Characterization of Swelling Clays as Components of the Engineered Barrier System for Geological Repositories. Results of an IAEA Coordinated Research Project 2002-2007

At the request of the Member States, the IAEA coordinates research into subjects of common interest in the context of the peaceful application of nuclear technology. The coordinated research projects (CRPs) are intended to promote knowledge and technology transfer between Member States and are largely focused on subjects of prime interest to the international nuclear community. This report presents the results of a CRP carried out between 2002 and 2007 on the subject of swelling clays proposed for use as a component in the engineered barrier system (EBS) of the multibarrier concept for disposal of radioactive waste. In 2002, under the auspices of the IAEA, a number of Member States came together to form a Network of Centres of Excellence on Training in and Demonstration of Waste Disposal Technologies in Underground Research Facilities (URF Network). This network identified the general subject of the application of high swelling clays to seal repositories for radioactive waste, with specific emphasis on the isolation of high level radioactive waste from the biosphere, as being suitable for a CRP. Existing concepts for geological repositories for high level radioactive waste and spent nuclear fuel require the use of EBSs to ensure effective isolation of the radioactive waste. There are two major materials proposed for use in the EBS, swelling clay based materials and cementitious/concrete materials. These materials will be placed between the perimeter of the excavation and the waste container to fill the existing gap and ensure isolation of the waste within the canister (also referred to as a container in some EBS concepts) by supporting safety through retardation and confinement. Cementitious materials are industrially manufactured to consistent standards and are readily available in most locations and therefore their evaluation is of less value to Member States than that of swelling clays. There exists a considerable range of programme development regarding qualification of swelling clay materials. Some Member States with advanced repository concepts have identified potentially suitable swelling clay materials for use in these underground facilities. Given the quantities of clay material needed for a repository application, the identification of potentially suitable materials located within or near to Member States is of considerable interest, particularly for those with more limited resources to apply to their repository programmes. This report provides: - An overview of the repository concepts of the Member States involved in the CRP; - A general description of key material properties and a means of assessing those properties of relevance to screening potentially suitable swelling clays for repository use; - A summary of the properties measured for the candidate materials selected by each of the participating Member States and a preliminary assessment of their potential suitability for use as a component of the EBS of a deep geological repository. Overall, it is concluded that the major technical goal to assist in the identification of suitable clay deposits in Member States has been achieved. Moreover, by participating in the CRP the Member States appear to have advanced their programmes in a number of other ways. Specifically, by their involvement, the participants have joined and enlarged the international group of experts able to assist in the safe disposal of high level radioactive waste