Calculation Methods
The Federal Institute for Geosciences and Natural Resources (BGR) uses computer-aided numerical simulations of processes to assess the safety of final repositories, as well as improve system understanding in conjunction with laboratory and field tests.
Numerical simulations are performed to determine the stress on geological or geotechnical structures and predict their long-term response to thermal, hydraulic, mechanical, and chemical (THMC) effects. The Finite Element Method (FEM), which enables two-dimensional or three-dimensional numerical simulation of coupled processes in underground environments is utilized for this purpose.
The modeling process typically starts with a geological structure model and the geometry of a final repository as its foundation. This forms the basis to create a computational model encompassing a specific section of interest. For parameterization, this section is often grouped into homogeneous regions characterized by uniform material properties. The next step involves discretizing this computation model; dividing it into finite elements or mesh generation for numerical analysis. With such an approach, essential physical processes like heat propagation and deformation can be spatially calculated over time along with groundwater flow patterns.
Process coupling plays a significant role in these simulations where results offer insights including temperature changes in the underground spanning one million years ahead of schedule; evolution of mechanical stresses/deformations or dilatant areas within the rocks themselves as well predictions about how water moves through them - all made possible by various software tools employed at BGR:
- JIFE (Java Application for Interactive Nonlinear Finite-Element Analysis in MultiPhysics),
- OpenGeoSys,
- Flac 3D RHINO / GRIDDLE,
- INCA/PATRAN/TecPlot/Paraview and
- GINA_OGS.
Numerical modeling of coupled processes is highly complex without standard solutions or software readily available; hence continuous development tailored to specific requirements remains essential while staying updated with global scientific advancements through participation in national and international research projects like DECOVALEX, BENVASIM, EJP-EURAD, Bastion, Basal etc., ensuring adherence to best practices worldwide.
The outcomes from these numerical models find application within various contexts including site selection studies for nuclear waste repositories (e.g. Morsleben, Konrad, Asse), assessing stability issues related to geological and geotechnical barriers' integrity during long term storage periods as well aiding interpretation/designing lab-based experiments conducted at sites like Äspö, Mont Terri among others.
Beyond simulating real systems numerically, virtual experiments allows researchers an opportunity not only investigate impacts due changes made either regarding material characteristics but also geometric dimensions while comparing different assumptions about how materials behave under certain conditions thus enhancing overall understanding through comprehensive analysis facilitated by these powerful tools. Lastly yet importantly numerical techniques prove invaluable when it comes down supporting field tests both during their design phase as well post-execution stages where they aid interpretation efforts significantly.
In the context of evaluating potential sites for high level radioactive waste repositories, safety assessments heavily rely on such simulations to evaluate rock confinement capabilities over extended periods ensuring minimal environmental impact.