Nuclear Waste Disposal in Deep Geological Formations: What are the Major Remaining Scientific Issues?
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Nuclear Waste Disposal in Deep Geological Formations: What are the Major Remaining Scientific Issues? Pierre Toulhoat1,2 1 Institut des Sciences Analytiques, Universite de Lyon, 43 avenue du 11 novembre 1918, Villeurbanne, 69622, France 2 Scientific Direction, INERIS, Parc Technologique ALATA, BP2, Verneuil-en-Halatte, 60550, France
ABSTRACT For more than thirty years, considerable efforts have been carried out in order to evaluate the possibility of disposing of high level wastes in deep geological formations. Different rock types have been examined, such as water-undersaturated tuffs (USA), granites or crystalline rocks (Canada, Sweden, and Finland), clays (France, Belgium, and Switzerland), rock-salt (Germany). Deep clays and granites, (provided that the most fractured zones are avoided in the second case) are considered to fulfill most allocated functions, either on short term (reversibility) or long term. Chemically reducing conditions favor the immobilization of actinides and most fission products by precipitation, co-precipitation and sorption. If oxidizing conditions prevail, the safety demonstration will mostly rely on the performance of artificial confinement systems. Rock-salt offers limited performance considering the issue of reversibility, which is now perceived as essential, mostly for ethical and sociological reasons. However, several issues would deserve additional research programs, and as a first priority, a clear description of time/space succession of processes during the evolution of the repository. This will allow a better representation of coupled processes in performance assessment, such as the influence of gases (H2) generated by corrosion, on the long term dynamics of the re-saturation. Geochemical interactions between the host formation and the engineered systems (packages + barriers) are still insufficiently described. Additional gains in performance could be obtained when taking into account processes such as isotopic exchange. Imaginative solutions, employing ceramic- carbon composite materials could be proposed to replace heavy and gas-generating overpacks, or to accommodate the small but probably significant amount of « ultimate » wastes that will be inevitably produced by Generation IV reactor systems. INTRODUCTION Several extensive and carefully documented studies have been carried out under the responsibility of implementing bodies. The most recent examples are the demonstration of disposal feasibility by Nagra (Switzerland) [1] and the Dossier 2005, issued by ANDRA (France) [2], presented during this conference [3]. They have been approved, and have led in France to a new law, voted on June 28th 2006, proposing the commissioning of a disposal facility for high level wastes in 2025: “ Reversible waste disposal in a deep geological formation. Corresponding studies and investigations shall be conducted with a view to selecting a suitable site and to designing a repository in such a way that, on the basis of the conclusions of those studies, the
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