Development of the technology for pyroprocessing of minor actinide nitride fuel

Hayashi, Hirokazu ; Sato, Takumi  ; Tsubata, Yasuhiro   

Transmutation of long-lived radioactive nuclides including minor actinides (MA: Np, Am, Cm) is expected to be effective to reducing the burden of high level radioactive wastes and using repositories efficiently. 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 nitride fuel has been chosen as the first candidate fuel for MA transmutation using ADS in Japan Atomic Energy Agency (JAEA). To improve the transmutation ratio of MA, reprocessing of spent fuel and reusing MA recovered from the spent fuels is necessary. Our target is to transmute 99 % of MA arisen from commercial power reactor fuel cycle, with which the period until the radiotoxicity drops below that of natural uranium can be shorten from about 5000 years to about 300 years. Pyroprocessing has been proposed as the first candidate for reprocessing of the spent MA nitride fuel. This paper overviews the current status of development of the technology for pyroprocessing of MA nitride fuel. It contains studies on detailed behavior of the elements that are thought to exist in spent MA nitride fuels, including fission product elements and inert matrix elements such as zirconium (Zr) and titanium (Ti). Progress of the development aiming at an engineering-scale apparatus for pyroprocessing of nitride fuel is also introduced.