"The improper mix in the barrel, including the wrong sort of cat litter used to absorb liquids, sparked a chemical reaction causing it to heat up and generate gases that dislodged its lid, spewing radioactive materials, investigators found."

I like that word "spewing," as in, "expel large quantities of (something) rapidly and forcibly."  But only after the "chemical reaction" caused the waste to heat up, " [dislodge] its lid," and subsequently forcibly expel large quantities of radioactive waste.  
https://www.theguardian.com/environment/2015/mar/27/cat-litter-blamed-for-240m-radiation-leak-at-new-mexico-nuclear-waste-dump

But, what the heck.  It was only plutonium.  What have future generations ever done for us?