Design and Synthesis of Novel Actinide Selective Ligands for Future Spent Nuclear Fuel Reprocessing

Bulmer, Rachel (2019) Design and Synthesis of Novel Actinide Selective Ligands for Future Spent Nuclear Fuel Reprocessing. Doctoral thesis, Northumbria University.

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Abstract

At the end of electricity generation through nuclear power, spent nuclear fuel remains highly radiotoxic due to the presence of the minor actinides, americium(III), curium(III) and neptunium(III). The separation of these requires highly selective ligands with soft N-donor atoms that are capable of distinguishing between the actinides and the much more abundant and chemically similar trivalent lanthanides.

This thesis discusses the development of novel classes of N-donor ligands, using an innovative ligand design approach, to improve on the current benchmark ligands developed. In particular the ligand design will take inspiration from the pharmaceutical industry, introducing hydrogen bond donor and/or acceptor groups and limiting the aromaticity introduced. This approach is hoped to improve the two drawbacks of currently available ligands, most notably poor solubility and slow rates of extraction.

Introduction of an amine bridge between the triazine and linker (e.g. phenanthroline) was found to have a drastically negative impact on the ability of the ligands to extract. The additional flexibility that was introduced into these ligands resulted in a ligand conformation incapable of forming a complex with the minor actinides. Efforts to introduce some rigidty into these molecules offered no improvements.

further investigation considered two of the dominant diketones used to form the 1,2,4-triazine ring, notably tetramethyl-cyclohexyl-1,2-diketone and camphorquinone. These groups were functionalised further to validate the proposed design approach. The most promising novel ligands developed were based upon the BTPhens, with additional hydrogen bond donor and acceptor groups present. These ligands showed improved rates of extraction as well as achieving a sufficiently high separation factor of the minor actinides from the trivalent lanthanides. Studies on the complexing properties of some of the ligands with trivalent lanthanides are also reported.

Further ligand designs and synthesis, and the subsequent extraction results, are discussed in this thesis. Analysis of the subsequent results supports the proposed design approach as a potentially effective method in which to streamline future ligand design.

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