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Conference Article: Research and development on the partitioning process at JAERI

Morita, Y.; Yamaguchi, I.; Kondo, Y.; Shirahashi, K.; Yamagishi, I.; Fujiwara, T.; Kubota, M. (Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment)

Abstract

A wet partitioning process has been developed in Japan Atomic Energy Research Institute (JAERI) for separating elements in high-level waste (HLW) into four groups. Transuranium elements (TRU), Tc-platinum group metals (PGM), SR-Cs and the other elements. Extraction with diisodecylphosphoric acid (DIDPA) was studied for the separation of TRU from HLW. Trivalent actinides, Am and Cm, can be extracted with DIDPA from the solution of around 0.5 M nitric acid. In addition, Np that is initially in the pentavalent state can be extracted. Experiments on counter-current continuous extraction of Np from a simulated HLW showed that more than 99.96% of Np was recovered with 14-stages extraction and with the addition of hydrogen peroxide. Since the Np extracted in the presence of hydrogen peroxide is in the tetravalent state, it is easily stripped with oxalic acid. Selective stripping of Am and Cm from DIDPA with diethylenetriaminepentaacetic acid (DTPA) is being studied for their separation from rare earths (RE). Batch experiments showed that the separation factor between Am and RE (ratio of distribution ratios) was more than 10. Continuous experiments are now in progress to find the optimum process condition. Theses results offer a promising prospect of separating TRU by the DIDPA extraction process that consists of the four steps. Simultaneous extraction of TRU with DIDPA, first stripping of Am and Cm with DTPA, second stripping of RE with 4 M nitric acid and third stripping of Np and Pu with oxalic acid. For the separation of Tc-PGM, two methods are studied. One is adsorption with an active carbon and the other is precipitation with reducing the acidity by denitration. The pretreatment of HLW for the DIDPA extraction is also being studied.

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key words: Fast Neutron Spectrum Systems, Nuclear Technology
Reference:
Safety and environmental aspects of partitioning and transmutation of actinides and fission products. Proceedings of a technical committee meeting, Vienna, 29 November - 2 December 1993
International Atomic Energy Agency, Vienna (Austria)
IAEA-TECDOC--783, pp:93-104