Thermodynamics of chromium in UO2 fuel: A solubility model

Abstract The solubility and speciation of chromium in doped uranium oxide are measured in carefully controlled temperature and oxygen potential conditions using electron probe microanalysis (EPMA) and scanning electron spectroscopy (SEM). The examination of the samples by X-ray Absorption Spectroscopy (XAS) provides evidence that (i) chromium is soluble in the UO 2 matrix under the +3 oxidation state only regardless of the sintering conditions which is in accordance with a soluble species of type CrO 3/2 and (ii) soluble chromium exhibits octahedral symmetry with 6 atoms of oxygen forming CrO 6 patterns in the UO 2 structure. In consistency with all available experimental information including previously published data, the solubility of chromium in UO 2 corresponding to each two-phase field with either Cr, CrO and Cr 2 O 3 may be described in the ranges 1500 °C T μ O2 2 for the three chromium phases are derived.