Postirradiation Observations of Mixed Oxides with Initial Addition of Fission Product Elements

A mixed oxide (U,Pu)O₂ containing five elements (Mo, Ru, Ba, Zr, and Ce) representative of the fission product yield at 150 000 MWd/t has undergone a short-term irradiation to obtain the characteristic microstructure changes and redistribution of additional elements. The most important postirradiation observations on these oxides are

1. the absence of the columnar structure in the samples containing molybdenum
2. a plutonium enrichment in the center of some stoichiometric oxides
3. the presence of a metallic ingot at the upper end of the central void in one of the pins containing ruthenium.

The thermal behavior has been shown to be unfavorably affected by fabrications parameters in the case of low O/M, low density, and addition of soluble elements, whereas stoichiometric composition and possibly addition of molybdenum are favorable. characteristics. The O/M ratio has been found to be the most important parameter to govern the migration of actinides and fission products.