Decommissioning

This week Dounreay Site Restoration Lts is our profiled company. We get the latest on the radiation survey of its thorium plant and provide filmed coverage of the milestone effort.

By Katherine Steiner-Dicks

Twenty years ago a chemical plant was built in the UK to process fuel from Germany’s high temperature nuclear reactor programme.

Today, that plant is being scrapped and marks the latest piece of Dounreay to be shut down and turned into radioactive waste.

David Manson, senior project manager at Dounreay Site Restoration Ltd, said: “For six weeks, the team entered the containment built around the redundant equipment in airline suits and used a variety of standard size-reduction techniques, such as metal saws and the like, to clear out the plant.”

“We are now surveying the inside of the empty containment area to make to make sure radiation levels are low and contamination has been removed before we open up this area of the building again.

“When that’s done, we’ll dismantle the containment, move it into position around the next part of the plant scheduled for decommissioning and begin the process again.”

The filmed survey workers looked like they were participating in the latest Steven Spielberg film, donning protective suits to obviously protect them from any residual radioactivity.

Even special housing was built around the process line to contain any radioactive contamination released during its dismantling.

They are now carrying out a radiation survey of the empty floorspace and walls where the process line once stood – the final step before its decommissioning can be declared complete.

The process line was installed inside Dounreay’s uranium recovery plant in 1990 when the site won a contract to recycle 70 tonnes of unirradiated fuel designed for the Thorium High Temperature Reactor, or THTR, at Julich, Germany.

The fuel was in the form of more than 360,000 graphite balls, each of which contained micro-spheres made from enriched uranium, thorium, silicon carbide and graphite.

Each sphere was mechanically broken down to allow the micro-spheres to be separated from the bulk graphite, before the micro-spheres were crushed and dissolved so the heavy metal could be chemically separated and recovered for re-use.

Processing of the fuel took place between 1992 and 1996, when the line was mothballed.

The rest of the uranium recovery works shut down in 1998 and the entire plant is now being decommissioned.

The final piece of the thorium line to be removed was an evaporator.

Its successful removal means approximately one-third of the whole uranium plant has been safely dismantled so far and consigned as radioactive waste. Dismantling the thorium line generated almost nine tonnes of low-level waste and 315kg of intermediate-level waste.

The entire building is on course for demolition in 2019.

Click here to watch a video of the plant being decommissioned.