Heat capacity, thermal conductivity and thermal diffusivity of uranium–americium mixed oxides

• The (U1-y,Amy)O2-x mixed oxides with y = 0.0877 and 0.1895 and x = 0.01–0.03 was studied.
• Enthalpy increments measured from 425 K up to 1790 K by drop calorimetry.
• Thermal diffusivity was measured from 500 to 1550 K.
• Heat capacity of the (U, Am)O2-xO2-x solid solution was thus obtained for the first time.
• For thermal conductivity a correlation using a classical phonon transport model is proposed.

The enthalpy increments of (U1-y,Amy)O2-x mixed oxides with y = 0.0877 and 0.1895 and x = 0.01–0.03 were measured using drop calorimetry in the temperature range 425–1790 K and the heat capacity was obtained as differential of the obtained enthalpy increments with respect to temperature. The thermal diffusivity was measured using the laser flash technique from 500 to 1550 K. The thermal conductivity was calculated from the measured thermal diffusivity, density and heat capacity. Measured enthalpy increments of the (U1-y,Amy)O2-x solid solutions are very close to the end members, indicating no excess contribution. The derived heat capacities for the two intermediate compositions are slightly higher than that of UO2 and in a good agreement with literature data of AmO2 up to 1100 K. For the thermal conductivity of (U, Am)O2−x mixed oxides a correlation using the classical phonon transport model in crystal structures is proposed.