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04.06.2002 12:00

Posiva chooses the access way - a tunnel leads in to the underground characterization facility

In the next few years, Posiva will start to construct an underground characterization facility on the island of Olkiluoto in Eurajoki, which has been selected as the site for the final disposal facility of spent nuclear fuel. This characterization facility is called ONKALO, and it will be used to acquire detailed information about the bedrock in Olkiluoto, to be utilised in the planning of the final disposal facility. After an evaluation of various access way types for ONKALO, it has been decided to use an access tunnel. Another alternative that was considered would have been a shaft type access way.

The underground characterization facility consists of the access tunnel and an associated ventilation tunnel, as well as research levels at depths of 300, 400 and 500 metres. ONKALO will finally be used as part of the final disposal facility.

The selection of the access way type was based on thorough comparison of the alternatives, focusing on long-term safety, as well as the requirements related to research activities and technical implementation. The access tunnel was chosen over the shaft type solution as it creates better opportunities to engage in the research activities already during the construction period, and will also be a more flexible solution from the point of view of the final disposal facility. Transport functions (e.g. transport of equipment and the excavated rock) are also easier to carry out in a tunnel than in a shaft.

Finland possesses high-class expertise in the construction technology of access tunnels and the project can be completed by Finnish contractors. The influence of the access tunnel on the characteristics of the final disposal bedrock can be managed by careful selection of the tunnel's location, by maintaining a sufficient distance to the actual final disposal area and by using adequate sealing. The total length of the access tunnel will be some five kilometres and it will reach a depth of ca. 500 metres.

According to the plans, the application of the construction licence for ONKALO will be filed with the Municipal Council of Eurajoki by the end of this year. The construction of the tunnel is scheduled to start in 2004 and the total length of the construction period is estimated to be 5-6 years. Research activities at the main research level at a depth of 400 meters can probably be started already 3-4 years after the excavation work has commenced.

Once ONKALO has been constructed and the underground characterization studies completed, the project will move on to the construction of the actual final disposal facility. The final disposal of spent nuclear fuel is scheduled to start in 2020.

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