Influence of bed conditions on the effective thermal conductivity of ceramic breeder pebble beds using thermal DEM (TDEM)

•The effective thermal conductivity of ceramic pebble beds is influenced by various parameters with inherent interactions. The packing fraction, hydrostatic stress and the stagnant gas pressure are predominantly varying the thermal conductivity.•The patterned regular packing formation of pebbles near the wall is observed to be advantageous in increasing the thermal conductivity (10 to 15% higher than the bulk region) due to the formation of uniformly distributed force network.•A significant increase in the ETC in desired direction by addition of secondary particles with higher thermal conductivity is achieved through layering of secondary particles amongst primary particles. The knowledge of effective thermal conductivity (ETC) of the pebble beds is vital in designing the breeder units for fusion reactors. The ETC of pebble beds in general depends on various parameters characterizing the bulk material and microstructural properties. Establishing correlations between the ETC and the governing system parameters through experiments is very expensive and not feasible in some cases as the particle scale data is not readily available. Hence, Thermal Discrete Element Method (TDEM) is employed in this paper to investigate the influence of various parameters on the effective thermal conductivity of pebble beds. Influence of parameters such as packing fraction, stress, bed temperature, pebble size and stagnant gas pressure on the ETC is investigated for lithium ceramic pebble beds in stagnant Helium/Air. Further, the variation of the ETC from the wall region to the bulk for pebble beds formed in prismatic containers is presented. Subsequently, dual phase pebble beds have been investigated to identify configurations that will enhance the ETC of the bed.