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    A study of uranium and thorium migration at the Koongarra uranium deposit with application to actinide transport from nuclear waste repositories
    (Macquarie University and Australian Nuclear Science and Technology Organisation, 1991-01) Payne, TE
    One way to gain confidence in modelling possible radionuclide releases is to study natural systems which are similar to components of the multibarrier waste repository. Several such analogues are currently under study and these provide useful data about radionuclide behaviour in the natural environment. One such system is the Koongarra uranium deposit in the Northern Territory. In this dissertation, the migration of actinides, primarily uranium and thorium, has been studied as an analogue for the behaviour of transuranics in the far-field of a waste repository. The major findings of this study are: 1. the main process retarding uranium migration in the dispersion fan at Koongarra is sorption, which suppresses dissolved uranium concentrations well below solubility limits, with ferrihydrite being a major sorbing phase; 2. thorium is extremely immobile, with very low dissolved concentrations and corresponding high distribution ratios for 230Th. Overall, it is estimated that colloids are relatively unimportant in Koongarra groundwater. Uranium migrates mostly as dissolved species, whereas thorium and actinium are mostly adsorbed to larger, relatively immobile particles and the stationary phase. However, of the small amount of 230Th that passes through a 1μm filter, a significant proportion is associated with colloidal particles. Actinium appears to be slightly more mobile than thorium and is associated with colloids to a greater extent, although generally present in low concentrations. These results support the possibility of colloidal transport of trivalent and tetravalent actinides in the vicinity of a nuclear waste repository.
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    Effect of indium and niobium segregation on the surface vs. bulk chemistry of titanium dioxide (rutile)
    (University of Western Sydney, 2013-01-01) Atanacio, AJ
    Since the landmark paper in 1972 by Fujishima and Honda [1], TiO2 has become one of the most promising candidates of a new generation of solar energy materials capable of generating clean hydrogen fuel using only sunlight (photo-electrochemically) to dissociate water. TiO2 has both bulk properties and surface properties which contribute to its functional performance. Considering that all of the electrochemical reactions induced by light occur at the surface of TiO2, it becomes clear that understanding the surface properties of TiO2 is of crucial importance for its performance; specifically the conversion of solar energy into chemical energy. The surface phase of TiO2 can be substantially different from that of the bulk phase as a result of a phenomenon known as segregation. Segregation involves the transport of certain lattice species from the bulk phase to the surface, driven by excess surface energy. To date, developments in the understanding of TiO2 solid solutions and related properties have mainly been centred on bulk properties. In comparison, relatively little work has been reported on segregation in TiO2 solid solutions and its influence on functional properties, such as reactivity and photoreactivity. The present work has studied the effect of indium (acceptor-type ion) and niobium (donor-type ion) segregation on the surface chemistry of well-defined In-doped and Nb-doped TiO2 solid solutions. Specifically, examining the relationship between imposed sample processing conditions, such as the gas phase oxygen activity, on segregation-induced surface enrichment. This was achieved using a range of complimentary analysis techniques including X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), Rutherford backscattering (RBS) and proton-induced X-ray emission (PIXE). Copyright © 2013 Western Sydney University
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    New materials for selective separations at the back end of the nuclear fuel cycle
    (University of Sydney, 2016) Veliscek-Carolan, J
    Storage and recycling of nuclear waste are important issues that will increase in importance if nuclear power becomes more widely adopted worldwide. Recycling of used nuclear fuel is of benefit both in terms of increasing the nuclear lifetime (ie the number of years nuclear power will be a viable option for power generation) and decreasing the hazards (radiotoxicity, volume and longevity) of nuclear waste. Currently, most reprocessing of used nuclear fuel is performed using liquid-liquid extraction. However, use of solid sorbent materials has many advantages such the lack of organic solvent wastes. This research involves development of materials that are able to selectively remove specific target elements from solutions of used nuclear fuel. Once loaded with radionuclides, these materials may be utilised as transmutation matrices or wasteforms. Therefore, radiolytically and hydrolytically stable materials able to withstand the conditions of nuclear separations, such as titania and zirconia, have been targeted. Further, ordered porosity has been introduced into these titania and zirconia framework materials to improve their sorption capacity and kinetics. In order to impart selectivity to these materials, organic ligands are incorporated. Functional groups, including phosphonates, amines and peptides, have been chosen or designed based on their selectivity for elements relevant to the nuclear fuel cycle. Elements of interest include uranium, which constitutes >96% of used nuclear fuel and can be recycled; minor actinides, which contribute significantly to the radiotoxicity of nuclear waste and can also be recycled in fast neutron reactors; and lanthanides, which are targets for separation from the minor actinides as their high neutron absorption cross sections prevent transmutation of the minor actinides. Novel hybrid materials have been synthesized and their sorption characteristics, including selectivity, capacity and kinetics, evaluated. © 2016 The Author.