Effects of bed dimension, friction coefficient and pebble size distribution on the packing structures of the pebble bed for solid tritium breeder blanket

Abstract

• Effects of bed width on the packing structures of pebble bed were investigated by DEM simulation. • Effects of pebble properties (friction coefficient between pebbles, pebble size distribution and pebble density) on the packing fraction of pebble bed were simulated and analyzed. • Packing structures of both the tritium breeder (Li 4 SiO 4 , Li 2 TiO 3 ) and the neutron multiplier (Be, Be 12 Ti) pebble beds were simulated and analyzed by DEM. In solid tritium breeder blanket, the packing structures of the tritium breeder pebble bed and the neutron multiplier pebble bed are very important to analyze the tritium breeder ratio and the heat and mass transfer process in the pebble bed. In this study, the numerous simulations were conducted to investigated the effects of bed dimension, friction coefficient between pebbles, pebble size distribution and pebble density on the packing structures of the ceramic tritium breeder (Li 4 SiO 4 , Li 2 TiO 3 ) pebble beds and the neutron multiplier (Be, Be 12 Ti) pebble bed by discrete element method (DEM), respectively. The simulation results reveal that the pebble bed dimension, friction coefficient and pebble size distribution have a significant impact on the pebble bed packing fraction. As the width of the pebble bed container increases, the average packing fraction of the pebble bed gradually increases, meanwhile the influence of volume fraction of the wall effect gradually decreases. In addition, a lower friction coefficient between pebbles (smoother surface of the tritium breeder and the neutron multiplier pebbles) and wider pebble size distribution will result in a higher packing fraction of the pebble bed. However, the material density of the ceramic tritium breeder (Li 4 SiO 4 , Li 2 TiO 3 ) pebbles and the neutron multiplier (Be, Be 12 Ti) pebble seems to have no obvious effect on the packing fraction of the wider pebble bed for the solid tritium breeder blanket.