Mass spectrometric study of the oxygen potential at the UO2−x–U(l) phase limit

Activity measurements of UO2 at the phase boundary U(l)–UO2−x have been performed by high temperature mass spectrometry in order to solve discrepancies observed in earlier works. The direct measurement of the UO2 activity was performed using the multiple Knudsen cell method and a special collimation device in order to (i) circumvent any usual calibration methods (ii) discard any earlier observed parasitic contributions in this system. The oxygen potential is then directly calculated on the basis of pure UO2(s) accurate thermodynamic data for the diphasic U(l)–UO2−x domain in the 2000–2250 K range.