Patent Number: 046860797
Section: summary

BACKGROUND OF THE INVENTION This invention relates to a fuel assembly, and more particularly to a fuel assembly having a fuel spacer consisting of a large number of circular members. As a fuel assembly for use in a boiling water reactor, a fuel assembly is known which has a fuel spacer consisting of a large number of circular sleeves. This fuel assembly is disclosed in Japanese patent Laid-Open No. 65287/1984 (basic application: U.S. Patent application Ser. No. 410124 filed on Aug. 20, 1982), and is illustrated in FIG. 2 of the Japanese reference. The fuel spacer is produced by arranging a large number of circular sleeves, into which fuel rods are inserted, in grid form and coupling adjacent circular sleeves with one another by welding. A water rod is also inserted into the circular sleeve in the same way as the, fuel rods. The support of the fuel spacer by the water rod is shown in FIGS. 8A-8C and 9A-9B of the Japanese reference. Development of a fuel assembly, which includes a water rod having an increased outer diameter, has also been made. An example of such fuel assemblies is shown in FIG. 1 of Japanese patent Laid-Open No. 65792/1984. The outer diameter of the water rod in this fuel assembly is about twice the outer diameter of the fuel rod. SUMMARY OF THE INVENTION It is an object of the present invention to provide a fuel assembly with low pressure loss, which can increase a flow path area inside the water rod. It is another object of the present invention to provide a fuel assembly which can reduce the danger of contact between the fuel rods and the water rod. One of the characterizing features of the present invention resides in that the fuel spacer includes bridge members, whose both ends are fitted to two adjacent circular members among those circular members which are arranged close to a water rod having an outer diameter greater than that of fuel rods, in such a manner as to encompass the water rod, and projections disposed on the side surfaces of the water rod support the bridge members of the fuel spacer. Another characterizing feature of the present invention is that both ends of each bridge member exist between the water rod and the circular members to which the bridge member is fitted.