DEVELOPMENT OF A BACKFILL MATERIAL WITHIN THE BELGIAN CONCEPT FOR GEOLOGICAL DISPOSAL OF HIGH-LEVEL RADIOACTIVE WASTE: AN EXAMPLE OF SUCCESSFUL INTERNATIONAL CO-OPERATION

摘要

The development of concepts for radioactive waste disposal is narrowly linked to the national context. However, due to the very specialised as well as the multidisciplinary nature of R&D related to repository development, international co-operation has proved to be essential. In this paper, we describe the international experiences and perspectives of the Economic Interest Grouping EURIDICE (EIG EURIDICE, formerly known as EIG PRACLAY), a joint venture between the Belgian Nuclear Research Centre SCK?CEN and the Belgian Radioactive Waste Management Agency NIRAS/ONDRAF. The mission of EIG EURIDICE consists in demonstrating the current concept for geological disposal of High-Level radioactive Waste in Belgium. EIG EURIDICE also manages the underground facilities (constructed by SCK?CEN in the eighties) and is currently extending these to allow for large-scale demonstration. This demonstration experiment requires many scientific and technical skills, and therefore EIG EURIDICE is also working with external partners. A successful example of such co-operation is the development of materials for backfilling the disposal galleries. For several years, EIG EURIDICE has closely collaborated on this subject with the Waste Storage and Disposal service (SESD) of the French Atomic Energy Organisation (CEA). Starting from a well defined list of specifications on the desired thermal, hydraulic and mechanical characteristics, several candidate backfill materials have been developed, tested and manufactured, both on a laboratory and on an industrial scale. Two main types have been developed and tested at large scale: precompacted blocks and high-density pellets (mixed with powder). The precompacted blocks have been developed to fill up the space between a central disposal tube (containing the waste forms) and the lining of the disposal galleries (horizontal configuration), and are currently tested in a surface mock-up. The pellets-powder mixtures are intended for the backfilling and sealing of a shaft and are presently being tested in vertical boreholes and shafts. Current investigations do not only deal with the behaviour (thermal, hydraulic, mechanical, chemical) of the materials at real scale, but also with their application (mechanised installation techniques), and the development of appropriate techniques for the measurement of for example the swelling pressure, and the evolution of hydration. The large expertise built up by CEA through the years proves to be very useful in the current design works of a HLW disposal site. The current large-scale tests on the other hand give very interesting feedback on the performance of the engineered materials. Other joint international research programmes have allowed external organisations to use these facilities, which has proven advantageous to both the owner as the visiting organisation. The international co-operation allows EIG EURIDICE to better assess its different scientific and technical approaches related to the radwaste disposal research; the co-operating organisations profit from the readily available infrastructure with scientific and technical resources for a successful experimental set-up. They range from mechanical workshops, drilling equipment, numerical modelling tools for geomechanical and geochemical processes, in situ instrumentation, up to the management and interpretation of the measurement data. To obtain an optimal scientific valorisation of the opportunities created by the extension of the current underground facilities, EIG EURIDICE promotes a policy of active participation by external organisations. This approach will lead to perspectives for EIG EURIDICE (get in touch with organisations which may develop specific parts of the current concept), and to opportunities for prospective partner organisations (use of the infrastructure and know how in various domains).