Site-descriptive modelling for a final repository for spent nuclear fuel in Sweden

The handling and safe disposal of spent fuel from nuclear power plants has been an issue since the 1950s when the first suggested method, geological storage in salt formations, was proposed in the US. Since then a number of methods have been developed for different types of bedrocks and waste types. One common need applicable to all these methods is to describe features and processes essential in repository design and demonstrations of long-term safety. So far, most methods have not described, nor emphasized, the importance of site-specific understanding of key parameters related to a specific repository design. Furthermore, the need of interdisciplinary research and the benefits gained when handling the site as a unified connected and mutually interrelated system (from bedrock to surface) have not been fully discussed. During a 30-year period, research has been performed in Sweden to demonstrate feasibility and long-term safety of underground geological disposal of spent nuclear fuel. In this paper, the overall strategy and discipline-specific modelling methods used in the site description of a final repository in Sweden are described, as exemplified by the Forsmark site. The resulting site description covers understanding of the historical evolution of the site, site data describing the current situation as well as spatially variable models needed to design the repository and evaluate long-term safety after closure. Finally, lessons learnt from this work are summarized, which are important when employing this method in the future.