| 摘要 |
PROBLEM TO BE SOLVED: To increase burnup and improve reactivity worth of burnable position by suppressing the lowering of control rod worth regardless of the use of short size fuel rods and preventing the lowering of core shutdown margin. SOLUTION: A MOX fuel assembly 1 arranges in a square grid MOX fuel rods 2 (fuel rod indexes 1,2 and P)charging plutonium oxide and uranium oxide, uranium fuel rods 2 (fuel rod indexes G1, G2) containing gadolinia charging uranium oxide and containing burnable poison and water rods 3. The uranium fuel rods 2 with gadolinia (fuel rod indexes G1 and G2) include uranium fuel rods 2 with gadolinia (fuel rod index G1) arranged in the periphery of the square grid array, and uranium fuel rods 2 with gadolinia (fuel rod index G2) arranged in the grid position adjacent to the water rods 3. The gadolinia concentration g1 of the uranium fuel rods 2 which gadolinia is less than the gadolinia conceration g2 of the uranium fuel rods 2 with gadolinia (fuel rod index G2).
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