Host rock formations (rock salt, mudstone, crystalline)
Image: Thomas Hies/Docuvista Filmproduktion
Deep geological repositories are regarded as the most secure concept for the disposal of long-lived and/or radioactive waste nowadays. Worldwide, a multi barrier system is applied to ensure a long-term isolation of the waste material. This system consists of 1) the waste material itself, 2) canisters of either copper or stainless steel, 3) a geotechnical barrier and 4) the geological barrier. With regard to the latter, crystalline rocks, rock salt and clay-rich formations are being explored in Germany due to their low permeability in a depth of several hundreds of meters.
Research of the working group of Applied Geology focuses mainly on two parts of the multi barrier system. For the geotechnical barrier the stability of bentonite is examined. Special attention is paid to the influence of glacial melt water and potential erosion and discharge of radionuclides from the barrier material. Different bentonites (MX-80-Bentonite, GMZ-Bentonite) as well as the mechanical development of compacted bentonite are examined in the framework of several projects, e.g. KOLLORADO-e de3, BEACON de and ELF-China-Pilot de. With regard to the geological barrier, granitoide crystalline rocks are examined. Within those, fissures and cracks are most important for radionuclide transport and retention as they act as water pathways. Key aspects for the evaluation are geometry and roughness of the fissure/crack surface, geochemistry and mineralogy of the rock as well as secondary precipitates. All of those are targeted for example in the project WTZ-Granit de.
Lab experiments to understand processes (erosion, diffusion and sorption experiments) as well as a wide range of analytical methods to characterize the materials are key parts of the work. Results are also implemented in codes and data bases for (reactive) transport modelling. Besides, there are collaborations with underground research laboratories as the Grimsel Test Site (CH). At those sites, processes can be examined and migration experiments can be conducted directly in the geosphere at a depth close to that of a potential geological repository. This is done for example in the framework of the CFM consortium, which is responsible for the iBET experiment (in situ bentonite erosion test).
Fissures and cracks are also important in rocks close to the surface. In contrast to the surroundings of a deep geological repository, there are stronger interactions with the biosphere, especially through the groundwater close to the surface. An example for this is the catchment area of the Lake Laach located in the volcanic field of the East Eifel. Over- and underground area are explored to generate a hydrogeochemical groundwater model for volcanic porous aquifers.