[sefarkas]

possibility of a molten core melting through the containment vessel

What is possible is different than what is likely. What some are hypothesizing requires a complete melt of the core into one lump -- this is possible but unlikely given the shape of the various structures inside a BWR reactor vessel. Then, #2, the heat from the corium would have to work its way into a thick reactor vessel wall made of steel. Then, #3, instead of just deforming, a hole would actually have to form in the reactor vessel. Then, #4, the whole corium mess would have to get out of the hole and once again collect all in one place. Then, #5, the corium would have to work its way through the steel plate that is the drywell. Unlike the reactor vessel, there is rebarred concrete behind the steel plate -- so the steel plate could not deform/bubble out. Then, #5, these previous steps would have to happen before the fission products decayed away (removing the heat source). All items above are unlikely if at any time there is a pool of water above the corium. The probability of running out of sea water is pretty close to zero.

[Errant]

Thanks, that's probably the best hypothesis I've seen concerning what's possible and what's likely.

In discussing additional possibilities, wouldn't the high heat of molten fuel rods vaporize any cooling water after some critical point.

Which brings to mind; why not build smaller reactor cores and containment vessels capable of handling complete meltdowns without the dependency on cooling?