(418b) Electrochemical Separation of Cs from Molten Salts Using Liquid Metal Electrodes

The feasibility of removing Cs from LiCl-KCl-CsCl (eutectic-3 mol%) using liquid Bi, Sn, and Pb electrodes was examined via thermodynamic properties measurements as well as electrochemical depositions. The accumulation of Cs¹³⁷ in the LiCl-KCl-UCl₃ electrorefiner electrolyte leads to frequent replacement and disposal as high level nuclear waste due to the high heat density and short half life of Cs¹³⁷. Unfortunately, in the chloride system Li and K are less noble than Cs, making Cs difficult to remove from a LiCl-KCl-based electrolyte. However, by leveraging the strong atomic interactions between Cs and liquid metals such as Bi, Sn, and Pb, we examine the possibility of selectively removing Cs from chloride-based molten salt, providing a pathway to reducing this particular source of nuclear waste. Electrochemical depositions on these liquid metal working electrodes were performed up to a depth of 100 C g^-1, resulting in co-deposition of Cs and Li up to (4 mol% Cs - 12 mol% Li) at 500 ^°C in Bi. Electrochemical deposition experiments were complimented by electromotive force measurements for the Cs-Bi system to elucidate the thermodynamic properties (namely, the activity of Cs in Bi) leading to the observed shift in expected deposition behavior due to the liquid metal electrode. This work suggests the possibility of using liquid metal electrodes to remove Cs from molten salts and present a potential path towards reducing the volume of nuclear waste generated from the electrorefining process.