A nuclear reprocessing plant in Cumbria, northeast England, was partially closed Friday following "the detection of elevated levels of radioactivity". Plant operator Sellafield Ltd. said the site would run at "reduced manning levels today" after radioactivity readings exceeded naturally occurring levels. Sellafield said no evidence of a radioactive release or accident had been found; however, "there can be no guessing on nuclear sites." "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. It stressed in a statement there was no risk to the public or workforce. "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," said Rory O'Neill, director of stakeholder relations. The authorities said that they were in constant contact with Sellafield but had no reason to believe it was any more serious than they had said. The plant, about 480 km northwest of London, is the largest nuclear site in Britain. It has played a key role in Britain's nuclear industry since the 1940s. A fire broke out in one of the site's reactors in 1957, the worst nuclear accident in Britain