The thermodynamic constraint relating the standard free energy of form
ation of an oxide (MO(C)) to its oxygen potentials by DELTAG(f)0(MO(C)
) = 1/2 integral-C/0 DELTAG(O2)BAR dC' has been used to develop the fu
ll spectrum of oxygen potentials of the U-O and Zr-O systems at high t
emperatures. Henry's law is applied to the metal region in the U-O sys
tem. Oxygen dissolution in liquid Zr has been shown to deviate only sl
ightly from Henry's law, despite the high solubility. Minor modificati
ons of the previously reported oxygen pressures in the two-phase regio
ns of both of the U-O and Zr-O systems result from the requirement of
satisfying the integral constraint. Oxygen pressures in the oxygen-con
taining metal regions where no data are available have also been estim
ated. The ensemble of the results is displayed in the form of oxygen i
sobars superimposed on the phase diagrams of the U-O and Zr-O systems.
The oxygen pressure-temperature-composition relation of tetragonal (b
eta) ZrO2+/-x has also been established.