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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 longterm 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.

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In preparation for coming site investigations for siting of a deep repository for spent nuclear fuel, the Swedish Nuclear Fuel and Waste Management Company, SKB has carried out the long- term safety assessment SR 97, requested by the Swedish Government. The repository is of the KBS-3 type, where the fuel is placed in isolating copper canisters with a high-strength cast iron insert. The canisters are surrounded by bentonite clay in individual deposition holes at a depth of 500 m in granitic bedrock. Geological data are taken from three sites in Sweden to shed light on different conditions in Swedish granitic bedrock.The future evolution of the repository system is analyzed in the form of five scenarios. The first is a base scenario where the repository is postulated to be built entirely according to specifications and where present-day conditions in the surroundings, including climate, persist. The four other scenarios show the evolution if the repository contains a few initially defective canisters, in the event of climate change, in the event of earthquakes, and in the event of future inadvertent human intrusion.The principal conclusion of the assessment is that the prospects of building a safe deep repository for spent nuclear fuel in Swedish granitic bedrock are very good. The results of the assessment also serve as a basis for formulating requirements and preferences regarding the bedrock in site investigations, for designing a program for site investigations, for formulating functional requirements on the repository's barriers, and for prioritization of research.