a so called "melt down" should be impossible, if it isnt, someone is going to have to answer some questions with some damn good answers.
In Chernobyl, the rods were lowered into the reactor, in order to make the heat. when the control systems failed, the weight of the rods, held them in the reactor under gravity, and they could be pulled out.
since chernobyl, its been flipped.
the rods default position (due to gravity mainly) is OUT, not IN.
the rods have to be actively held into the core, and if anything goes wiggy, they should fall out due to gravity.
a high tech dead mans handle arrangement.
if they pump that moves the water around the reactor has failed, no one is getting power ANYWAY, so they will just shut it down and it will begin to cool.
i would IMAGINE, if the station is "gravity fed", the UN and other such "masters of the universe for the forces of good" are going to have a SHITFIT, though this is just extrapolation.