A wide spectrum of argillaceous media are being considered in NEA member countries as potential host rocks for the final, safe, near-surface or at-depth disposal of radioactive waste, and/or as major constituents of repository systems in which waste will be emplaced. These media have a number of favourable generic properties such as homogeneity, low groundwater flow, chemical buffering, a propensity for plastic deformation and self-healing of fractures by swelling and a marked capacity to chemically and physically retard the migration of radionuclides.
In this context, in 1990 the NEA established a working group on argillaceous media, informally known as the "Clay Club".
The Clay Club examines those various argillaceous rocks that are being considered for the deep disposal of radioactive waste, ranging from soft clays to indurated shales. These rocks exhibit a wide spectrum of characteristics which make them useful as barriers to the movement of water and solutes and as repository construction materials. Studies include clay media characterisation and modelling.
The Clay Club is organising the International Workshop on Microscopic Observations and Imaging Techniques for Clays. The workshop will take place on 6-8 September 2011 at the Karlsruhe Institute of Technology (KIT) in Germany. The objective of this workshop is to share state-of-the-art microscopic observation methods and modelling techniques to enhance understanding of properties of micro-structure, water flow and mass transport processes in clay, which are key processes in the long-term safety assessment of geological disposal. Participants will include not only researchers already involved geological disposal, but also researchers from other fields (e.g. petroleum exploration) to encourage further interaction at the multidisciplinary research level and to obtain potentially transferable knowledge for research on geological disposal.
The 20th anniversary of the Clay Club took place on 21-23 September 2010 in Toronto, Canada. The meeting included two days of technical discussions and a one-day technical tour of the Bruce site in co-ordination with the Nuclear Waste Management Organisation (NWMO), co-sponsored by the Clay Club. A special session was organised to share knowledge on anomalous heads in sedimentary formations. As a result of the discussion, the Clay Club noted that anomalous pressures are commonly observed in sedimentary environments and that multi-disciplinary studies [e.g. thermal, hydraulic, mechanical and chemical (THMC) coupling] and improvement of measurement techniques (e.g. anomalous pressure in low permeability) are needed to further investigate this scientific question and incorporate the results into site investigation strategy. Although the role of anomalous pressures in the safety case was not discussed by the Clay Club at this stage, it noted that anomalous heads constitute an interesting topic. Follow-up on this topic in the context of the safety case is expected in the coming years.
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Last reviewed: 10 May 2011