Thermal conductivity of hypostoichiometric low Pu content (U,Pu)O2-x mixed oxide

The 'laser flash' method was used to measure the thermal diffusivity of PWR mixed oxide fuels with Pu contents ranging from 3 to 15 wt% and oxygen to metal ratio (O/M) ranging from 2.00 to ∼1.95. The temperature range extends from 700 to 2300 K. The fuel thermal conductivity is derived using heat capacity values of the mixed oxides calculated by Kopp's law from recommended values for the heat capacities of UO2, PuO2 and O2. We observe an effect of the deviation from stoichiometry on the conductivity smaller than what is recommended for high plutonium content FBR fuel. Our results are fitted in the low temperature range to a classical phonon transport model. Abeles's simplified theory of phonon diffusion by point defects is used to discuss the results. We propose a new thermal conductivity relation, which takes into account the effect of the O/M ratio