Fuel assemblies for use in BWR type reactors

Purpose: To suppress the power peak value below a standard value by using nuclear fuels of a uniform enrichment degree for BWR type reactor fuel assemblies. Constitution: A plurality of fuel rods in which fuel pellets are stacked and sealed within cladding tubes are bundled in a square lattice. The degree of enrichment of nuclear fuel materials contained in the fuel pellets of all of the fuel rods is made uniform, and a core defined to a concentrical circular shape and made of non-fissile material is formed to the fuel pellet of the fuel rod. Further, a burnable material is incorporated into the core of the fuel rod comprising fuel pellets having such core portion. That is, the amounts of the fissile material and the burnable material of the fuel rods in the nuclear fuel assembly are previously adjusted so as to provide a distribution corresponding to the suppression of the power peak value in the fuel assembly, so that the power distribution in the transversal cross sectional of the fuel assembly may be flattened throughout the entire operation period. (Moriyama, K.)