Enthalpies of thoria-urania from 2300 to 3400 K

The enthalpies of some thoria-urania solid solutions - (Thsub(0.70)Usub(0.30))O2, (Thsub(0.85)Usub(0.15))O2, and (Thsub(0.92)Usub(0.08))O2 - were measured from 2300 to 3400 K, using an induction-heated drop-calorimeter system. The enthalpy measurements from this work were compared with other reported lower-temperature data, analyzed, and fitted to equations. Discontinuities in the slopes of the enthalpy-temperature curves were found for the various thoria-urania solid solutions at temperatures, Tsub(r), equal to about 0.8 of the melting temperature. This behavior is consistent with that observed for both ThO2 and UO2. Heat capacities below the transition temperature, Tsub(r), derived from the enthalpy equations were as predicted from mole averages calculated from ThO2 and UO2 data. (orig.)