Hiroshi Couchi from a Japanese accident survived 83 days.

Against his own and his entire families wishes...

Dude was in the absolute worst amount of pain imaginable the entire time, but the Japanese government wanted to try everything they could think of to treat radiation, so they just wouldn't let him die.

The demon core guys knew they were cooked when they saw a blue flash from the water ionizing off their eyeballs, and knew enough about nuclear power to know whatever happened next they just got an expiration date. Which is what motivated them to stay and try to mitigate damage rather than panic and run.

Also, I'm pretty sure demoncore was when the fuel rod pinned a dude to the ceiling? That's the reason we started using negative power coefficient reactors. It's a lot safer to slam a rod into a core than to yank it out. Going off memory one of the dudes who saw the blue flash just did everything he could to get it to eject, literally jumped on an overheating core and started whacking it with a wrench to avoid full meltdown. Some full on Fallout type shit.