| 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, each 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 locking engagement and a lower unlocking position wherein the adapter plate is releasable from the guide thimble upper end portion. Also, cooperating means are defined on the locking tube and the guide thimble for retaining the locking tube at either of its upper or lower positions. The guide thimble cooperating means includes a pair of upper and lower circumferential bulges defined on the guide thimble upper end portion below the adapter plate. The bulges are axially spaced from one another such that the upper bulge is located to retain the locking tube at its upper locking position and the lower bulge is located to retain the locking tube at its lower unlocking position. The locking tube cooperating means includes a circumferential bulge defined on a lower portion of the locking tube which is seatable in either of the bulges of the guide thimble and several slots defined in the locking tube which extend upward along its lower portion from a lower edge thereof. The slots allow radial compression and expansion of the lower portion of the locking tube for facilitating its movement between and positioning at its upper and lower positions.
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