Britain's biggest nuclear reprocessing plant said on Friday it had detected raised levels of radioactivity and ordered all non-essential staff to stay at home.
Sellafield, on the coast of the Irish sea in northwest England, said the levels of radioactivity detected were above naturally occurring radiation, though there was no risk to the public or the workforce and the facilities were operating normally.
The British government said it was in constant contact with the site but had no reason to believe it was any more serious than the plant had said.
Sellafield said in a statement that "as a result of a conservative and prudent decision, the Sellafield site is operating normally but with reduced manning levels today", adding that only essential workers were being asked to report to work.
"All our facilities have positively confirmed there are no abnormal conditions and are operating normally," it said. "There is no risk to the general public or workforce."
Sellafield processes spent fuel and no longer produces power from nuclear. It is undergoing a decommissioning and dismantling programme, run by a consortium of British company Amec, French group Areva, and U.S. firm URS.
The plant, about 480 km northwest of London, employees over 10,000 and says it is the largest nuclear site in Europe.
It was the site of Britain's worst nuclear accident when a fire broke out in one of its reactors in 1957.
It also contains what its deputy managing director George Beveridge described in 2009 as "the most hazardous industrial building in western Europe", housing a 150-metre-long (490 feet) pond used to store spent nuclear fuel.
Britain's Prime Minister "David Cameron" has thrown his weight behind building new nuclear power stations as a way to replace ageing coal and nuclear power plants.
The government last year signed a $26 billion deal to build a new nuclear plant in southwest England with the support of France's EDF and two Chinese partners.
In April 2005, leaked radioactive waste was discovered from Sellafield's THORP reprocessing plant which may have started as early as August 2004. It was categorised as a level 3 event on the International Nuclear Event Scale, and resulted in fines.
Sellafield is a large and complex nuclear chemical facility located in West Cumbria.
The site has played a pivotal role in Britain's nuclear industry since the 1940s. Site operations include fuel reprocessing, fuel fabrication and storage of nuclear materials and radioactive waste.