Inherently safe reprocessing and N-15 high enrichment for nitride fuel development

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Nitride fuel has promising characteristics, such as high melting point, high thermal conductivity, high breeding ratio etc. However, the natural nitrogen cannot be used because the major isotope ^<14>N adsorbs neutrons, resulting in generation of radioactive ^<14>C. Another stable isotope ^<15>N, of which natural abundance is only 0.366%, is usable, but high enrichment above 99.5 %, preferably 99.9 % is necessary. The scope of the present research project initiated in 2004 has two targets; one is to develop the process for high enrichment of ^<15>N by ion exchange and the other is to develop inherently safe reprocessing which is appropriate for nitride fuels discharged from fast breeder reactors.Concerning ^<15>N enrichment, super high enrichment of 99.99% ^<14>N was attained at the first step. Then, enrichment of ^<15>N from natural level of 0.366 % was studied and 21.5 % ^<15>N was obtained. Based on these results, high enrichment of 99.91 % ^<15>N was successfully attained by ion exchange chromatography.For the development of inherently safe reprocessing, we obtained fundamental information on the innovative reprocessing system of ion exchange resin and HCI solutions. In the present work, our attention was directed to three major aspects, (1) recovery of platinum group elements, (2) recovery of technetium and (3) separation of minor actinides, americium and curium, from lanthanide elements. It was found that a set of tertiary pyridine resin and HC1 acid system has excellent property as total element separation system. Platinum group elements, Ru, Rh and Pd, and Tc are adsorbed at low HC1 solutions, and Tc is recovered with 6 M HC1 solution. At high concentration of HCl, americium and curium is adsorbed and separated from lanthanides.