Studies for the improvement of radioactive waste repositories Radioactive waste is never an easy issue to deal with. Aside from its impact both on environment and human health, its storage requires highly specific treatment. Even underground repositories need to be assessed through unscrupulous testing. Climate Change and Environment To make underground repositories safe for the storage of radioactive waste, specialised barriers are needed to prevent or contain leakage. To derive the best performing repository, a number of scientific investigations are needed to verify the optimal repository design, construction and long-term performance values in rock salt. In particular the study looked at three primary issues: the host rock-including the Excavation Disturbed Zone around emplacement rooms, the backfill made from crushed salt and finally, the materials used for the durable waste containers. The investigation had four branches: in-situ studies, laboratory investigations, modelling and desk studies. The in-situ studies conducted in the salt mine Asse assessed the complex behaviour of backfill and rock salt during and after dismantling of the large-scale "Thermal Simulation of Drift Emplacement" experiment. The experiment involved the electrical heating of two simulated emplacement drifts over more than eight years. Each was heated to around 170-200 degrees Celsius by disposal-cask mock-ups. For one such drift, samples of the native salt and the consolidated backfill were assessed in laboratories in order to gain data required for the analysis of the repository performance. The lab tests were more focused on the effects of the in-situ experiments, looking at both the properties of extracted rock specimens as well as assessing over 280 candidate container material specimens for material performance regarding corrosion after more that ten years of exposure. Geophysical properties of rock samples were evaluated in order to map the attributes of rock with advanced stages of compaction and deformation. Modelling studies were performed aimed at advancing the numerical computer programmes by which the thermomechanical performance of the repository can be predicted. Finally, desk study investigations sought to establish the boundary conditions necessary for the retrievability of radioactive wastes as well as to understand the consequences of doing so. This further contributed towards the future design and development of repository systems. image shows: Opened disposal cask mock-up in the consolidated crushed salt
