Contribution to the understanding of the point defect influence on some transport properties in UO 2+x

A point defect model is developed in hyperstoichiometric uranium dioxide, UO2+x,in order to explain some experimental results of deviation from stoichiometry and electrical conductivity existing in the literature. This model takes into account both singly charged uranium vacancy, V''U , and two types of Willis clusters, characterized by two kinds of interstitial oxygen atoms that are located on two different sites and two oxygen vacancies, namely 2(Oi"Oi''Vȯ)4'' and . The electron holes, ḣ , are also introcued to ensure the crystal global electroneutrality. An adjustment procedure of the most convincing experimental data of the literature, corresponding to the temperature and oxygen partial pressure dependencies of departure from stoichiometry,x, and electrical conductivity, [sigma] , has been undertaken. The fit model/experience obtained has been found fairly good, justifying, a posteriori, the relevance of the nature of the selected defects in the model