Electrochemical Investigation of Uranium and Corrosion Products in Chloride-Based Molten Salts

The first molten salt experiments were conducted in 1953 and continued until 1980.
Over the past decade, interest in molten salt reactor technology has reemerged and,
along with that, there have been numerous publications describing the use of
electrochemistry and spectroscopy to the determine diffusion coefficient (D) for analytes
like U(III)/U(IV), Cr(III/II), Ni(II/III)and Eu(III/II). From these studies, inconsistent values for D
have been reported. A primary source of discrepancy comes from the approach used to
calculate the surface area of the working electrode. Several different methods have
been described in literature, although none are widely accepted. While electrochemical
techniques depend on the electrode surface area, spectroelectrochemistry does not,
providing a reference point for comparison. There are also limited resources for
evaluating the heterogeneous electron transfer rate constant (k) for a quasi-reversible
system, which is typically the case in molten salts for the analytes mentioned above. In
this work, D and k for U(III)/U(IV), Cr(II/III), Ni(II/III) and Eu(II/III) were determined by a variety of
electrochemical and spectroelectrochemical techniques and compared with literature
values. The aim of this study was to investigate discrepancies in D and k, explore the
limitations of each technique used, and outline an accurate method to calculate these
fundamental parameters with a free-standing boron-doped diamond electrode.