Laboratory experiments on bentonite pellet saturation
Dagmar Trpkošová, Petr Večerník, Jenny Gondolli, Václava Havlová, Jiří Svoboda, Irena Hanusová, 2017. "Laboratory experiments on bentonite pellet saturation", Radioactive Waste Confinement: Clays in Natural and Engineered Barriers, S. Norris, J. Bruno, M. van Geet, E. Verhoef
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The aim of the DOPAS project is to address the design basis, reference designs and strategies for the plugs and seals to be used in geological disposal facilities. The Czech ‘Experimental Pressure and Sealing Plug’ (EPSP) experiment has the following objectives: to develop, monitor and verify the functionality of an in situ experimental plug, and to determine and describe in detail the materials to be used with respect to experimental plug construction. The functionality of the experimental plug will be verified by means of conducting pressure tests after the construction phase of EPSP. The internal bentonite section of the EPSP will be constructed from bentonite pellets with a dry density of 1850 kg m−3; the pellets will disintegrate following saturation and swelling to form a homogeneous material with a dry density of around 1400 kg m−3. This process leads to the question of the pore space of the bentonite material: that is, whether it will be possible to employ a numerical model for homogeneous compacted bentonite powder porosity instead of that of the double pore/void space of the bentonite pellets used in the experiment. For this reason, a laboratory physical model (PHM – physical hydraulic model) was incorporated into the DOPAS project for the purpose of describing the saturation and disintegration of the bentonite pellets. The aim of this paper is to describe the results of the space distribution of relative humidity in a sample consisting of bentonite pellets with a view to subsequent numerical modelling and to extend the current knowledge concerning the behaviour of the bentonite pellets used in the EPSP experiment. The results show that following water saturation and the swelling of the bentonite the pellets form a homogeneous mass in the same way as does the compacted bentonite powder. After a period of 160 days, the pellets attained 100% relative humidity at a distance of 12.5 cm and swelling pressure recorded at the end of the model was seen to slowly increase over this time period.
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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.