|Location of Japanese Nuclear Power Plants|
First, before you do anything else, please go read this article by Keith Yost in the The Tech (an MIT newspaper).
Ok, now you have the basics of what is actually going on. No need for ill-informed journalists with editors who don't know the difference between nutrients and neutrons. No need for random idiots to show up on fluff news shows, like the Today Show, and tell the public that we all need to have potassium iodide tablets on hand.
So, the reactors survived the earthquake quite well. But the tsunami and flooding is what really caused the trouble. The flooding knocked out the generators which were pumping water to cool the reactor (and moderate the neutrons, if my reactor design understanding is correct). No water, no cooling. That is a problem.
If you want to keep up to speed on the actual facts of what is going on in Japan regarding their nuclear power plants, the best site I have seen which is updated a few times a day, is Information on the Japanese Earthquake and Reactors in that Region by the Nuclear Energy Institute.
So, stay informed. Ask questions of people who know, not from people who are only concerned about ratings. And remember, the nuclear reactors survived the earthquake. A catastrophic earthquake. A 9.0 earthquake. That is quite amazing in my opinion.