DEM-CFD simulation of helium flow characteristics in randomly packed bed for fusion reactors

The helium cooled pebble bed (HCPB) packed spherical pebbles of lithium orthosilicate (Li4SiO4) blanket has been applied widely in fusion reactors. Helium flow and tritium transport characteristics are important for the design of the tritium breeding blanket. In this paper, the geometric models of randomly packed bed with different tube-to-particle diameter ratios (D/Dp) were established by discrete element method (DEM) to investigate helium flow characteristics. The results show that the wall effect can't be neglected, and the particle friction factor (fp) decreases with the increase of D/Dp. In addition, the relationships among porosity, velocity, and pressure distributions were investigated. It is found that the dimensionless velocity (Uave/U) and the dimensionless pressure (P/ΔP) distributions are not related to the inlet velocity, but only depend on the structure of bed. Besides, the transient tritium transport simulation shows that the transport efficiency in the regions away from the wall mainly depends on the velocity distribution. The efficiency in the regions near the wall is lower than other positions due to the wall effect. The steady tritium transport simulation shows that the transport efficiency depends not only on the velocity distribution but also on the distribution of tritium production.