Zirconolite ceramics are candidate hosts for the containment of minor actinides from the reprocessing of spent fuel in France. Although actinide-doped or rare earth-doped zirconolite ceramics have been successfully produced from pure chemical precursors, there has been little focus on the effect of impurities on the zirconolite microstructure. However, this aspect is crucial for technical feasibility to guarantee a microstructure acceptable for nuclear waste management needs.
First, chemical elements from the reprocessing process that could enter into the actinide flux as impurities were listed. We considered rare earths, zirconium, platinoids (Ru, Rh, Pd), molybdenum, barium, cadmium, silver, caesium, iron, and strontium. As we know rare earths and zirconium entering into the zirconolite microstructure they were not included in the study. For each other impurity listed, a zirconolite batch containing 1 wt% oxide impurity, and enriched in Nd simulating minor actinides, was synthesised then examined by SEM. Impurities were then categorised into those digested into the zirconolite microstructure, those partially digested into the zirconolite microstructure but also forming their own phases, and those that did not enter into zirconolite and formed their own separate phases.
A sample was then produced containing all the impurities, to assess any interference effects. Three minor phases were observed: barium molybdenum oxide, noble metal alloy and zirconium titanium dioxide. These minor phases should not decrease the chemical durability of the ceramic, and therefore, we can conclude that zirconolite is not seriously affected by the impurities introduced.