Laboratory Investigations in Support of Fluid Bed Fluoride Volatility Processes. Part Iv. the Fluid Bed Fluorination of U$sub 3$O$sub 8$ PDF Download

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In one of the processes under development, the uranium and plutonium content of a spent reactor fuel of the Dresden type would be fluorinated in a fluid-bed reactor to produce the volatile uranium and plutonium hexafluorides. The study of the fluorination of U/sub 3/O/sub 8/ was undertaken because it is the major product obtained in an oxidative decladding step that is being proposed for the removal of uranium and plutonium from stainless steel-clad and Zircaloy- clad fuel elements. The study Will also provide data needed for the development of apparatus and procedures for future work with mixtures of uranosic oxide and plutoniam dioxide. Experiments were performed to determine the optimum reaction conditions for the conversion of U/sub 3/O/sub 8/ to uranium hexafluoride and for minimizing the elutriation of unreacted U/sub 3/O/sub 8/ from the fluid bed. Elutriation of U/sub 3/O/sub 8/ from the fluid bed was minimized when a fluid bed height of 8 in. of 120 mesh alumina, a fluorinating gas phase containing 20 vol% fluorine, and a reaction temperature of 500 deg C were employed. Conversion of greater than 99% of the U/sub 3/O/sub 8/ to uranium hexafluoride was obtained when the feeding-fluorination period, in w, hich the U/sub 3/O/sub 8/ powder was fed into the fluid bed and the major part of the fluorination was accomplished by reacting the oxide with 20 vol % fluorine, was followed by a recycle-fluorination period of 5 hr at 500 deg C with 100% fluorine. Kinetic data for the fluorination of U/sub 3/O/sub 8/, obtained by means of a thermobalance, are reported for the temperature range from 300 to 400 deg C. The data were treated by the diminishing-sphere model. Experimental results are also presented for the oxidative decladding of stainless steelclad and Zircaloy-clad uranium dioxide pellets. (auth).