Recent progress on development of the pyrochemical process of spent nitride fuels for MA transmutation

Hayashi, Hirokazu ; Sato, Takumi  

Transmutation of long-lived radioactive nuclides including minor actinides (MA: Np, Am, Cm) has been studied in Japan Atomic Energy Agency (JAEA). Pb-Bi cooled sub-critical accelerator-driven system (ADS) is regarded as one of the powerful tools for transmutation of MA under the double strata fuel cycle concept. Uranium-free MA-Pu nitride fuel was chosen as the first candidate for MA transmutation. Reprocessing of spent ADS fuel and reusing MA recovered from the spent ADS fuels is necessary to improve the transmutation ratio. A pyrochemical process has been proposed as the first candidate for reprocessing of the spent nitride fuel for MA transmutation. Main process of the proposed pyrochemical treatment of nitride fuels consists of molten salt electrorefining and renitridation of actinide elements recovered in Cd cathode. Recently, we have proposed an innovative anode concept to improve anodic dissolution rate on the electrorefining process; a large electro-conductive crucible is used as an anode crucible. Applicability of this concept has been verified by confirming high anodic current on the experiments using surrogate materials such as DyN pellets. As for renitridation process, an apparatus with 100g-Cd scale cold tests has been designed and manufactured. Suitable conditions of the renitridation process (via nitridation-distillation method) with the scale-up apparatus are being studied using surrogate materials such as Dy-Cd alloy.