Phase composition of the murataite-based ceramics containing 10 wt.% ThO2, UO2, NpO2 or PuO2 and leaching of actinides using a MCC-1 procedure were studied. The ceramics were prepared by melting of oxide mixtures in Pt ampoules in air at ∼1500 °C. They are composed of predominant murataite-type phases and contain traces of extra phases (rutile, crichtonite, perovskite). At least two murataite-related phases with five- and eight-fold elementary fluorite unit cell (5C and 8C) were simultaneously observed. Minor phase 3C (murataite) in the ceramics doped with ThO2 and UO2 was also found. In the Th-bearing sample the 5C phase prevails over the 8C phase. In the U-bearing ceramic they co-exist in comparable amounts. The sample produced at 1500 °C contains crichtonite whereas the ceramic produced at lower temperature (1400 °C) contained rutile. Higher temperature favors further rutile reactions with formation of crichtonite. The Np- and Pu-doped ceramics are also composed of major the 5C and the 8C phases and minor rutile and crichtonite (in Pu-loaded sample only). Unlike the sample prepared under slightly re-ducing conditions (in glassy carbon crucible) the Pu-doped ceramic produced under neutral conditions (in Pt ampoule) doesn’t contain perovskite-type phase. Occurrence of perovskite in the first sample was sup-posed to be due to reduction of some Pu(IV) to Pu(III) during experiment. Leach rates (7-day MCC-1 test, 90 °C) of the actinide elements from all the ceramics studied are at the level of 10-6-10-7 g/(m2·day).
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Stefanovsky, S.V., Yudintsev, S.V., Nikonov, B.S. et al. PHASE COMPOSITIONS AND LEACH RESISTANCE OF ACTINIDE-BEARING MURATAITE CERAMICS. MRS Online Proceedings Library 893, 8930523 (2005). https://doi.org/10.1557/PROC-0893-JJ05-23