Workers quickly evacuated the Plutonium Finishing Plant at Hanford Thursday after an alarm indicated that a criticality, or uncontrolled chain nuclear reaction, might have occurred.
Ninety minutes after the alarm sounded at 10:30 a.m. officials had confirmed that it was a false alarm. It sounded as maintenance was being done on the alarm system.
The criticality alarm is supposed to sound when monitors detect a large amount of radiation, which could indicate a criticality. An investigation to determine why it sounded during maintenance work is continuing.
About 50 workers left the building as a precaution and were surveyed for radiation contamination, said Geoff Tyree, Department of Energy spokesman. The worker checks were completed about 1 p.m. with no contamination found on any workers.
“Workers responded appropriately and safely evacuated the facility according to response plans,” Tyree said.
Environmental cleanup workers preparing the plant for demolition were not expected to return to their jobs inside the plant Thursday.
The plant was being checked for radiation that could have been spread during the evacuation. Usually workers take off anti-contamination protective gear as they exit areas of the plant known to have radioactive contamination to make sure it does not spread to areas of the plant without contamination.
Removal of the protective gear outside the plant slowed checks for worker contamination.
Protective suits are removed through a careful and deliberate process to make sure that any contamination on the gear is not spread as the suits are removed.
The Plutonium Finishing Plant in the central part of the nuclear reservation is Hanford’s most hazardous facility demolition project, according to DOE officials. Areas of the plant are highly contaminated with radioactive materials, including plutonium that easily disperses into the air.
The plant was used through the Cold War to turn plutonium in a liquid solution into buttons the size of hockey pucks for the nation’s nuclear weapons program.
Demolition on the production portion of the facility is expected to start this summer.