The watchdog organization Hanford Challenge said this week it found traces of radioactive americium in the engine filters of two employee vehicles that had been parked at the Hanford Site’s Plutonium Finishing Plant. The vehicles had previously been checked at Hanford and declared clean in the wake of a radioactive contamination spread from the plant demolition site, according to the group.
Four workers volunteered to have their vehicles checked, and Hanford Challenge collected five filters from them when the vehicles were off Hanford in the nearby Tri-Cities in central Washington state. Marco Kaltofen, president of Boston Chemical Data Corp. and an affiliate research engineer at the Worcester Polytechnic Institute, was in charge of the analysis.
“The fact that vehicles were checked and released to these workers, only to find that they were still contaminated, raises disturbing questions about the credibility of Hanford’s program” to check for contamination spread, said Tom Carpenter, Hanford Challenge executive director, in a press release. The group plans to survey filters from other employee vehicles.
The Department of Energy said it was not given the opportunity to split samples and arrange for its own analysis of the filters.
The contamination reported by Hanford Challenge was at levels below what could be detected with handheld equipment used to survey vehicles for radiation at the DOE facility, according to Hanford officials. The most-contaminated sample was measured at 0.9 picocuries per gram of material. The Energy Department said Tuesday that its “survey equipment and processes are designed to detect contamination levels well below regulatory and worker-protection requirements.”
Contractor officials in charge of recovery from the contamination spread on Wednesday sent a memo to workers for contractor CH2M Hill Plateau Remediation Co., comparing the reported levels detected in air filters to the amount of americium commonly used in home smoke detectors. The detectors contain up to 1 million picocuries of americium sealed inside an ionization chamber, according to the Nuclear Regulatory Commission. Hanford Challenge responded that airborne americium should not be compared to americium safely contained within a smoke detector.
In response to Hanford Challenge’s discovery, a Hanford employee issued a stop work order on Tuesday for use of government vehicles until such vehicles at the Plutonium Finishing Plant demolition were checked for radioactive contamination. Because of the contamination spread discovered at the plant in mid-December, workers are required to park their cars and use offices well away from the plant. They are shuttled back and forth to the plant in government vehicles.
By Thursday, surveys of 54 government vehicles had found no contamination, and the employee who issued the stop work order agreed to lift it. The vehicles already had been surveyed at least once since the December contamination spread, according to Hanford officials.
Previously, the air filters of two government vehicles and one private vehicle with the highest levels of contamination were checked, with no radioactive material found on the filters. Seven workers who requested checks of their homes in December also had their vehicles and vehicle filters checked, with no contamination detected.
With more bioassay results returned, the number of workers known to have inhaled or ingested radioactive particles after the December spread has increased to 10. The dose assigned to workers over 50 years is 10 to 20 millirem for one worker, 1 to 10 millirem for seven workers, and less than 1 millirem for two employees. For comparison, the NRC estimates the average American is exposed to about 300 millirem from background and natural radiation annually.
A total of 294 central Hanford workers have requested bioassays since December. With 242 negative results and 10 positive results, 42 test results still are pending. The most recent bioassays are in addition to bioassays conducted after a July spread of contamination at the plant. Results from those showed that 31 workers inhaled or ingested radioactive contamination.
CH2M Plateau Remediation suspended demolition of the Plutonium Finishing Plant, which is nearly complete, on Dec. 17 after the contamination spread was detected. The pause remains in place, and new CH2M owner Jacobs has taken over the project to eventually bring the plant down to slab on grade.
