A New Evaluation of the Urania Equation of State Based on Recent Vapor Pressure Measurements

New experimental results on the vapor pressure of UO₂ up to extremely high temperatures have recently become available. These vapor pressure data, obtained by advanced experimental techniques, are lower than the ones used thus far at Kernforschungszentrum Karlsruhe. It was, therefore, appropriate to carry out a completely new evaluation of the equation of state (EOS) of UO₂- Eyring’s significant structures theory, which was extended to the case of nonstoichiometric urania, was applied for this work. The extended theory is described in some detail. By a suitable choice of the model parameters, good agreement of the evaluated EOS with recent experimental data was obtained, which is additional evidence of the reliability and consistency of the recent data. The extrapolation predicts a critical temperature of 10 600 K, which is higher than earlier predictions.