Diver robot to scour seabed in £25m Dounreay clean-up

Published on Friday 23 July 2010 15:38

A ROBOT the size of a small bulldozer is to sieve through the seabed off Dounreay to collect radioactive particles that have caused concern for more than quarter of a century.

The remotely operated vehicle (ROV) will be lowered from a barge anchored 550 yards off the Caithness complex later this month.

Specialist staff will control its movements using an umbilical cable and are expected to cover 31 acres, an area the size of 17 football pitches, in the first of three summer campaigns.

The tracked, seabed crawler is based on technology developed for the offshore oil and gas industry. It features a 7ft-wide detection system capable of finding particles buried at least 2ft deep in sediment.

About 20 workers will work around the clock in shifts. Particles will be collected in two on-board tanks which will be returned to the surface and emptied aboard the barge before being returned to Dounreay.

It is thought up to 700 particles may be found in the target area. Of these, more than 200 are thought to present a "significant" risk to health.

A Dounreay spokesman said: "Last year a smaller system by a different company recovered 115 particles from just over 18 acres of seabed with a lower predicted particle population. Of these, 28 particles were significant."

The particles, or hotspots, are fragments of irradiated nuclear fuel discharged into the sea during the 1960s and 1970s.

The scale of the problem was only realised by the UK Atomic Energy Authority in the late 1990s. Particles were removed from beaches, but those on the seabed were only monitored. Divers were later used to map the area of particles and remove any found before this was considered too dangerous.

In 2007, after a two-year consultation, it was decided to remove the most hazardous offshore particles while continuing to recover those on beaches.

The spokesman added: "Once released to the seabed, particles behave like grains of sand.

"Some have been buried in the seabed, with more than 1,100 recovered so far. Others have been transported to foreshores, with more than 400 recovered.

"Some particles will have joined silt in deep water."

Dounreay Site Restoration, the company in charge of the decommissioning, awarded a contract to Land and Marine Project Engineering this year to build and operate the underwater system.

Decommissioning over the next 15 years will cost about 2.6 billion. Up to 25 million will be spent combing an area of seabed the size of 60 football pitches and monitoring until the 2020s. The independent Dounreay Particles Advisory Group estimates seabed sediment contains 1,500 potentially harmful hotspots.