Modelling thermal properties of actinide dioxide fuel

Modelling of the behaviour of fuels and targets containing minor actinides is still difficult because of very limited information on their thermal and mechanical properties. Integral analysis based on the sound physical models and on the similarity principle can be very useful in this situation. In the current article, a combination of macroscopic and microscopic approaches is used for development of an equation of state (EOS) for actinide dioxide fuels. Based on simple but physically complete models of phonon and electron spectra, the EOS was deduced in quasi-harmonic approximation, and useful relationships bounding thermal and mechanical properties were obtained. They were firstly tested with calculation of the specific heat and the coefficient of thermal expansion of UO2 and ThO2. A good agreement with the experimental data was demonstrated in the temperature range of 30-1600 K. Then the model was successfully applied to NpO2 and PuO2. Lack of experimental data on thermal properties of AmO2 and CmO2 in open literature did not allow the reliable comparison.