Thermodynamic functions of Sm₆UO₁₂ and Eu₆UO₁₂

Rare earth elements produced in the reactor during irradiation can interact with the fuel. Under transient conditions, compounds of formula, RE₆UO₁₂ with rhombohedral crystal structure are expected to be formed. There are no experimental enthalpy data for these uranates. Hence, enthalpy increment measurements on Sm₆UO₁₂ and Eu₆UO₁₂ were carried out by inverse drop calorimetry in the temperature range 533-1738 K and computed the thermodynamic functions. Sm₆UO₁₂ and Eu₆UO₁₂ samples were prepared by combustion synthesis using citric acid as the fuel. Stoichiometric ratio of nuclear grade U₃O₈ and Sm₂O₃ and Eu₂O₃ of 99.9% purity were used for preparation of uranates. The formation of Sm₆UO₁₂ and Eu₆UO₁₂ were confirmed by XRD. The samples were analysed for carbon impurity (<100ppm) by using carbon analyser (M/s. Eltra, Germany). For drop calorimetric measurements, powders of these samples were compacted in to pellets of 5mm in dia. and sintered at 1673 K in air for 8 hrs