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 Monday.
Four drums containing solid radioactive waste 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 such 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 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.
