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Selected soft N-donor ligands are highly effective extractants for the separation of trivalent actinides (An(III)) from lanthanides (Ln(III)) in the partitioning and transmutation (P&T) strategy. Comparative structural investigations using X-ray absorption spectroscopy (EXAFS) on An(III) and Ln(III) complexed with tris[(2-pyrazinyl)methyl]amine (TPZA) and 2,6-di(5,6-dipropyl-1,2,4triazin-3-yl)pyridine (BTP) are performed in order to evaluate if ligand extraction performance is reflected in coordination structure differences, specifically in variations in the metal cationeN bond lengths. We observe U(III) to generally exhibit a decrease in the bond distance over that expected for pure ionic binding for the ligand complexes investigated and interpret this as higher covalent character of the U(III)eN binding. In contrast, no measurable differences for Am(III), Cm(III), and the Ln(III) elements in the middle of the 4f series are observed. Time-resolved laser fluorescence spectroscopy (TRLFS) investigations on solution BTP complexed with Cm(III) and Eu(III) reveal that the selective extraction behavior of this ligand can be explained by the large difference in conditional stability constants of their 1:3 complexes (K 13 ). The K 13 value for CmeBTP 3 is a number of orders of magnitude larger than that for EueBTP 3 .

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The immobilization of technetium dissolved in salt brines, which are in contact with simulated spent fuel and HAW glass packages, has been studied under aerobic conditions at room temperature. The retention effect of spent fuel packages has been investigated by adding U0 2 , hull (zircaloy-4) and container material (iron) in appropriate ratios to NaCl-and MgCl 2 -rich salt brines containing an initial TcOi concentration of 10" 5 mol/L. The time dependence of the Tc concentration, pH and Eh has been measured simultaneously. Analoguous investigations have been carried out with borosilicate HAW glass. According to this scenario, container material (stainless steel) has been added to the salt solutions. In the system simulating the disposal of spent fuel, the Tc concentration decreases to less than 10~8 mol/L within 50 days, while in the system simulating the disposal of vitrified HAW, the immobilization of Tc is less efficient. In the latter case, even after 500 days there are still about 50-80% of the initial Tc dissolved. In both systems the addition of sulfide has a positive influence on the immobilization of Tc. The results are discussed in terms of reduction of Tc(VII) to sparingly soluble Tc(IV) hydrous oxide, sorption of technetium and precipitation of Tc 2 S 7 .

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