Patent Number: 
Section: claims

1. A nuclear fuel assembly comprising:a perforated plate support, which supports dual-cooled fuel rods, each of which has concentric outer and inner tubes and is coupled with upper and lower end plugs at upper and lower ends thereof, and guide thimbles, each of which is used as a passage for a control rod,wherein the perforated plate support is formed as a support plate having the shape of a flat plate, which includes internal channel holes, each of which has a diameter corresponding to an outer diameter of the inner tube, guide thimble holes, each of which has a diameter corresponding to an outer diameter of the guide thimble, and sub-channel holes around each internal channel hole,wherein the upper or lower end of the dual-cooled fuel rod is coupled to the support plate such that the outer diameter of the inner tube is matched with the diameter of the internal channel hole,and wherein the internal channel holes are arranged in such a manner that lines extending from centers of the neighboring ones of the internal channel holes form square grids, and the sub-channel holes are disposed in centers of the square grids, respectively. 2. The nuclear fuel assembly as set forth in claim 1, wherein the dual-cooled fuel rod is segmented into at least two dual-cooled fuel rods. 3. The nuclear fuel assembly as set forth in claim 2, wherein the first of the dual-cooled segmented fuel rods is located on the support plate and is coupled to the internal channel hole at a lower end thereof, and the second dual-cooled segmented fuel rod is located under the support plate and is coupled to the internal channel hole at an upper end thereof. 4. The nuclear fuel assembly as set forth in one of claims 1 through 3, wherein the upper or lower end of the dual-cooled fuel rod is coupled to the support plate. 5. The nuclear fuel assembly as set forth in claim 1, wherein each sub-channel hole has a diameter identical to the outer diameter of the outer tube. 6. The nuclear fuel assembly as set forth in claim 1, wherein the internal channel holes form a 12×12 array. 7. The nuclear fuel assembly as set forth in claim 1, wherein the support plate overlaps with another support plate so as to form two layers coupled up and down. 8. The nuclear fuel assembly as set forth in claim 1 or 7, wherein the support plate includes steps around each internal channel hole, each step having arcuate contact faces so as to correspond to the outer diameter of the outer tube. 9. The nuclear fuel assembly as set forth in claim 8, wherein the outer tube comes into contact with the steps and is welded to the steps. 10. The nuclear fuel assembly as set forth in claim 1 or 7, wherein the inner tube protrudes outwardly from the upper or lower end of the dual-cooled fuel rod, and the protruding inner tube is inserted into the internal channel hole. 11. The nuclear fuel assembly as set forth in claim 10, wherein the support plate includes steps around each internal channel hole, each step having arcuate contact faces so as to correspond to the outer diameter of the outer tube. 12. The nuclear fuel assembly as set forth in claim 11, wherein the outer tube comes into contact with the steps and is coupled to the steps. 13. The nuclear fuel assembly as set forth in claim 1, wherein the support plate is coupled with an outer plate along an outer circumference thereof which has guide taps and flow mixture vanes alternately formed. 14. The nuclear fuel assembly as set forth in claim 13, wherein the outer plate is coupled to the support plate so as to protrude from one of upper and lower surfaces of the support plate. 15. The nuclear fuel assembly as set forth in claim 14, wherein the two support plates are coupled to each other, and the surfaces of the two support plates which do not face each other are provided with the outer plates.