By Annette Cary / Tri-City Herald
New test results show that monitoring for airborne radioactive contamination has not protected Hanford nuclear reservation workers as the site’s highly contaminated Plutonium Finishing Plant is demolished.
Two more Hanford workers have inhaled or ingested small amounts of airborne radioactive material, with tests for 180 workers still pending, according to the Department of Energy.
The most recent results were for the first 91 workers who requested testing after a spread of radioactive material was discovered in mid-December.
In addition, air samples collected and analyzed at sites outside the demolition zone around the plant show that airborne radioactive contamination was not found in 2017 by other monitoring methods meant to more quickly warn of a potential danger to workers.
A memo with the latest results for both checks for radioactive contamination of workers and for air monitoring results was sent to Hanford workers Wednesday afternoon by Doug Shoop, manager of the DOE Hanford Richland Operations Office.
In one case, airborne contamination that appeared to be linked to demolition of the plant was found about 10 miles away, near the K Reactors along the Columbia River, workers were told. The finding follows an earlier discovery of airborne contamination in June at the Rattlesnake Barricade, a secure entrance to Hanford just off public Highway 240.
The levels of contamination in the air at the reactors and near the highway were so low that they did not pose a health risk, according to the Washington state Department of Health, which collected the samples.
Although contamination likely from the demolition of the Plutonium Finishing Plant in central Hanford has been found not far from areas accessible to the public, none has been detected in air samples collected off the site.
Open-air demolition of the plant and the loading of demolition rubble has been stopped since mid-December after the demolition of the part of the plant expected to be the most contaminated, the Plutonium Reclamation Facility, was mostly completed.
After demolition stopped, specks of radioactive material were found outside a radioactive contamination zone established around the demolition area, with more contamination spread found after a wind storm about two days later.
Since then, 271 workers have requested bioassays — or checks of their body waste — to determine if they inhaled or ingested radioactive contamination.
After an earlier spread of contamination at the Plutonium Finishing Plant in June, the tests for 31 workers showed they had radioactive contamination in their bodies. The highest radiation dose would expose the worker to an estimated 10 millirem over 50 years.
For the two more recent positive bioassays, one worker could receive an estimated dose of 1 millirem over 50 years from contamination within his body, and the other could receive an estimated dose of 10 to 20 millirem, workers were told. The results are being reanalyzed to verify the estimated dose.
Both were well below the Department of Energy administrative limit set for workers. The average person receives about 300 millirems a year annually from natural background radiation.
The remaining worker test results are expected to be received by early March. Workers are being told their results as soon as they are available.
During the June contamination spread, airborne contamination was detected in the air in near-real time, and workers were ordered to take cover indoors.
But airborne contamination since then has not been detected by the continuous air monitoring, or CAM, systems.
Workers were told on Wednesday that analysis of DOE air samples collected from from October to early January and analysis of Washington State Department of Health samples collected in November and December showed airborne contamination in the vicinity of the Plutonium Finishing Plant.
The results showed plutonium and americium, another radioactive material, in the air at levels below regulatory limits outside the radiological control zone, an area set up to contain any spread of radioactive contamination.
“My expectation is that no contamination above background would be detected,” Shoop said in the memo.
DOE previously thought contamination spread outside the radiological control area at the plant was limited to days in December.
“Given the close proximity of the monitoring locations to PFP, and the detection of plutonium and americium, the contamination most likely came from demolition of PFP,” Shoop said.
Contamination was found at air detectors near both the defunct U Plant and REDOX plant. Although the control area around the Plutonium Finishing Plant was widely expanded this month, including to close some streets, the area does not include the REDOX plant.
DOE used the highest airborne contamination readings detected from samples collected near the Plutonium Finishing Plant in November through the halt of demolition work by Dec. 18 to calculate a worst-case scenario for exposure to a worker. The scenario would be highly unlikely, according to DOE.
Around the clock exposure would result in a dose of radiation that still is below the annual administrative limit set by DOE for nonradiological workers of 100 millirem, Shoop said in the memo.
The Department of Health detection of airborne plutonium and americium near the K Reactors was from combined high volume air samples collected in two-week periods in the first six months of 2017, said John Martell, manager of the Radioactive Air Emissions Section of the of the Department of Health Office of Radiation Protection.
It was not detected in November and December as workers were told in the DOE memo, he said. But Department of Health officials did discuss the finding and their concerns that plutonium and americium were being found miles from the Plutonium Finishing Plant with DOE officials in December, he said.
The Department of Health also found contamination that appeared to be linked to the plant in late 2017 at the US Ecology commercial low-level radioactive waste disposal site on leased land at Hanford.
DOE contractor CH2M Hill Plateau Remediation Co. is not allowed to restart demolition at the Plutonium Finishing Plant under DOE conducts a thorough review of the incidents and improvements in procedures are made, Shoop told workers.
A map showing where airborne radiation was detected near the Plutonium Finishing Plant and the analysis results of different samples is posted at www.hanford.gov under the Jan. 24 update for the plant. Click on the rotating banner at the top of the page.