A judge has ruled that the operators of the Dounreay nuclear plant breached safety regulations.
Radioactive particles have been found on a beach
The decision, at the Court of Session in Edinburgh, marks a partial victory for businessman Geoffrey Minter, who lives near the nuclear plant in Caithness.
Mr Minter went to court after radioactive particles were found on Sandside Beach, which he owns.
By the time the case reached court in February the number of particles was 22 but it had jumped to 38 before the proceedings ended.
In a written decision, the judge, Lady Paton, said the law did not allow her to order the detailed clean-up which Mr Minter had demanded in place of the current monitoring regime.
Mr Minter owns the nearby Sandside beach
But she held that the UK Atomic Energy Authority (UKAEA), which operates the Dounreay plant, had failed its duty under the Nuclear Installations Act 1965.
This says the UKAEA must ensure that nuclear material causes no injury or damage to property.
She added that, despite the stress and anxiety claimed by the Minters and
the effect on their property, no personal injury had been suffered.
The Scottish Environment Protection Agency had told the court the radioactivity of the particles was so low there would be "no directly observable effects on human health".
Mr Minter welcomed the ruling and said he had been motivated by a desire
to "restore" the beach for his family and the public.
He said: "UKAEA has always denied this failure to comply with its statutory duties.
"We have no doubt the matter will now be resolved properly. We continue to
follow sound legal advice."
Mr Minter said he was considering whether to seek compensation.
He also said he would continue to call for the "full removal" of
particles from the beach.
The UKAEA said it would continue to seek guidance from its Dounreay Particles
Advisory Group, a panel of scientists set up to monitor appearances of particles
around the power station.