Patent Number: 
Section: claims

1. A system for separating and coupling a nuclear fuel assembly having guide thimbles from/to a top nozzle including a flow channel plate for flow of coolant having guide holes, the system comprises:a lock insert comprising a body in a hollow shape coupled with the guide thimble; and an insertion part provided on a top portion of the body and configured to be inserted into the guide hole, the circumference of the insertion part being variable in size, thereby being capable of being inserted into the guide hole, to support the nuclear fuel assembly to the top nozzle by being coupled to the guide hole provided in a flow channel plate of the top nozzle; anda separation member configured to separate the lock insert from the guide hole,wherein,the insertion part comprises:a first latching member having a step with which a top surface of the flow channel plate is brought into contact; anda second latching member having a step with which a bottom surface of the flow channel plate is brought into contact,wherein the first latching member comprises a latching groove, and the top surface of the flow channel plate is provided a protruding member protruded from the top surface, the protruding member being of the same shape as the latching groove to be inserted into the latching groove, andthe separation part is configured to provide a space accommodating an outer circumferential surface of the first latching member protrudingly provided on the top surface of the flow channel plate, to apply external force to the outer circumferential surface of the first latching member while accommodating the outer circumferential surface of the first latching member, thereby the size of the circumference of the insertion part being varied to release the coupling between the lock insert and the flow channel plate. 2. The system of claim 1, wherein the insertion part is provided with at least one predetermined slot along a longitudinal direction of the insertion part, thereby the circumference of the insertion part is variable in size.