88. The OECD/NEA Report on Self-sealing of Fractures in Argillaceous Formations in the Context of Geological Disposal of Radioactive Waste

Self-sealing of fractured geologic media is of prime importance in the understanding of long-term radionuclide mobility and safety of deep geological repositories for long-lived radioactive waste and spent fuel. It is often cited as one of the decisive factors favouring the choice of argillaceous formations as host rocks for deep disposals. A report of the Nuclear Energy Agency (NEA) of the Organisation for Economic Co-operation and Development (OECD) provides an overview and synthesis of the current understanding of, and conceptual approaches to, the processes that lead to sealing of natural and induced fractures in argillaceous media at typical repository depths. Systematic evidence of self-sealing is collected with reference to laboratory tests, underground research laboratory (URL) field tests and geologic and geotechnical analogues, whereby the bulk of the information stems from the URLs at Bure (Callovo-Oxfordian formation), Mol (Boom Clay) and Mont Terri (Opalinus Clay). The physical, mechanical, geochemical and hydro-mechanical processes and mechanisms are reviewed and their respective contribution to sealing of fractures assessed. It is concluded that the scientific knowledge on self-sealing has progressed to a level which, for soft and slight to moderately indurated argillaceous formations, justifies the inclusion of sealing processes in the performance assessment (PA) of deep geological repositories.