Right, that's what the containment vessel is there to prevent. It is to contain the fuel in event of a core meltdown. Chernobyl did not have a containment vessel hence the heightened concern then.
Appears the problem is they’ve been attempting to pump seawater among three reactors with all but one pump itself failing...so it’s not enough working pumps available to get the sea water where it needs to go...thus all three are at some point of exposed rods...meltdown in all three.