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.
I think even a partial meltdown means they’ll be pumping water in there for a long time. I.e, if the rods deformed conventional cooling is out of the question as sustained higher temps are likely from the deformed mass of fuel providing greater density of reactive material. Deformed rods will likely stay unusually hot for a long time until they’ve spent themselves. So they’ll be pumping sea water in for quite some time I think.