Reduction study of UO2F2 at high temperature in air and dihydrogen

The aim of this work was to clarify the reduction process of UO2F2 and to identify some intermediate compounds likely to be formed in the course of this process. Gravimetric studies have been carried out in water or molecular hydrogen atmospheres. Each compound isolated has been identified by X-ray diffraction analysis. We first investigated the conversion of UO2F2 into U3O8 in a water partial pressure of 300 mbar at 700, 750 and 800 C. Thus, we have determinated the influence of the temperature on the reaction kinetics at a fixed vapor pressure. After identification of the two intermediates β-UO3 and UO2,9, we have proposed differents mechanisms. As well, the reduction of UO2F2 in a dihydrogen atmosphere at 700 C was investigated. This reaction leads, in two steps, to the nuclear fuel by the way of U3O8. (orig.)