Thermoanalytical investigation of the reactions causing the transuranic waste drum breach that occurred in the Waste Isolation Pilot Plant

[Display omitted] •Self-sustaining reactions between drum waste components start at room temperature.•Dry mixtures of nitric acid and wheat-based pet litter can lead to thermal runaway.•Hydrogen- and hydrogen-metal-triethanolamine nitrates react violently above 200°C.•Water inhibits low temperature reactions from self-accelerating to thermal runaway.•Lead nitrate reduces oxidation onset of nitric acid/wheat-based pet litter mixture. In February 2014, an energetic gas-producing chemical reaction occurred in remediated plutonium processing waste emplaced in the Waste Isolation Pilot Plant causing the drum’s seal to fail and release radioactive material into and outside of the plant. This article provides results of our probative study using simultaneous thermogravimetric and differential thermal analysis and accelerating rate calorimetry to determine the thermal sensitivities of selected simulated characteristic remediated wastes such as hydrogen- and hydrogen, metal-triethanolamine nitrates and nitric acid solidified and stabilized with wheat-based pet litter. These studies found that these nitrate wastes were chemically unstable and susceptible to gas-producing thermal runaway reactions. If undried or partially dried, self-sustaining or accelerating-exothermic reactions were delayed in nitrate- and organic-containing materials to above 100°C while air-dried nitric acid and pet litter began self-heating exothermic reactions near 30°C that led to thermal runaway. Caution must be exercised when managing nitrate-containing wastes.