NATURALLY occurring radiation was the cause of this morning's disruption at Sellafield, the nuclear processing company has confirmed.
It had been running at 'reduced manning levels' after elevated levels of radioactivity were discovered to the north end of the site.
Only essential workers were asked to report for work.
However this afternoon the company said: "Sellafield Ltd can confirm that the radioactivity detected by one of our in-air monitors overnight is not attributable to any issue or problem with any of our operations on site.
"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.
"The number one priority for us is, at all times, safe secure stewardship of the Sellafield site, which is the most complex and challenging nuclear site inEurope.
"As such we act in a safety conscious manner, and take cautious, conservative decisions, such as the one taken overnight to ask non-safety essential staff to stay at home this morning, rather than come to the site.
"All of our plants and storage facilities were quickly confirmed as operating normally, and we were always confident that the issue posed no risk to the workforce or public because the levels being detected, whilst above background radiation levels, were still low.
"This view was reinforced by the fact that none of our other installed monitors were picking up any kind of increased levels – however, we take such issues so seriously that we investigated fully to confirm that everything was okay.
"Standard weekend working operations will continue, with day staff due back in on Monday as normal.
"We would like to thank our staff and the wider West Cumbrian community for their calm and mature response to events this morning."