RICHLAND, Wash. -- Thousands of workers at the Hanford Nuclear Reservation were told to stay home Wednesday as efforts began to plug a hole that developed in the partial collapse of a tunnel containing dangerous radioactive waste from the building of nuclear bomb materials.
A gravel road was built to the site of the roof collapse, and workers were expected to begin filling the hole with dirt on Wednesday, said Destry Henderson, a spokesman for the U.S. Department of Energy.
"We intend to start filling the hole today," Henderson said Wednesday.
Hanford, located in southcentral Washington state, has about 9,000 employees and most of them were told to stay home Wednesday, Henderson said.
A 400-square foot (37 square meters) section of the tunnel roof was discovered to have collapsed Tuesday morning, forcing thousands of workers to shelter-in-place for several hours.
Officials have detected no release of radiation and no workers were injured in the collapse of the unoccupied tunnel, Henderson said.
The rail tunnel was built in 1956 out of timber, concrete and steel, and topped by eight feet of dirt. It was 360 feet long (109.73 meters).
Radioactive materials were brought into the tunnel by rail cars for about a decade. The tunnel was sealed in 1965, with eight rail cars loaded with nuclear waste stored inside.
The tunnel is a prime example of the sort of temporary methods to store radioactive waste that abound in the nation's nuclear weapons complex. The government has been working since the late 1980s to clean up Hanford, and the work is expected to last until 2060 and cost another $100 billion.
U.S. Sen. Ron Wyden, D-Ore., a frequent Hanford critic, said the cave-in shows that the temporary solutions the Energy Department has used for decades are starting to fail.
"The longer it takes to clean up Hanford, the higher the risk will be to workers, the public and the environment," Wyden said.
Hanford, built by the Manhattan Project in World War II, contains the nation's greatest volume of radioactive waste left over from the production of plutonium for nuclear weapons. The most dangerous are 56 million gallons of waste stored in 177 aging underground storage tanks, some of which have leaked.
The tunnel roof collapse caused soil on the surface above to sink 2 to 4 feet (half to 1.2 meters) over a 400 square foot (37 square meters) area, officials said.
The anti-nuclear group Beyond Nuclear said the incident helped show "radioactive waste management is out of control."
Democratic U.S. Sen. Maria Cantwell of Washington said worker safety must be the priority.
"My thoughts are with the first responders who are working to assess the situation on the ground," she said.
Worker safety has long been a concern at Hanford, which is located about 200 miles (322 kilometers) southeast of Seattle.
Washington Attorney General Bob Ferguson filed a lawsuit last fall against the Energy Department and its contractor, Washington River Protection Solutions, contending vapors released from underground nuclear waste tanks posed a serious risk to workers.
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.
Lawyers for the Energy Department have said no evidence has been provided showing workers have been harmed by vapors.
The cause of the collapse was not immediately known. It was discovered Tuesday as part of a routine inspection.
Workers near the site were evacuated and hundreds of others farther away were told to remain indoors for several hours, the federal agency said.
"No action is currently required for residents of Benton and Franklin counties," the Energy Department said, referring to the nearly 300,000 residents near the site. "There is no indication of a release of contamination at this point."
U.S. Energy Secretary Rick Perry was briefed on the incident that Washington Gov. Jay Inslee called a serious situation.
"Ensuring the safety of the workers and the community is the top priority," said Inslee, a Democrat who previously represented the Hanford region in Congress.
The accident occurred at a plant known as the Plutonium Uranium Extraction Facility, or PUREX, located in the middle of the 500-square-mile (1,295-square-kilometer) Hanford site — half the size of Rhode Island.
The PUREX building is the length of three football fields and was used to recover plutonium from irradiated fuel rods.
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.
New Jersey Rep. Frank Pallone said the incident underscores the need for the department to take all necessary precautions to ensure the safety and security of workers.
The committee oversees the department's management of the cleanup efforts.
The Hanford site was built during World War II and made plutonium for most of the U.S. nuclear arsenal, including the bomb dropped on Nagasaki, Japan, at the end of the war.