WIPP = Waste Isolation Pilot Project, a deep undreground repository for transuranic-contaminated wastes (TRU wastes). Transuranic elements are human-made radioactive materials such as plutonium, americium, neptunium, and curium, all of tnem created inside nuclear reactors when uranium atoms absorb one or more neutrons without splitting, thereby becoming heavier than uranium or “transuranic”. These wastes are associated with the nuclear weapons industry in the USA.
In February 2014 a sealed steel drum filled with TRU wastes, deposited in a chamber some 655 metres underground, overheated and exploded, turning the drum into a flame thrower and spreading alpha-radiation-emitting dust throughout the underground workings. Some of this plutonium-contaminated dust found its way vertically upwards, rising 2/3 of a kilometre to the surface, where it contaminated 21 workers and drifted downwind toward Carlsbad, New Mexico. The WIPP facility had to be shut down for more than three years and a lot of money (costing US taxpayers about $2 billion) had to be spent to try to decontaminate the shafts and chambers as much as possible before resumign operations.
The reason why the steel drum exploded and burst into flames was because of chemical reactions taking place between the organic kitty litter that was used as a filler apacking material and the radioactive wastes themselves. Radioactive wastes are not inert materials, they are active. They are thermally active (generating heat because of the unstoppable release of nuclear energy known as radioactivity), chemically active (dur to the ionizing effects of the subatomic projectiles that we call atomic radiation), and radio-active (as the nuclei of unstable atoms continue to disintegrate for hundreds of thousands of years).