Modelling heat capacity, thermal expansion, and thermal conductivity of dioxide components of inert matrix fuel

Based on a simplified model of the phonon spectrum, on the statistical thermodynamics, and on the generalised Klemens model for thermal conductivity, some useful relationships bounding the specific heat capacity, the thermal expansion coefficient, the bulk modulus and the thermal conductivity of dioxides, often used as components in inert matrix fuel, were deduced in a quasi-harmonic approximation. The developed models were first verified with urania UO2, then applied for prediction of the isobaric specific heat, the isobaric thermal expansion coefficient, and the thermal conductivity of ThO2 and of one inert matrix material: ZrO2. The similarity principle was used in the cases where the input data were missing. The obtained results were compared with the available experimental data, and satisfactory agreement was demonstrated in the temperature range of 30 to 1600 K. In most of the cases the predicted values were within the region of the dispersion of the experimental data. The largest difference was observed for the thermal conductivity of ZrO2 at high temperatures, which could be explained by unaccounted photon contribution.