Update 3:05 PM: The Hanford Joint Information Center has released a video statement on the tunnel collapse:
Update 1:12 PM: It is now confirmed that the tunnel led to a plutonium-uranium extraction plant, not a plutonium finishing plant as previously reported. It is also confirmed that no workers were inside the tunnel when it collapsed, and all workers at the site have been evacuated.
In a statement to the AP, Randy Bradbury, a spokesperson for the Washington State Department of Ecology, said that there has been no release of radiation into the atmosphere.
Original Text: A tunnel containing radioactive materials has in Hanford, Washington. Workers at the plant are in a "take cover" position as a precaution.
The tunnel contained radioactive materials like train cars that were used to transport nuclear fuel rods. It's unknown whether the collapse released radioactive material into the atmosphere. Plant workers are being instructed to "secure ventilation" in their buildings and to "refrain from eating or drinking" in case of contamination.
Reports indicate that road work nearby may have triggered the collapse.
The Hanford site is also home to the LIGO gravitational wave observatory, although it is unknown whether the observatory is affected.