[aruanan]

Basically, the way I understand it is, nuclear power results from a controlled nuclear explosion.

A bomb set off in a pile of uranium is not a nuclear bomb. It may be dirty and highly radioactive, but it's not a nuclear explosion. Nuclear power is from controlled fission. A nuclear explosion results from a huge amount of fissioning in a very short period of time. Power rods in a nuclear power plant, whether melted or not, at about 3% enrichment do not have a sufficiently high concentration of fissionable material for this to occur. They would have to have about 30X higher concentration than they do and it wouldn't happen spontaneously: it would take a highly engineered device with critical timing to result in a nuclear explosion.

[Razzz42]

Okay, I partially get it. Even with (re-) criticality you get heat but not an explosion per se, referred to as nuclear excursions.

In a spent fuel pond exists tons and tons of volatile elements that without a moderator present i.e. exposure to air, heat, shock-waves, vacuums, etc. I’m not sure all the possible scenarios have been explored yet.

Thanks for help in understanding guys.