Thesis

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Browsing Thesis by Subject "Actinides"

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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.