I saw this tweeted by @PeterDaou a few minutes ago and just posted it for educational purposes.
Short and sweet: I'm not a physicist by any stretch of the imagination but there is a video of a professor suggesting that flooding the reactors with seawater prevented 3 massive explosions that would have made all of northern Japan uninhabitable. It's not all that healthy as it is now, but it could have been a lot worse, or so we are told.
Video and link on the flip.
The Japanese government finally admitted that there was a full, 100% core melt in all three Fukushima Daiichi reactors, despite numerous earlier denials. The massive influx of seawater is the only thing that stopped the cores from exploding. The water absorbed the heat. Dr. Kaku says it's in no textbook anywhere that seawater will stop an explosion of this nature; it was a last ditch effort. He says the seawater is now very contaminated and that children will be exposed to radiation levels twenty times what an atomic worker is exposed to. Neighboring countries are furious at the contamination the leak has caused in the oceans and to the sealife.
The Japanese government forced the utility company to flood the reactors; the company wanted to save its investment. But if they hadn't flooded the reactors with seawater, there would have been three giant explosions -- he calls it "three Chernobyls" and northern Japan would have been lost. Radiation is still coming from two breaches in the contaiment vessels. The professor flat out states that "we came this close to losing all of Northern Japan." It's pretty shocking. Take a look:
NOTE: you have to watch an ad before you get to see it, so be warned. It's 15 seconds so you can turn your volume down and not be exposed to it.
The professor indicated that the utility company running the plant was actually trying to salvage the plant - apparently thinking they could save money and such - even though 3 meltdowns were underway.