STUDIES ON THE SEPARATION OF MINOR ACTINIDES FROM HIGH-LEVEL WASTES BY EXTRACTION CHROMATOGRAPHY USING NOVEL SILICA-BASED EXTRACTION RESINS

To develop an advanced partitioning process by ex-traction chromatography using a minimal organic sol-vent and compact equipment to separate minor actinides such as Am and Cm from nitrate acidic high-level waste (HLW) solution, several novel silica-based extraction resins have been prepared by impregnating organic extractants into the styrene-divinylbenzene copolymer, which is immobilized in porous silica particles (SiO2-P). The extractants include octyl(phenyl)-N, N-diisobutyl-carbamoylmethylphosphine oxide (CMPO), di(2-ethylhexyl)phosphoric acid (HDEHP), and bis(2,4,4-trimethylpentyl)dithiophosphinic acid (Cyanex 301). Compared to conventional polymer-matrix resins, these new types of extraction resin are characterized by rapid kinetics and significantly low pressure loss in a packed column. The results of separation experiments revealed that trivalent actinides and lanthanides can be separated from other fission products, such as Cs, Sr, and Ru in simu-lated HLW solution containing concentrated nitric acid by extraction chromatography using a CMPO/SiO2-P resin-packed column. Satisfactory separation between Am(III) and a macro amount of lanthanides from simu-lated HLW solution with pH 4 was achieved by using a newly purified Cyanex 301/SiO2-P resin. However, the Am(III) separation was very sensitive to the purity of Cyanex 301, and the improvement of its stability is an important task for practical utilization