Reusable locking tube in a reconstitutable fuel assembly

Abstract

In a reconstitutable fuel assembly, a top nozzle attaching structure, which has an outer socket formed by a circumferential groove defined in the top nozzle adapter plate passageway wall and an inner socket formed by a circumferential bulge defined in the guide thimble upper end portion being capable of seating within the circumferential groove, incorporates an improved reusable tube disposable at a locking position for releasably locking the inner socket in locking engagement within the outer socket when the circumferential bulge is seated within the circumferential groove. The reusable locking tube includes an elongated hollow metal tubular body and at least a pair of small dimples preformed on the tubular body exterior prior to initial insertion of the locking tube to its locking position. The dimples are so preformed and configured to have a generally pyramidal shape such that the metal forming the dimples substantially resists yielding and dimensional change regardless of the number of insertions and withdrawals of the tubular body into and from the locking position. Also, the dimples are located along the exterior of the tubular body and have outer tips diametrically displaced from one another across the tubular body such that when the body is inserted to the locking position, the dimples extend into the circumferential bulge defined in the guide thimble upper end portion and provide a positive interference fit with the guide thimble upper end portion above the circumferential bulge therein and with the upper portion of the adapter plate passageway wall which prevents inadvertent withdrawal of the tubular body from the locking position.