SPOKANE, Wash. -- Workers at a Washington state nuclear site where a tunnel filled with nuclear waste in railroad cars partially collapsed have safely sealed off a large sinkhole that emerged as a result of the collapse, U.S. Energy Secretary Rick Perry said Thursday.
Authorities also revealed that the 400-square foot sinkhole they filled with soil could have been there since last weekend before it was discovered Tuesday. That's because the area around the Hanford Nuclear Reservation's waste-filled tunnels is not observed every day by workers who patrol the site's sprawling grounds.
Authorities have detected no signs that radiation emanated from the collapsed tunnel, and the hole was filled with 53 truckloads of dirt delivered by workers wearing protective gear, Perry said.
Tuesday's discovery of the sinkhole prompted the evacuation of some nearby Hanford workers and an order for thousands more to stay inside buildings for several hours at the 500-square-mile expanse in Washington state's remote interior. No one was injured.
The plugging of the sinkhole "was accomplished swiftly and safely to help prevent any further complications," Perry said in a statement. "Our next step is to identify and implement longer-term measures to further reduce risks."
Beginning in 1943, Hanford made plutonium for nuclear weapons for more than 40 years, including for the bomb dropped over Nagasaki, Japan. Now, about 8,000 people are working on a cleanup that is expected to cost more than $100 billion and last through 2060.
The cause of the tunnel's partial roof cave-in is under investigation, said Mark Heeter, a spokesman for the Energy Department.
"We're not sure how long that will take," he said.
Also under investigation is when the cave-in happened. There is a vast amount of nuclear waste stored at the Hanford site, about the size of Rhode Island, and not all of the storage sites are inspected daily, Heeter said.
Authorities "don't know exactly when it occurred," he said, but they believe the cave-in could have happened as many as four days before the hole was found.
The agency said there was no sign that radiation escaped from the hole.
"The issue is whether or not there's sufficient wind to start sucking materials out of that tunnel and into the environment," said Tom Carpenter, executive director of Hanford Challenge, a Hanford watchdog organization.
Carpenter said radioactive gamma rays are "certainly" coming out of the tunnel, but those diffuse quickly with distance and are not carried by wind. If radioactive dust or soil were to be released from the site, it would be a different story.
Radiation levels within the tunnels were lethal within an hour, according to Heart of America NW, another Hanford watchdog group.
The state of emergency declared at Hanford ended late Wednesday and most of the site's 9,000 workers were told to report back to work Thursday.
The tunnel collapse reinforced long-standing criticism that toxic remnants at Hanford are being stored in haphazard and unsafe conditions, and time is running out to deal with the problem.
Washington state officials on Wednesday demanded that the federal Energy Department immediately assess the integrity of all the Hanford tunnels.
"The infrastructure built to temporarily store radioactive waste is now more than a half-century old," said Maia Bellon, director of the state Department of Ecology, which oversees and regulates the federal government's Hanford cleanup.
The 360-foot long rail tunnel that collapsed was built in 1956 from timber, concrete and steel and covered with 8 feet of dirt. Eight flatbed railroad cars loaded with radioactive material were parked there in 1965.
A much larger nearby tunnel built in 1964 has 28 railroad cars with radioactive waste.
The Energy Department was warned in a 2015 report it commissioned that both tunnels were vulnerable to a collapse from an earthquake or deterioration of tunnel building materials caused by intense radiation, the report said.
And in 2016, the Hanford Advisory Board advised cleanup authorities to "expeditiously investigate" the risks posed by the tunnels.
The nearby Yakama Nation said it has warned about the safety of the tunnels for several years.
"No preventative action was taken," the tribe said in a statement.
The tribe also said the tunnels should be cleaned of radioactive waste and radiation long before a 2042 deadline set by a cleanup agreement between the federal and state governments.
The cleanup of Hanford's waste is expected to last until 2060 and cost an additional $100 billion over the $19 billion already spent.
Information for this article was contributed by Nicholas K. Geranios of The Associated Press and by Bob Young of The Seattle Times.
A Section on 05/12/2017