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Bigger clean-up machine heads for Dounreay seabed

July 19, 2010

A computer-generated image of the seabed crawler

The next phase of work to remove particles from the seabed at Dounreay will get underway later this month.

Dounreay Site Restoration Ltd awarded a contract to Land and Marine Project Engineering Ltd earlier this year to build and operate an underwater system.

Its system is due to be lowered onto the seabed from a 60m-long surface barge later this month.

Following trials, it is expected to cover 12.5 hectares - equivalent to more than 17 international football pitches - of seabed where the particle population is highest, in the first of up to three summer campaigns.

The tracked, seabed crawler is similar in size to a small bulldozer and features a two metre-wide detection array supplied by Nuvia, similar to that used successfully to monitor local beaches, and capable of detecting particles buried at least 60 centimetres deep in the sediment.

Particles will be collected in two on-board tanks which will be returned to the surface and emptied aboard the barge. Separated particles will be returned to Dounreay.

The ROV is based on technology developed for the offshore oil and gas industry. It will be controlled using a 500-metre long umbilical cable and operated by specialist staff aboard the barge anchored 500 metres offshore from the site.

Approximately 20 workers employed by Land and Marine, Nuvia and DSRL will work around the clock in shifts on the barge.

Data from previous surveys of this part of the seabed predict that up to 700 particles may be located in the target area. Of these, more than 200 are thought to be in the category that, if encountered, could represent a “significant” risk to health.

Last year, during the first full season of seabed clean-up, a smaller system operated by a different company recovered 115 particles from just over 7.5 hectares of seabed with a lower predicted particle population. Of these, 28 particles were “significant”.

The particles – small fragments of irradiated nuclear fuel - were released from Dounreay via an old seabed discharge outlet used historically to dispose of effluent from the site’s fuel reprocessing plants. These plants are now being decommissioned and demolished as part of the site closure.

Once released to the seabed, particles behave like grains of sand. Some have been buried in the seabed, with more than 1100 recovered there so far. Other particles have been transported to local beaches and foreshores, with more than 400 recovered to date. Some particles will have been eroded and joined silt deposits in deep water where they are likely to remain.

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