Linking the solid state and solution thorium aqua structures: A solid state powder neutron diffraction investigation

A understanding of the aqueous chemistry of the actinide ions is not as well developed as for transition metals or the lanthanides. Fundamentally important information such as the number of coordinated water molecules is still under debate. This has relied on EXAFS, but this technique cannot give precise coordination numbers. In this work we aim, for the first time, to use neutron diffraction techniques to explicitly locate the coordinated water molecules in three thorium compounds (with bromide, sulfate and chloride ions) of increasing complexity, and understand how these interact with the second coordination shell. In a related submission, we will examine the solution phase structures to gain further information on the structures and stability of these. This information is vital for the storage of spent nuclear fuel either in a geological repository or solution phase processing.