Large-scale geological characterization
Geochemical data from the deep aquifer system below the Boom Clay in NE Belgium have been collected and reinterpreted. The data were obtained between 1980 and 2014 within the framework of radioactive waste disposal studies. Currently, groundwater in the deep aquifer system mainly ranges between NaHCO3 type and NaCl type. Because of the low groundwater velocity in this aquifer system, re-equilibration with the mineralogical composition of the host formations generally occurs. The main geochemical indicators point out that the current formation waters are a mixture between the original saline marine porewaters and freshwater recharge. SE–NW gradients of increasing ion concentrations are observed and can be explained in agreement with the pattern of natural groundwater flow. Calcite dissolution and cation exchange are still ongoing in this freshening aquifer system. A low sulphate content in the deep aquifer system indicates sulphate reduction associated with organic matter degradation. Inverse modelling along a flow path using PHREEQC generally confirms the reactions that have been derived in the data analysis.
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It is internationally accepted that the safest and most sustainable option for managing radioactive waste is geological disposal, utilizing both engineering and geology to isolate the waste and contain the radioactivity.
This Special Publication contains 25 scientific studies presented at the 6th conference on ‘Clays in natural and engineered barriers for radioactive waste confinement’ held in Brussels, Belgium in 2015. The conference and this resulting volume cover many of the aspects of clay characterization and behaviour considered at various temporal and spatial scales relevant to the confinement of radionuclides in clay, from basic phenomenological process descriptions to the global understanding of performance and safety at repository and geological scales.
The papers in this volume consider research into argillaceous media under the following topic areas: large-scale geological characterization; general strategy for clay-based disposal systems; geomechanics; mass transfer; bentonite evolution and gas transfer.
The collection of different topics presented in this Special Publication demonstrates the diversity of geological repository research.