| 摘要 |
PROBLEM TO BE SOLVED: To provide a fuel assembly whose fuel economy is improved by optimizing its axial enrichment and the distribution of the concentration of burnable poisons, without increasing the manufacturing cost, while enhancing or maintaining reactivity of conventional fuel assemblies. SOLUTION: The fuel assembly includes fuel rods of the first group, which have a low-reactivity region at upper and/or lower ends in the axial direction and one or more other fuel rods, whose low-reactivity regions at upper and/or lower ends in the axial direction are shorter than the fuel rods of the first group. The difference in the length of the low-reactivity regions between the fuel rods of the first group and the other fuel rods is 4/24 or less at the upper ends in the axial direction and 2/24 or smaller at the lower ends in the axial direction. The fuel rods of the first group are also located at positions other than the outermost periphery in the fuel assembly. Moreover, the fuel rods of the first group are located at positions where their faces are not adjacent to water rods or water channels in the fuel assembly. Furthermore, the fuel rods of the first group are located at positions, except four corners in the second layer from the outermost periphery and positions adjacent to the four corners in the fuel assembly. COPYRIGHT: (C)2005,JPO&NCIPI
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