Investigation into the structural relations of actinide brannerites

Actinide brannerites (prototypically UTi2O6) have been proposed as ceramic wasteforms for disposal of high actinide content radioactive wastes arising from civilian nuclear power generation. The crystal structures of the end-member brannerites UTi2O6, ThTi2O6, and CeTi2O6 have been previously determined, but little information is available on doped or otherwise unusual structures within the brannerite system. In particular, one of the polymorphs of ThTi2O6 has an unusual structure, the presence of which, or conversion to/from the brannerite structure, may have a deleterious effect on the performance of the final wasteform. Similarly, though there are many previous reports of doped uranium brannerites (U,M)Ti2O6, research on the effect of Ti-site doping U(Ti,M)2O6 is scarce, despite observations that the crystal chemistry of the brannerite structure is more complex than expected.