A tunnel collapse at Washington's Hanford Nuclear Reservation on Tuesday morning caused workers to flee for cover and officials to prioritize the site's cleanup.
Currently considered to be the most contaminated nuclear weapons plant in the US, the Hanford site - which is about half the size of Rhode Island - has leaked over 1 million gallons of radioactive material into the surrounding earth.
The collapse was discovered when site workers at 8:26 Tuesday morning noticed that the ground above the tunnel was four feet lower than usual.
The tunnel containing rail cars full of highly contaminated materials collapsed.
Hundreds of workers went into a "take cover" position after the tunnel, which was hundreds of feet long and contained plutonium uranium extraction (PUREX), collapsed.
The PUREX compound was built in the early 1950’s and processed more than 70,000 tons of uranium fuel rods while it was operational.
Robots are being used to detect possible air contamination.
However, officials say no radiation was released in the collapse, and no one was hurt.
Investigations show that 20 feet of the 100-foot-long tunnel had collapsed. The US Department of Energy reported that the collapse covered 400 square feet (37.1 square meters), instead of the 16 square feet (1.4 square meters) first reported.
Speaking to NBC News, Hanford Joint Information Center Deputy News Manager Destry Henderson said, "I would underscore this is confined to a small area of the Hanford site. The facility does have radiological contamination right now but there is no indication of a radiological release."
Though original orders from a manager ordered personnel to "secure ventilation" in their buildings and "refrain from eating or drinking," those orders were eventually repealed.
Earlier, a radio alert in the area of the plant said, "Due to the emergency in the 200 east area at PUREX, 200 east area personnel are allowed to move to the nearest buildings to use the restrooms. Once in the buildings, personnel are to stay in the buildings."
This warning was also repealed, and employees were allowed to go home.
Washington Governor Jay Inslee said in a statement, "This is a serious situation, and ensuring the safety of the workers and the community is the top priority. Our understanding is that the site went into immediate lockdown, in which workers were told to seek shelter, and all access to the area has been closed."
During his confirmation hearing, Energy Secretary Rick Perry said, "I am committed to working with you in prioritizing what is one of the most dangerous, polluted sites we have in the country. The country’s commitment to do this has been a failure, from my perspective."
Over 8,000 people are working to clean up the Hanford site, but cleanup, which began in 1989, is expected to take 50 years.
Meanwhile, the 1-million-gallon "double shell" tanks which hold most of the site's nuclear waste are aging and need to be replaced: The waste has already breached the inner tank, and some experts worry it has breached the outer tank as well.