Structure of top nozzle for nuclear fuel assembly

A joining structure for joining a top nozzle and a guide thimble, the joining structure comprising:

• an outer guide post having a hollow cylindrical shape and an external thread formed on an outer circumferential surface of a lower end portion of the outer guide post;
• an inner-extension tube head comprising
• an annular retaining part formed on an upper end portion of the inner-extension tube head and having an outer diameter greater than that of other portion of the inner extension tube head, and
• an internal thread formed on an inner circumferential surface of a medial portion of the inner-extension tube head;
• an inner-extension tube body having a hollow cylindrical shape and including
• a first external thread formed on an outer circumferential surface of an upper portion of the inner-extension tube body, and
• a second external thread formed on the outer circumferential surface of a lower end portion of the inner-extension tube body;
• and
• a wedge having a hollow cylindrical shape and including at least one stop protrusion formed on a bottom surface of the wedge, the stop protrusion extending a predetermined length in an axial direction of the wedge, the wedge being separated from the inner-extension tube body and the outer guide post,
• wherein the inner-extension tube body is coaxially inserted into the outer guide post,
• the inner-extension tube head is mounted on a top of the outer guide post, the first external thread of the inner-extension tube body is engaged with the internal thread of the inner-extension tube head,
• the second external thread of the inner-extension tube body is engaged with an internal thread of the guide thimble, and
• the wedge is mounted on the outer circumferential surface of the inner-extension tube body and disposed between a bottom end of the outer guide post and the guide thimble.