| 摘要 |
PROBLEM TO BE SOLVED: To provide a fuel assembly for a D-grid, capable of increasing takeout combustibility by enhancing average enrichment, while securing thermal tolerance by reducing local output peaking to an appropriate value. SOLUTION: This fuel assembly comprises a plurality of first fuel rods 2 containing no combustible poison and a plurality of second fuel rods 3, 4 containing combustible poison, which are arranged in a square grid consisting of nine rows and nine lines. The first fuel rods, placed within two layers from the outermost periphery, on a cross section in which the enrichment of each fuel pellet used is 5 wt.% or less and average enrichment on the cross section is 4.5 wt.% or more, are all of maximum enrichment, and when the cross section is divided into two by a diagonal 7 connecting the centers of two of the outermost-periphery corner fuel rods located at diagonal positions, all the outermost-periphery fuel rods on one side are the first fuel rods of the maximum enrichment except those at the corners, and one or more first fuel rods of the maximum enrichment and three or more first fuel rods that are not of maximum enrichment are placed in positions on the other side at the outermost periphery except at the corners.
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