"All good engineering works on the principle of defence in depth."That line is as much a sound-bite at this point as anything you'll hear on cable television. Yes, good engineering has many levels of fall-backs and redundancies. But when you've reached the point that you've evacuated the last fifty people from your site because it's no longer safe for them to be there, then you've exhausted your defenses. There's no more depth.
Let's stop whistling past the graveyard: a meltdown is, in fact, a really big deal. Maybe the "wide concrete tray" will capture the waste. Maybe it won't. But in the meantime, you're hoping that there's not a secondary fire from the heat, or a steam explosion, or some other kind of explosion that flings radioactive particulate for miles around. You're hoping that the fuel won't melt, form a critical mass in the bottom of the reactor, and re-initiate a reaction that's hard to stop. You're hoping that the containment doesn't breach, and that vast quantities of radioactive waste aren't exposed to the elements before the whole system calms down again. You're hoping that the whole system calms down again.
The point is: they've lost control. The 'engineering' that they're doing right now is desperate and hacky, and they're very nearly out of options. It might be comforting to pretend that this whole thing is scripted out on some intricate Japanese checklist somewhere, but that's really nothing more than a fantasy. I certainly hope that things aren't as bad as they sound, but this isn't just a matter of bad PR by some pessimistic, nuclear-energy skeptics. These guys are actually in trouble.