Chemical erosion of the bentonite buffer: do we observe it in nature?
Heini M. Reijonen, Nuria Marcos, 2017. "Chemical erosion of the bentonite buffer: do we observe it in nature?", Radioactive Waste Confinement: Clays in Natural and Engineered Barriers, S. Norris, J. Bruno, M. van Geet, E. Verhoef
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It is planned to use bentonites as buffer materials in various types of geological repositories designed to host radioactive waste. For the bentonite materials, the hydrological and hydrogeochemical conditions are two of the main environmental factors affecting their evolution, assessed for a period of up to 1 Ma. Since it has been observed in laboratory tests that smectite, in particular montmorillonite, forms colloids and disperses in very dilute conditions, a scenario for chemical erosion has been discussed at length, especially in relation to geological repositories located in future glaciated terrains and locations otherwise potentially hosting dilute groundwaters. General understanding, based on laboratory experiments, is that bentonite erosion does not occur when the total charge equivalent of cations in groundwater is higher than 4 mM. However, based on current knowledge, it seems that chemical erosion is not observed in repository-relevant natural systems where groundwater conditions are below the given limit. Further investigation is therefore suggested to provide a better scientific understanding of the mechanisms involved in stabilizing smectites in these natural systems.