Nitride formation behavior of actinides recovered into liquid Cd cathode by electrorefining

Nitride fuel is a candidate fuel of the accelerator driven system for minor actinides transmutation and the advanced fast reactors. In regard to the reprocessing technology, pyrochemical process has several advantages over conventional wet process for treating spent nitride fuel. Nitride formation behavior of plutonium and uranium recovered into liquid cadmium by molten salt electrorefining was experimentally investigated in this study. Heating the cadmium alloy containing plutonium and uranium at 973 K under nitrogen gas stream resulted in almost completion of nitridation of actinides and distillation of cadmium simultaneously. Further, small amounts of rare earth elements contained in the cadmium alloy were also converted to nitride as a solid solution of mononitride. On the other hand, nitride formation of plutonium in liquid cadmium phase by passing nitrogen gas at 773 K did not proceed owing to high thermodynamic stability of plutonium in liquid cadmium phase. It was demonstrated that the nitridation-distillation combined method is applicable to nitride formation of actinides recovered into liquid cadmium cathode in pyrochemical reprocessing of nitride fuel cycle. (author)