| 1. |
- André, Magnus, et al.
(författare)
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Determining sorption coefficients in intact rock using an electrical potential gradient as a driving force for migration
- 2006
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Ingår i: Scientific Basis for Nuclear Waste Management XXIX. - WARRENDALE, PA : MATERIALS RESEARCH SOCIETY. - 1558998896 ; , s. 975-982
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Konferensbidrag (refereegranskat)abstract
- The transport of radionuclides in indigenous rock is greatly affected by the sorption of cations in the porous rock matrix. For the determination of sorption coefficients, batch experiments have traditionally been used. For these experiments, the rock sample is crushed into fine particles to reduce the experimental time. However, this procedure increases the specific surface area of the sample and the new surfaces created could have different sorption qualities than the naturally occurring surfaces, which may impair the results of sorption coefficient determinations. A new method for determining sorption coefficients in intact rock is being developed, using electromigration as a means to speed up the transport process, thereby allowing for faster equilibration between the rock sample and the tracer solution. Here, we report results from preliminary experiments, using cesium as a sorbing tracer, showing a consistent difference between sorption coefficients obtained using electromigration methods on intact rock samples and traditional batch experiments on crushed samples.
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| 2. |
- Cera, E., et al.
(författare)
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Modelling experimental results on radiolytic processes at the spent fuel water interface. II. Radionuclides release
- 2006
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Ingår i: Mater Res Soc Symp Proc. - : Springer Science and Business Media LLC. - 1558998896 - 9781558998896 ; , s. 537-546
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Konferensbidrag (refereegranskat)abstract
- Experimental and modelling efforts in the last decade in the frame of nuclear waste management field have been focused on studying the role of the UO2 surfaces in poising the redox state of solid/water systems as well as the radionuclides release behaviour. For this purpose, an experimental programme was developed consisting on dissolution experiments with PWR spent fuel fragments in an anoxic environment and by using different solution compositions. Some of the collected data has been previously published [1], specifically those data concerning radiolysis products and dissolution of the matrix. The results and the modelling tasks indicated an overall balance of the generated radiolytic species and that uranium dissolution was controlled by the oxidation of the spent fuel matrix in 10mM bicarbonate solutions while in the tests carried out at lower or without carbonate concentrations uranium in the aqueous phase was governed by the precipitation of schoepite. This paper is the continuation of a series accounting for the data and modelling work related to investigating the release behaviour of minor radionuclides from the spent fuel. Uranium concentrations as a function of time showed an initial increase until reaching a steady stale, indicating a matrix dissolution control. The same behaviour is observed for neptunium, caesium, strontium, technetium and molybdenum indicating a congruent release of these elements with the major component of the fuel matrix. On the other hand, no clear tendency is observed for plutonium data where additional solubility limiting mechanisms may apply. Kinetic modelling of the trace elements: caesium, strontium, technetium and molybdenum is based on the congruent release of these elements with the major component of the fuel matrix. Rate constants have been determined. Kinetic modelling of neptunium data took also into account the. subsequent precipitation as Np(IV) hydroxide. Finally, measured Pu concentrations may be explained by the precipitation of Pu(IV) and/or Pu(III) solid phases.
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| 3. |
- Crawford, James, et al.
(författare)
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Epistemic and aleatory uncertainty in recommended, generic rock K-d values used in performance assessment studies
- 2006
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Ingår i: Scientific Basis for Nuclear Waste Management XXIX. - WARRENDALE, PA : MATERIALS RESEARCH SOCIETY. - 1558998896 ; , s. 251-258
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Konferensbidrag (refereegranskat)abstract
- Over the past decade or so there has been an explosion in the number of sorption modelling approaches and applications of sorption modelling for understanding and predicting solute transport in natural systems. The most widely used and simplest of all models, however, is that employing a constant distribution coefficient (K-d) relating the sorbed concentration of a solute on a mineral surface and its aqueous concentration. There are a number of reasons why a constant partitioning coefficient is attractive to environmental modellers for predicting radionuclide retardation, and in spite of all the shortcomings and pitfalls associated with such an approach, it remains the leitmotif of most performance assessment transport modelling. This paper examines the scientific basis underpinning the K-d-approach and its broad defensibility in a performance assessment framework. It also examines sources of epistemic and aleatory uncertainty that undermine confidence in K-d-values reported in the open literature. The paper focuses particularly upon the use of so-called "generic" data for generalised rock types that may not necessarily capture the full material property characteristics of site-specific materials. From the examination of recent literature data, it appears that there are still a number of outstanding issues concerning interpretation of experimental laboratory data that need to be considered in greater detail before concluding that the recommended values used in performance assessments are indeed conservative.
