A Mixed Ceramic-Metal Sphere-Pac Concept

Particle bed arrangements (e.g. sphere-pac and vipac) are considered as alternative fuel-forms for nuclear fission of actinides. The fuel material is potentially UO2, MOX or an Inert Matrix such as yttria-stabilized zirconia. A disadvantage of ceramic particle fuel is its low thermal conductivity at startup. The macroscopic structure of a particle bed (e.g. spherical particles in sphere-pac) hinders heat transport prior to sintering. To remedy this situation, a novel cer-met concept is proposed and studied in this work. In the sphere-pac model with two well differing size fractions, one material can be distributed evenly into the other one. In this case, the ceramic material (e.g. yttria stabilized zirconia) and the metallic component (e.g. zirconium) are the large and small size fractions respectively. Calculations for this initial fuel configuration show a significant enhancement of the thermal conductivity. Sintering occurs following startup and especially at the center of the fuel. The macroscopic sphere-pac arrangement then transforms into a porous-pellet-like structure. Sintering experiments have been performed to investigate these effects. In the cer-met arrangement the restructuring was enhanced. Therefore heat transport improves even as the metallic component becomes oxidized.