Separation of strontium from simulated oxide fuel using molten chloride salts

Abstract

The increased use of nuclear energy has led to a greater amount of used nuclear fuel, requiring an expansion of geological final disposal areas. The reduction of the disposal area can be achieved through the extraction of high heat-generating radioactive isotopes such as Sr-90 from used nuclear fuel. The chemical reaction of Sr with molten chloride salts is a promising technique to achieve separation. In this study, the separation of Sr from a simulated oxide fuel is investigated using various molten chloride salts, namely LiCl-CaCl2, MgCl2, LiCl-KCl-MgCl2, LiCl, and NaCl-MgCl2. As per the results, the highest separation efficiency is achieved with the LiCl-CaCl2 salt, which reacted with 97% of the Sr in the fuel, resulting in its dissolution. The second best separation is observed for MgCl2. Conversely, the Sr separation efficiencies from LiCl, NaCl-MgCl2, and LiCl-KCl-MgCl2 are found to be relatively much lower. Furthermore, to determine the Sr separation efficiency, the reactivity of SrO with the salts is studied. The high separation efficiency of Sr in the CaCl2 salt is due to the active reaction of SrO, which led to the formation of Sr4OCl6 and Ca0.46Sr0.54Cl2 and their dissolution in the salt. The reaction of SrO with MgCl2 produces SrCl2 and Sr4OCl6 in the salt. In contrast, NaCl and KCl do not react with the SrO. Therefore, the eutectic salts containing unreactive salts (NaCl-MgCl2, and LiCl-KCl-MgCl2) exhibit less reactivity with SrO.