Patent Number: 041475917
Section: claims

1. A nuclear reactor fuel assembly comprising, a wrapper tube for flowing coolant therethrough,  a plurality of cladding tubes filled with fuel material, said cladding tubes being provided with wound wire spacers and arranged within said wrapper tube,  spacing means mounted at upper end portions of said cladding tubes which are adjacent to said wrapper tube for keeping said cladding tubes from contact with said wrapper tube during the reactor operation. 2. A nuclear reactor fuel assembly as claimed in claim 1, wherein said spacing means are formed by thickening said cladding tubes at said upper end portions to a thickness which exceeds the thickness of remaining portions of said cladding tubes. 3. A nuclear reactor fuel assembly as claimed in claim 1, wherein said spacing means comprise ring-shaped spacers. 4. A nuclear reactor fuel assembly as claimed in claim 1, wherein said spacing means are formed by projections at said upper end portions of said cladding tubes adjacent to said wrapper tube, said projections extending outward beyond remaining portions of said cladding tubes. 5. A nuclear reactor fuel assembly as claimed in claim 1, wherein the nuclear reactor comprises a fast breeder reactor. 6. A nuclear reactor fuel assembly as claimed in claim 1, wherein said spacing means are separate from said wire spacers, and are mounted at said upper end portions of all cladding tubes which are adjacent to said wrapper tube. 7. A nuclear reactor fuel assembly as claimed in claim 1, wherein said spaceing means are mounted at said upper end portions of only thos cladding tubes which are adjacent to said wrapper tube. 8. In a fuel assembly for a nuclear reactor of the type comprising a plurality of cladding tubes filled with fuel material, said plurality of cladding tubes being assembled within a wrapper tube, and said plurality of cladding tubes each being of the type which are helically wound with a wire spacer, the improvement comprising separate spacing means provided at upper end portions of those cladding tubes which are adjacent to said wrapper tube for preventing said cladding tubes from coming into direct contact with said wrapper tube. 9. A fuel assembly according to claim 8, wherein said spacing means comprise ring spacers mounted over said upper end portions of said cladding tubes adjacent said wrapper tube. 10. A fuel assembly according to claim 8, wherein said spacing means comprise upper end portion wall thickness of said cladding tubes which are greater than remaining portions of said cladding tubes. 11. A fuel assembly according to claim 8, wherein said spacing means comprise salient projections at said upper end portions of said cladding tubes. 12. A fuel assembly according to claim 8, wherein said nuclear reactor is a fast breeder reactor.