Geotechnical investigations for a deep radioactive waste repository: drilling

Abstract

AbstractComprehensive geotechnical investigations of potential repository sites for deep disposal of low- and intermediate-level solid radioactive wastes at Sellafield, Cumbria and Dounreay, Highland Region included drilling and testing cored boreholes up to 2000 m deep. The drilling technology used combines geotechnical site investigation procedures with oil and gas drilling technology and mineral exploration wireline methods to produce high-quality continuous cores. The drilling programmes are closely linked to geophysical and hydrogeological and geochemical test schedules. At Sellafield, deep boreholes are drilled with standard diesel electric and mechanical oilfield land rigs modified with top-drive units for heavy-duty wireline coring and sensitive mud control, well control and automatic drilling systems. Lorry-mounted site investigation rigs are used for shallow boreholes which have been drilled for pump testing and in situ stress measurements. At Dounreay a hydraulic top-drive mining exploration rig was used for deep drilling. Triple tube corebarrels have been used throughout which include uPVC liners for core protection. By October 1994, 31 boreholes had been drilled, with over 19 km cored out of a total depth of 26'/2 km. A summary of the equipment and procedures adopted is presented together with some comments on the application of these experiences to future geotechnical investigations.