EURAD ACED – Modelling the geochemical evolution of disposal cells in deep geological repositories

The European Union’s Horizon 2020 project EURAD (European Joint Progamme on Radioactive Waste Management) aim is to implement a joint Strategic Programme of research and knowledge management activities at the European level, bringing together and complementing EU Member State programmes in order to ensure cutting-edge knowledge creation and preservation in view of delivering safe, sustainable and publicly acceptable solutions for the management of radioactive waste across Europe now and in the future. The broader scope of the work package ACED (Assessment of the chemical evolution in intermediate and high level radioactive waste disposal cells) in EURAD is the assessment of the chemical evolution at the disposal cell scale involving interacting components/materials and thermal, hydraulic and/or chemical gradients. Four generic disposal cells that are representative for the most important aspects of disposal designs in several national disposal programs throughout Europe, formed the basis for the research activities in this work package.

Conceptual, mathematical and numerical models were developed and implemented to describe the geochemical evolution in the combined engineered barrier system and the immediately surrounding host formation (clay or granite) from a more detailed scale up to a spatial scale of a few meters and time scales up to 100 000 y. ACED demonstrated the applicability of advanced coupled reactive transport models to provide an integrated view on coupled geochemical processes in the multi-barrier system of a deep geological repository. Insight in the geochemical evolution was obtained from more detailed numerical models at the scale of the waste package (neglecting influences from the host rock) up to models with the detailed geometry and the different materials in the disposal scale (depending on the system including nuclear glass, organic waste, metallic waste, steel, cementitious materials, bentonite, and host rock). Beside models that integrated as detailed as possible the available information, approaches were tested to decrease the model complexity while preserving the key findings of the more complex models; a process also known as model abstraction. Simplifications were made with respect to dimensionality, chemical complexity and numerical accuracy as well by implementing surrogate models based on machine learning tools to replace the parts of the models requiring the most computational time.

ACED made a significant step forward in process-based modelling of geochemical interactions  in the near field of a geological repository where the engineered barrier system interacts with the host rock. The models and insights obtained for the generic disposal cells can form a basis for more specific research studies in national disposal programs.

Acknowledgement: The research leading to these results was funded by the EURAD work package (European Joint Programme on Radioactive Waste Management of the European Union, EC grant agreement nº 847593)