To obtain fuel assemblies of uranium-plutonium mixed oxide fuel for boiling water reactors, aimed at high enrichment which fully ensures the margin for maximum burnup of pellet, in using uranium-plutonium mixed oxide fuel rods of single enrichment and also be proper for reactivity control.

In the fuel assemblies for boiling water reactors provided with as a fuel rod group, a plurality of uranium-plutonium mixed oxide fuel rods of fissile plutonium enrichment of one kind and 5 wt% or more, a plurality of uranium oxide fuel rods containing no plutonium and a plurality of uranium oxide fuel rods with burnable poison containing no plutonium, the uranium-plutonium mixed oxide fuel rods are arranged, excluding the outermost preiphery and in the vicinity of water rod positions. The fuel rods with burnable poison are arranged in the region vicinity of water rods.

COPYRIGHT: (C)2007,JPO&INPIT