[en] The proposed nuclear waste repository is to be constructed at Olkiluoto which is situated on the Precambrian rocks of the Fennoscandian shield. The rocks are made up of a complex mix of meta-sediments and meta-igneous units that have undergone several episodes of metamorphism and tectonic deformation. The latter have resulted in the formation of a variety of planar features including a regional fabric, ductile shear zones, fracture zones and discrete fractures. It is within this poly-metamorphosed foliated and fractured rockmass that the repository is to be sited. In order to position the repository appropriately it is necessary to determine the geometry, spatial organization and properties of these zones of weakness and the properties of the intact rock. This report critically examines the procedures and techniques used to determine these various parameters and the rational behind the proposed location of the underground rock characterization facility (ONKALO) and its access tunnels and shafts. Particular attention is given to understanding the current stress field operating in the rock, the effect of the zones of weakness on the stress orientation and the confidence levels with which the position, geometry and properties of the major planar zones are known at the depth of the proposed repository. (orig.)