Thermal diffusivity and conductivity of thorium–plutonium mixed oxides

The thermal diffusivity of (Th, Pu)O 2 (with 3, 8 and 30 wt.% PuO 2) mixed oxides and of the single oxides PuO 2 and ThO 2 was measured using the laser flash technique. In several samples, a further degradation in the thermal diffusivity due to auto-irradiation damage was noted, and a recovery could be achieved by thermal treatment. The ThO 2 and (Th, Pu)O 2 samples with 3 and 8 wt.% PuO 2 were found to be semitransparent and had to be coated with C for the thermal diffusivity measurement. The experimental thermal conductivity of the fuels was calculated and analysed. The introduction of PuO 2 in the ThO 2 was found to have an effect similar to that observed in (U, Pu)O 2 mixed oxides: small decrease in the range 3–8 wt.% PuO 2 and higher decrease at 30 wt.% PuO 2 content. Using the classical phonon transport model in crystal structures, a new correlation for the thermal conductivity of (Th, Pu)O 2 mixed oxides is proposed and is compared to the results of another correlation built after the Klemens–Callaway theory.