A tunnel inside a decommissioned nuclear production site in Hanford, Washington, collapsed on Tuesday. Employees were ordered to take cover over fears the collapse might have released radioactive material, but a state official told the Associated Press that radiation had not been released and there were no injuries. The Department of Energy previously said the tunnels contained “contaminated materials.” A source told KING 5 that road work nearby might have caused the collapse. Hanford, located along the Columbia River and 200 miles southeast of Seattle, is considered the most contaminated nuclear site in the United States. It was built during the Manhattan Project and produced plutonium used in the atomic bomb dropped on Nagasaki, Japan. The site was mostly decommissioned after the Cold War, and is the focus of a large environmental clean-up project. The site has 9,200 employees, not including contractors.