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| 4. |
- Gorbatov, O. I., et al.
(författare)
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Effect of magnetism on precipitation of Cu in bcc Fe : Ab-initio based modeling
- 2009
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Ingår i: Scientific basis for nuclear waste management XXXIII. - : Materials Research Society. - 9781605111667 ; , s. 469-476
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Konferensbidrag (refereegranskat)abstract
- Theoretical modeling of the decomposition in bcc Fe-Cu alloys has been performed using a combined approach which includes ab-initio calculations of the effective cluster interactions and statistical-mechanical (Monte Carlo) simulations. We showed that the effective Cu-Cu and Cu-vacancy interactions in the bcc Fe matrix have a strong dependence on the global magnetic state of iron. As a result, all the related thermodynamic properties of the alloys (such as solubility limit and diffusivity) are expected to have a pronounced non-Arrhenius temperature behavior, originated from variation of the global magnetization with temperature. We find that strong Cu-vacancy interactions in the bcc Fe matrix lead to a remarkable effect of vacancies on the Cu precipitation and significantly modify the alloy decomposition kinetics under irradiation.
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| 5. |
- Kapilashrami, Mukes, et al.
(författare)
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On the defect induced ferromagnetic ordering above room-temperature in undoped and Mn doped ZnO thin films
- 2009
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Ingår i: NOVEL MATERIALS AND DEVICES FOR SPINTRONICS. - Warrendale, PA : MATERIALS RESEARCH SOCIETY. ; , s. 3-8
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Konferensbidrag (refereegranskat)abstract
- Evidence for long range ferromagnetic order above room-temperature, RTFM, in pristine ZnO, In2O3, TiO2 nanoparticles and thin films, containing no nominal magnetic elements have been reported recently. This could question the origin of RTFM in doped dilute alloys if for example the ZnO matrix itself develops a defect induced magnetic order with a significant moment per unit cell. In this presentation we report a systematic study of the film thickness dependence of RTFM in pure ZnO deposited by DC Magnetron Sputtering. We observe a maximum in the saturation magnetization, Ms, value of 0.62 emu/g (0,018 ÎŒB/unit cell), for a -480 nm film deposited in an oxygen ambience of appropriate pressure. Above a thickness of around 1 ÎŒm the films are diamagnetic as expected. We thus see a sequential transition from ferromagnetism to para- and eventual diamagnetism as a function of film thickness in ZnO. We also find that in such a ZnO matrix with a maximum intrinsic defect induced moment, on doping with Mn the maximum enhanced Ms value of 0.78 emu/g is obtained for 1 at. % Mn doping. With this approach of appropriate doping in a defect tailored matrix, we routinely obtain RTFM in both undoped and Mn- doped ZnO thin films.
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| 6. |
- Lee, Sang Hwui, et al.
(författare)
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Fine keyed alignment and bonding for wafer-level 3D ICs
- 2006
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Ingår i: MATERIALS RESEARCH SOCIETY SYMPOSIUM PROCEEDINGS. - WARRENDALE, PA : MATERIALS RESEARCH SOCIETY. ; , s. 433-438
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Konferensbidrag (refereegranskat)abstract
- Precise wafer-to-wafer alignment accuracy is crucial to interconnecting circuits on different wafers in three dimensional integrated circuits. We discuss the use of fabricated structures on wafer surfaces to mechanically achieve higher alignment accuracy than can be achieved with our existing (baseline) alignment protocol. The keyed alignment structures rely on structures with tapered side-walls that can slide into each after two wafers are "pre-aligned" using our baseline alignment protocol. Results indicate that alignment accuracy is about a quarter micron, well below the one micron alignment accuracy obtained in our baseline alignment procedure using commercial state-of-the-art wafer alignment equipment. In addition to improving alignment, the alignment structures also hinder undesirable bonding-induced misalignment. The keyed alignment structures are also promising for nano-imprint lithography.
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| 7. |
- Li, F., et al.
