The latest radiation sweep of a public beach near Dounreay nuclear power plant has recovered the most active hot-spot so far detected.

Its discovery on Thursday came within hours of Dounreay being fined £140,000 at Wick Sheriff Court for releasing radioactive particles into the sea and illegally dumping radioactive waste over a 20-year period.

The fragment of metallic reactor fuel was found by the survey team on the west end of Sandside beach. It is the 85th particle discovered since Dounreay's operators, the UK Atomic Energy Authority, started monitoring the beauty spot 24 years ago.

A UKAEA spokeswoman said the latest find had an activity reading of 500,000 Becquerels. That is 20,000 Bq above the next hottest which was unearthed on January 22.

But Geoffrey Minter, whose estate company owns the beach, said: "This is a worrying trend and makes it all the more important that UKAEA gets on top of the issue."