The UK Atomic Energy Authority (UKAEA) has signed an agreement with six companies to carry out one of the most complex decommissioning projects in the Dounreay Site Restoration Plan.

The alliance will use robots inside the concrete vault of the site’s experimental fast reactor to cut up and remove more than 9km of pipework contaminated by the liquid metal coolant. Decontamination of the reactor vessel and its associated pipework is due to begin once most of the coolant has been drained and after work has started to remove the remaining breeder fuel. It will take until 2013 at least to complete and cost up to £30 million.

UK energy minister Brian Wilson said: “The decommissioning of the Dounreay Fast Reactor provides an excellent opportunity for UK companies to undertake the necessary clear-up work. I have made a particular commitment to maintain as much of the work as feasible within the local area and I am delighted that today’s announcement will benefit both UK companies and the Caithness economy.” UKAEA site director Peter Welsh said: “This is a milestone in the site restoration plan. When this alliance finishes its task, we will have successfully completed the first and most crucial stage of decommissioning a reactor that represents one of the major engineering and environmental challenges on this site.” The Dounreay Fast Reactor, which operated from 1959 until 1977, used an alloy of sodium and potassium (NaK) as its coolant. Seventy-three tonnes of the liquid metal was removed from its secondary circuit shortly after its closure but 57 tonnes remain in the primary circuit. A significant number of the 977 elements still in its breeder blanket are jammed. All fuel has been removed from the core except a single experimental fuel assembly.

“Before we can dismantle the primary circuit, we must drain the remaining NaK and begin cutting out the breeder fuel,” explained Bob Mathews, UKAEA’s head of decommissioning at Dounreay. “We plan to remove and destroy the bulk of the NaK during 2004-05 and expect to announce shortly a separate alliance to remove the breeder fuel.” The six companies in the Fast Reactor Primary Circuit Decontamination Alliance with UKAEA are Halcrow (design), Interserve (mechanical and electrical), Edmund Nuttall (building and civil works) Mitsui Babcock (plant operations), NNC (safety and environment) and Framatome ANP (robotics).

Approximately £10 million of the contract value is expected to go to locally-based companies, with an initial 50 jobs created or retained locally. A key feature of the alliance will be the transfer of specialist skills, such as robotics, from major contractors to local firms. This will improve their ability to compete for future decommissioning work at Dounreay and elsewhere in the world.

The cutting and removal of the labyrinth of pipes that carried the radioactive NaK coolant within the heavily shielded concrete vault must be carried out remotely because of the levels of radiation present. Remotely operated vehicles, working in a temperature of minus 18°C to eliminate the risk of ignition in the NaK-wetted circuits, will lay their own working platforms before cutting sections of pipework into pieces that will be removed for cleaning and disposal.