Spontaneous Reduction of Eu(III) in LiCl-KCl Melt: Spectroscopic and Rde Studies

Abstract

Pyrochemical process using molten salts has attracted much attention because of its potential to be applied to a future spent nuclear fuel management. In the pyrochemical process, electrochemical properties of lanthanide and actinide elements play a most important role in the recycling of the spent nuclear fuel. Therefore, it is important to know chemical and electrochemical behaviours of lanthanides and actinides in the molten salt for the successful developmentof the pyrochemical process. In this work, the spectro-electrochemical and rotating disk electrode (RDE) methods were employed to interrogate spontaneous reduction of Eu(III) ion, which is one of fission products, in LiCl-KCl eutectic at high temperature. By using the spectro-electrochemical system, the electrochemical potential of a working electrode can be controlled and, simultaneously, the evolution of the oxidation state of the Eu cation can be observed in the LiCl-KCl eutectic melt. RDE results can give information for electrochemical parameters such as diffusion coefficient, Tafel slope etc. as well as extent of the spontaneous reduction.Fig. 1 shows UV-Vis absorption spectrum (a) and RDE results (b) of Eu(III) in LiCl-KCl melt. In the UV-Vis absorption spectrum, Eu(III) exhibits two broad and intense bands at 257 nm and 321 nm which are assigned f-d transitions of Eu(II).In the RDE results, oxidation current is also observed over +0.6 V. These results confirm that Eu(III) is spontaneously reduced to Eu(II) in LiCl-KCl. In this work, we performed UV-Vis absorption and RDE measurements of the Eu cations in LiCl-KCl at various temperature and evaluate how much Eu(III) is spontaneously reduced. Fig. 1. UV-Vis absorption spectrum (a) and RDE results (b) of Eu(III) in LiCl-KCl melt. Figure 1