| 摘要 |
PROBLEM TO BE SOLVED: To arrange fuel rods for positioning inside of a square fuel assembly in triangle grid so as to be symmetrically arranged for crossing. SOLUTION: A nuclear fuel assembly has a plurality of narrow and long fuel rods, which are held between a lower tie plate arranged in a bottom side of the assembly and an upper tie plate arranged in a top side of the assembly, an outside channel for surrounding a plurality of fuel rods and practically having a square cross section block for guiding the cooling material/decelerating material from the bottom part to the top part of the assembly in the periphery of the fuel rods, and at least one spacer for positioning the fuel rods in a predetermined arrangement. A first group of the fuel rods are arranged in rectangular with the predetermined pitch, and a second group of the fuel rods are arranged in triangle with the predetermined pitch, and furthermore, a center of a plurality of fuel rods is positioned in the vertex of an isosceles triangle.
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