Rare Earth Silicide Formation on Si Electrode in LiCl-KCl Melt to Establish a Novel Used Salt Treatment Process

Abstract

After repeating the electrorefining of spent nuclear fuels, rare earth, alkaline earth, and alkali fission products accumulate in the used LiCl-KCl melt. This paper proposes a novel used salt treatment process where dominant fission products, rare earths, are recovered electrochemically from the used melt in a form of their silicides and the silicides are then oxidized to be dissolved in a glass matrix as the waste form. The glass waste form stabilizing a higher concentration of fission products than the conventional waste form provides a reduction in volume of the waste form. The results of cyclic voltammetry using a Si electrode in LiCl-KCl melt containing a rare earth chloride (LaCl3, CeCl3, PrCl3, NdCl3, SmCl2, EuCl2, or GdCl3) at 723 K indicated the corresponding lanthanide silicide formation. The rare earth silicides formed by potentiostatic electrolysis were analyzed by XRD and SEM-EDX. The obtained results confirmed a feasibility of rare earths recovery as silicides from the used LiCl-KCl melt, which was a key step of the proposed used salt treatment process.