In one of the many Superman stories I wrote, I had the Man of Steel save an island full of people from a tsunami. He used his heat vision to slice through its rock base and then lifted the entire island into the air above the onrushing wave. Once it passed, he lowered it back into place, with everyone and everything safe and intact.
I don't recall ever writing a story in which Supes dealt with a meltdown at a nuclear power plant, but it's a safe bet that at least one of my fellow writers put him in such a situation. And I'm sure he handled it as easily as he dealt with the tsunami, with no loss of life and minimal property damage.
And, of course, in Superman: The Movie, he stopped a massive earthquake along the San Andreas fault and then undid most of the damage by turning back time. (Something that he can't do in the comic books, by the way.)
Unfortunately, there is no Superman to save the people in Japan who have faced earthquake, tsunami, and now a potential nuclear meltdown. There are only the thousands of "ordinary" people performing search and rescue operations. And the exceptionally brave group of workers trying frantically to cool the reactor by any means possible.
It is easy for a writer to spin a tale in which the hero saves the day in the nick of time. In the real world, we know it doesn't always work out that way. So we can only hope and pray.