Dounreay Site Restoration Ltd -Shaft and Silo

Home
» Decommissioning
» Shaft and Silo

Shaft and Silo

A vertical shaft was built at Dounreay in the 1950s to remove rock spoil during excavation of a subsea tunnel for the site's effluent discharge pipes. In 1958, it was authorised by the Government as a disposal facility for what today is known as intermediate-level waste.

More than 11,000 disposals of waste occurred until 1977 when there was an explosion. It is thought to have been caused by a build-up of hydrogen gas caused by a reaction between water in the shaft and sodium present among the waste.

By the late 1990s, advances in technology lead to a decision to empty the shaft.

The first phase of decommissioning involves isolating the shaft from the groundwater that flows into the unlined shaft. Following public consultation, grouting of the rock fissures around the shaft was selected. This has involved building a raised working platform and drilling up to 400 boreholes around the shaft. Grout was injected through the boreholes to seal fissures in the rock creating a giant containment in the shape of a boot around the shaft, greatly reducing the amount of water that gets into the shaft.

The grout curtain was completed in 2008, ahead of programme and budget.

The next stage is the removal, treatment and storage of the waste. Concept designs have been developed for waste retrieval, treatment and storage facilities. These facilities will also be used to decommission the nearby wet silo, which succeeded the shaft in 1971 as a storage facility for the site's intermediate-level waste.

In March 2010, DSRL announced a delay to the construction of these facilities. Click here to read more.

Estimated lifetime costs of this work are in the region of £240 million.

Waste retrieved from the shaft and silo will be segregated, characterised and conditioned in containers of cement for above-ground storage pending a national management strategy for intermediate-level waste.

Retrieval of the waste is unique among nuclear decommissioning challenges worldwide. Extracting radioactive waste and sludges from a narrow vertical shaft represents one of the biggest jobs in the UK.

Artist's impression, in the foreground, of the waste retrieval facilities above the shaft and silo