Lanthanide and actinide speciation in molten fluorides: A structural approach by NMR and EXAFS spectroscopies

The objective of this paper is to describe the local structure in fluoride melts of nuclear interest. Our experimental approach combines NMR and EXAFS spectroscopies both sensitive to the microstructure of solid and liquid materials. These techniques allow identifying the complex formation in molten media. Thanks to the development of specific cells adapted to molten fluorides up to 1300 °C, we give some structural description of LiF–LnF3 systems (Ln = Y, Lu, Ce) and discuss the evolution of 19F spectra in terms of different fluorine configurations depending on the composition. This approach is further extended to the characterization of LiF–ThF4 system by 19F NMR in melts from 0 to 100 mol% ThF4 at temperatures ranging from 600 to 1100 °C. We report also very first EXAFS spectra obtained in situ at high temperature, at the Thorium LIII edge, in LiF–ThF4 molten mixtures.