position which permits the upper end portion to inwardly collapse to the compressed position upon insertion and removal of the adapter plate onto and from the upper end portion of the guide thimble. The locking tube includes upper and lower axially displaced protuberances adapted to mate with the upper and lower bulges of the guide thimble upper end portion when the locking tube is inserted at its locking position therein, and a top annular flange located above the upper protuberance for facilitating insertion and removal of the tube into and from the guide thimble upper end portion.