Water sorption fracture formation

The theory of bundle formation in the section Aggregation Prenomena in Solutions of Charged Polymers provides sizes, as well as electrostatic and elastic properties of ionomer bundles. The theory of water sorption and swelling, described in this section, gives a statistical distribution of pore size and local stress in pores. The merging point of both theories is a theory of fracture formation in charged polymer... 

The Koongarra U deposit in the Northern Territory of Australia has been studied to evaluate the processes and mechanisms involved in the geochemical alteration of the primary ore zone, and to model the formation of the secondary U ore zone and dispersion fan (Duerden 1991 Duerden Airey 1994). Studies of the distribution of the U in the dispersion fan (Murakami et al. 1991) have provided data on the fixation of U leached from the primary ore deposit. Their work has shown that, for this system, fractures are not only preferential pathways for ground-water movement but also contain secondary minerals with high sorption capacity for elements such as U. Even in the monsoonal climate, in which this deposit is located, a significant proportion of the uranium has not been released from the vicinity of the primary ore body. 

It is obviously not possible to make experiments with duration of hundreds of thousands of years and over distance of hundreds of meters in the tight rock formations of interest. It is therefore essential to understand the key processes so well that credible predictions can be made using models based on well-established laws of nature. The models must be supported by experiments that can credibly be extrapolated. The models used are based on the laws of mass and energy conservation and on laws of thermodynamics. The difficulties in applying these laws arise mainly from the fact that the rock mass cannot be described in detail. The location, orientation and detailed hydraulic properties of the fractures cannot be measured in detail. The diffusion and sorption properties of the interior of the rock mass under natural stress cannot be readily measured. Mixing processes of different water packages in fractures and at intersections are not fully understood. All this makes it difficult to build models that account... 

The efficiency of a rock formation as a transport barrier depends on fluid flow and on radionuclide retention in the rock due to a variety of physical and chemical processes. Open fissures or fractures in the rock provide pathways through which water and radionuclides may travel. Although most radionuclides have a strong tendency to sorb to mineral grains in the rock, tracers first have to diffuse from fractures into the rock matrix in order to access the extensive pool of sorption sites (Neretnieks, 1980). Diffusion in turn depends on mass transfer properties of the rock matrix and on the hydrodynamics of fracture networks, emphasizing the interaction between water flow, advective transport and retention processes. Although models for reactive transport in discrete fracture networks have been around for some time, it is only recently that a theoretical framework is available for systematic studies of the hydrodynamic impact on retention (e.g., Cvetkovic et al., 1999, 2002). 

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