| 1. |
- Butorin, Sergei M., et al.
(författare)
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Chemical Reduction of Actinides Probed by Resonant Inelastic X-ray Scattering
- 2013
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 85:23, s. 11196-11200
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Tidskriftsartikel (refereegranskat)abstract
- The study addresses the possibilities of immobilizing the mobile species of actinides in the geosphere using metallic iron. Sorption on corroding iron is well-known, but there have been uncertainties with regard to the possibilities of reducing the actinyl species to sparingly soluble oxides and, thereby, permanently immobilizing them. Resonant inelastic X-ray scattering (RIXS) measurements at the actinide 5d edges on Fe foils exposed to uranium(VI) and neptunium(V) solutions in groundwater unambigiously indicate reduction of actinides to, respectively, uranium(IV) and neptunium(IV) on iron surfaces. The reduction manifests itself in an appearance of distinct specific signatures of uranium(IV) and neptunium(IV) in the RIXS profile of 5f-5f excitations. Such signatures and RIXS intensity/cross-section behavior with varying energy of incident photons can be reproduced by model atomic-multiplet calculations of the RIXS spectra. By normalizing the RIXS signal of corresponding 5f-5f excitations to core-to-core 6p-to-5d characteristic fluorescence transitions of actinides, their reduction rates on Fe samples with different exposure to actinide solutions can be estimated. Observed reduction implies similar processes in the nuclear waste canister thus suggesting reduced probability of nuclear waste release with ground waters from the canister.
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| 2. |
- Hollmark, Håkan, et al.
(författare)
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Exposure of Oxidized Copper Surfaces to Aqueous Na2S Solution Studied with Soft X-Ray Spectroscopy
- 2011
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 158:1, s. C1-C5
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Tidskriftsartikel (refereegranskat)abstract
- We present results from X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering (RIXS) of oxidized polycrystalline copper surfaces [Cu(I) and Cu(II), respectively] exposed to a 1.0 mM aqueous solution of Na2S (sodium sulfide) for several hours. Scanning electron microscopy reveals that the Cu oxide surfaces attain a much rougher texture upon sodium sulfide exposure, and that the exposed Cu(II) oxide sample exhibits areas with crystallites. The XAS spectra show that sodium sulfide effectively reduces Cu(II) oxide to Cu(I) compounds. The RIXS spectra of the exposed surfaces closely resemble those of the Cu2O reference sample with the notable exception of their Cu LIII,II-RIXS spectra. We conclude that copper evidently forms a Cu(I) compound with oxygen but with a Cu 3d-band of much reduced width, pointing to the possibility of a more complex compound containing both oxygen and sulfur.
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| 3. |
- Hollmark, Håkan, et al.
(författare)
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X-ray absorption spectroscopy on electrochemically oxidized Cu exposed to Na2S
- 2011
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Ingår i: Corrosion Science. - Amsterdam : Elsevier. - 0010-938X .- 1879-0496. ; 54, s. 85-89
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Tidskriftsartikel (refereegranskat)abstract
- Copper surfaces have been investigated by X-ray absorption spectroscopy after electrochemical oxidation and subsequent exposure to sulfide solution. Oxide surface layers on bulk copper surfaces were electrochemically grown in anaqueous NaOH solution at two different potentials and the resulting chemical composition was investigated using X-ray absorption spectroscopy. At both potentials the resulting surfaces consisted largely of Cu2O. At the more strongly oxidizing potential, an admixture of Cu2+-containing phases – mostly Cu(OH)2 – was detected. Sulfide exposure of both surfaces was found to completely reduce the surface from Cu2+ to Cu1+ and resulted in the formation of Cu2S with an admixture of Cu2O.
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| 4. |
- Modin, Anders, et al.
(författare)
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Indication of single-crystal PuO2 oxidation from O 1s x-ray absorption spectra
- 2011
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 83:7, s. 075113-
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of single-crystal PuO2 is studied using O 1s x-ray absorption (XA) and x-ray emission. Interpretation of the experimental data is supported by extensive first-principles calculations on the basis of the density functional theory + U approach. The measured XA spectra show a significant difference in intensity for the first two peaks between different spots or areas on the single crystal. Our theoretical simulations show that the first peak, at similar to 531 eV, can be attributed to O 2p-Pu 5f hybridization, while the second peak, at similar to 533.4 eV, is due to hybridization of O 2p with Pu d states. The reasons for the observed differences in the O 1s XA spectra are explored by calculating a number of defect structures PuO2+x as well as by simulating the existence of Pu(V) sites. Our results indicate the presence of oxidation states higher than Pu(IV) in some areas of the single crystal. The findings also suggest that plutonium oxide with a Pu fraction in an oxidation state higher than Pu(IV) consists of inequivalent Pu sites with (PuO2)-O-(IV) and (PuO2)-O-(V) rather than representing a system where the Pu oxidation state is constantly fluctuating between Pu(IV) and Pu(V).
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| 5. |
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| 6. |
- Werme, Lars, et al.
(författare)
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The Role of the Actinides in a Performance Assessment of a Nuclear Waste Repository. SKB's Supporting Actinide Research
- 2010
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Ingår i: MRS Proceedings. ; 1265, s. AA01-07-
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Tidskriftsartikel (refereegranskat)abstract
- After a few hundred years, the actinides will dominate the radiotoxicity of spent nuclear fuel. This does not necessarily mean that the actinides will dominate the dose to organisms at the surface above a geologic repository. Quite the contrary, in most performance assessments this dose is dominated by long-lived fission products, activation products and, in the very long perspective, actinide daughters.This makes the far-field migration properties of the actinides less interesting for further research. There are, however, other aspects of the presence of actinides in spent nuclear fuel and some of these and SKB's research in these fields is presented and discussed here.
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