THE UNITED Kingdom Atomic Energy Authority (UKAEA) has applied for planning permission to carry out field trials in preparation for hydraulic isolation to safeguard the Dounreay nuclear waste shaft.
Isolation of the 4.5m diameter, 65m deep unlined shaft's toxic contents is being carried out to stop the flow of contaminated groundwater into the highly fractured surrounding rock.
Sealing the shaft will pave the way for removing the waste as part of the decommissioning of Dounreay, on the north east tip of Scotland.
The application to the Highland Council seeks consent for Scottish geotechnical contractor Ritchies to carry out a full-scale trial of the techniques that will be used to grout up rock fissures. Results will help finalise design of the proposed isolation works, subject to a separate planning application this year.
UKAEA geologist Warren Jones said: 'The purpose of the field trials is to determine practical parameters such as the number and spacing of boreholes that will be required. It involves the drilling up to 50 boreholes to a depth of 65m on unused ground outside the site boundary, 200m to the east of the shaft.
'This area shares similar geological features to the shaft. The trials will enable us to submit the detailed data required for the shaft isolation planning application.' Boreholes will be drilled in a ring, similar to that proposed for full isolation. Grout injection pressure, volume and mix will be investigated.
Boreholes will be sealed and capped once trials are finished.
The shaft was used as a repository for nuclear waste from 1959. In 1977 an explosion in the shaft put an end to disposal but 750m 3ofradioactive waste had accumulated.
Ritchies was awarded the £16M isolation contract in October (GE November 04). If it goes ahead, work is expected to take between two and four years.