Reply #11: Good question! My best opinion

[The Traveler]

We really don't know for sure. Too much depends on the details of the internal state of the reactor pressure vessels, which is obviously unobtainable.

Worst case scenario ... if the core slags, it eventually melts a hole through the floor of the pressure vessel and drips onto a area of the containment building floor intended to catch molten core.

The core material should spread out, which is necessary to prevent enough material from accumulating in a small enough volume to start a low rate chain reaction. Really, there should be no possibility of THAT occurring.

What happens next ... this stuff is obviously hot. Very hot. Hot enough to melt through some of the toughest steel ever manufactured. The floor has been designed to dissipate that heat and contain it until the decay products inside the core material stop decaying and producing heat. But it will erode slowly under the thermal load.

My concern is that we have no certainty that the containment floor structure is still up to spec. It has been through an 8.9 earthquake and many strong after shocks. If its structural integrity has been compromised ... the core material could penetrate the previously impenetrable containment floor.

What happens next would then be determined by local geology, which I know nothing about. If the molten core hits the water table, a major release of radioactive material could and probably would occur.

Now, that is really, really bad. Horrible. But Chernobyl was much, much worse than we are talking about here. That does not mean I think the worst case scenario is acceptable. "Not as bad as Chernobyl" does not automatically produce a judgment that "so nuclear power is OK". That's sort of like saying "Hurricane Katrina wasn't so bad because Haiti was so much worse."