Abstract
This paper examines the dynamics of the LiCl-KCl system over a range of temperatures in order to understand the local structure surrounding chlorine, which is the common ion in these systems, during molten salt pyro-processing. Chlorine-35 nuclear magnetic resonance (NMR) is sensitive to the local environments of the resonant nuclei and their motion on a diffusive timescale. Thus, it is a good probe of the atomic scale processes controlling the viscosities, diffusivities and conductivities of these molten salts. The average isotropic chemical shifts (((35)Cl)δ) and spin-lattice relaxation times (T1) of (35)Cl in (Li,K)Cl salt mixtures have been obtained over a compositional range of 0-100 mol% KCl with an interval of 10 mol% using high temperature nuclear magnetic resonance (NMR) spectroscopy from room temperature up to 890 °C. The ((35)Cl)δ in the two end member salts are consistent with the cation-anion radius ratio as previously measured on the solid halides and the average radius ratio of cation to anion, can be used to explain the variation of ((35)Cl)δ with composition. The quadrupolar interaction is found to be responsible for the spin-lattice relaxation of the (35)Cl, and the activation energies for T1 relaxation have been obtained for all compositions. The measured T1 ((35)Cl) activation energies do not vary linearly with composition and peak at 50% KCl, which also coincides with the Chemla point for this system. They also are in good agreement with the values from equivalent conductivity measurements. To investigate the response of the system to solutes, 8 wt% of CeCl3 was added to the pure LiCl as a surrogate actinide. The shift induced was 120 ppm and the activation energy for the T1 ((35)Cl) increased by a factor of four. This is a promising preliminary result for probing the effect of actinide dissolution on the dynamics of these pyro-processing salts.
Highlights
Molten (Li,K)Cl binary salts with eutectic composition (40.9 mol% KCl) are used as an electrolyte in pyrochemical processing to separate actinides from spent nuclear fuel
It is important to know the nature of the ionic species, and their interactions in the melt, in order to predict the physical and chemical properties of the melt precisely when there is a change of conditions, such as temperature, pressure or concentration. This enables the manipulation of the molten salt system with the goal of greater separation efficiency for the actinides
It has been shown that the 35Cl spin-lattice relaxation time (T1) is a result of the interaction between the electric quadrupole moment of 35Cl and the uctuating electric eld gradient caused by the rapid ionic exchange calculated by molecular dynamics simulation.[3]
Summary
Molten (Li,K)Cl binary salts with eutectic composition (40.9 mol% KCl) are used as an electrolyte in pyrochemical processing to separate actinides from spent nuclear fuel. The physical consequence of tuning activities is the occurrence of ion–ion interactions, such as the formation of ionic pairs or associates, which decrease the melt conductivity.[3,4,5] it is important to know the nature of the ionic species, and their interactions in the melt, in order to predict the physical and chemical properties of the melt precisely when there is a change of conditions, such as temperature, pressure or concentration This enables the manipulation of the molten salt system with the goal of greater separation efficiency for the actinides
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call