I've always found the Tokaimura accidents to be a little "creepier." A vat of liquid can end up in a state of mixture and configuration that causes it suddenly become critical. [0]
Wow what an interesting article, especially the part about the plutonium liquid vortex reaching criticality. Fascinating (but sad) stuff. Shame how his widow was treated afterwards.
[0]: https://en.wikipedia.org/wiki/Tokaimura_nuclear_accidents