Susannah Frame

KING-TV, Seattle

RICHLAND, Wash. — Hundreds of workers at Hanford Nuclear Reservation were evacuated Tuesday after part of a tunnel, which stores rail cars filled with radioactive waste, collapsed.

Officials detected no radiation release, and no workers were in the tunnel when it caved in, said Randy Bradbury, a spokesman for the Washington state Department of Ecology. Around 11 a.m. PT, a robot was being used to sample contamination in the air and on the ground and did not find evidence of a release of contamination.

Hanford contractors working nearby were removed from the area immediately while those farther away on the the 586-square-mile site were told to remain indoors, but by 3 p.m. all nonessential personnel were told they could go home, according to the U.S. Department of Energy.

The complex, about half the size of Rhode Island and located along the Columbia River, has more than 9,000 employees.

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Early in the morning, a manager sent a message to all personnel telling them to "secure ventilation in your building" and "refrain from eating or drinking." Those restrictions were lifted around noon but most workers were told to continue to shelter in place.

The tunnel, which is hundreds of feet long and covered with about 8 feet of soil, contains highly contaminated materials such as trains that transported nuclear fuel rods. It connects to the Plutonium Uranium Extraction Facility, known at the site as PUREX.

The 20-foot-by-20-foot collapse occurred at one of two rail tunnels under the PUREX site, Bradbury said. In the past, rail cars full of radioactive waste were driven into the tunnels and buried.

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This incident caused the soil above the tunnel to sink 2 to 4 feet, according the Energy Department.

The closed PUREX plant was part of the nation’s nuclear weapons production complex.

Hanford — about 20 miles northwest of Richland, 150 miles southeast of Seattle and less than 50 miles from the Oregon border — was built during World War II and processed the plutonium for most of the U.S. nuclear arsenal, including the atomic bomb dropped on Nagasaki, Japan. For decades afterward, workers made plutonium for nuclear weapons.

Edwin Lyman, a senior scientist with the Union of Concerned Scientists, said the tunnel collapse is of great concern due to the potential for a release of radioactivity.

“It’s a wake-up call that there are risks across the nuclear weapons complex that are possibly quiescent, that can emerge at any time,” Lyman said. “I don’t think the Department of Energy is providing enough resources to address these issues with the urgency that they need.”

Another costly accident occurred at an underground nuclear waste repository in New Mexico in February 2014, when a drum filled with radioactive waste blew up. The facility was forced to close for nearly three years andreopened in January.

“We don’t know yet what the consequences of what happened at Hanford will be, but that has the potential to have a much more serious environmental release,” Lyman said. “They’re going to have to stabilize that site.”

Hanford's emergency operations center was activated at 8:26 a.m., and long-time workers think it may be the first time it was opened for a possible radioactive release. Oregon's Department of Energy also activated its own emergency operations center.

“Hanford is 35 miles away from Oregon,” said Rachel Wray, Oregon Energy Department spokeswoman. “We are concerned about Oregonians’ health and that concerns the food we eat.”

Winds at the time of the collapse were light at about 3 mph and variable, primarily from the south and southeast, according to Weather Underground.

More than 50,000 people live to the southeast in Richland, and almost 30,000 Oregonians live farther south in nearby communities of Boardman, Hermiston, Irrigon and Umatilla. About 6,000 people live in Desert Aire and Mattawa, Wash., less than 25 miles northwest of Hanford and downwind at the time of the incident.

Today the Hanford site contains 56 million gallons of radioactive waste and is the largest depository of radioactive waste from the Defense Department. Contractors are in the midst of a decades-long process of cleanup.

Contributing: Tracy Loew, (Salem, Ore.) Statesman Journal. The Associated Press. Follow Susannah Frame on Twitter: @SFrameK5