Just a thought, a consequence for having core temps in the red, small chance that a block of coolant in a passive reactor will evaporate. Maybe also have a passive coolant access port so that more of it can be piped into the reactor instead of having to break it to put more in it.

Passive coolant access port is a duplicate suggestion as #93. I'd rather not add core evaporation - not only does it not make sense (it's a sealed vessel, things can't evaporate out of a sealed vessel), but it adds tedium in to the game.

The thing you're probably looking for is more like a steam explosion, which is on the roadmap as an optional disincentive to redlining reactors.