New data has raised questions about the efficacy of monitoring for the spread of radioactive contamination during demolition of the Plutonium Finishing Plant at the Hanford Site in Washington state.
The Department of Energy on Wednesday released additional results from the analysis of samples collected at DOE and state Department of Health air sampling stations. They showed low levels of airborne plutonium and americium outside the Plutonium Finishing Plant’s radiological control zone in November and December.
“We previously thought that contamination outside the radiological control area for PFP demolition was limited to December,” said Doug Shoop, manager of DOE’s Richland Operations Office at Hanford.
A spread of radioactive contamination was discovered at the plant in mid-December just after demolition finished on the majority of the most contaminated portion of the Plutonium Finishing Plant, an annex called the Plutonium Reclamation Facility. The assumption that radioactive particles had not spread in prior weeks was based on other monitoring methods, including continuous air monitoring (CAM) systems, and checks for contamination on metal “cookie” sheets.
Since the discovery last month of contamination spread, 271 Hanford workers have requested bioassays to check for internal contamination. In a memo to workers Wednesday, Shoop said the first 91 bioassays had been completed, finding two workers had inhaled or ingested low levels of radioactive particles.
One worker could receive an estimated dose of less than 1 millirem over 50 years and the other could receive an estimated dose of 10 to 20 millirem over 50 years, according to DOE. The results are being reanalyzed to confirm the findings. The Energy Department sets an administrative control limit of 100 millirem radiation dose annually for nonradiological workers.
The results for those two workers are in addition to 31 workers with positive bioassays after a June spread of radioactive contamination associated with demolition at the plant. Results for the remaining 180 bioassays requested following the spread discovered in December should be available by early March, Shoop told workers.
The June airborne contamination incident was detected in near-real time and workers at the plant were ordered to take cover. But the late 2017 spread was not detected by continuous air monitor systems.
The analysis of state and DOE air samples collected for various two-week periods from late October through late December found radioactive contamination outside an expanded zone set up earlier this month to control access to a wide area around the Plutonium Finishing Plant, including closing some streets. The air sample analysis showed possible contamination as far away as the defunct REDOX plant, which is about a half mile outside the Plutonium Finishing Plant’s new access control boundary.
“The levels are below regulatory limits, but my expectation is that no contamination above background would be detected,” Shoop said in the message to employees. The Energy Department calculated possible worker radiation doses in a worst-case scenario for the highest detected reading of plutonium and americium, concluding that a dose for a worker exposed around the clock would be below the annual administrative control limit for nonradiological workers. “Since no one will experience this scenario, the potential dose to Hanford Site workers is expected to be significantly less,” Shoop wrote.
The Department of Health also reported detecting very low levels of plutonium or americium 10 miles away from the Plutonium Finishing Plant close to the K East and West reactors near the Columbia River. The level was below regulatory limits and there was no risk to human health, but state officials were concerned about finding airborne contamination so far from the plant, said John Martell, manager of the Radioactive Air Emissions Section of the Health Department’s Office of Radiation Protection. State officials discussed the findings with DOE in December, he said.
While Shoop’s memo to employees said the contamination near the river was discovered in November and December, Martell said it actually was from combined high-volume air samples collected in the first half of 2017. The Department of Health also found airborne contamination that coincided with the June take-cover incident at the Rattlesnake Barricade, a secure entrance to Hanford just off public Highway 240. The June contamination, which also was below regulatory limits, was reported to workers earlier.
The Department of Health reported that radioactive contamination that appeared to be linked to Plutonium Finishing Plant demolition also was found in late 2017 on a sample of vegetation collected at the US Ecology low-level radioactive waste disposal site on leased land at Hanford. The contamination was well below regulatory limits, according to DOE.
Demolition and work to load out construction debris has been stopped at the Plutonium Finishing Plant since Dec. 17. Contractor CH2M Hill Plateau Remediation Co. will not be allowed to resume demolition until DOE conducts a thorough review of the incidents, identifies corrective actions, and conducts a robust assessment of the contractor’s readiness to resume demolition, Shoop said.
