Geological disposal of radioactive waste
Disposal concepts for spent fuel and radioactive waste in deep underground repositories are based on a multi-barrier concept to ensure the required levels of safety for thousands of years. Engineered barrier systems (EBS) play a central role in these systems. Therefore, a clear and highly detailed understanding of the thermo-hydro-mechanical and -chemical (THM-C) processes at work within these barriers is crucial. The EU-funded PEBS (Long-term performance of engineered barrier systems) project studied these processes in engineered barriers made out of bentonite clay – a favourable material due to its water absorbing and swelling behaviour. The influence of the barrier behaviour on the long-term safety function and implications for performance assessment criteria was evaluated. Experimental researchers and modelling experts worked closely together to achieve the project’s aims. These included developing a procedure to validate computational modelling of THM-C processes, and an updated long-term safety assessment. The work also involved extrapolating experimental data into a long-term model that spans thousands of years. The projects main scientific achievement was to acquire a comprehensive insight into the behaviour of EBS, in particular the complex interactions between various materials and its evolution over time. It provided a comprehensive scientific and technical basis for geological disposal by increasing understanding of the coupled process in the EBS with time. By extrapolating experimental data and modelling results of the initial state of a barrier, PEBS has taken important steps in predicting its long-term performance. In addition, the initiative clarified the importance of remaining uncertainties with regard to long-term performance assessment. This work will help improve the safety of radioactive waste repositories all over the world.
Keywords
Radioactive waste, underground repositories, engineered barrier systems, PEBS, bentonite clay, geological disposal