Single-step process for preparation of uranium dioxide from uranium hexafluoride

UF6 is converted to UO2 by reacting it with a stoichiometric excess of a gaseous mixture of hydrogen and either oxygen or water vapour at a temperature > 1100 DEG C. and a pressure \sO 20 torr. To produce sinterable powder, the hydrogen is preferably in at least 4 times, e.g. 15-20 times the stoichiometric proportion, and the O2 or water vapour in at least 1.5 times, e.g. 8-10 times, the gases being premixed at 800-1000 DEG C., e.g. 900-1000 DEG C. at a pressure < 20 torr. whereby solid particles, probably UO2F2, are formed, and reacting at \sP 1100 DEG C., pref. 1200-1500 DEG C. at a pressure of < 20 torr. A solid deposit is produced when the H2 is in at least 5 times, and the O2 or water vapour in at least 1.5 times the stoichiometric amounts at \sP 1100 DEG C., e.g. 1200-1500 DEG C., and < 10 torr., the UO2 being deposited on a refractory surface e.g. alumina. For a smooth-surfaced body, the H2 is in 5-20 times, and the O2 or water vapour is in 1.5-10 times the stoichiometric amounts, and for a tubular body, the former used is the inner surface of a refractory tube. Crystalline UO2 is produced if the H2 is in 30-90 times, and the O2 or water vapour is in 10-90 times the stoichiometric amount. The product has a low fluorine content and may be used, in tubular form, as a nuclear fuel element. missing page 174