I'm amazed they still have things under somewhat control. The plant was hit by a magnitude 9.0 quake, a 1 in 1000 year occurrence. They shut down all the reactors successfully but then the tsunami knocks out all 12 back up power generators. Without power they lose the ability to cool and control the reactors safely. Magnitude 5.0 or more aftershocks are still hitting Japan at about 100 per day. Despite all this the plant and all 4 reactors are intact for the time being.
I think the nuclear plant has been superbly designed after all the punishment it has taken.