Computer simulation of packing structure in pebble beds

In HCPB blankets, pebble beds are composed of nearly spherical particles in the state of random closed packing. The packing structure is important to understand responses of pebble beds, e.g., mechanical stresses and effective thermal conductivity. In this paper, an algorithm for random close packing of polydisperse particles is presented which can be used for arbitrary pebble bed containing geometries. The microstructure of a packed bed in both the bulk and near-wall regions can be determined. Computer-generated samples are compared to recent X-ray tomography results of non-compressed pebble beds, including the packing factors and coordination number. Moreover, initial configurations obtained by this method can be used in discrete element simulations of random configurations of pebbles to investigate the overall behaviour of pebble beds under fusion-relevant conditions.