THERMODYNAMICS OF NONSTOICHIOMETRIC URANIUM DIOXIDE.

This is a review of the data on the thermodynamics of oxygen in uranium oxides: the experimental techniques used in obtaining the data are described and their relative precision discussed. Each measurement involved the determination of the oxygen partial pressure at equilibrium with an oxide of a given oxygen-to-metal ratio. It is believed that the pressure meaurements were relatively accurate but that characterization of the oxide phase was difficult and this could have led to appreciable errors in the data for slightly hyperstoichiometric uranium dioxide. Statistical analysis of the data has been carried out and the most probable set of data for hyperstoichiometric uranium dioxide indicated. Similar calculations for hypostoichiometirc dioxide were not possible because of the dearth of data. It is shown how the data can prove useful in assisting fuel preparation. The data can also help to explain second-phase particles in uranium oxides and oxygen redistribution during irradiation of oxide fuels. (auth)