As part of research into the geological disposal of radioactive waste in Belgium, the HADES underground research laboratory (URL) was constructed in a clay formation in the early 1980s. This was the world's first purpose-built URL in a deep clay formation. Over the past four decades, the HADES URL has played an important role in the research, development and demonstration (RD&D) of geological disposal. It enabled the in situ characterization of the clay host rock, it allowed experiments to be performed under realistic geological conditions and it demonstrated the feasibility of constructing, operating and closing underground repositories. This volume presents several key contributions of the HADES URL to both Belgian and international research into geological disposal. It not only compiles some important RD&D results, but also illustrates the essential role URLs such as the HADES URL have played in developing concepts for the geological disposal of radioactive waste.

This Special Publication highlights the importance of clays and clayey material, and their multiple roles, in many national geological disposal facilities for higher activity radioactive wastes. Clays can be both the disposal facility host rock and part of its intrinsic engineered barriers, and may be present in the surrounding geological environment. Clays possess various characteristics that make them high-quality barriers to the migration of radionuclides and chemical contaminants, e.g. very little water movement, diffusive transport, retention capacity, self-sealing capacity, stability over millions of years, homogeneity and lateral continuity.

Deep Geological Disposal of Radioactive Waste presents a critical review of designing, siting, constructing and demonstrating the safety and environmental impact of deep repositories for radioactive wastes. It is structured to provide a broad perspective of this multi-faceted, multi-disciplinary topic: providing enough detail for a non-specialist to understand the fundamental principles involved and with extensive references to sources of more detailed information. Emphasis is very much on "deep geological disposal – at least some tens of metres below land surface and, in many cases, many hundred of metres deep. Additionally, only radioactive wastes are considered directly – even though such wastes often contain also significant chemotoxic or otherwise hazardous components. Many of the principles involved are generally applicable to other repository options (e.g. near-surface or on-surface disposal) and, indeed, to other types of hazardous waste. - Presents a current critical review in designing, siting, constructing and demonsrating the safety and environmental impact of deep repositories for radwaste - Addresses the fundamental principles of radioactive waste with up-to-date examples and real-world case studies - Written for a multi-disciplinary audience, with an appropriate level of detail to allow a non-specialist to understand

This technical report describes the results of the Nuclear Energy Agencys CLAYTRAC project, in which natural tracer data from nine sites was evaluated to assess potential impacts of disposal of radiological waste in geological repositories. It shows scientific information from numerous sites and applies robust analytical methods to improve the understanding of radionuclide migration and evolution of sites for deep geological disposal. These results improve the understanding of sites, and thus the confidence in safety, for geological disposal of radioactive waste.

The international Mont Terri rock laboratory in Switzerland plays a central role in the safety and construction of deep geological nuclear repositories in clay formations. The laboratory has developed and refined a range of new measurement and evaluation methods: it has e.g. advanced the determination of rock parameters using innovative borehole geophysics, improved the methodology for characterizing pore-water and microbial activity in claystones, and greatly improved our understanding of diffusion and retention processes of radionuclides in and through claystones. The methods and insights described in this compendium can also be applied to low-permeability rocks at various sites around the globe, and in other fields of application.