International Geologiical Congress - Oslo 2008

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NWG-02 Geology and disposal of nuclear waste: Nordic approach - special aspects of the disposal in crystalline bedrock

 

Äspö Hard Rock Laboratory most essential results in a 20 year perspective

 

Peter Hultgren, Swedish Nuclear Fuel and Waste Management Co (Sweden)
 

 

The Äspö Hard Rock Laboratory (HRL) provides an important scientific and technical basis for the programme of implementation and operation of a future deep repository in Sweden. The need for such an underground laboratory was identified at an early stage in the Swedish programme. Initially, the Stripa mine could be used, but at the beginning of the 1980's it was realised that an underground laboratory at a virgin site would be needed, because Stripa was an abandoned iron mine and disturbance on water flow in fractures had occurred in decades. Äspö HRL was constructed 1990 ?1995 to provide an opportunity for research, development and demonstration in a realistic and undisturbed rock environment down to the depth planned for a future deep repository for spent nuclear fuel. Äspö HRL is located on the Äspö Island in the municipality of Oskarshamn some 230 km south of Stockholm and c. 20 km north of the town of Oskarshamn. The site is dominated by well preserved intrusive rocks belonging to the c. 1.8 Ga generation of the Transscandinavian Igneous Belt (TIB). The bedrock in the Äspö area is dominated by generally porphyritic rocks of quartz monzodioritic to granodioritic, composition. Subordinate rock types comprise granite, generally porphyritic, fine-grained granite and various mafic rocks.
The ÄspÄ HRL is a laboratory for the development and testing of methods for detailed characterisation of the rock volume from excavated tunnels. Further, Äspö is a full scale laboratory for testing construction and handling techniques and for the demonstration of important parts of a repository system. Finally, it provides a multitude of data for development of our knowledge of important processes in deep crystalline bedrock and for testing of models for groundwater composition, groundwater flow and radionuclide migration. It is, in essence, a dress rehearsal for the deep repository.
Outcome of some key experiments were:
• A comparison between the prediction from pre-investigation data and the outcome from tunnel documentation has made it possible to judge the reliability of the site investigation methods based on surface and borehole data.
• Comparison of excavation induced damage of drilling and blast compared to full face drilling has been made. Advance studies of Excavation Disturbed Zone (EDZ), looking at cross sections from tunnel walls by sawing cuts was fruitful to understand the distribution of the damaged zone around the tunnels.
• Rock stress measurements, both from boreholes drilled from the surface and boreholes in the tunnel, have determined the rock stresses at Äspö HRL. Rock mass properties have been obtained from different locations in the tunnel.
• Special designed experiments in different scales have improved our understanding of how radionuclides are transported in a fractured network.

 

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