Safe and sustainable geological nuclear waste disposal poses major scientific challenges to the efforts to minimize the environmental footprint of nuclear energy for extremely long periods of time. To that purpose, safety assessment models must account for radionuclides behavior over time- and distance- scales spanning from that of the storage (e.g. years and meters) to environmental scales (kilometers) and periods (up to 1 million years). The behavior of radionuclides was therefore thoroughly determined thanks to a very large set of experimental measurements, conducted either on cored samples (through-diffusion and batch experiments probing chemical interactions with clay minerals) and in-situ.Complementary to this experimental work, the understanding of the interactions of radionuclides with natural and engineered barriers (consisting mostly of clay and cementitious materials) and their behavior in the geosphere was numerically modeled on various scales: from the molecular-level adsorption and transport in clay and cement nanopores to the larger scale geochemical mobility in macroscopically heterogeneous systems.The understanding of materials, interfaces, and radionuclide transport processes is achieved on the fundamental molecular level by performing detailed quantitative studies of the energetics, structure, and dynamics of ions and water molecules in clay nanopores using computational molecular modeling techniques. New larger-scale models of clays have been developed to allow a more realistic representation of the layer change disorder in the materials. Site-specific free energy profiles of adsorption and other thermodynamic and structural parameters are obtained through the potentials of mean force calculations to improve the understanding and the justification of the currently used thermodynamic, geochemical and transport models.Recent molecular simulation results illustrate not only the powerful capabilities of such computational molecular modeling approaches in clay geochemistry, but also test potential limits of their applicability, presenting new challenges and opportunities for future research.

Computational molecular modeling of the adsorption and transport in clay nanopores in the context of nuclear waste disposal applications

247th National Meeting (2014)

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