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Summary:
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The purpose of the ONKALO Underground Characterisation and Research Programme (UCRP) is to explore Olkiluoto rock conditions and thereby enhance the current geoscientific understanding of the site, to allow the submission of an application for a construction licence for the deep repository. The characterisation programme has the following geoscientific goals:
- to develop and demonstrate techniques for detailed characterising volumes of rock from the underground,
- to update the current descriptive model of Olkiluoto bedrock and to increase confidence in this model such that it will serve the needs of construction and the Preliminary Safety Assessment Report (PSAR) in the construction
licence application, and
- to identify volumes of rock that could be suitable for housing parts of the repository.
The development of ONKALO will be based on coordinated investigation, design and construction activities. Mapping data from the tunnel front and data obtained from short probe holes will constitute most of the data needed to control the construction of ONKALO. Pilot holes will be drilled along the tunnel profile as the excavation proceeds and investigations will be carried out for geological, rock mechanics, hydrogeological and hydrogeochemical characterisation. Investigations cover more detailed mapping and sampling in parts of the tunnel, mapping and sampling of potential groundwater inflows to the tunnel and investigations from characterisation bore holes drilled from ONKALO. In addition, monitoring is planned in surface-drilled boreholes, in boreholes drilled from ONKALO, and in ONKALO itself. Monitoring will reveal changes in bedrock conditions and thus provide important information for site characterisation.
The information collected by characterisation and monitoring will all be assessed in an integrated modelling effort. The aim of this modelling is both to successively enhance the description and understanding of the rock volume around ONKALO and to assess potential impacts of ONKALO's construction and operation. Basically all geoscientific disciplines, geology, hydrogeology, geochemistry and rock mechanics follow the same workflow. Integration between modelling in different disciplines is essential and an integrated modelling task force will be formed.
Posiva will also use ONKALO for tests and experiments, in which the site-specific conditions at Olkiluoto have to be taken into account. The detailed programme for such testing will be developed once the tunnel progresses further. Already at present specific tests are planned related to construction and characterisation issues. These involve exploration of the mechanical and chemical impact on the rock and the impact of grouting.
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