About 350 people at Hanford were ordered to take cover indoors as a precaution after a monitor detected low levels of airborne radioactive contamination on Thursday.
Open-air demolition using heavy equipment was being done at the Plutonium Finishing Plant in central Hanford when the alarm sounded. Work to tear down the building has been underway since Nov. 1.
The alarm went off just before 7 a.m., and the take-cover order was lifted about 10:45 a.m. Initial surveys for contamination have been completed, showing workers were not at risk.
Some small spots of low-level radioactive contamination were found outside the area marked for radiological control near the demolition, according to Hanford officials. Before the take-cover order was lifted, a fixative was applied to the spots to glue contamination in place and keep it from becoming airborne.
The alarm sounded as crews were using a shear on the end of an excavator arm to peel off the outer face of a large glove box along the length of the highly contaminated Plutonium Reclamation Facility at the plant.
The tall central area of the facility, called a canyon, is lined with two levels of glove boxes on either side, and work was being done on the upper glove box on one side of the canyon. The outside of the building had been torn down to expose the glove boxes within.
Work crews immediately stopped demolition and applied fixative to the glove box to help contain any further spread of radioactive material, according to a Department of Energy statement.
By mid-morning, low levels of radioactive contamination had been found near the demolition zone, including on sidewalks. The contamination also was found near a station where employees pick up respirators and near a vehicle access gate.
No injuries were reported and no contamination was found on the skin of workers, who were wearing protective clothing. There was no evidence that radioactive particles had been inhaled, said Destry Henderson, spokesman for Hanford contractor CH2M Hill Plateau Remediation Co.
“Air monitoring alarms during demolition are not unexpected,” DOE said in a statement. “This is one of the monitoring tools used to ensure demolition of the plant proceeds safely.”
As the plant is torn down with heavy equipment, water is sprayed to suppress dust and bright blue fixative is sprayed to glue any contamination in place. It colors most of the demolition area.
The canyon of the Plutonium Reclamation Facility is considered the most contaminated area of the Plutonium Finishing Plant, and the overall plant is considered the most hazardous demolition project at Hanford, according to DOE officials.
Open air demolition is challenging. That’s why we spent years preparing for demolition and have robust mitigation and monitoring in place.
Destry Henderson, CH2M spokesman
The canyon stands 34 feet tall and covers a 30-by-66-foot area. Skinny tanks, called pencil tanks, were hung in the canyon for use in a Cold War process to remove valuable plutonium from scrap material to increase production for the nation’s nuclear weapons program.
The canyon’s glove boxes are part of the structure of the building and could not be removed intact, as many of the glove boxes elsewhere at the Plutonium Finishing Plant were. Workers would reach their hands through heavy gloves attached to portals on the boxes to work with radioactive material inside the boxes, viewing the work through thick, leaded glass windows.
Work to clean out the Plutonium Finishing Plant for demolition took about 20 years, starting with stabilizing plutonium left in a liquid solution in the plant at the end of the Cold War.
Preparation work included removing equipment in the glove boxes at the Plutonium Reclamation Facility canyon. Crews then removed as much contamination from the glove boxes as possible and applied fixative.
“Open air demolition is challenging,” Henderson said. “That’s why we spent years preparing for demolition and have robust mitigation and monitoring in place.”
Workers also took cover at the Plutonium Finishing Plant on Jan. 27 when an air monitoring alarm sounded at the Plutonium Reclamation Facility. Because it was late afternoon on a Friday, fewer people were at the plant. Many Hanford workers are scheduled for 10-hour shifts Monday through Thursday.
In that incident, debris from demolition was being moved with heavy equipment, and contamination became airborne and spread beyond the zone where it was planned to be contained.
Radiological surveys found low levels of contamination on workers’ protective clothing, but no contamination was found on the street clothing they wore underneath or on their skin. Nasal smears found no evidence of inhaled contamination.
There also was a broader take-cover order for more than 3,000 Hanford workers on May 9 after a breach was discovered in central Hanford tunnel storing highly radioactive waste. Some workers remained indoors for several hours. No injuries or spread of contamination were reported in the incident.
The hole in the roof of the tunnel has been filled with sand and soil and plastic has been used to cover the entire waste storage tunnel as a temporary protective measure.