Modeling of the oxidation of uranium dioxide in a steam atmosphere
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The uranium dioxide oxidation model developed on the basis of the theory of adsorption of water molecules enables a satisfactory description to be given of the known experiments on the oxidation of reactor fuel. This model was also applied to a description of the process of a reduction in the concentration of oxygen in fuel when it interacts with the gaseous phase enriched in hydrogen. In conclusion, let us indicate the range of conditions and parameters for which it is possible to use the developed adsorption model for the oxidation of uranium dioxide in a steam atmosphere.
The temperature range is 1200–2000 K. It excludes low temperatures where phase transition processes in the UO2+x play an important part with a change in the oxygen content. The model also excludes the high-temperature region where evaporation of uranium oxides with a high oxygen content can be very important.
The samples are small (the minimum size is less than 1 cm), so that the diffusion of oxygen takes place considerably more rapidly than the oxidation reaction.
The steam pressure does not exceed 3.5 atm. Since the difference between the results of the physical models is not so great as unambiguously to indicate a decisive oxidation mechanism, experiments at increased pressures would make it possible to describe the oxidation dynamics under reactor conditions.
The present work was performed with the partial support of the Russia Fund for Fundamental Research (project code No. 96-02-18686).
KeywordsPhase Transition Steam Uranium Oxygen Content Oxidation Mechanism
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