Use of soft heterocyclic N-donor ligands to separate actinides and lanthanides

The removal of the most long-lived radiotoxic elements from used nuclear fuel; the minor actinides, is foreseen as an essential step towards increasing the public acceptance of nuclear energy as a key component of a low carbon energy future. Once removed from the remaining used fuel, these elements can be used as fuel in their own right in fast reactors or converted into shorter-lived or stable elements by transmutation prior to geological disposal. The SANEX process is proposed to carry out this selective separation by solvent extraction. Recent efforts to develop reagents capable of separating the radioactive minor actinides from lanthanides as part of a future strategy for the management and reprocessing of used nuclear fuel are reviewed. The current strategies for the reprocessing of PUREX raffinate are summarised and some guiding principles for the design of actinide-selective reagents are defined. The development and testing of different classes of solvent extraction reagent are then summarised, covering some of the earliest ligand designs right through to the current reagents of choice; the bis-1,2,4-triazine ligands. Finally, we summarise research aimed at developing a fundamental understanding of the underlying reasons for the excellent extraction capabilities and high actinide/lanthanide selectivities shown by this class of ligands, and our recent efforts to immobilize these reagents onto solid-phases