Study on exchange current density of La, Ce, and U in high temperature LiCl-KCl molten salt

Abstract

Pyroprocessing is the future key technology to recycle spent nuclear fuel in the Republic of Korea. Because of its economics, non-proliferation, and the reduction of high-level nuclear waste, a number of scientists have paid their interests in the development of pyroprocessing and many researches have being still studied. Especially, they have been focusing on the simulation of the electrorefining and electrowinning processes, which enable to separate uranium and transuranium elements (TRU) from other elements in spent nuclear fuel with electrochemical process, for their optimization with high efficiency.

The exchange current density is one of the important parameters in Butler-Volmer equation, which is mainly used to simulate and evaluate the electrorefining process. When a redox potential is applied to the system, the amount of the reduction is proportional to the exchange current density so that the exact value of exchange current density is required to make the simulation of electrochemical processes more accurate. However, a few researches were merely performed to study the exchange current density of lanthanides and actinides, and even the performed researches have shown quite different results from each other.

In this study, the exchange current densities of lanthanum (La), cerium (Ce), and uranium (U) in high temperature LiCl-KCl molten salt were obtained and compared by two different electrochemical methods. For the measurements, the Tafel plot and the linear polarization were employed and the cyclic voltammograms were measured to obtain the equilibrium potentials for La, Ce, and U. At the equilibrium potential, the experimental dynamic range for the Tafel plot and the linear polarization was determined. Using the Tafel plot, the charge transfer coefficient, which makes it possible to understand the electrochemical reaction of metal ions in the LiCl-KCl molten eutectic system more reliable and accurate, was calculated as well.

As a result, the ...