Abstract

The oxidation of UC granules has been studied in dry CO 2 and in CO 2 containing ~ 2 vol % water vapour at 200–600° C. In dry CO 2 the initial rate of oxidation was rapid at all temperatures and an approximately linear relationship was observed. The product of oxidation of UC was UO 2. The presence of moisture in the CO 2, in general, accelerated the rate of oxidation of UC. At 200° C a linear relationship was observed whereas at 400°–600° C the oxide film was more protective and an approximately parabolic relationship was obtained. The product of oxidation at 200° C was U 3O 8 and the formation of this oxide is attributed to oxygen impurities in the gas. The oxide formed at 600° C was, however, UO 2. High density UO 2 containing major inclusions of UC-UC 1−xO x undergoes rapid oxidative breakdown in dry CO 2 at 400°–600° C due to preferential oxidation of the carbon-rich regions and disintegration of the compacts. It has also been shown that oxidation of carbon/carbide-rich centres in UO 2 compacts prepared from UO 2 powder of high surface area (4–10 m 2/g) (without removal of the powder-binder before sintering) occurs preferentially at 800° C. This may also lead to disintegration of the compacts.

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