An actual meltdown at sea would have the now-molten uranium come in contact with seawater, which would instantly flash to high-pressure steam, throwing the uranium into a cancer-causing cloud that the world has never yet seen.

This is absolutely a terrible idea about how to deal with a meltdown.

Doing the math, it looks like the amount of uranium in pre-disaster Chernobyl is 200 metric tons. Apparently, that can bring 333ML (133 Olympic sized swimming pools) of room temperature water to a boil.