A fluid-bed method was developed for the direct preparation from uranium hexafluoride of dense, spheroidal uranium dioxide particles for dispersion and packed fuel element applications. The uranium hexafluoride is reacted with mixtures of steam and hydrogen in a bed of uranium dioxide maintained at 650 to 700 deg C, the solid reaction products depositing as a dense layer on the surface of the bed particles. The operating procedure involves alternating periods of uranium hexafluoride feed wi h periods of fluoride cleanup when only steam and hydrogen are fed. Uranium dioxide particles in the size range -- 16 + 140 mesh and having densities of 9.5 g/cc and 9.75 g/cc (up to 89% of theoretical density) were produced at 650 deg C and 700 deg C, respectively, using a uranium hexafluoride feed rate of 25 g/min STA44 lb uranium/(hr)(sq ft reactor cross section)!. The average residual fluoride content of the uranium dioxide was about 300 ppm. The densest material was obtained when 0.75 to 1.4 times the stoichiometric steam requirement (based on the reaction UF/sub 6/ + 2H/sub 2/O + H/sub 2/ yields UO/sub 2/ + 6HF was used. The effect on product density of other process variables such as uranium hexafluoride feed rate, hydrogen concentration, bed height, and duration of hexafluoride feed period was also determined. Further densification of the material to 10.4 to 10.6 g/cc, up to 96.5% of theoretical density, and reduction of the fluoride content to about 5 ppm was achieved by sintering in hydrogen at about 1700 deg C for 2.5 hours. (auth).

A fluid-bed process for the preparation of dense, spheroidal uranium dioxide particles directly from uranium hexafluoride for dispersion and compacted fuel element applications has been developed. In the process, a uranium hexafluoride is reacted with mixtures of steam and hydrogen in a bed of uranium dioxide fluidized by the reactant gases and maintained at 650 to 700 degrees C. The solid reaction products deposit as a dense layer on the surface of the bed particles. The operating procedure involves alternating periods of uranium hexafluoride feed periods of fluoride cleanup when only steam and hydrogen are fed. Product is withdrawn at the end of each cleanup period.

A new, dry process for the production of uranium dioxide powder from uranium hexafluoride by fluidization and particle-coating techniques was developed. The process involves direct conversion of uranium hexafluoride to a solid, UO2F2, by hydrolysis with steam and the reduction of the UO2F2 to the dioxide by reaction with was carried out in 3-in.-diameter Monel reactors.

A one-step, continuous, fluid-bed process for the conversion of uranium hexafluoride to uranium dioxide was successfully carried out in preliminary experiments in a 1 1/2-inch-diameter Monel reactor. Hydrogen and steam were used for simultaneous reduction and pyrohydrolysis reactions carried out at 600 deg C, resulting in the formation of a dense coating of dioxide on the starting bed of uranium dioxide. The effects of uranium hexafluoride feed rate and reactant excesses on conversion were investigated. Results of fluid-bed steam pyrohydrolysis runs on uranium tetrafluoride are also presented.

A new, dry process for the production of UO2 powder from UF6 by fluidization and particle-coating techniques was developed. The process involves direct conversion of UF6 to a solid, UO2F2, by hydrolysis with steam and the reduction of the UO2F2 to the dioxide by reaction with was carried out in 3-in.-dia. Monel reactors. In continuing studies, dense, spheroidal UO2 particles in the range --20 +200 mesh are being prepared. A simultaneous (steam and H2) reaction procedure at temperatures up to 7OO deg C is being used. Particle densities ranged to 9.75g/ cc or about 89% of theoretical. Sintering in H2 at about 1700 deg C for 2.5 hr gave final densities of 10.4 to 16.6 g/cc or up to about 96.5% of theoretical density. (auth).