38 'high-risk' particles are found in sea at Dounreay

Published on Wednesday 6 July 2011 13:41

MORE than 350 radioactive particles have been recovered from the seabed off Dounreay in the past nine weeks, with 38 said to be large enough to pose a significant health risk.

The particles were retrieved using a remotely operated vehicle working at depths of up to 30 metres. Over an area equivalent in size to 36 football pitches, the vehicle picked up 351 particles.

The latest haul, recovered in an operation which began in May and ended last week, takes the total number of radioactive particles found on the seabed and beaches near the Caithness nuclear site to more than 2,300.

Data from the operation is now being compiled and will be shared with the Particles Recovery Advisory Group, a team of independent experts who advise the Scottish Environment Protection Agency and Dounreay Site Restoration Ltd (DSRL), the company overseeing the decommissioning of the nuclear plant.

Bill Thomson, senior particles specialist at DSRL, said: "Analysis of the information from this year's work will allow us to assess how successful it has been and plan the scope of next year's offshore phase.

"The company modified some of the equipment and changed some of its practices after the 2010 campaign, and we're pleased with the improvements in performance this year."

The particle recovery operation costs more than 1 million a year. So far 384 of the particles recovered have been regarded as "significant", which means they have radioactivity greater than a million becquerels of caesium 137.

At such levels, particles can cause visible effects within a few hours if kept in stationary contact with skin, and serious ulceration after one or two weeks.

Routine monitoring is also continuing at beaches near Dounreay. A total of 481 particles have been recovered onshore, primarily from the Dounreay foreshore and nearby Sandside beach. The particles are fragments of irradiated nuclear fuel discharged to sea as a result of practices in reprocessing during the 1960s and 70s.

The most hazardous fragments have been found close to the old discharge point on the seabed, and their disintegration is believed to be the source of smaller, less hazardous particles detected on beaches.

The particles have caused concern at Dounreay for more than quarter of a century and their clean-up is a significant part of the decomissioning of the plant.

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.

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

The remotely operated vehicle is now used to sieve through the seabed off Dounreay while the specialist staff control its movements using an umbilical cable attached to a barge. The tracked, seabed crawler, based on technology developed for the offshore oil and gas industry, features a detection system capable of finding particles buried at least two metres deep in sediment.

Up to 25m will be spent on particle recovery. The work is part of the decommissioning of the Dounreay site over the next 15 years, at a cost of about 2.6 billion.