Determination of the oxygen coefficient for hyperstoichiometric uranium-plutonium mixed oxide by a solid- electrolyte-based coulometric technique

The cubic phase of the uranium-plutonium mixed oxide U 1− z Pu z O 2+ x has a wide range of homogeneity relative to x. The oxygen potential of the phase is a single value function of stoichiometry and temperature and is of importance in the use as nuclear fuel. For determination of the oxygen coefficients of hyperstoichiometric uranium-plutonium mixed oxide the solid-electrolyte-based coulometric technique has been used. The sample to be analysed is reduced in a Ar-H 2-H 2O gaseous mixture. The changes in hydrogen concentration according to the reaction U 1− z Pu z O 2 + x + xH 2 → U 1− z Pu z O 2 + xH 2 O are continuously measured by coulometric titration with a solid electrolyte cell. The standard deviation of the measurement was found to be Δx = ± 0.0004. During the storage of the powdered samples a slow oxidation occurs.