抄録
In order to optimize sphere-pack fuel pin fabrication process, internal structure of fuel pin under small particle infiltration process was observed by micro focus X-ray CT system. During the settling of small particles through the bed of large particles, some small particles are localized in the space between large particles. When small particles reach the bottom of the fuel column, they fill the space between large particles forming a complete packing layer. Sphere-pack process proceeds with the growth of the layer from the bottom to the top of the column. A unique layer is formed near the top of fuel column. In the layer, small particles completely intrude between large particles and pin wall. The structure did not change after the completion of small particle infiltration process. The formation of the unique layer was controlled by the strength of a constraint of the layer surface.
