The Defense Nuclear Facilities Safety Board (DNFSB) says the Energy Department should do more to reduce the risk of combustion of stored radioactive waste sludge similar to the April 2018 accident at the Idaho National Laboratory in which four drums blew off their lids.
In a March 12 letter, the DNFSB asked Energy Secretary Rick Perry to respond within 45 days to questions about the incident. The board intends to hold a public hearing on the issue by May, although it was not listed on the DNFSB’s online calendar Thursday.
Four containers of solid radioactive waste, recently repackaged from old to new drums, became overpressurized and ejected their lids around 10:30 p.m. April 11 at the Accelerated Retrieval Project No. 5 (ARP-5) facility within the Radioactive Waste Management Complex. As a result, radioactive material spewed within ARP-5. “The four drums can be described as having exploded, according to definitions cited in the DOE Handbook,” the DNFSB said in a December staff report attached to the letter to Perry.
Cleanup contractor Fluor Idaho and DOE were fortunate the event was not worse, the DNFSB said. First, the drum lids were ejected at night while the ARP-5 facility was unoccupied. Second, the drums blew open inside a building with a confinement ventilation system, which held radiological material inside the structure. The contractor often moves repackaged waste drums to storage locations without such a ventilation system, according to the report.
The DNFSB asked if the Energy Department will alert other sites to the risks of this type of exothermic event. The board also seeks the agency schedule for measuring flammable gas concentrations at certain other drums at INL and assessing the risk. In addition, it wants to know if similar risks have been identified at other defense nuclear facilities.
The contractor said in an October analysis that the temperature inside the drums increased to about 150 degrees Celsius after depleted uranium contacted air for the first time in years. Fluor Idaho learned that material from the drums generated methane, a flammable gas. The waste originally came from the former Rocky Flats nuclear weapons plant near Denver, and had been buried on-site at INL for decades.
The board said Fluor Idaho and DOE could learn more from past mishaps, such as a 2005 event in which a drum caught fire while being dug up from the subsurface disposal area at INL, as well as a 2017 fire at the Advanced Mixed Waste Treatment Project (AMWTP). The DNFSB staff considers the April 2018 drum breach “an opportunity to broadly examine the hazards posed by flammable gases and undesired chemical reactions,” according to the letter.
For shipments to the Waste Isolation Pilot Plant (WIPP) in New Mexico, the Energy Department requires drums to have filter vents. But here the DNFSB suggested the Radioactive Waste Management Complex might place too much reliance on the ability of filter vents to keep a drum within the “lower flammability limit” for methane.
Further, after Fluor Idaho repackages waste into a new drum it is possible sampling for a flammable gas analysis won’t be taken until months later. “Thus, there could be drums on-site with flammable mixtures of gases, and site personnel may not be aware of this condition for several months,” the DNFSB said.
Prior to the accident, the ARP 5 facility processed and repackaged about 9,500 drums of sludge-contaminated waste to remove liquids and prohibited items prior to shipment to WIPP, Fluor Idaho said last spring.
In preparing its report, the DNFSB staff met with Fluor and Energy Department managers in Idaho between September and November of 2018.
“Fluor Idaho appreciates the feedback from independent sources such as the DNFSB,” company spokesman Erik Simpson said in a Thursday email. “As we’ve stated previously, we look forward to working with the DNFSB as they complete their important work on this subject.”
A similar tone was struck by an Energy Department spokesperson. “DOE-EM’s top priorities are protection of the environment and the health and safety of its workforce.” The agency is reviewing the letter and “will collect information to help the DNFSB address its concerns.”
