Campaigners have criticised the group

But nuclear campaigners said it does not go far enough.

The continuing discovery of particles on the site foreshore, a local beach and the seabed has been a thorn in the side of management at Dounreay.

The advisory group set up to help trace the source and the scale of the problem has praised efforts made to date.

But it said improvements must be made in offshore work.

Its report said the equipment surveying the seabed could not discriminate between the natural radiation and radioactivity from hotspots.

Clean-up call

Dounreay, which is operated by the UK Atomic Energy Authority, said it is already investigating the use of updated techniques.

It has agreed to respond positively to the group's recommendations.

But Scotland Against Nuclear Dumping has criticised what it sees as the advisory group's failure to put any pressure on the UKAEA to actually start cleaning up the seabed.

Twelve particles have been found close to Dounreay since 1983.