I gave one clear example - the pools below Chernobyl causing a secondary steam explosion that would've resulted in Reactor 3 and potentially 1/2 melting down as

I gave one clear example - the pools below Chernobyl causing a secondary steam explosion that would've resulted in Reactor 3 and potentially 1/2 melting down as well.. naively making that disaster 3x worse than it was. In Fukushima, the explosion and subsequent power loss caused the spent rods from the 4th reactor to nearly boil the water away, had workers not been able to gain access to the site and manually spray the rods, they would've been just burning in the air releasing clouds of radioactive gases. Clearly this would've been much worse than what happened already, but is mostly unaccounted for when people proclaim that the accidents we've seen are evidence that those are the worst possible outcomes. But the whole point is that we don't know the universe of bad things that can happen..