Patent Number: 055286410
Section: claims

1. A fuel assembly comprising: a lower tie plate having fuel supporting portion at the top thereof;  a plurality of fuel rods each supported by said fuel supporting portion at the lower end thereof;  a plurality of water rods arranged between said fuel rods,  a lower tie plate having fuel supporting portion at the top thereof;  a plurality of fuel rods each supported by said fuel supporting portion at the lower end thereof;  a plurality of water rods arranged between said fuel rods, 2. The fuel assembly as defined in claim 1, wherein the smallest part of said cross-sectional area is the coolant inlet port of said coolant ascending path. 3. The fuel assembly as defined in claim 1, wherein a pipe of one of said ascending path and said descending path is inserted into a connecting member and the upper end of said pipe is welded to said connecting member, and wherein a the other pipe is welded to the lower part of said connecting member, a cover member being installed between said connecting member to form a passage for communicating said coolant ascending path and said coolant descending path. 4. The fuel assembly as defined in claim 1, wherein a pipe-form part projecting upwardly and partitioning said coolant ascending passage in said coolant path is disposed in said ascending passage of said coolant ascending path, and wherein said coolant ascending path at a position upstream of said pipe-form part and said coolant descending path at a position downstream of said pipe-form part are communicated through an opening formed in a side wall of said pipe-form part. 5. The fuel assembly as defined in claim 1, wherein said fuel assembly has two water rods, and the largest cross-sectional area parts of said fuel rods adjoin the area where seven fuel rods can be located, and wherein each of said descending path of said water rods is arranged between said adjoining fuel rods that oppose to said ascending path. 6. The fuel assembly as defined in claim 5, wherein the descending path of one water rod and the descending path of another water rod are arranged in the reverse direction each other in the diagonal direction of the fuel assembly. 7. The fuel assembly as defined in claim 5, wherein one of the pipes of said ascending path is inserted into a connecting member and the top end of said pipe is welded to said connecting member, and wherein the other pipe is welded to the lower end of said connecting member, a cover member being installed between said connecting members to form a passage for communicating said coolant ascending path and said coolant descending path. 8. A fuel assembly comprising: 9. The fuel assembly as defined in claim 8, wherein said coolant inlet port is the smallest part of the cross-sectional area. 10. The fuel assembly as defined in claim 8, wherein said coolant inlet port is provided in the side wall of said ascending path. 11. The fuel assembly as defined in claim 8, wherein the cross-sectional area of said coolant descending path is smaller than that of said coolant ascending path. 12. The fuel assembly as defined in claim 10, wherein the cross-sectional area of said coolant descending path is smaller than that of said coolant ascending path. 13. The fuel assembly as defined in claim 8, wherein the pipe-form part projecting upwardly that partitions said coolant ascending path is disposed in said coolant ascending path, and the upper part of said coolant ascending path is communicated with the lower part of said coolant ascending path than said pipe-form part through an opening formed in the side wall of said pipe-form part. 14. The fuel assembly as defined in claim 8, wherein a pipe of one of said ascending path and said descending path is inserted into a connecting member and the upper end of said pipe is welded to said connecting member, and wherein a the other pipe is welded to the lower part of said connecting member, a cover member being installed between said connecting member to form a passage for communicating said coolant ascending path and said coolant descending path. 15. The fuel assembly as defined in claim 8, wherein a pipe-form part projecting upwardly and partitioning said coolant ascending passage in said coolant path is disposed in said ascending passage of said coolant ascending path, and wherein said coolant ascending path at a position upstream of said pipe-form part and said coolant descending path at a position downstream of said pipe-form part are communicated through an opening formed in a side wall of said pipe-form part. 16. The fuel assembly as defined in claim 8, wherein said fuel assembly has two water rods, and the largest cross-sectional area parts of said fuel rods adjoin the area where seven fuel rods can be located, and wherein each of said descending path of said water rods is arranged between said adjoining fuel rods that oppose to said ascending path. 17. The fuel assembly as defined in claim 16, wherein a pipe of one of said ascending path and said descending path is inserted into a connecting member and the upper end of said pipe is welded to said connecting member, and wherein a the other pipe is welded to the lower part of said connecting member, a cover member being installed between said connecting member to form a passage for communicating said coolant ascending path and said coolant descending path. 18. The fuel assembly as defined in claim 16, wherein a pipe of one of said ascending path and said descending path is inserted into a connecting member and the upper end of said pipe is welded to said connecting member, and wherein a the other pipe is welded to the lower part of said connecting member, a cover member being installed between said connecting member to form a passage for communicating said coolant ascending path and said coolant descending path.