Equation of state of uranium oxide

Abstract

The experimental and theoretical efforts on the equation of state of UO₂ are reviewed. An overview of the transient-type dynamic pulse heating techniques, using laser, electron and neutron pulse heating is given. Two complementary approaches for the calculation of the oxygen potential, described as the macroscopic ‘mixture’ model and the microscopic ‘defect’ model, lead to good agreement in their calculated pressures up to 5000 K. A combination of mass-spectrometric, Langmuir probe and high-voltage diode studies resolved previous discrepancies and revealed consistency between thermodynamic extrapolations and direct measurements. For the total equilibrium pressure over liquid UO₂ log (p/MPa)=–2.717 – 201 31/T+ 1.925 log T, is recommended for the temperature range from the melting point at 3130 K up to 5000 K. The model predictions of the critical point data of UO₂ are summarised.