The number of workers with positive bioassay results has increased to seven since the spread of radioactive contamination was discovered in mid-December at the Hanford Site Plutonium Finishing Plant demolition zone. The seven workers are in addition to 31 workers discovered to have ingested or inhaled radioactive particles after a June spread of contamination during demolition of the plant at the Energy Department site in Washington state.
After the December incident, 282 central Hanford workers requested bioassays. Of those tests, 227 have had negative results and 48 have yet to be completed, according to the Department of Energy.
Estimated doses for the seven workers who most recently inhaled or ingested radioactive particles are small. The highest estimated dose was 10 to 20 millirem over 50 years from radioactive particles within the worker’s body. Five of the estimated disease were between 1 and 10 millirem and one was less than 1 millirem. In comparison, the average person in the United States receives about 300 millirem annually from natural background radiation, according to the Nuclear Regulatory Commission.
More contamination has been discovered outside the plant’s radiological control area, where workers are checked as they leave to make sure they have not been contaminated, as well as outside the access control area. A large area has been established around the Plutonium Finishing Plant campus where worker access is controlled. Personnel use offices and park elsewhere and are shuttled to the large access control area, which encompasses three nearby tank farms, U Plant, and some central Hanford streets.
On Feb. 8 a spot of radioactive contamination the size of a 50-cent piece was found on the step of one of the trailer offices lately being used by the Plutonium Finishing Plant project outside the access control area, and the step was removed. The office has been used for plant work since January. Although no cause has been determined for the Feb. 8 incident, Hanford officials have widened a buffer zone around the radiological control area and workers have their shoes and hands checked for contamination before they leave the zone to catch shuttles back to their offices or parking lots.
No vehicles with specks of radioactive contamination have been found for several weeks. The latest count is 36 contaminated vehicles: seven owned by workers and 29 contractor or government vehicles. The private vehicles were decontaminated soon after radioactive particles were discovered, but most of the work vehicles still need to be decontaminated. A tent is being constructed for the work.
Demolition of the portion of the plant that remains standing and load-out of demolition rubble remains halted until the Department of Energy agrees it can be done safely. Plans call for contractor CH2M Hill Plateau Remediation Co. to prepare a report with an analysis of the cause of the spread of contamination and some initial corrective actions. An expert panel will review the report and then DOE could approve a modified approach to demolition. If the Washington state Department of Ecology does not agree the work can be done safely, it has the authority to halt it.
