Study of the Effects of Potential Impurities from Actinide Flux on the Zirconolite Microstructure
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6WXG\RIWKH(IIHFWVRI3RWHQWLDO,PSXULWLHVIURP$FWLQLGH)OX[ RQWKH=LUFRQROLWH0LFURVWUXFWXUH G. Leturcq, B. Auzemerie CEA Valrhô, DEN/DIEC/SCDV/LEBM – B.P. 17171 – 30207 Bagnols/Cèze cedex France $%675$&7 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. ,1752'8&7,21 Zirconolite-rich ceramic has been considered as a candidate for the immobilisation option for the final disposal of excess weapon Pu [1-3], and also of minor actinides from a possible enhanced reprocessing of spent nuclear fuel [4-7]. Fabrication and chemical durability testing of zirconolite enriched materials have been carried out over the last twenty years. Different synthesis routes have been studied. A ceramization process involving hydrolysis of an alkoxide mixture by nitrate solutions, followed by sintering at 1400Û&ZDVGHYHORSHGLQWKHODWH V>@ Another process involves high-temperature melting of oxide mixtures at 1450–1700°C for several hours, usually in a cold crucible melter, followed by controlled cooling to obtain zirconolite in glass-ceramic [4-6] or ceramic form [5,6]. For glass ceramics, the role of impurities is less critical, as they can enter into the glassy phase. However, for pure ceramics, like those obtained by the ceramization process, the effect of impurities on the zirconolite microstructure has to be studied, in order to guarantee the containment capability of the ceramic, depending on the separation level. The a
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