Materials chemistry aspects in pyrochemical reprocessing

Full text: Metallic fuels will be introduced in the Indian commercial Fast Breeder Reactors (FBR) in the next decade. Molten salt electrorefining is the pyrochemical method ideally suited for reprocessing spent metallic fuels. Hence development of the molten salt electrorefining as well as the associated processes of metal fuel cycle is of interest. In this process, carried out at 773 K, spent metallic fuel of U-Pu-Zr alloy is used as the anode and the eutectic salt of LiCI-KCI is used as the electrolyte. There are two options for the cathode: either a solid rod or liquid cadmium. The process exploits the differences in the thermodynamic stabilities of the chlorides of fuel materials and fission products. In this process, the fuel materials, U and Pu from the spent metallic fuel are selectively transported to the liquid cadmium cathode and deposited. In the case of solid rod cathode, only U will be deposited. The difference in the deposition behaviour is attributed to the differences among the thermodynamic stabilities of the chlorides of fission products and fuel materials as well as the thermodynamic activities of U and Pu in the respective cathode. The separation factors for the lanthanides compared to the actinides are relatively lower in this process compare to the aqueous reprocessing method. However, the separation factors can be increased by using aluminium as the cathode wherein the thermodynamic stabilities of the intermetallic compounds of lanthanides and actinides with aluminum play an important role. Further, materials chemistry plays in important role in the selection of materials for the electrorefining vessel and the equipment for the associated processes such as consolidation, injection casting, directo oxide reduction etc. These materials chemistry aspects will be discussed in this paper