Dounreay waste shaft plan

1 October 2004

UKAEA has announced plans to begin its £16 million waste shaft isolation project at its Dounreay site in Scotland. The contract for the work has been awarded to Scotland-based Ritchies, the specialist geotechnical division of Edmund Nuttall.

The shaft isolation work is the first step towards removing 850m3 of mixed waste from the 65m deep shaft via special shielded headworks. A 10m-thick band of rock around the shaft will be sealed with micro-fine cementatious grout. A series of exploratory boreholes and grouting trials are scheduled over the next 12 months before work to isolate the shaft begins in Autumn 2005. Between 350 and 400 boreholes will be drilled in an oval-shaped ring around the shaft and these will be injected with grout in an operation expected to take 2-4 years to complete. The programme of work includes the reinforcement of a plug at the base of the shaft with high-strength concrete to ensure it can withstand the changes in water pressure that are expected to occur when waste retrieval begins.

Norman Harrison, director of the Dounreay site, said: “With that grout ‘curtain’ in position, we will be able to say with real, absolute confidence that the shaft contents are isolated from the environment.”

Currently, most of the groundwater entering the shaft is pumped out, checked and discharged to sea. However, a small amount is known to have flowed through the shaft since the 1950s, transporting radioactivity that has contaminated the rock on the seaward side. Surveys indicate this is equivalent to 3% of the activity routinely pumped out and discharged to sea.

Meanwhile, Harrison used the launch of the project to warn of the consequences to safety and the environment of cheaper decommissioning contracts. He fears the result of site management competition after the onset of the Nuclear Decommissioning Authority (planned for April 2005) could be poor quality work, detrimental environmental effects and a lack of commitment to the local community. His warning stems from past experience at Dounreay, when increased use of contractors led to a highly critical safety audit by regulators.

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