The radioactive material, ruthenium, was released when part of the complex used to encase high-level nuclear waste in glass was being warmed up after a week-long shut down for maintenance, according to a spokeswoman for British Nuclear Fuels.
"It was a higher than normal discharge from the vitrification plant stack but it did not break any legal limits. There was no danger to public health," she said.
All activities in the plant were stopped so the area could be checked and no radiation was found inside the building. But 250 workers employed to build an extension at the site downed tools on Tuesday in a one-day unofficial strike.
"We believe they think they were not properly informed about what happened, but we briefed the contractors and its up to their employers to tell them what happened," the spokeswoman said.
An urgent inquiry had been launched into the cause of the discharge she said.Reuse content