[en] The spent fuel from the Finnish nuclear power plants will be disposed of in the Finnish bedrock. Pos iva Oy is responsible for the site selection programme carried out in accordance with the governmental decisions. Preliminary site investigations were made in five areas in 1987-1992. Based on the results, three areas, Romuvaara in Kuhmo, Kivetty in Aeaenekoski and Olkiluoto in Eurajoki, were selected for the detailed site characterization in 1993-2000. The final site will be selected by the end of the year 2000. The interim reporting of the detailed studies of the three areas was made in 1996. In 1997, the island of Haestholmen, as the host to the Loviisa NPP, was included as a fourth candidate site in the programme for the detailed site investigations. The goal is to characterize this site also in detail by the end of 2000 to attain the same level of knowledge as available from the three other sites. The background information existing from the studies made for the construction of the repository for the low-and intermediate-level wastes will create a good basis to reach the target. The research programme for the detailed site characterization has mainly been focused on groundwater flow and geochemistry due to their importance in terms of long-term safety of the repository. Equipment and methodology development by Posiva has introduced new tools that provide more accurate data on relevant parameters than the ones used in previous stages of site characterization. The programme also contains studies for additional information of the structural and geological properties of the bedrock towards the depth. Also predictive modelling has been made for evaluating the relevance of the assumptions made. The methods applied in the site characterization have comprised, e.g., geological mapping, deep core drilling, groundwater sampling and analyzing, hydraulic testing and geophysical measurements