A 3-in.-diam, fluidized-bed coater was developed at Los Alamos Scientific Laboratory (LASL) for the deposition of high-density, oriented pyrolytic car ton with a smooth microstructure. Such a coating is required as an outer, resistent layer for good retention of melt above 2450°C in improved coated particles that have Gulf General Atomic experimental UC2 cores with a complete graphite shell and have an inner, sacrificial layer of high-density, isotropic pyrolytic carbon. The coater has a baffle system consisting of a l/2-in.-wide lip at the top of the coating chamber and a 3 l/2-in. -diam plate above that, to con fine the fluidized bed so that high flow rates of the coating gas mixture can be used. The reduced residence times of the gas at high flow rates prevents coot particles from forming in the costing chamber and becoming incorporated into the coating. About 5 Kg U of improved coated particles with the outer layer deposited in this coater on the 575-g-U scale were prepared at LASL for use in Rover experimental graphite-matrix fuel elements. The thermal stability of these particles was very comparable to that of control particles coated in 1-in.-diam equipment.
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