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An oxidation-fluorination process for the recovery of uranium from graphite-base nuclear reactor fuels has been studied on a pilot plant scale. The graphite fuel was burned with oxygen and the residue, containing U3O8, was made to react with fluorine to form volatile UF6. These exothermic reactions were carried out within a fluidized bed of refractory alumina particles, which served as an inert heat transfer medium for control of temperature. In the oxidation step the oxygen was fed continuously to the reactor, while the graphite fuel was added intermittently at intervals of approximately 1 hour. Under these conditions and at 700°to 750°C ., an oxidation rate equivalent to 1 3.6 kg. of carbon per hour per feet squared of reactor cross section could be readily maintained. In the fluorination step the bed material containing the nonvolatile oxidation products was introduced as a single charge into a separate reactor and brought in contact with fluorine at 450°to 550°C. Over-all uranium recoveries of >99% were obtained.

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Investigations of the flow of fluids through granular materials generally have been limited to such studies as filtration, ground‐water movement, flow of gases through packed columns, etc., in which the fluid passes through an assemblage of stationary particles. There are however, at least two other phenomena often encountered in engineering practice which appear in be essentially identical to filtration but which have received little or no fundamental consideration (The term, filtration, as used throughout this paper designates a condition of flow.) Those are commonly referred to as “expansion”, in which the particles are suspended in an upward‐flowing fluid while the particle‐column as a whole is stationary, and “hindered settling”, in which the particles settle in the fluid with a uniform terminal velocity while the fluid‐column remains stationary. In each of these three cases of the general problem of flow through granular materials, the factors which influence the resistance to flow, namely, velocity, particle‐size, density viscosity, and porosity, are essentially the same; hence, a single equation should satisfy the requirements of all three cases.