Nuclear fuel assemblies for use in BWR type reactors

Purpose: To suppress the cross-sectional and axial power peak value to less than standard values by using the nuclear fuel materials of a certain enrichment degree. Constitution: The enrichment degree of the nuclear fuel materials contained in fuel pellets for all of the fuel rods charged in the fuel assembly of a BWR type reactor is uniform and the fuel pellet comprises core made of ZrO2, Al2O3, Fe2O3, SiO2, CaO and the like. The fuel rod contain burnable poisons such as Gd2O3 in the core and the amount of the burnable poisons is made greater in those fuel rods disposed nearer to the circumference of the fuel assembly, while the amount of the nuclear fuel materials is also made greater in those fuel rods at the center of the fuel assembly. In this way, the cross sectional power peak value in the fuel assembly is suppressed to less than a predetermined standard value through the entire burning period. (Horiuchi, T.)