| 摘要 |
PROBLEM TO BE SOLVED: To simplify the manufacture process, and at the same time, to improve the controllability of a reactor such as the optimization of surplus reactivity by reducing the amount of absorption of neutron per combustible poisonous granule-mixed fuel rod, and at the same time, by increasing the usage ratio. SOLUTION: In the fuel assembly for a light-water reactor, a fuel rod where a combustible poisonous granule 23 with a large grain diameter is thinly dispersed in a fuel granules 16 for mixing and is sealed to a covering pipe 15 by oscillation filling or the like is used, for example, 60% of the total fuel rods. The combustible poisonous granule 23 should be a solid solution, for example, with depleted uranium dioxide containing approximately 45% gadolinia, and has a nearly spherical shape and an average grain diameter of 0.5 mm or more, for example, approximately 1 mm. The density of the number of the combustible poisonous granules 23 in the fuel rod is set so that the ratio of the total area of a granule to the surface area of the fuel part of the fuel rod is set to 1 or less, for example, approximately 1/2. When the surface area is reduced, the amount of the absorption of a neutron can be reduced. Also, when the grain diameter is increased, the suppression of excess reactivity is ensured from the beginning to the end of a cycle.
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