May 10 (UPI) -- Workers began filling in a tunnel containing radioactive waste collapsed at the Hanford Nuclear Reservation in southeastern Washington, the Department of Energy said Wednesday.
On Tuesday, nearly 4,800 employees took shelter indoors for five hours after a 20-foot-by-20-foot section of 360-foot-long tunnel containing eight railcars filled with radioactive material caved in. Non-essential workers were told to not return to work Wednesday.
Overnight, Crews worked laid a gravel bed to make a road for heavy equipment, the Department of Energy said in an advisory.
On Wednesday morning, crews began using soil to fill the cave-in. About 50 truckloads of soil would be needed to "stabilize that portion of the tunnel," the department said.
Workers are wearing protective suits and breathing masks, said the department, which issued a video of the remediation.
"All personnel are accounted for, there are no injuries," Hanford emergency center spokesman Destry Henderson said Tuesday. "There is no evidence of a radiological release."
The tunnel, which was sealed in 1965, contains 780 cubic yards of waste.
The Hanford Site is a mostly decommissioned nuclear production complex operated by the U.S. government on the Columbia River.
The 580-square-mile site produced plutonium, including material used in the first nuclear bomb, from from World War II through the Cold War. Hanford made more than 20 million pieces of uranium metal fuel for nine nuclear reactors along the Columbia River.
About 8,000 people are working on a massive cleanup that is expected to cost more than $100 billion and last through 2060.
On Wednesday, Washington Gov. Jay Inslee said the state Department of Ecology will ask the U.S. Department of Energy to determine the cause of the collapse, assess immediate risks and require actions to ensure the safe storage of the radioactive material.
"I am extremely concerned about what happened yesterday and how the Department of Energy can give us confidence that this will not happen again," Inslee said at a news conference.
"If you have collapsing tunnels that could expose workers this is a very dramatic concern."
Last year a new legal deadline required the Department of Energy to work toward assessing the waste disposal tunnels by September of this year.