The last big problem in Japan that I heard about was at a processing facility. The stupid sods decided to circumvent the automated processes by manually pouring stuff into the reacting tanks! Result was a bit of a bang when they managed to get critical mass in there. IIRC the dummies doing it got what they deserved, which was that two of the three operators died. Some leak of radiation too, inevitably. That's what worries me about the human aspect of it - how stupid can some people be?!

Yeah, sodium being very reactive with oxygen, it ain't friendly with air or water. Provided you can keep it inside though, it's good. I believe sodium-cooling is a more recent system, so I don't know if the Detroit reactor would have had it.

Quick check on Google (and hence Wikipedia) suggests the cause of the Enrico Fermi partial meltdown was an internal blockage in the cooling system, not a leak as such. Also says that there was no contamination outside the containment vessel (the "shell" around the plant) so I guess some of the "design" part worked to mitigate failure of other bits. I don't know anything about that one, so I'd appreciate info if you've got links.

Graham.