Near field waste-water interactions

The near field of the repository includes the engineered barrier system (EBS, i.e., canister and buffer) and the waste form. Also included in the near field is the interface between the buffer and the host rock, denoted as excavation disturbed zone (EDZ). In terms of waste/water interactions, the geochemical evolution of the near field is essential as it controls the composition of the fluids that will eventually contact the waste. 

The interaction of cesium ions with feldspars at 150°C and 200°C has been studied in distilled water, granite groundwater and saline solution Pollucite, CsAlSi206, was identified by infrared spectroscopy, and was formed as a cubic crystalline phase. Surface analytical techniques (XPS, SAM, SIMS and SEM/ EDX) show Cs to be sorbed onto the mineral surfaces and alteration products. The mechanism of pollucite formation and its relevance to cesium transport/ retardation in the near field of a nuclear waste-disposal vault is discussed. 

The application of SCFs to the treatment of wastes and pollutants and to the extraction of contaminants from soil will be extended to other fields in the near future. The cost for the construction of plants will be reduced by the improvement of equipment and materials. The Wnd of fluids to be used will also be improved and many other technologies will be developed according to world needs. On the other hand, reactivities of SCFs, the nature of intramolecular bonds and intermolecular interactions, which are closely related to the reactivities, are not well elucidated yet. Studies on thermodynamics and thermochemistry and intra- and intermolecular interactions from microscopic points of view of SCFs will help solve some of these problems. Furthermore structural studies of SCFs have rarely been made for compounds other than water. Structural investigations of liquids at high temperature and high pressure are also very attractive and important in relation to life sciences. Further investigations into this area should be encouraged. 

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