Twenty workers at a nuclear reprocessing plant have been contaminated with radioactive particles.
The alarm was raised after radiation was detected on the shoes of one worker at the Dounreay plant in Caithness, northern Scotland, the UK Atomic Energy Authority (UKAEA) said.
Two members of staff in the D2001 plant were found to have contaminated particles on their hands, while one of the pair also had particles on their face.
Radioactive dust was found on the shoes of a further 18 workers.
A UKAEA spokesman said: "The operation was stopped and the building was sealed off.
"There was no radioactive release to the environment and there is no evidence that any of the workers ingested any radiation."
Of the two staff found to have contamination on their skin, the spokesman added: "They were taken to our occupational health unit where efforts were made to clean the particles from their skin.
"Most of the contamination was cleaned from their skin and they were sent home wearing rubber gloves. It is difficult to quantify at the moment but we believe the risk to them to be low."
The cause of the incident is not yet known and an investigation is under way. The Health and Safety Nuclear Safety Inspectorate has been informed and is expected to launch a separate investigation into what went wrong.
At the time of the incident, 70 workers at the D2001 plant were carrying out decommissioning work using robotics arms to lift radioactive materials, which were shielded from them by protective screens.