| 摘要 |
PURPOSE: To provide a fuel assembly for improving reactor stopping margin without reducing fuel weight per fuel assembly and deteriorating limit output for a lattice-shaped fuel assembly where especially the reactor stopping margin easily decreases when targeting the high combustion of the fuel assembly. CONSTITUTION: In a fuel assembly 18 where a bundle of fuel in that fuel rods 2 and 3 are bundled in a lattice (9 rows×9 columns) is surrounded by a channel box 9, eight of fuel rods 3 with short length are dispersed and arranged at one portion of a second-layer fuel rod from the outermost fuel rod and at the same time are used with a degree of combustion where an average degree of take-out combustion is equal to or more than 50Gwd/t and the relationship among the average degree of take-out combustion E(Gwd/t), a gap (a) between a channel box inner wall and the outermost periphery fuel rod, and a pitch (b) between fuel assemblies is expressed by (a/b)>=0.07×(a/b)>=0.07×E-0.65(%).
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