Observation of Small Particles Infiltration Process in Sphere-Pac Fuel Pin Fabrication

Ishii, Katsunori ; Suzuki, Masahiro ; Kihara, Yoshiyuki; Fujii, Kanichi*

To optimize sphere-pac fuel pin fabrication process, internal structure of fuel pin under small particles infiltration process was observed by micro focus X-ray CT system. Some small particles block the space among large particles. Small particles arrive at the bottom of fuel column, and fill the space among large particles, and form completed packing layer. Sphere-pac process progresses with growth of the layer from bottom to top of the column. A unique layer is formed around the top of fuel column shot time after starting vibration. Small particles completely intrude between large particles and pin wall in the layer. The structure never changes after completion of small particles infiltration process. The formation of the unique layer can be qualitatively explained by simulation.