CH2M Hill Plateau Remediation Co. stopped demolition of the Hanford Site’s Plutonium Finishing Plant for two days this week after laboratory results came back positive for air samples collected in seven monitors.
The monitors were worn by workers on their lapels to detect radioactive contaminants near the air they breathe. A positive result could mean the workers inhaled airborne radioactive particles. The monitors were worn on three different days by six workers, with one worker turning in monitors on two days that tested positive.
CH2M suspended demolition Wednesday morning before work began after lab results came back positive for four lapel monitors worn the day before. The results were in addition to three other positive results in recent days. The Hanford Atomic Metal Trades Council (HAMTC), an umbrella group for 15 Hanford unions, issued a stop work order the same day about noon. Both parties agreed late Thursday afternoon that work could resume after two days of surveying for any spread of radioactive contamination.
The contractor expanded the boundaries of the control area around a demolition zone where airborne contaminants are more likely and where increased worker safety precautions are required.
The Plutonium Finishing Plant was used at the Washington state facility from 1949 to 1989 to convert plutonium in a liquid solution into oxide powder or buttons the size of hockey pucks for use in U.S. nuclear weapons.
The first two lapel monitors to test positive were worn on Dec. 8 in an area well away from demolition activities. The area is used to mix water and fixative to spray on areas being demolished to prevent the spread of radioactive particles. A monitor worn by a worker the next day in an area where demolished waste is loaded out for disposal also tested positive. A check for radiation in both areas found nothing unusual, and a recheck of the three air samples was ordered. The monitors can pick up readings from radon, which quickly decays.
The last four monitors that tested positive also were worn in the two work areas. CH2M halted work before a retest, which showed three of the positive results identified Tuesday were caused by radon. That left four monitors with positive results. Workers who turned them in have agreed to receive bioassay checks for contamination within their bodies, as recommended by CH2M. Results should be available in January, according to the Department of Energy. Chest counts, another check for internal radiation, also are being conducted.
The highest positive reading from one of the personal air monitors was for a potential dose of 11 millirems. However, some, but not all, of the potential reading appeared to be from radon. In comparison, the average U.S. resident is exposed to about 300 millirems annually from natural sources of radiation.
“We take this very, very seriously,” said Ty Blackford, president of CH2M at Hanford. “We are dealing with a form of contamination that is very, very hard to manage.” Radioactive particles at the plant, including plutonium, are flighty and must be managed carefully to keep them from becoming airborne.
In June about 31 workers at the Plutonium Finishing Plant inhaled low levels of radioactive contaminants. In that instance a continuous air monitor sounded an alarm during plant demolition and about 350 workers were ordered to take cover. But in the last few days no alarm sounded to indicate the presence of airborne contamination. Two other monitoring systems – stationary air monitors and sheets of metal checked for surface contamination – also showed no positive results in recent days. Workers who leave certain areas where radioactive material could be present are checked routinely for contamination, and none was found on their protective clothing or skin.
The two-day stop work order came as CH2M is close to finishing demolition first on the Plutonium Finishing Plant’s Plutonium Reclamation Facility, an area of the plant with the heaviest contamination, and then on what remains of the main plant. Blackford said demolition of the entire plant to slab on grade could be completed in a couple weeks.
