EASY RELEASE AND COUPLING JOINT BETWEEN GUIDE TUBE AND UPPER-END-FITTING WHICH HAS AN INNER-EXTENSION WITH LOCKING DEVICE

摘要

A top nozzle and a coupling structure of guide tube are provided to prevent separation of a guide tube and an internal insertion tube in separating a top nozzle by forming a rotation preventing unit in the internal insertion tube and a flow plate. A spacer grid of a nuclear fuel assembly is coupled in a guide tube. A top nozzle comprises a flow plate(160), an outer guide pillar(120), and an internal insertion tube. The flow plate is positioned on a top of the guide tube. A coupling through hole is formed on the flow plate. A bottom part of the outer guide pillar is coupled in the coupling through hole of the flow plate. The internal insertion tube includes a main body(130) and a top head(140). The main body is inserted in the outer guide pillar. The top head connects the internal insertion tube and the outer guide pillar. A rotation preventing surface is locally formed in an outer circumference of the main body. A fitting protrusion for preventing rotation is formed in an inner circumference of the coupling through hole contacted with the rotation preventing surface.