(författare)
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Colloidal crystal wires from directed assembly
- 2005
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Ingår i: Micro- and Nanosystems-Materials and Devices. - : Materials Research Society. - 1558998268 ; , s. 477-482
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Konferensbidrag (refereegranskat)abstract
- Colloidal crystal wires with tubular-like packings are prepared by the directed assembly of spheres into cylindrical one-dimensional channels. Silica spheres are infiltrated into porous silicon membranes, treated with silane, and annealed. Single annealing cycles are found to result in colloidal crystal wires with varied packing geometries, while repeated annealing produces a thin translucent silica sheath around the wires. Packing in the wires varies with the relative channel diameter of the silicon membrane where typical wires contain 4 to 7 helical strands. Both chiral and achiral packing geometries are observed. The fabrication of these wires is discussed and the relationship between channel size and packing structure detailed.
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| 8. |
- Li, Shanghua, et al.
(författare)
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Fabrication of transparent polymer-inorganic hybrid material
- 2005
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Ingår i: Materials Research Society Symposium Proceedings. - : Springer Science and Business Media LLC. - 9781558998308 ; , s. 190-194
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Konferensbidrag (refereegranskat)abstract
- Polymer-inorganic hybrid materials composed of polymethyl methacrylate (PMMA) and zinc compounds were prepared by sol-gel in-situ transition polymerization of zinc complex in PMMA matrix. Zinc acetate dihydrate dissolved in ethanol was used as the inorganic precursor. Monoethanolamine (MEA) acted as a complexing agent to control the hydrolysis of zinc acetate to produce a zinc compound network, and then PMMA, formed in-situ through a radical polymerization, were chemically bonded to the forming zinc compound network to realize a hybrid material. Transparent homogenous hybrid materials with slight colours from pink to yellow were fabricated by varying the composition. TEM, FT-IR were employed to investigate structural and physical properties. The UV-shielding effect was evaluated by UV-VIS. The low content of zinc (around 0.02 wt%) and the fine particle size rendered it visibly transparent and capable of greatly attenuating UV radiation in the full UV range.
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| 9. |
- Moeck, P., et al.
(författare)
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Structural effects of transition metal oxide calcinations on wurtzite type semiconductors that are ferromagnetic at room temperature
- 2007
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Ingår i: Novel semiconductor materials for room-temperature ferromagnetism. - : Materials Research Society. - 9781605604336 ; , s. 31-36
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Konferensbidrag (refereegranskat)abstract
- Gallium nitride powders and zinc oxide powders were each calcined with a few weight percent of copper oxide and/or magnesium oxide either in air or N2. Powder X-ray diffractometry, transmission electron microscopy, energy dispersive X-ray spectroscopy, and electron energy loss spectroscopy were performed in order to observe calcination induced structural effects on these wurtzite type semiconductors. We note that our earlier magnetic results on Cu doped GaN are qualitatively consistent with recent first principle calculations [Wu et al., Appl. Phys. Lett. 89 (2006) 62505].
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| 10. |
- Moreno, Luis, et al.
(författare)
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Modelling of transport in fractures with complex matrix properties
- 2006
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Ingår i: Scientific Basis for Nuclear Waste Management XXIX. - WARRENDALE, PA : MATERIALS RESEARCH SOCIETY. - 1558998896 ; , s. 267-274
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Konferensbidrag (refereegranskat)abstract
- In the ongoing Swedish site investigations it has been found that the rock matrix adjacent to many open fractures has been altered. The alteration can extend from mm to several cm. The altered rock can have different sorption and diffusion properties compared to the undisturbed rock and this may influence the retardation of the nuclides. The paper presents how the Channel Network model has been adapted to handle diffusion into a matrix composed of several layers with different properties in addition to the infinite undisturbed matrix. For one channel, the solution for the Residence Time Distribution, RTD, may be found in the Laplace-plane. For the transport in the Channel Network, a particle tracking technique is used to determine the paths followed by solute particles. The RTD for this path is obtained using convolution, which in the Laplace-plane means multiplication of the transfer functions for each channel. The inversion to the time-plane is made by numerical inversion of the Laplace transforms for each path. The method has been tested with data from the TRUE (Tracer Retention Understanding Experiments) project, Task 6F, fluid flow and solute transport in two features in 100 in scale where a complex matrix was modelled. The model was used to predict the transport of the tracers (I-129), Cs-137, and Am-241) over some 20 m. The paper also addresses how the RTD is influenced by the different retardation mechanisms under Site Characterisation (SC) as well as Performance Assessment (PA) conditions.
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