A tunnel collapse was discovered at the Hanford nuclear site Tuesday, months after experts called the Washington state facility "the most toxic place in America" and a "Chernobyl waiting to happen." Some 4,800 workers at the site were told to shelter indoors Tuesday morning after crews discovered the roof of a tunnel housing rail cars filled with radioactive waste had caved in, the Seattle Times reports. Nonessential workers out of a workforce of more than 9,000 were later told to go home early. Emergency officials told flights not to pass over the 580-square-mile Columbia River site, which produced plutonium for tens of thousands of nuclear weapons during the Cold War.
By Tuesday evening the incident was "moving from the emergency phase towards the recovery phase," with no workers injured or any sign of a release of radiation, the Department of Energy said. It's not clear, however, how the facility plans to deal with the 400-square-foot hole in the tunnel roof, reports the Spokesman-Review. "Sometimes you run into unexpected situations like this and our employees are figuring out a path forward to deal with it," an Emergency Operation Center spokesman says. The AP reports that the collapse has added to calls for improved worker safety at the site, which is undergoing a 50-year, $110 billion cleanup not expected to finish until 2060. (Read more nuclear waste stories.)