ABSTRACT
In long-term safety assessments for nuclear waste repositories in deep formations, geological time scales have to be considered. Possible future climate changes are expected to alter the boundary conditions, the flow regime and the geochemical environment in the aquifers. The codes d³f (Distributed Density-Driven Flow) and r³t (Radionuclides, Reaction, Retardation, and Transport) are being developed to simulate contaminant transport in large heterogeneous areas over long periods of time, considering hydrogeochemical interactions and radioactive decay. A new methodology to use temporally and spatially variant sorption coefficients depending on the geochemical environment is being developed by introducing the transport of relevant components in solution and a pre-computed matrix of sorption coefficients with values being dependent on these components. In this respect, possible future climate changes are being investigated for the reference site Gorleben in Northern Germany. A marine transgression will lead to a decrease of the flow velocities and a horizontal salinity-dependent stratification of the groundwater, while permafrost formation in the upper aquifer and an inflow of glacial melt-water into the lower aquifer will lead to low salinities and high flow velocities in unfrozen zones. Transport simulations employing conventional sorption coefficients are the basis for future analyses employing the new methodology.
