Working Group on the Characterisation, the Understanding and the Performance of Argillaceous Rocks as Repository Host Formations (Clay Club)
29th Clay Club meeting, Toronto, Canada, September 2019.

The Working Group on the Characterisation, the Understanding and the Performance of Argillaceous Rocks and Repository Host Formations (Clay Club) advises the Integration Group for the Safety Case (IGSC) on major and emerging issues related to the understanding of multi-scale characterisation, numerical model simulation and barrier performance of argillaceous media.

Argillaceous (i.e. clay-rich) media are being considered in many NEA member countries as potential host rocks for the long-term, safe, near-surface or at-depth disposal of radioactive waste, as well as serving as major constituents in repository systems into which waste will be placed. Argillaceous rock formations have several favourable properties, such as homogeneity, low groundwater flow, chemical buffering capacity, a propensity for plastic deformation and self-healing of fractures by swelling, as well as a demonstrated capacity to chemically and physically retard the migration of radionuclides.

In this context, the NEA established an international working group on argillaceous media in 1990, informally known as the Clay Club. The role of the Clay Club is to examine those argillaceous rocks that are being considered for the deep disposal of radioactive waste, which range from soft clays to indurated shales. These rocks exhibit a wide array of characteristics that make them useful both as barriers to the movement of water and solutes and as repository construction materials. Studies include clay media characterisation (mineralogy, geochemistry, porosity, pore geometry, hydraulic properties, etc.) and complementary numerical modelling.

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Mode of operation

The work programme and modus operandi of the Clay Club emphasise the pooling of resources, the sharing and synthesis of knowledge and experiences and the communication of findings to various audiences.

The mode of operation of the Clay Club meeting is discussed and refined at the group’s plenary meetings. In addition to the discussions at the plenary meetings to evaluate the work programme and to review progress on specific activities, the Clay Club may also periodically undertake more in-depth evaluations to assess the effectiveness of the Clay Club and to update the overall directions of the programme of work.

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