Three-Dimensional Modelling of a Large-Diameter Sealing Concept in a Deep Geological Radioactive Waste Disposal.

The French National Radioactive Waste Management Agency is leading the design of a deep geological radioactive waste disposal to be located in the Callovo-Oxfordian formation. At the disposal main level, large-diameter galleries will ensure access to the storage cells and connection between zones. After a long operational period, the disposal will be closed by sealing structures located at some key positions to ensure post-closure safety over the long term. The seals are intended to prevent the flow of water and the migration of radionuclides from the disposal to the biosphere throughout the entire storage life. Thus, the long-term safety of the disposal relies to a large extent on the performance of these structures. The paper presents the work carried out to assess and simulate the phenomena underlying the response and performance of a large-diameter sealing concept under real disposal conditions. The complexity of the problem is addressed by considering in the simulations large-scale 3D geometries, advanced constitutive models, complex coupled phenomena, key geometric details at decimetre scale, and all the phases from the excavation to the post-closure period (~ a few thousand years). Highlights: The three-dimensional hydro-mechanical modelling of a large structure concept, foreseen to seal access galleries in a clayey rock deep disposal, has been carried out. Model considers large geometry (order of tens of meters), anisotropy, constitutive laws of different complexity, interfaces, and relevant geometrical details (order of cm). Results evidence a progressive hydration and swelling of the sealing core during more or less 2000 years after disposal closure. The concrete plugs placed at both ends of the sealing structure move longitudinally, but core density and swelling pressure do not change significantly in seal central part. Swelling core recompresses partially the excavation-induced damaged zone in the area of lining deposition. [ABSTRACT FROM AUTHOR]