The long-term programme aimed at selection of a site for a deep repository was initiated in Finland in 1983. This programme has come to end in 2001 and a new phase aimed at implementation of the geological disposal of spent fuel has been started. In this new phase the first milestone is the application for a construction license for the disposal facility around 2010. To fulfil the needs for detailed design of the disposal system, an underground rock characterisation facility (URCF) will be constructed at the representative depth at Olkiluoto. The excavation of this facility will start the work for underground characterisation, testing and demonstration, which is planned to be a continuous activity throughout the whole life cycle of the deep repository. The overall objectives for the underground site characterisation are 1) verification of the present conclusions on site suitability, 2) definition and identification of suitable rock volumes for repository space and 3) characterisation of planned host rock for detailed design, safety assessment and construction planning. The objective for verification aims at assessing that the Olkiluoto site meets the basic criteria for long-term safety and as well the basic requirements for construction and thus justifies the site selection. The two other main objectives are closely related to design of the repository and assessing the long-term safety of the site-specific disposal system. The most important objective of ONKALO should allow an in-depth investigation of the geological environment and to provide the opportunity to allow validation of models at more appropriate scales and conditions than can be achieved from the surface. In some areas, such as in demonstrating operational safety, in acquiring geological information at a repository scale and in constructional and operational feasibility, the ONKALO will provide the only reliable source of in situ data. The depth range envisaged for URCF called ONKALO is between 400 and 600 m. The location and underground geometry of access ramp is of significance. Development of ONKALO will begin in 2003 and it consists of surface facilities, access ramp and vertical shaft to the depth of 500 metres and characterisation and demonstration facilities. Total volume of the ONKALO underground facilities is approximately 250 000 m3. The development will be completed around 2010. The reconciliation of construction and investigations plays an important role through the project. Other major issues will be the management of groundwater conditions, workplace safety and documentation of the work.
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