Basis and tests for a service life model of cement based engineering Barrier materials of the low and medium radioactive waste Repository of El Cabril-Cordoba-Spain

The main cement based materials used as engineer barrier in the repository of El Cabril for low and medium radioactive wastes are the Cells, the Containers and the mortar filling the gaps between the drums introduced in the containers. Cells and containers are made of the same concrete composition while the mortar was specifically designed to be pump able and with high impermeability. The repository has a design life of 300-500 years and therefore, these structures should remain until this target service life. The possible aggressions that the cement based materials can suffer have been identified to be: carbonation, water permeation (leaching) and reinforcement corrosion. More unlikely might be the bio-attack. Chlorides are not in the environment but they are inside the drums as part of analytical wastes. In order to resist for the target period the concrete and mortar have been properly designed. The cement used is of low alkali content to avoid alkali-aggregate reaction and in spite there are not significant amount of sulphates in the groundwaters the cement is of low C3A content. The resulting concrete has a characteristic strength higher than 50 Mpa. Tests of mercury porosimetry, water absorption, oxygen and air permeability. carbonation depths, chloride diffusion coefficients and reinforcement corrosion rate. are currently carried out in order to control the actual production of containers and to monitor the aging of the existing structures. A service life model is being developed taking into account several scenarios with different concentrations of aggressive substances. A preliminary version of this service life model RSS presented in the paper. In conclusion: the establishment of a suitable model of service life of CBM used in repositories of radioactive wastes has the main difficulty of the lack of proper calibration of existing models and their use for much shorter service lives. In addition, there are still important items to be measured and collected as they are the characterization of the environment and for the correct identification of key parameters involved in long term durability. (authors)