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Melting Temperature Variation and Electrochemical Study of Lanthanide Elements in LiCl-KCl Eutectic Molten Salt
Chemical and Materials Engineering
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The core objective of this project was to provide the supportive information for the pyrochemical reprocessing of spent nuclear fuels. The specific goals were to determine the thermodynamic and electrochemical data base of lanthanide elements in LiCl-KCl eutectic molten salts which is required for the better process control of pyrometallurgical reprocessing of spent fuels. In this thesis, two different scopes related to reprocessing of spent fuels were studied. The first study was to determine the melting temperature variation of LiCl-KCl eutectic mixture in presence of lanthanide elements and the second was study of the reduction behavior of lanthanide elements mixed with LiCl-KCl eutectic. The first study was performed by thermal analysis in order to determine the temperature variations of LiCl-KCl eutectic mixture in the presence of lanthanide elements. The result of single, as well as multi-component lanthanide elements below 5 mol% contain in LiCl-KCl eutectic mixture is presented. The results showed that the lanthanide elements below 5 mol% do not vary the melting temperature significantly. The mixture temperatures are well below the melting temperature of LiCl-KCl eutectic melting temperature. For the second case cyclic voltammetry studies were carried out to determine the changes occurring in reduction potentials when multi-components lanthanide elements are present in molten salt containing LiCl-KCl eutectic mixture. The result of mixtures containing binary, ternary and quaternary systems showed that the initiation of cathodic waves occur at lower cathodic potential than the standard redox potential of the component presents in the system. The cathodic wave potentials are shifted to less negative values, and in some cases closer to -1.7 V Ag/AgCl at 500 °C. This reduction potential is closer to the redox potential of Pu(III)/Pu system. These results indicate that presence of multiple fission products in the LiCl+KCl eutectic could affect the separation kinetics of the actinides.