Development of a Criticality Evaluation Method Involving the Granular Flow of the Nuclear Fuel in a Rotating Drum

Particle dynamics of nuclear fuel material has not been considered in conventional nuclear criticality evaluations. However, the particle motion influences nuclear criticality significantly. In the present study, the criticality calculation is combined with the discrete element method (DEM) to investigate the effects of the particle macroscopic behavior on nuclear criticality. Particle motion is analyzed in a rotating drum by the DEM, and then, the nuclear calculation is carried out. This paper focuses on particle size distribution, size segregation, and change of surface area of the particle bed. The particle size distribution has an important influence on the nuclear criticality evaluation because it affects not only the particle movement but also the atomic number densities in the bed. The surface area of the particle bed shows a close correlation with the multiplication factor. On the other hand, the size segregation does not have a significant effect on nuclear criticality.