Workers evacuated or took cover and turned off ventilation systems after minor damage was discovered in the wall of a transport tunnel, a spokeswoman for the Department of Energy said by telephone from the Hanford Joint Information Center.
The collapse took place at the intersection of two tunnels used to store contaminated equipment since the 1950s, the statement said.
Right now, Hanford seems to be issuing blanket permissions for all non-essential workers in the larger "200 East" area to go home early, but again, there is no specific evidence of any health risk to workers in the station itself, let alone for those in the surrounding area.
Crews are still monitoring for contamination, but have not yet found any indication that contamination was released in the cave-in. The tunnel that is possibly affected is next to a plutonium uranium extraction facility. The source also said that crews doing road work nearby may have created enough vibration to cause the collapse, and that Vit Plant employees were in cover mode as well.
Washington Gov. Jay Inslee says the safety of Hanford's 9,000 employees is the top priority.
No spent nuclear fuel is stored in the tunnel, Energy Department officials said.
The 500-square mile Hanford reservation was established by the Manhattan Project during World War II to make plutonium, a key ingredient in nuclear weapons.
"There are concerns about subsidence in the soil covering railroad tunnels near a former chemical processing facility", a statement on the Hanford emergency information page says.
Randy Bradbury, a spokesman for the Washington state Department of Ecology, told the Associated Press there had been no release of radiation and no workers were injured.
The PUREX building is the length of three football fields and was used to recover plutonium from irradiated fuel rods. Most of the 56 million gallons of radioactive waste held at the facility is in underground tanks.
The Energy Department says no one was injured in the collapse and no radiation has been released. Energy Department Secretary Rick Perry has been briefed on the incident.
The committee oversees the department's management of the cleanup efforts. Hanford made the plutonium for the atomic bomb that was dropped on Nagasaki, Japan, and much of the plutonium for the nation's nuclear arsenal.