Electrochemical processing in molten salts – a nuclear perspective

Abstract

Nuclear power provides a sustainable, long-term energy source that is an important technology in efforts to curb greenhouse gas emissions. However, issues related to construction, safety, risk of proliferation, poor public perception and the perpetual issue of end-of-life waste management remain of serious concern. A large body of work has employed molten salt-based electrochemical techniques as practical and viable methods to reprocess spent nuclear fuel and nuclear materials, in addition to producing refractory metals of broader technological relevance. This review summarises the essential aspects of the design of electrochemical reactors for electroreduction, -winning and -refining technologies. Specifically, a critique of materials choice in relation to temperature is presented alongside the effects of different metal oxide feed precursors and molten salt selection. A thorough discourse is provided on each of the actinides (Am, Cm, Np, Pu, Th and U) and lanthanides (Eu) with an evaluation of the performance of several precursor cell types and designs. The type of feed precursor, metal oxide-to-salt ratio and oxide ion concentration are factors that must be considered with regards to current efficiency and are critical to the scaling of current laboratory technologies to pilot-scale. However, a challenge remains in this transition due to potential irradiation hazards of materials under a neutron flux. There is still a need to understand the mechanism by which different radioisotopes are formed and their interaction with metallic compounds in molten salts, yet data in this area is scarce and further work is needed.