A nuclear fuel assembly has a plurality of fuel rods each containing a multiplicity of fuel pellets. The fuel rods include a plurality of first fuel rods and a plurality of second fuel rods. Each of the first fuel rods contains a burnable poison over substantially the entire axial length thereof. The first fuel rod also has a greater means enrichment in the upper axial region thereof than that in the lower axial region thereof. Each of the second fuel rods contains no burnable poison and has a uniform enrichment distribution over substantially the entire axial length thereof. In each cross-section of the fuel assembly perpendicular to the axis thereof, the outer peripheral portion has a greater mean enrichment than the central portion. The first fuel rods are disposed in the peripheral portion except the outermost peripheral portion of the cross-section of the fuel assembly.
