Radial oxygen distribution in the fuel of irradiated mixed oxide fuel elements with different final stoichiometries

The radial gradients of the oxygen potential and the oxygen/metal ratio O/M in the fuel of irradiated mixed oxide pins at the end of life have been determined from the Mo and MoO2 concentrations in the metallic and ceramic inclusions. The measurements were carried out on uranium-plutonium oxides with different initial stoichiometries (O/M)0 of 1.96, 1.98 and 1.99, resp., after fast neutron irradiation under identical conditions. Using the measured overall final stoichiometries and the stoichiometry shifts during burnup, the initial stoichiometries of the three investigated oxides have been recalculated, giving (O-M)0 values of 1.961, 1.978, and > 1.985, resp. (Auth.)