US nuclear plant evacuated after tunnel collapse

Hundreds of workers at a nuclear site in the US state of Washington were ordered to take cover after a storage tunnel filled with contaminated material partially collapsed yesterday, but there was no indication of a radioactive leak.

Employees at the sprawling Hanford Site plant, located about 275 kilometres southeast of Seattle, were sent an early morning alert by management telling them to "secure ventilation" and refrain from "eating or drinking."

Federal officials said there was no sign that any radioactive material had leaked after crews discovered that a six-metre section of a  tunnel - containing rail cars filled with nuclear waste - had caved in.

By early afternoon, eating and drinking were allowed, and some workers were being authorized to leave -- but the areas closest to the tunnel remained in lockdown.

"All employees have been accounted for, there were no injuries and there is no indication of a spread of radiological contamination," said Destry Henderson, a spokesman for the Hanford Emergency Center.

The Hanford nuclear site was used to produce plutonium for the bomb that brought an end to World War II.

The Hanford Site was part of the Manhattan Project, which led to the production of the first atomic bombs, including the ones dropped on Hiroshima and Nagasaki in World War II. 

Its last reactor closed down in 1987 but millions of gallons of leftover waste are contained in tanks at the site.

Henderson said the alert was raised early Tuesday after employees at the Plutonium Uranium Extraction Facility (PUREX), a former chemical processing plant, noticed during a routine inspection that soil had sunk over one of two tunnels in the area.

"At that point... an emergency was declared and about half a dozen employees at the facility were evacuated," he said. 

He added that workers in other areas were told to take cover after emergency crews discovered that the roof of the tunnel had collapsed.

"There is no indication of a release of contamination at this point," a statement by the US Department of Energy said. "Responders are getting closer to the area where the soil has subsided for further visual inspection."

A photo posted on the Hanford Emergency Center's website shows a large hole in the roof of the tunnel.