Spent nuclear fuel constitutes one of the most hazardous parts of radioactive waste. Its final reposition is accordingly challenging. DHI assists the Swedish Nuclear Fuel and Waste Management Co (SKB) in the planning and construction of a deep repository in Sweden by elucidating the complex dynamics of water and soil as well as solute transport patterns today and in the distant future.
The deep repository will be situated at Forsmark on the Swedish east coast. There, in the granite bedrock at a depth of about 450 metres, the fracture frequency is low and the groundwater velocity very slow. Nevertheless, ensuring the safety of such a deep repository – both during the construction as well as the operation and closing phase – requires a detailed understanding of its hydrological and hydrogeological setting. Based on comprehensive site investigations by SKB, DHI applied its modelling suite to investigate possible effects of the construction activities on surface hydrology, potential inflows into the tunnel system as well as flow patterns. Moreover, DHI carried out detailed studies of the effect of the construction activities on local wetland water levels, in order to ensure the protection of the Pool Frog. This red listed amphibian native in the wetlands surrounding Forsmark is very sensitive to even small changes in water levels.
In March 2011, after years of thorough research, SKB submitted applications to the Swedish authorities, seeking permission to build the final repository. "Forsmark is now surely one of the most well-investigated areas in Europe", Erik Mårtensson from DHI Sweden comments. "We are dealing with probably the most extensive set-up of hydrological and hydrogeological models for a single area ever made." It not only includes a set-up, calibration and validation of models for today's conditions, but also several models for future conditions. These include possible climate scenarios and associated models revealing changes in shore-lines, landuse and regolith (the layer of loose material covering solid rock). The hydrological models describing future scenarios are used as input in the safety assessment describing the long term safety of the repository.