The interdisciplinary project iCROSS combines research competencies of Helmholtz scientists related to the topics of nuclear, geosciences, biosciences and environmental simulations in collaborations overarching the research fields energy and earth and environment. The focus is to understand and analyse close-to-real long-term evolutionary pathways of radioactive waste repositories across nanoscales to repository scales.

The project is subdivided into work packages dealing with laboratory studies, field experiments in underground research laboratories (URLs), advanced modelling studies and the integration and alignment of data and information using virtual reality methods. In this sense, the project structure aims at a holistic view on relevant processes across scales in order to comprehensively simulate potential repository evolutions.

Within the multi-barrier system of a repository for heat-generating radioactive waste, a number of complex reactions proceed, including dissolution, redox processes, biochemical reactions, gas evolution and solid/liquid interface and (co)precipitation reactions. At the same time, thermal and external mechanical stress has an impact on the conditions in a deep geological repository. All those processes are highly coupled, with multiple interdependencies on various scales and have a strong impact on radionuclide mobility and retention. In recent years, substantial progress was achieved in describing coupled processes in numerical simulations. A realistic and concise description of those on different time and spatial scales is, at present, a largely unresolved scientific and computational challenge. The close interaction of experimental and simulation teams aims at a more accurate quantification and assessment of processes and thus, the reduction of uncertainties and of conservative assumptions and eventually to a close-to-real perception of the repository evolution.

One focus of iCROSS is directed to relevant processes in a clay rock repository. In this context, the project partners became a full member of the international Mont Terri consortium and work in close collaboration with international and German institutions in this URL project. Respective experiments specifically deal with coupled processes at the reactive interfaces in a repository near field (e.g. the steel/bentonite and bentonite/concrete interfaces). Within iCROSS, the impact of secondary phase formation on radionuclide transport is investigated. At Mont Terri, experiments are in preparation to study radionuclide transport phenomena in clay rock formations within temperature gradients and in facies exhibiting significant heterogeneities on different scales (nm to cm). Beside those studies, high resolution exploration methods for rock characterization are developed and tested and the effect of temperature and other boundary conditions on the strength, creep properties and healing of faults within Opalinus clay are quantified. Multiphysics models coupled to reactive transport simulation have been further developed and applied to laboratory and field experiments. Results are digitally analysed, in order to enhance the comprehension of coupled processes in repository systems across scales.

Project partners:

• Forschungszentrum Jülich GmbH (FZJ, cooordinator)
• GFZ German Research Centre for Geosciences (GFZ)
• Helmholtz-Zentrum Dresden-Rossendorf (HZDR)
• Karlsruhe Institute of Technology (KIT)
• Helmholtz Centre for Environmental Research (UFZ)

Project runtime: 01/07/2018-31/03/2022

Financial support: This research is funded by the German Federal Ministry of Education and Research (BMBF, project number 02NUK053D) and the Helmholtz Association (project number SO-093).