Bosses at Sellafield played down concerns after workers were told to stay away from the nuclear plant yesterday after a radiation scare.

The company launched an investigation after higher than normal radiation was detected at the reprocessing plant in Cumbria.

Sellafield Ltd insisted there was no danger, while the Prospect union said the part-closure of the plant was just a precaution.

Management said a perimeter alarm had been triggered at the north of the site, leading to buildings being checked by safety staff. They said no abnormal readings were found inside buildings.

"Levels of radioactivity detected are above naturally occurring radiation but well below that which would call for any actions to be taken by the workforce on or off the site," the company said.

"The site is at normal status and employees and operational plants are continuing to operate as investigations continue.

"All our facilities have positively confirmed there are no abnormal conditions."

Gill Wood of Prospect, which represents 5,000 nuclear specialists at Sellafield, said: "Non-essential staff have been advised to stay at home today while the relevant specialist team investigates.

"The company's decision to partially close some areas at the site is a precautionary and measured decision."

But Nuclear Free Local Authorities chairman Councillor Mark Hackett called for a full and independent inquiry.

He welcomed the prompt investigation but added: "This is another example of the ongoing danger of dealing with such sensitive and potentially harmful materials."