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European Commission

Short description of the work
Radiation stability of extractants (CyMe4-BTBP and CyMe4-BTPhen) and the influence of solvent irradiation on its extraction properties are an important factors for use in a processes, such as European SANEX and/or Ganex proces.
The solutions of CyMe4-BTBP or CyMe4-BTPhen ligands were dissolved in various alkylated cyclohexanone derivatives or FS-13 (phenyl trifluoromethyl sulfone) and were irradiated by gamma source with the dose from 20 kGy to 1000 kGy to study the radiation stability of CyMe4-BTBP and CyMe4-BTPhen in various diluents. The selected cyclohexanone-based diluents were cyclohexanone, 3 methylcyclohexanone and 2,6-dimethylcyclohexanone. Some of the samples were irradiated also in the presence of the nitric acid solutions.
The irradiated samples were transported to CTU in Prague and the extraction properties of the irradiated solvents were compared with the extraction properties of non-irradiated solvents to estimate the influence of the degradation products in the organic phase.
The irradiated samples are still analysed for the degree of extractant degradation.

 

Short description of the work

In the framework of the proposed study, batch incubations of depleted uranium (DU) corrosion product with five different soils were performed with artificial rain events during several weeks. The resulting DU-contaminated soils were collected in function of depth and characterized for mineralogy and chemistry. The goal of the bulk and micro-XAS and micro-XRD experiments conducted at SLS was: (1) identify the bulk DU speciation in various soils that were in contact with DU corrosion product; (2) characterize mineralogical changes in the corrosion products at the microscale under various geochemical conditions.
The results obtained for bulk XANES indicate that U(VI) is the dominant oxidation state in the soils. Additionally, micro-XANES data show that U(VI) is distributed diffusely in the soils while there are mixed U(IV)-U(VI) hotspots in both StSul soil (agricultural soil) and Ins soil (organic-rich low pH). Moreover, U-Ca correlation seems observable at the U hotpsots of the Ins soil, while U and Fe seem not correlated.

 

Short description of the work

The structures of Tc and Np complexes generated during a reaction between Tc species at selected oxidation states and Np(III and VI) ions have been studied by EXAFS. 9 samples containing a mixture of Tc and Np compounds and a reference sample containing initially Tc(IV) in the presence of nitric acid were prepared at HZDR in Dresden. The Tc K-edge EXAFS spectra were recorded for all solutions using a fluorescence detector. The energy scales for XANES scans for Tc and Np were calibrated with Mo (Mo K-edge at 20000 eV) and Y (Y K-edge at 17038 eV) metals foils, respectively.
The results of the experiments show that in strongly acidic media the pertechnetates are reduced by Np(III) to technetium(III/IV or IV) species while Np(III) ions are transformed not only to Np(IV) but also to Np(VI). Neptunyl(VI) ions are probably generated by a disproportionation of Np(V) ions, the latter species are unstable products of Tc(VII)-Np(III) interaction. In the presence of nitric acid technetium(III/IV or IV) species are completely oxidized to pertechnetates while neptunium is transformed to species with valence states of +4 and +6. An analysis of the oxidation states of neptunium showed that the concentration ratio of Np(VI)/Np(IV) generated during Tc(VII)-Np(III) interaction increases from 0.08 for 0.7M HNO3 to 0.18 for 3M HNO3.
An analysis of the samples containing various concentration of technetium and fixed concentration of neptunium in acidic media confirmed multistep pathway of Tc(red)-Np(ox) interaction. These observations point out to a significant role of Tc(V) and Np(V) in redox chemistry of both elements.

 

Short description of the work

The overall goal of the proposed study is to unravel the effects of solute and surface speciation of redox sensitive radionuclide and of the nature of Fe associated to clay minerals on the RN reduction kinetics and efficiency. Structural iron affects the physicochemical properties of clay minerals and, depending on its redox state, may oxidize or reduce radionuclides at their surface thus altering their mobility and/or (bio) availability. The study focuses on a natural montmorillonite (SWa), but also on a nontronite (a Fe rich smectite) interacting with two different radionuclides: Tc and the actinide U. By performing Tc(VII)/U(VI) and Tc(IV) adsorption/reduction experiment on clay samples with increasing levels of reduction, and by combining Tc/U EXAFS analysis and 57Fe Mössbauer analysis to wet chemical analyses (especially Tc/U retention and solid Fe speciation), it is possible to discriminate the contributions of the different mechanisms leading to the overall Tc(VII)/U(VI) adsorption and reduction kinetics. Tc experiments will be a good test to judge if predictive adsorption/reduction model could be established based on the changes of the clay surface properties as a function of pH and redox while U experiments will help to understand the effects of surface and solute speciation changes on redox interactions.

 

Short description of the work

Using the TALISMAN pooled facilities at KIT-INE, we were able to study the extraction capabilities and coordination chemistry of a family of newly designed ligands based on DTPA and EDTA appended with amino acids using nuclear magnetic resonance (NMR) and time resolved laser induced fluorescence spectroscopy (TRLIFS) spectroscopies. The precursors are readily available and affordable, allowing effective separation of trivalent lanthanides and actinides in the reprocessing of spent nuclear fuel. The process we have developed is a simplified approach to lanthanide/actinide separations based on a modified TALSPEAK process. In our hands, the polyaminocarboxylates DTPA and EDTA are appended with a series of amino acids that act to self-buffer the solution and lower the pH of the extraction processes to that of the pKa of the amino acids themselves (ca. 1.5). Our preliminary results show that the ligands show high selectivity for An(III) over Ln(III) with separation factors over 100, importantly without the need for an additional buffer agents or modifiers. The pooled facilities enabled us to examine the separation behavior of four ligands containing representative amino acids; DTPA-bis-alanine, DTPA-bis-histidine, EDTA-bis-alanine and EDTA-bis-histidine. In addition to the extraction experiments over the pH range 1-3 with all ligands and americium(III) and lanthanide(III), we were able to study the coordination environment of all ligands with americium(III) by NMR spectroscopy and that of the curium(III) derivatives by TRLIFS. Both these spectroscopic techniques showed that all the ligands possess fast complexation kinetics and verified the 1:1 binding motif of the chelates in solution, additionally giving information on the relative stabilities of the curium(III) complexes.

 
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