The radioactive material release last year at the Waste Isolation Pilot Plant nuclear waste repository in New Mexico was due to mixing of nitrate salt residues, organic sorbent (Swheat Scoop cat litter), and neutralization agent (triethanolamine), according to a Department of Energy summary of the investigation into the incident:
The [Technical Assessment Team] concluded that chemically incompatible contents in Drum 68660, in addition to the configuration of materials in the drum, supported exothermic chemical reactions that led to a thermal runaway. In other words, a series of ever-increasing heat releasing reactions occurred, which led to the creation of gases within the drum. The resulting build-up of gases within the drum displaced the drum lid, venting radioactive material and hot matter that further reacted with the air or other materials outside the drum to cause the observed damage in P7R7 of WIPP.
Investigation by the Santa Fe New Mexican previously indicated that the switch from an inorganic to an organic sorbent was the result of a typo.