Flawed packing of radioactive waste caused sparks to fly from a container at Los Alamos National Laboratory in late February, prompting evacuation of the work area and later the underground disposal site near Carlsbad where two similarly packed canisters were stored.
The sparking caused no injuries, damage or radiation to be released, according to a letter the lab wrote to the New Mexico Environment Department.
But any combustion involving transuranic nuclear waste is deemed dangerous and calls up memories of the 2014 incident in which a ruptured container from Los Alamos closed the Waste Isolation Pilot Plant in southern New Mexico for three years and cost almost $2 billion to clean up.
Both the lab and the state Environment Department are investigating the Feb. 26 incident, which happened as workers were preparing waste shipments to WIPP.
"We consider any potential threat to human health and the environment as a serious incident that must be fully evaluated under federal and state law, rules and permits," Kaitlyn O'Brien, an Environment Department spokeswoman, wrote in an email.
The incident resulted from questionable practices by LANL employees in characterizing and packaging the waste materials, O'Brien wrote.
Operations have been halted in the work area where the incident occurred until the investigation is finished, she added.
A watchdog group said the lab's continued miscues in handling nuclear waste show it is not ready to produce plutonium pits used to detonate warheads.
"This is yet another reminder that as the lab ramps up plutonium 'pit' bomb-core production, it has yet to resolve its chronic nuclear waste and safety problems," said Jay Coghlan, executive director of the nonprofit Nuclear Watch New Mexico.
Workers stuffed two HEPA filters into a bag and placed the bag and a metal object into the drum, according to a March 9 letter the lab wrote to the state Environment Department, summarizing the events.
The metal item tore the bag, and when it made contact with the air filters, workers noticed sparks coming from the drum, the letter said.
Workers pulled a fire alarm, left the area and called the fire department, the letter said.
A fact-finding probe suggests the HEPA filters contained fragments from titanium welding that had been done in a glove box, the letter said, referring to a sealed compartment that allows workers to safely handle radioactive materials.
Air entered the torn bag and oxidized the metallic powder on the filters, which caused the sparking, the letter said.
Investigators determined the lab had four drums containing similar contents. On March 4, the lab notified WIPP it might have two drums with those materials, which would not comply with its waste acceptance guidelines.
The next day, WIPP ordered workers to evacuate the facility until officials could determine the waste posed no threat.
"Subsequently, a rigorous analysis confirmed that the two drums located at WIPP do not present any danger to employees or the environment and are compliant with the waste acceptance criteria," a spokeswoman at the National Nuclear Security Administration wrote in an email.
Lab workers will resume packing and transporting most waste materials in the next couple of weeks, she added.
A thorough inspection of waste drums at the lab's Area G found none containing the materials that sparked, she wrote.
Area G is where much of the lab's massive waste generated during the Cold War and Manhattan Project can be found.
The lab will do a follow-up report to provide more details on why the incident happened and how to prevent a recurrence, O'Brien wrote, adding the agency will look at whether the lab complied with correct procedures.
This story first published in the Santa Fe New Mexican, a sibling publication of the Taos News.
Los Alamos National Laboratory's letter to the state Environment Department about the incident: bit.ly/3uj7d0F.