Calorimetric measurements on uranium–plutonium mixed oxides

Enthalpy increments of U1−yPuyO2 solid solutions with y=0.21, 0.28 and 0.40 were measured using a high-temperature differential calorimeter by employing the method of inverse drop calorimetry in the temperature range 1000–1780 K. From the fit equations for the enthalpy increments, other thermodynamic functions such as heat capacity, entropy and Gibbs energy function have been computed in the temperature range 298–1800 K. The results indicate that the enthalpies of (U,Pu)O2 solid solutions obey the Neumann–Kopp molar additivity rule.