Evaluating reducibility of strontium and barium-containing oxides by lithium metal in molten LiCl during oxide reduction of pyroprocessing

Oxide reduction (OR), the first electrochemical step in pyroprocessing of used nuclear fuel, converts oxide fuel constituents into metals in molten LiCl. During this process, many fission products, including Sr and Ba, transfer from the fuel matrix into the salt phase through chemical reactions and dissolution, with over 70% reported to dissolve. However, the specific chemical pathways remain unclear because the original chemical forms of these species (e.g., binary oxides, complex oxides, ABO x phases) and their interactions with Li or LiCl are not well identified. Some oxides may first be reduced by Li before reacting with LiCl, but this has not been systematically examined. This study investigates the reducibility of representative Sr- and Ba-containing oxides (SrO, SrZrO 3 , SrMoO 4 , BaO, BaZrO 3 , BaMoO 4 ) by Li metal at 650 °C to clarify their behavior during the initial stage of OR. Metal–salt reactions were also examined using pure Sr and Ba. Simple oxides and some complex oxides underwent partial reduction, whereas BaZrO 3 and BaMoO 4 were hardly reduced. Metallic Sr and Ba reacted with LiCl to form soluble chlorides, indicating that oxides with higher reducibility are more likely to convert to chlorides and partition into the salt during OR.