To improve thermal characteristics of core by flattening axial power distribution at initial burning in a MOX fuel assembly and reduce the number of kinds of MOX fuel rods by preventing lowering of reactor shutdown margin and simplifying the enrichment distribution.
A long fuel rod 2 comprises first long fuel rods 11, and 12, a third long fuel rod 13 and a second long fuel rod 14. The third long fuel rod 13 is filled with uranium fuel added by burnable absorber and the second long fuel rod 14 is filled with uranium without added by burnable absorber. A short fuel rod 3 is constituted of a short uranium fuel rod 15 containing gadlinia. The uranium fuel is uranium produced in the enriching process of natural uranium and has depleted uranium with lower fraction of uranium 235 than natural uranium as mother material. The short fuel rod 15 and the third long fuel rods 13 are arranged in the adjacent positions in the first and the second layer from the outermost part of a fuel assembly.
IZUTSU SADAYUKI
SASAGAWA MASARU
HIRANO YASUSHI
FUJIMAKI SHINGO
YOSHIDA MANABU
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