Sellafield partly closed after 'above normal' radiation
The Sellafield nuclear reprocessing plant in Cumbria is partially closed after "elevated levels of radioactivity" were detected.
Each building was checked after a perimeter alarm was triggered at the north of the site.
The company later said it was naturally occurring background radiation and not attributable to any issue or problem with any operation on site.
A spokesman stressed there was no risk to the public or workforce.
He added: "There can be no guessing on nuclear sites".
Rory O'Neill, director of stakeholder relations, said: "One of the 20-odd site perimeter monitors that we have is registering above normal levels of radiation.
"It's not a level that would trigger any kind of activity on or off site. It's below levels that would demand us to do sheltering or anything like that."'Right decision'
In a statement, The Department of Energy and Climate Change said: "We are in constant contact with Sellafield, but we have no reason to believe that it is any more serious than they've said."
Part of the plant is being cleared to allow detailed investigations and the "relevant experts" are on site, a Sellafield spokesman said.
- The plant is being decommissioned, infrastructure dismantled and nuclear waste decontaminated
- The cost of decommissioning the plant has been estimated at over £70bn
- In April 2005 a leak of radioactive waste was found at Sellafield's Thorp plant which was categorised as a level three event (out of seven) on the International Nuclear Event Scale and resulted in fines
- In 2010 the government said Sellafield was one of eight possible sites considered suitable for future nuclear power stations
- A year later it said it hoped an electricity generating company would choose to build a power station there by 2025
- Objections to the site have been raised by Ireland, Norway and the Isle of Man which are concerned by the risks of contamination
- Source: Reuters
David Moore, chairman of the West Cumbria Cumbria Stakeholders' Group, an independent watchdog funded by the Nuclear Decommissioning Authority, said the company's actions did not imply "anything has gone wrong on the site".
"They've never been scared to raise the levels for safety," he said. "I think they've taken the right decision here."
Sellafield later said in a statement: "Our in-air monitors are extremely sensitive and pick up on any abnormality.
"Overnight the monitoring system initially indicated elevated levels of activity.
"Following investigation and analysis, we can now confirm these levels to be naturally occurring background radon.
"We would like to thank our staff and the wider West Cumbrian community for their calm and mature response to events this morning."
Day personnel, agency staff and contractors have been told to stay at home until Monday.
Other workers, including transport and utilities personnel, are working as normal "in support of plant continuity requirements".
Paddy Regan, professor of nuclear physics at the University of Surrey, said removing staff from site in such circumstances was "standard protocol" and a "sensible precaution" although rare.
The alarm would be reported to the International Atomic Energy Agency, but was not currently at a level measured by the International Nuclear Event Scale, Sellafield said.
As well as reprocessing nuclear fuel, Sellafield houses most of the country's highly radioactive waste and its whole civil plutonium stockpile.
Malcolm Grimston, an energy expert from thinktank Chatham House, said there had been a "real cultural change" at the company which meant it was "much more open and honest".