Factors Influencing the Direct Electrochemical Reduction of UO2 Pellets to Uranium Metal in CaCl2-48 mol% NaCl Melt

The electrochemical conversion of solid oxide preforms to metal by molten salt electrolysis is influenced by many parameters like duration of electrolysis, temperature, applied voltage, open porosity of the preform and mode of electrolysis. The effect of these parameters on the electro-reduction of UO2 pellets in CaCl2-48 mol% NaCl melt was studied in the temperature range 923-1173 K with graphite rod as the counter electrode. U metal formation started at the surface of the dense UO2 pellets (95% TD) and it extended towards the bulk with time. Enhanced electrochemical activity was observed during the initial phase of electrolysis with porous UO2 pellets (52% TD). The rate of deoxidation increased with increase in the electrolysis temperature from 923 K to 1023 K, but decreased on further increase to 1173 K, due to sintering of U particles on the surface of the pellet. The thickness of U metal layer increased with increase in the applied voltage from 3.1 to 3.3 V whereas no reduction of the oxide occurred at 2.8 V. The behavior of the graphite anode, in relation to the electro-reduction of the UO2 pellets under different experimental conditions, was studied by determining the mass loss of the electrode and discussed.