Advances in Classifications for Structural Modelling of the Olkiluoto Site
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$GYDQFHVLQ&ODVVLILFDWLRQVIRU6WUXFWXUDO0RGHOOLQJRIWKH2ONLOXRWR6LWH Tiina Vaittinen, Henry Ahokas, Pirjo Hellä & Pauli Saksa Fintact Oy Hopeatie 1 B, FIN-00440 Helsinki, Finland $%675$&7 The site characterization for the construction of the repository of spent nuclear fuel is carried out at Olkiluoto in Finland. The results of geological, geophysical, and hydrogeological investigations are integrated in a bedrock model to describe rock types, fractured zones and potential hydraulic connections. In modelling it is essential to determine structures important for construction of underground facilities. This question encompasses objectives and scale of the modelling. Important parameters in structural modelling are fracture frequency and hydraulic conductivity. The definitions need to be evaluated site-specific, because the geological circumstances control the properties of structures. An important issue is the possible existence of a boundary zone close to structures. ,1752'8&7,21 Posiva Oy is carrying out site characterization for the repository of spent nuclear fuel in Finland. The results of geological, geophysical, and hydrogeological investigations are integrated in a bedrock model to describe rock types, fractured zones and potential hydraulic connections. In modelling it is essential to determine structures important for construction of underground facilities. This question encompasses objectives and scale of the modelling. Several versions of the Olkiluoto bedrock model in site scale have been made during the past ten years. During the years the structure definitions have developed. In the near future also the local scale modelling will be introduced. Effects of the scale to the structure definitions are discussed. This presentation focuses on the definitions based on borehole data. The Olkiluoto bedrock model covers area of 35 km2 to the depth of 1.5 km. The modelled rock types of Olkiluoto are migmatitic mica gneisses, grey gneisses, granite pegmatites, and diabases. Migmatitic mica gneisses form the main volume of the rock mass. 2%-(&7,9(62)02'(//,1*$7',))(5(1767$*(62)&+$5$&7(5,6$7,21 The Olkiluoto Island has been one of the six sites investigated for the final disposal of the spent nuclear fuel in Finland. After screening the whole country, Olkiluoto was one of the selected sites for preliminary site characterisation carried out during 1987–1992. After the first stage, supplementary site characterisations brought new, more detailed information about the site. In 2001 Olkiluoto was selected as a primary disposal site alternative. The objectives of the bedrock model of Olkiluoto have been evolved with investigation stages. Three disciplines are described in the model, rock types, fractured zones, and potential hydraulic connections. In this presentation the terms ‘structural intersection’ and ‘structure’ are used for borehole intersections and modelled objects defined on the basis of both fracturing and hydraulic properties.
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