Cleanup contractor Fluor Idaho should have taken greater precautions in repackaging sludge prior to an April 11 incident in which four drums of the radioactive waste overheated and blew off their lids at a building inside the Energy Department’s Idaho National Laboratory.
That is the crux of a report Thursday from the company, and overseen by DOE, which finds the breaches occurred after depleted uranium inside the drums contacted air for the first time in about 40 years.
The drums involved in the accident contained sludge originally from the Rocky Flats nuclear weapons plant in Colorado. The waste had been stored for decades in a subsurface area of INL and handled by a number of contractors prior to Fluor Idaho taking over cleanup duties in June 2016.
In sludge repackaging, the original Rock Flats waste containers are dug up and taken inside the Accelerated Retrieval Project 5 building, within the lab’s Radioactive Waste Management Complex. The drums are then opened and processed to remove forbidden items, such as aerosol cans, that might cause an ignition.
A drum containing depleted uranium had been taken into the building in April for this procedure, which resulted in the waste being placed into four “daughter drums.” The drums underwent an exothermic reaction about eight hours later, according to the report.
It appears oxidation of a “non-roaster” oxide depleted uranium metal happened over several hours, which caused the drum to heat up. Also, flammable methane was produced by a secondary chemical reaction from beryllium carbide and possible other uranium carbide reactions.
The escalating heat and pressure inside the drums resulted in them ejecting the lids, starting around 10:30 p.m.
While there were no injuries, that was partly because the incident occurred at an hour when there were no employees nearby, according to an executive summary of the 300-plus page report.
Waste acceptance documents for the drums “did not adequately describe the attributes of the waste including some known prohibited items” and the potential for combustion, according to the report. This combined with the failure by the contractor to do an adequate chemical compatibility test, meant effective controls were not in place.
The report faults the nuclear safety culture at Fluor Idaho. “The overall approach was not conservatively based, lacked documentation and procedures for key safety requirements, and was focused on processing waste to meet milestone requirements rather than compliance with requirements.”
Some workers at the facility “stated they did not feel comfortable” telling management about issues that might delay production objectives at the Idaho Cleanup Project, according to the report.
In 1995, Idaho entered into a settlement with the Energy Department and the U.S. Navy to resolve a state lawsuit over storage of out-of-state waste at INL. The settlement called for repackaging 65,000 cubic meters of radioactive waste and shipping it as transuranic waste to DOE’s Waste Isolation Pilot Plant by the end of 2018. “Schedule pressure was felt by contractor personnel,” according to the report.
The four breached drums had not yet been certified for shipment to WIPP.
The INL fire crew responded to an alarm as the incident advanced, but they did not know the accident had released airborne contaminants as continuous air monitors had failed to issue an alert.
Inside the tension membrane fabric building the fire crew found one smoldering 55-gallon drum with a missing lid. A thermal imaging camera indicated the temperature inside the drum was 190 degrees Fahrenheit and rising. After trying unsuccessfully to douse the hot spots in the drum, the firefighters retreated from the building.
Two loud noises or booms were heard from inside the building after midnight. During a recovery trip on April 19, a crew found the four drums had overheated and ejected their lids.
Natalie Creed, hazardous waste unit manager for the Idaho Department of Environmental Quality, said she and her staff are reviewing the report. Fluor and DOE continue to identify and implement corrective actions, based on the investigation results, she noted, adding possible changes to the state’s hazardous waste permit might be necessary.
Fluor Idaho has already started additional raking the sludge, to spot forbidden substances, and 24-hour thermal monitoring of the waste prior to repackaging. The company did not respond to requests for comment by press time.
Fluor Idaho, a Fluor Corp. subsidiary, with subcontractor partners comprised of CH2M, North Wind, Portage, and Waste Control Specialists are in charge of cleanup. The vendor has a five-year, $1.4 billion contract to manage the Idaho Cleanup Project. The project includes reducing environmental risk, and protecting the Snake River Plain Aquifer, as well as waste repackaging operations.
