As a part of the detailed site investigation programme for final disposal of high-level nuclear waste in Finland, rock stress measurements were carried out at three candidate sites. Both hydraulic fracturing and overcoring methods were used. Overcoring measurements were conducted successfully at three depth levels; 300 m, 450 m and 600 m in water-filled boreholes. The hydraulic fracturing method was used between 300 m and 800 m depth levels. The measured magnitudes (σH) were lower than anticipated from previous measurements conducted in Finland.
Comme une partie du programme des investigations detaillees de chantier pour enlèvement final des dechets nucleaires de haut niveau en Finlande, des mesurages des contraintes dans la roche ont ete effectues sur trois chantiers differents. Toutes les deux methodes "fracturation hydraulique" et "mesurage tridimensionel des contraintes" ont ete utilisees. Des mesurages tridimensionels des contraintes ont ete pratiques avec success a trois niveaux de profondeur, soit 300 m, 450 m et 600 m dans des forages plein d'eaux. La methode de fracturation hydraulic a ete utilisee du niveau de profondeur de 300 m a la profondeur de 800 m. Les magnitudes mesurees (σH) ont ete plus faibles que prevues en comparaison des mesurages presedents realise en Finlande.
Als ein Teil des detaillierten Baustellen-Untersuchungsprogramms zur Endlagerung stark radioaktiver Abfalle in Finnland, wurden an drei Stellen Gebirgsspannungsmessungen Vorgenommen. Sowohl Hydrofrac-Spannungsmessung als auch Überbohrverfahren kamen zum Einsatz. Die Überbohrmessungen wurden erfolgreich auf drei Tiefenniveaus 300 m, 450 m, und 600 m in wassergefuellten Bohrlöchern ausgefuehrt. Das Hydrofrac-Spannungsmessung- Verfahren wurde auf Tiefenniveaus zwischen 300 m und 800 m durchgefuehrt. Die gemessenen Größen (σH) lagen niedriger als dies nach vorherigen in Finnland durchgefuehrten Messungen zu erwarten war.
In Finland electricity is produced by four nuclear power reactors at two sites. Teollisuuden Voima Oy (TVO) operates two BWR units at the Olkiluoto nuclear power plant in Southwestern Finland and Imatran Voima Oy (IVO) operates two PWR units at the Loviisa plant in Southern Finland. The preliminary bedrock investigations concerning the final disposal of the spent nuclear fuel were completed during 1987–1992 in five areas (TVO 1992). The site investigation programme continues with detailed site investigations between 1993–2000 in three areas. The three areas (Figure 1), Kuhmo Romuvaara, Äanekoski Kivetty and Eurajoki Olkiluoto, were selected as the most suitable for further examination as a result of the preliminary site investigations. The final site for disposal of highlevel waste will be selected in the year 2000. After confirmatory investigations the construction of the repository will commence in the year 2010. The final disposal will be commissioned in the year 2020.
The guiding principle in the selection of the sites for investigation has been the notion that emerged from the safety analysis that it is not necessary to select a site which possesses one specific quality of bedrock but that it is sufficient for the bedrock of the site selected to be suitable for the final disposal of nuclear waste in accordance with the multiple barrier principle. The purpose of the site investigations is to define the properties of the site with a view to adapting the repository design to it and to present the results in a comprehensible manner for use in the safety analysis and technical planning.
