The importance of structural geology in site characterisation of geoenergy and nuclear waste sites

Heating and cooling in both industry and households in Europe has become increasingly important but it is still heavily dependent on fossil fuels. Shifting to low-carbon alternatives cuts emissions, strengthens energy security, and enhances the efficiency for these energy systems in the future. These goals can be achieved with a combination of efficient energy storage and clean energy production. Two example solutions within this field are the Cavern Thermal Energy Storage (CTES) and Deep Geological Repositories (DGR), the first used to store thermal energy and the second to solve the waste issue in climate-neutral nuclear energy production. These two solutions have the common requirement of needing advanced structural geological studies. During the last decade research have focused, for example, on developing CTES, which rely on subsurface caverns in low-permeable rocks that are near surface and remain stable when injected with hot and cold water. Today, there is broad international scientific consensus that high-level nuclear waste should not be stored at the surface in the long term. DGR are considered the best solution as they enclose the radioactive waste in suitable host rock formations located several hundreds of meters below the surface. DGR has also been extensively researched and advanced in several countries, and Finland is a global leader in developing the concept for the storage of nuclear waste within crystalline bedrock.

These storage concepts in crystalline bedrock depend on selecting rock blocks that lack major deformation zones and contain few faults and fractures. Hence, the structural geological modelling is an important tool to mitigate uncertainties and to assess the applicability of the bedrock volume for storage. Several methods exist to assess the bedrock, such as non-intrusive geophysical surveys and intrusive drilling of boreholes into the bedrock. State-of-the-art research shows that best results are achieved by combining multiple research methods within a well-designed research framework to define a 3D geological model of the site.   

Successful implementation of these energy storage projects requires the definition of parameters at early stages of the project to define the constrains for the structural geological 3D model. Detailed structural geological modelling enables evaluation of key aspects and mitigation of uncertainties, such as groundwater conditions, seismic risks, mechanical and thermal properties, as well as environmental factors for the project. This exploration approach can significantly reduce time constrains and costs during every step of these projects. In addition, these geological 3D models serve as an important tool for presenting and communicating projects, including their uncertainties, to policy makers, stakeholders and the public.