Electrochemical Fluorination of Uranium to UF6

Abstract

The development of efficient and environmentally benign methods to reprocess used nuclear fuel will be enabling technologies for the nuclear renaissance. The primary large scale method for processing used nuclear fuel is aqueous and generates large volumes of high level radioactive waste. The use of electrochemical and fluorination methods for reprocessing used nuclear fuel have been proposed and researched by various groups, but combinations of electrochemical and fluorination methods have not been investigated. Fluorinating agents are extremely potent oxidizers and may electrochemically fluorinate metallic used nuclear fuel with no input of electricity. A galvano-fluorination process has been developed at Savannah River National Laboratory. This electrochemical non-aqueous process enables efficient gas phase uranium recovery while allowing for control of the reaction. Thermodynamic modeling of the electrochemical fluorination process has shown UF6 to be the first gaseous fission product produced during fluorination. Further thermodynamic modeling was used to determine the feasibility of oxide reduction required for oxide fuel before electrochemical fluorination and for experiments. A chemical reactor system for electrochemical fluorination of U with NF3 in a fluoride molten salt was constructed along with vessels for product collection and analysis. This work has proven that an electrochemical reaction happens between U and NF3 which confirms the feasibility of electrochemical fluorination and the development of a processing scheme.