(GRS 566) Groundwater Flow and Transport in Complex Real Systems

A. Schneider, S. Britz, A. Gehrke, K.-P. Kröhn, M. Lampe, A. Nägel, S. Reiter, G. Wittum, H. Zhao

The code d³f++ has been developed for modelling density-driven flow and nuclide transport in the far field of repositories for hazardous material in deep geological formations. It is applicable in porous media as well as in fractured rock or mudstone, for modelling salt- and heat transport as well as a free groundwater surface.

The growing and varying demands on groundwater flow and transport modelling evoke constantly rising requirements for code enhancement and improvement. With the objective to enable d³f++ for the modelling of short-term field-scale experiments with pressureinfluenced transient processes the flow equation is extended by a storage term. New projectors for an intelligent grid refinement with better resolution of the model geometry were implemented to improve pre-processing and grid generation.

Improving speed-up and robustness of the multigrid solvers is a permanent task. To speed-up solving of the nonlinear problem, two versions of LIMEX methods were investigated. Very promising results could be achieved for various test cases. Additionally, new types of smoothers using downwind numbering ILU and ILUβ were tested. The coarse grid correction was enhanced by implementing a Galerkin projection and a special matrix dependent interpolation. Additionally, Filtering Algebraic Multi-Grid Methods (FAMG) were adapted to thermohaline flow and implemented in d³f++. To strengthen the robustness of the parallelization, ideas from computer graphics were adapted to get an adaptive anisotropic refinement strategy, and downward numbering algorithms were parallelized to improve load balancing. Special attention was spent to a substantially stabilization of the levelset method and, therefore, the modelling of free groundwater surfaces.

A short review of various concepts of diffusion and sorption of radioactive nuclides in crystalline rock is presented. As a result of this process a two-zone approach is used for modelling the transport of four different tracers in Task 9b of the SKB Task Force on Groundwater Flow and Transport of Solutes.

In the scope of this work d³f++ was applied to three 3d groundwater flow models at regional scale, in porous media as well as in crystalline rock. These are the Äspö Site Descriptive Model (SDM), the overburden of the Waste Isolation Pilot Plant (WIPP) site, a repository for transuranic waste in bedded salt in New Mexico, and the Čihadlo candidate site in the Czech Republic.