Model for determining the effective thermal conductivity of particle beds with high solid-to-gas thermal conductivity ratio

A Be-packed bed between the high-temperature breeder and low-temperature coolant has been proposed for an ITER solid breeder base blanket. The design offers the possibility of adjusting the solid breeder temperature through active control of the packed-bed effective conductivity; such control can potentially be achieved by varying the pressure or flow rate of the helium purge flowing through the Be-packed bed. A modeling effort directed at estimating the effective thermal conductivity of pebble beds with high solid-to-gas conductivity ratios (such as Be and He) is described. The model can account for different particle sizes and surface contact characteristics which are particularly important in determining the extent to which the bed effective thermal conductivity can be controlled through pressure variation for high ratios of solid-to-gas conductivity. >