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Abstract: The Swedish Nuclear Fuel and Waste management Co. is planning for a future nuclear waste repository, and there is a need of describing the rock conditions accurately to fulfill the high demands on site descriptions for design and safety assessment purposes. One of the important factors is the in situ rock stress conditions, in terms of orientation and magnitude. This paper gives a description of the effort made to develop a robust method specifically for determination of stress orientation. The methodology, which has been tested with promising results, is to study thermally induced borehole breakouts. The orientation of breakouts found in ordinary cored boreholes at the investigated repository site Forsmark, is fairly constant but the breakout occurrence is limited and varying. A study concerning correlation between breakouts and the drilling conditions and rock types has therefore been performed. A quite strong degree of correlation is found between breakout occurrence and rock type and rock alteration. Some degree of correlation is also found between breakouts and drill water flow and breakouts and drill core bit changes. These findings lead to recommendations concerning the continued investigations and method development. 1 BACKGROUND The Swedish Nuclear Fuel and Waste management Co. (SKB) is planning for a future underground nuclear waste repository located in Forsmark (SKB 2009). The design and construction of a repository for spent nuclear fuel must consider the site condi-tions that may impact the long-term safety of a repository. Many of the constraints that are needed to ensure the safe performance of a final repository facility with respect to radionuclide containment are unique for the repository, and the designers have to find a design and layout that meets both the operational requirements for such facility and the long-term safety requirements related to nuclear-waste containment.
- Geology > Rock Type (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Water & Waste Management > Solid Waste Management (1.00)
- Energy > Power Industry > Utilities > Nuclear (1.00)
- Energy > Oil & Gas > Upstream (1.00)
Abstract: The Swedish Nuclear Fuel and Waste Management Co (SKB) has conduct-ed site investigations for a final repository in Sweden during the period of 2002–2008. The site investigations have established site descriptive models for two candidate sites. These models are the result of an interaction of several geoscientific disciplines, in-cluding rock mechanics. Within the framework of the rock mechanics program, a very large number of la-boratory tests were carried out. Intact rock and fractures were investigated by laborato-ry methods such as uniaxial- and triaxial compressive tests, indirect- and direct tensile tests, direct shear tests and tilt tests. Besides these laboratory methods the site investi-gation program also included a number of measurements uncommon in ordinary site investigation programs. For instance were micro crack volume measurements per-formed and the crack initiation stress investigated. Furthermore, the influence of alter-ation on the strength of the rock was also investigated. The paper outlines some im-portant experiences gained within the laboratory program and presents a couple of results with the focus on the tests that are infrequent in ordinary site investigation pro-grams. 1 INTRODUCTION 1.1 Site investigation program In order to identify a suitable location for a geological repository for spent nuclear fuel at approximately 500 m depth in saturated granitic rock, the Swedish Nuclear and Fuel Management Company (SKB) has carried out a series of site investigations between 2002 and 2008 in two different areas, Forsmark (SKB 2008) and Laxemar (SKB 2009). Data collected from these site investigations have been interpreted and analysed to achieve a full site description of the area based on models for geology, thermal proper-ties, rock mechanics, hydrogeology, hydrogeochemistry, bedrock transport properties and surface ecosystems. All together these models build up an integrated understand-ing of the investigated sites (SKB 2008, 2009).
- Energy > Oil & Gas > Upstream (0.94)
- Water & Waste Management (0.91)