Abstract
We describe simulation studies of the dynamics of spouted beds used for CVD coating of nuclear fuel particles. Our principal
modeling tool is the Multiphase Flow with Interphase eXchanges (MFIX) code that was originally developed by the National
Energy Technology Laboratory (NETL) for fossil energy process applications. In addition to standard MFIX features that
allow coupling of transient hydrodynamics, heat and mass transfer, and chemical kinetics, we employ special post-processing
tools to track particle mixing and circulation as functions of operating conditions and bed design. We describe in detail one
major feature of the dynamics, which is the occurrence of very regular spontaneous pulsations of gas and particle flow in the
spout. These pulsations appear to be critically linked to the entrainment and circulation of solids, and they produce readily
accessible dynamic pressure variations that can be used for direct comparisons of model predictions with experiments.
Spouted-bed dynamics are important from a CVD perspective because they directly determine the magnitude and variability
of the concentration and species gradients in the zone where reactant gases first come into contact with hot particles. As this
unsteady spouted-bed environment differs from other types of CVD reactors, the design and scale-up of such reactors is likely
to involve unique modeling issues. Our primary goal here is to lay the groundwork for how computational simulation can be
used to address these modeling issues in the specific context of nuclear fuel particle coating.
