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Database on the extraction of zirconium and technetium, present separately and simultaneously, into 30% TBP is presented. With increasing temperature, the distribution ratio of Zr without Tc increases, and that of Tc without Zr decreases; however, because of the coextraction, the temperature dependence of the distribution ratios of these elements, present simultaneously, is leveled off. In the presence of uranyl nitrate, the effect of Tc on the extraction of Zr is preserved, whereas the effect of Zr on the extraction of Tc decreases to fully disappear in the case of the solvent saturation with uranyl nitrate. The interactions in the system are described within the framework of a new approach to modeling using five additional chemical equations. Their apparent equilibrium constants and coefficients of the temperature dependence are determined. The temperature coefficients are determined for the constants of six previously introduced equations of the extraction of zirconium and technetium, including the extraction in the presence of uranyl nitrate.

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The careful control of actinide distribution between 30% tributylphosphate (TBP) in organic diluent and nitric acid is vital to the successful operation of nuclear fuel reprocessing plants. Uranium (VI) and tetravalent actinides are extracted into the organic phase as the nitrate complexes UO 2 (NO 3 ) 2 (TBP) 2 and An(NO 3 ) 4 (TBP) 2 respectively. The presence of dibutylphosphate (HDBP), a tributylphosphate decomposition product, affects this distribution due to the formation of strong, organic soluble, complexes between the phosphate and the actinide ions. This paper describes the investigation of U(VI), U(IV), Np(IV) and Pu(IV) complexation with HDBP in 30% TBP/organic diluent solutions. The distribution of U(VI) between nitric acid and 30% TBP/organic diluent solutions containing HDBP and subsequent analysis of the organic phases by 31 P nuclear magnetic resonance spectroscopy, absorption spectroscopy and extended X-ray absorption spectroscopy indicates that U(VI) can form a range of complexes with HDBP. At comparatively high HNO 3 loading in the organic phase, HDBP can displace TBP groups to form either UO 2 (NO 3 ) 2 (HDBP)(TBP) or UO 2 (NO 3 ) 2 (HDBP) 2 . At lower HNO 3 loadings HDBP can also deprotonate and act as a chelate ligand displacing nitrates to form either UO 2 (DBP) 2 -

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