Siting of a nuclear waste repository requires measurement of the in-situ stress state. Two sites are currently being investigated in Sweden to depths of 1000 m. At both sites there is existing stress data in the vicinity which is being used to help with the interpretation of stress data obtained from the site investigation program. In both cases the geological environments appear quite different; one being a thrust-fault environment and the other being a strike-slip fault environment. To evaluate the suitability of both sites, consideration must be given to the repository permeability, depth, footprint layout and tunnel stability. All of these factors are influenced by the stress magnitudes and orientation; hence every effort must be made to constrain the stress tensor as much as practical.
1. INTRODUCTION
The Swedish Nuclear and Fuel Waste Management Company (SKB) is owned by the power utilities, and is responsible for the management of all radioactive waste from the power plants in Sweden. SKB has developed a system with facilities for intermediate storage of the spent fuel in rock caverns (the CLAB facility), an underground repository for the final disposal of low and intermediate reactor waste (the SFR facility) and is currently carrying out site investigations for siting of a repository for disposal of the spent fuel. The site investigations began in 2002 and will be completed in 2007 (Fig. 1).
The site investigations are being carried out at the Forsmark site in the Östhammar community 170 km north of Stockholm, and at the Simpevarp and Laxemar sites in the Oskarshamn community 330 km south of Stockholm (Fig. 2). All areas are located close to the coast of the Baltic sea. The sites being investigated and the immediate surroundings covers an area of between 5 and 10 km2. The objective is to collate sufficient knowledge about the rock mass and its properties to enable SKB to produce both a site description and a plant description, and to conduct a safety analysis. The Forsmark site is close to the SFR facility, and the Simpevarp and Laxemar sites are close to the CLAB facility and the Äspö Hard Rock Laboratory (HRL), so there are experiences with underground constructions in close proximity to all ongoing site investigations. The aim of the first phase, called the Initial Site Investigation (ISI), is limited to investigations at depth to see if the requirements of the host rock are full-filled [1]. The ISI will be completed at the end of 2004. In mid 2005 there will also be a decision if investigations shall proceed at the both sites.
The Complete Site Investigations (CSI) runs to the middle of 2007. SKB shall then evaluate the results and make a decision for the final disposal. If at least one site is found feasible, SKB will present an application for siting and construction of the repository for spent fuel. In parallel to the Site Investigations for the deep repository there is the design and siting process for an encapsulation plant which is also currently in progress (Fig. 1).
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