An Application of the Photochemistry of Uranyl Ion to Nuclear Fuel Reprocessing

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Photochemical reactions of uranyl ion (UO_2^<2+>) in nitric acid have been investigated from a point of applications to a spent nuclear fuel reprocessing.Quantum yields of fluorescence from excited uranyl ion in nitric acid were determined by comparing with the photoemission of quinine in sulfuric acid taken as a refernce. It was found that the yields is an order of 10^<-3> and concentration dependence of nitric acid was measured. The emission is strongly affected by the presence of additives and quenching parameters for some additives were determined. The evaluated values were consistent with reported. Further, a simple method is proposed to evaluate the absolute concentration of uranyl ion from the quenching measurements in the presence of quenchers as impuruties.Quantum yield of photoreduction of uranyl ion to uranous ion (U^<4+>) by ethanol in nitric acid was determined. On the basis of the concentration dependence of nitric acid and ethanol, and effects of oxygen, and concomitant ions of [H^+] and [NO^<3->], mechanism of the photochemical reactions was derived. Finally, it is concluded that photoreduction of uranyl ion by ethanol could be used for developing new techniques of the nuclear fuel reprocessing.