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This paper draws the main lines of the scientific strategy adopted by CEA for its R&D programme dedicated to the study of the long-term behaviour of cement-based materials in relationship with cemented nuclear waste management. In the framework of the safety assessment analysis, the long-term stability of waste package confinement and mechanical properties is required. This analysis was achieved considering the different environmental conditions – atmospheric and water saturated environments – which could affect the waste package. As far as the unsaturated phase (storage) is concerned, corrosion and air carbonation of reinforced concrete were identified as the two main phenomena which could jeopardize the waste package long-term performances. During the disposal phase, underground water leaching may significantly contribute to the chemical degradation of concrete. The understanding and modelling of phenomena and mechanisms responsible of such degradation are therefore essential to make relevant and robust long-term predictions. With this aim, CEA has developed an extended research programme to assess the long-term degradation of concrete through a chemistry-transport and mechanical coupled approach. The relevancy and validity of such a programme are discussed here.

This paper draws the main lines of the scientific strategy adopted by CEA for its R&D programme dedicated to the study of the long-term behaviour of cement-based materials in relationship with cemented nuclear waste management. In the framework of the safety assessment analysis, the long-term stability of waste package confinement and mechanical properties is required. This analysis was achieved considering the different environmental conditions ? atmospheric and water saturated environments ? which could affect the waste package. As far as the unsaturated phase (storage) is concerned, corrosion and air carbonation of reinforced concrete were identified as the two main phenomena which could jeopardize the waste package long-term performances. During the disposal phase, underground water leaching may significantly contribute to the chemical degradation of concrete. The understanding and modelling of phenomena and mechanisms responsible of such degradation are therefore essential to make relevant and robust long-term predictions. With this aim, CEA has developed an extended research programme to assess the long-term degradation of concrete through a chemistry-transport and mechanical coupled approach. The relevancy and validity of such a programme are discussed here.

Abstract: We have developed an INAA techniques for analyzing single crystals extracted from rocks. Trace element contents have been measured in a large variety of mineral species, as well as isotopic ratios of some REE in minerals related to natural fission reactions. The sensitivity of INAA allows to avoid the main shortcomings of usual mineral geochemistry: (1) only very short quantities of minerals are needed (down to a few mgrg), so that even very sparse minerals could be analyzed, (2) purity of minerals is carefully checked, and (3) the heterogeneity of a population may be studied. The method is especially useful when applied to minerals acting as tracers for some element families, e.g. REE in Ca-bearing minerals (fluorite, apatite, titanite, gamet) and Zr-bearing minerals, or chalcophile elements (Co, Ni, As, Sb, Mo, Ag, Au and Se) in sulfides. We present an application of the method to the Oklo U deposit in Gabon showing that features outlined above are of special interest for the study of hydrothermal processes.