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European Commission

Short description of the work
X-ray fluorescence (XRF), X-ray diffraction (XRD) and X-ray absorption spectroscopic (XAS) measurements have been performed on single and agglomerates of micrometer sized uranium particles at the MicroXAS beamline (PSI, Villigen, Switzerland) in order to determine the physio chemical properties.
Monodisperse microspheres were produced at Forschungszentrum Juelich GmbH by spray pyrolysis with sintering temperatures ranging from 400 °C to 593 °C using uranyl nitrate and uranyl acetate precursor solutions. These microspheres are intended to be used as (certified) reference materials with respect to the isotopic composition and uranium content. As the stability of these property values is of high importance, structural information about the microspheres is required. The different microspheres have been investigated to determine the optimal production route to obtain stable microspheres.
XRF measurements confirmed the presence of uranium and provided auxiliary assurance that the particles do not contain significant impurities. XRD measurements showed for all these microspheres an orthorhombic phase similar to U3O8 and XANES measurements confirmed the presence of U3O8. It can be derived that the microsphere production using an uranyl nitrate precursor solution and sintered at 500 °C yielded in results with consistent and desired quality, although an unexpected behavior compared to literature data for bulk materials was observed.

 

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.

 
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