A major demolition project at Hanford was halted two days this week after air monitors worn by several workers showed they might have inhaled radioactive particles.
About 5 p.m. Thursday, work was cleared to resume after radiological control zones were expanded at the nuclear reservation’s highly contaminated Plutonium Finishing Plant.
“We take this very, very seriously,” said Ty Blackford, president of Department of Energy contractor CH2M Hill Plateau Remediation Co. “We are dealing with a form of contamination that is very, very hard to manage.”
DOE officials have called the work at the the Plutonium Finishing Plant at Hanford the most hazardous demolition project at the nuclear reservation and among the most dangerous across DOE’s environmental cleanup complex.
The plant, particularly its Plutonium Reclamation Facility, is contaminated with plutonium. The radioactive particles are flighty, becoming airborne easily.
Seven lapel monitors worn by six workers at the Plutonium Finishing Plant complex since last Friday tested positive for radioactive particles at levels of concern, according to laboratory results.
The highest potential exposure was 11 millirems for one of the workers.
For comparison, the average person in the United States is exposed to 300 millirems of radiation annually from natural sources, such as radon or radiation bombarding Earth from outer space.
The first indication there might be a problem was when laboratory testing on lapel monitors worn by two workers on Dec. 8 came back with positive results for airborne radioactive particles.
Workers wear the monitors near their faces as a check for airborne radioactive particles that could be inhaled. Air is sucked through the monitors with a pump.
The workers had been mixing water and fixative sprayed on demolition areas to help prevent airborne contamination and were well away from where demolition is being done on two areas of the Plutonium Finishing Plant.
A lapel monitor worn by a worker the next day at an area where demolition waste is loaded to be hauled away also showed a positive reading in laboratory tests.
The usual procedure was followed to survey the areas where the workers had been for radioactive contamination. The air samples also were sent to be retested, since positive results frequently turn out to be radon that quickly radioactively decays away, according to Hanford officials.
Before demolition work at the plant started Wednesday morning, the lab results for four more lapel monitors worn at both the mixing and the waste load out areas came back positive.
The finding was unusual enough for CH2M officials to call a halt to the demolition project, Blackford said.
The Hanford Atomic Metal Trades Council also issued a stop work order for its employees about noon Wednesday. HAMTC is an umbrella group for about 15 Hanford unions.
In June, about 350 people at the Plutonium Finishing Plant were ordered to take cover indoors as a precaution after a monitor detected low levels of airborne radioactive particles and sounded an alarm.
Later, small spots of contamination were found on the ground outside the area marked for radiological control near the demolition area.
Some 31 workers were later found to have inhaled or ingested small amounts of radioactive particles. The worst case would mean 10 millirems of exposure over 50 years.
But in the recent incidents, no continuous air monitor alarmed, Blackford said.
The site has stationary air samplers, none of which tested positive for airborne radioactive particles.
CH2M also uses “cookie sheets,” or steel plates, that are checked for radioactive particles. No particles were found on them.
In addition, routine surveys found no contamination on workers’ skin or protective clothing.
The surveys are of all workers leaving areas where radioactive contamination might be expected.
Of the four positive tests on lapel monitors worn Tuesday, all but one was determined to have been triggered by naturally occurring radon.
The fourth test result was the one that measured 11 millirems of possible internal contamination to the worker. However, further testing showed that part, but not all, of the reading likely was because of radon.
That leaves four lapel monitors at two sites with elevated readings that indicate workers were at risk of inhaling radioactive contamination.
CH2M recommended bioassays — checks of body waste for radiological contamination within the body — and the workers elected to have the checks. Results are expected in January, according to DOE.
They also are expected to have chest counts, another check for radioactive contamination within their bodies.
Since work was stopped Wednesday, surveys have been done to look for spots of radiation.
The control zone around the demolition area also was expanded. It had already been expanded after the June incident.
At the end of Thursday afternoon, CH2M and HAMTC leadership agreed that work could resume.
On Friday, demolition work is expected to continue on the Plutonium Reclamation Facility, a project close to completion.
CH2M also expects to have the rest of the Plutonium Finishing Plant torn down to a slab on the ground, work that could be completed in a matter of weeks, Blackford said.
Demolition of the plant began in November 2016.
The Plutonium Finishing Plant operated during the Cold War as the last stop for plutonium produced at Hanford before it was sent off site to a nuclear weapons manufacturing plant.
About two-thirds of the nation’s weapons program plutonium came out of the Hanford plant.