An electrochemical process using a molten LiCl has been developed to reduce metal oxides from spent fuel (SF) from nuclear power plants, under the name of an electrolytic reduction process as a part of pyroprocessing. The researches on the electrolytic reduction have been investigated to determine the process conditions such as the shape of cathode, the form of feed material, and cell configuration. SF contains various kinds of oxides and chalcogen and halogen (group VIB and VIIB) compounds are expected to be dissolved into LiCl which is adopted as an electrolyte of the electrolytic reduction process. However, the behaviors of such compounds have not been experimentally clarified yet. In this work, the chemical and electrochemical behaviors of chalcogen and halogen compounds during the electrolytic reduction process were thermodynamically analyzed to understand their stability and final forms. LPP diagrams were used to determine the probable compounds on cathode and anode, respectively. Chemical and electrochemical calculations were carried out to find that it is required to suppress the reactions associated with chalcogens to protect anode and increase current efficiency. [GRAPHICS] .