Hydrodynamic Simulation Studies For Spouted Bed Nuclear Fuel Coater

Solid fuel molten salt reactor uses fluoride molten salt as coolant and sphericalfuel element as fuel. The coated fuel particles are dispersed in the graphite matrix ofthe fuel zone inside the spherical fuel element. TRISO particle is UO2or ThO2kernelcoated with four layers of (1) a low density porous PyC buffer layer,(2) an inner highdensity isotropic PyC layer,(3) a SiC layer, and (4) an outer high density isotropic PyClayer. The coating layers are added to the kernel using a stepwise chemical vapor dep-osition process carried out in a spouted bed reactor. The coating process is a combina-tion of spouted bed technology and chemical vapor deposition technology. In thespouted bed fuel coater, particles are fluidized by fluidizing gas. When reactant gasesare heated to high temperature, gas pyrolysis enables solid-carbon or SiC layer to bedeposited on surface of particles. The hydrodynamic characteristics of spouted bedssuch as particles distribution, flow pattern and circulation trajectory are critical to coat-ing layer quality. Studies of the hydrodynamics of spouted beds are very important tothe design and process optimization of the nuclear fuel coater.TRISO fuel coater is a shallow spouted bed operating with heavy particles. Basedon the features of spouted bed nuclear fuel coater, the two-fluid model of Fluent is usedto study the hydrodynamics of spouted bed nuclear fuel coater. Firstly, the effect offriction packing limit, the coefficient of restitution of particles as well as the drag modelon the simulation are investigated. The results show that numerical simulation matcheswell with the experiment results by using the Gidaspow drag model with the frictionpacking limit being set at0.58and the coefficient of restitution of particles being set at0.9. Secondly, the influence of conical angle and inlet gas velocity on the hydrodynam-ics of spouted bed are studied. It is found that the gas–particle contact efficient is quitehigh while avoiding the particle bed floating in spouted bed with conical angle being set at60. When setting the inlet gas velocity at1.5Ums, the gas–particle contact is sat-isfactory and the particle-wall collision can be greatly reduced. Finally the influence ofparticle properties which change during coating process is investigated to provide ref-erences for optimization of TRISO fuel coating process control. It is found that fountainheight and particle quantity in spout zone decrease with coating process. Gas heatingrate in spout zone decreases due to the increase in particle diameter and decrease inparticle volume fraction.