A nine-week operation has recovered more than 350 particles of irradiated nuclear fuel from the seabed near Dounreay.
It takes the total number of particles now recovered from the marine environment around the former atomic research site to more than 2300.
The latest phase of underwater work yielded a total of 351 from an area equivalent in size to 36 international football pitches.
They were detected and retrieved using a remotely-operated vehicle working at depths of up to 30m.
All 351 were taken to Dounreay and are now being analysed. Provisional results indicate 38 are sufficiently large to be a “significant” risk to human health.
The ROV (remotely operated underwater vehicle) was operated from a 60m-long barge, LM Contractor, where a team of 22 worked around the clock.
Land and Marine, the main contractor, was set a target to cover 16.5ha. The ROV was lowered onto the seabed at the beginning of May and was withdrawn on 3 July, when it had completed 23.5ha. Approximately 3 weeks were lost to bad weather.
Data from the work is now being compiled and will be shared with the Particles Recovery Advisory Group, a group of independent experts who advise the Scottish Environment Protection Agency and DSRL.
“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,” said DSRL senior particles specialist Bill Thomson.
“This was the second year of the larger Land and Marine system. 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.”
Routine monitoring continues of beaches near Dounreay. A total of 481 particles have been recovered onshore, primarily from the Dounreay foreshore and nearby Sandside beach.