Measurements of O/U ratio and oxygen potential for UO2+x (0 ≤ x ≤ 0.1)

Abstract

The O/U ratios of UO2+x (0 ≤ x ≤ 0.1) were determined at 1,000 and 1, 200°C, using a thermobalance in atmospheres of controlled oxygen pressures set by CO/CO2 gases. The oxygen potentials corresponding to the x values were measured in situ with a solid electrolyte oxygen sensor. For x ≥ 0.015 the present Δ GO2 data agree well with the previously published data. In the range of 0 < x< 0.015, the increasing disagreement at smaller values of x was indicated; the present Δ GO2 values are 2 to 15 kcal/mol more negative than the prior thermogravimetric data. The results also showed that a reverse in Δ GO2 at 1,000 and 1,200°C occurs in the range of 2.003 <2.015. The maximum in the plot of the partial molar entropy Δ SO2 vs. O/U ratio has consequently been found near Δ SO2 = 11e.u. for O/U = 2.007. This ΔSO2 value is considerably high in comparison with Markin & Bones’ EMF data, suggesting a characteristic configuration of oxygen in the lattice near UO2.007. © 1983 Taylor & Francis Group, LLC.