| 摘要 |
In a reconstitutable fuel assembly, a top nozzle attaching structure for mounting the top nozzle adapter plate in releasable locking engagement upon the guide thimble upper end portions includes several improved features. First, a locking tube is mounted within the guide thimble upper end portion for movement between an upper locking position wherein the adapter plate and guide thimble upper end portion are maintained in the locking engagement and a lower unlocking position wherein the adapter plate is releasable from the guide thimble upper end portion. Also, a plurality of protrusions are attached on the locking tube so as to extend outwardly thereof and through axial slots defined in the guide thimble upper end portion. The protrusions are yieldable for engaging and releasing from a groove in the passageway of the adapter plate. The purpose of the adapter plate passageway groove is to receive a bulge on the guide thimble upper end portion when the guide thimble is engaged with the adapter plate. When the protrusion is engaged in the groove, the locking tube will be retained at its upper locking position. On the other hand, when the protrusion is released from the groove, the locking tube can move to its lower unlocking position. Finally, an opening is defined in the guide thimble upper end portion aligned and connected with each one of the slots through which one of the protrusions extends for receiving the protrusion when the locking tube is moved to its lower unlocking position. The opening provides sufficient clearance with respect to the protrusion extending through it to permit inward elastic collapse of the guide thimble upper end portion for withdrawing the bulge from the passageway groove and thereby releasing the adapter plate from the guide thimble upper end portion. Each of protrusions is in the form of a spring attached in cantilevered fashion to the locking tube and axially extending along the tube generally parallel with one of the slots in the guide thimble upper end portion. Also, each of the springs includes an outwardly protruding portion which extends through the one slot.
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