In the 1950s and 1960s, two tunnels were constructed next to PUREX, in an industrial area near the center of Hanford that is called the 200 East Area.
It was unclear if any radioactive materials were released into the air.
"The Hanford Fire Department is on scene", the Department of Energy reports.
Access to the affected area, which is located in the center of the Hanford Site, has been restricted to protect employees.
The senior Democrat on the House Energy and Commerce Committee said he is requesting that the Energy Department brief the committee on the root cause of the collapse. It is now being dismantled and cleaned up by the Energy Department.
A tunnel near the site contains several rail cars that have been temporarily buried because they were used to transport irradiated fuel rods and remain contaminated.
Antonio Conte hopes Chelsea wrap up Premier League title at West Brom
Fabregas became the first player in the history of the Premiership who had 10 or more assists in 6 different seasons. Antonio Conte wants Chelsea to claim the Premier League title at the first opportunity at West Brom on Friday.
The U.S. Department of Energy spends about $6 billion a year on managing waste left from the production of nuclear weapons.
Ferguson said that since the early 1980s, hundreds of workers have been exposed to vapors escaping from the tanks and that those breathing the vapors developed nosebleeds, chest and lung pain, headaches, coughing, sore throats, irritated eyes and difficulty breathing.
Washington Gov. Jay Inslee says the safety of Hanford's 9,000 employees is the top priority.
Previously, plutonium to be used for nuclear weapons was manufactured at Hanford.
He added that workers in other areas were told to take cover after emergency crews discovered that the roof of the tunnel had collapsed. Workers are also monitoring the air in the vicinity, using robots to detect any contamination. The U.S. Department of Energy said the collapse covered about 400 square feet (37.1 square meters) instead of the 16 square feet (1.4 square meters) first reported. That tunnel feeds into a longer tunnel that extends hundreds more feet and contains 28 rail cars loaded with more contaminated equipment, according to the Department of Energy. It was created by the USA government to produce huge amounts of plutonium, which is used in the creation of nuclear weapons.
A section of an underground storage tunnel in a plutonium uranium extraction (PUREX) plant collapsed at the Hanford Nuclear Reservation early Tuesday morning, prompting authorities to declare emergency at the Washington state site.
Personnel at the site have been evacuated, the department says, and workers nearby have been sent indoors "as a precaution". The site handled huge quantities of radioactive material, including the creation of more than 20 million pieces of uranium metal fuel, the processing of more than 110,000 tons of fuel and the discharge of 53 million gallons of radioactive waste to underground tanks, according to the DOE's website.