Controlling and predicting the high temperature mechanical behaviour of nuclear oxide fuels is essential to guaranteeing the integrity of fuel rods during normal or incidental operating conditions. Although in the past many studies have been devoted to the creep behaviour of uranium dioxide, few have focussed in detail upon the effect of non stoichiometry. In those which have dealt with this issue, strain rate was usually considered as a function of deviation from stoichiometry although the true intensive thermodynamic variables are the chemical potential, temperature and stress.
In this work we describe very recent developments involving a high temperature compression creep furnace which has been equipped with a system enabling the control and measurement of the oxygen activity in the gas phase. This guarantees the oxygen activity in the solid in equilibrium with it. We report the first creep experiments carried out under these controlled conditions. We also discuss the development of a material model and associated kinematic hardening behaviour law capable of reproducing the near constant strain rate experiments carried out. Although we show that the data may be interpreted in terms of uniaxial loading, due consideration is given to multi-dimensional effects. The physical significance of the material behaviour law parameters is presented, particularly when the parameter is sensitive to oxygen activity. Our ultimate aim is to relate internal variables of the model to the local microstructure. Post test Electron BackScatter Diffraction is shown to be a prospective technique for providing this information and based on it, parallels can be drawn between the mechanisms via which the material accommodates mechanically induced strain and its response to radiation damage.