3 Answers

Well, I don't know the exact reason either, but from what I hear I think it is not that simple. First of all, they have to prevent (or stop) the process of uncontrolled nuclear fusion, which would cause even more disaster. Only after managing to do that, which is not done easily, can they think of actually fixing the entire reactor. Right now they are trying to cool the entire thing down so it won't blow up.

I have been an engineer in charge of seriously large steam turbine Plant.
When turbine machinery this size gets out of control it is frightening beyond belief.
Most of the staff would be vomiting with fright while the experienced would be watching rows and rows of red lights with klaxons making speech impossible. You stand there like a wet rag waiting to see which auxiliary engines and pumps will cut in automatically and which you have to start manually.

Have you ever had a car that would not start when you really needed to get off the railway lines? Call the AA. Oh sucks I am the AA. Must remember to bring a change of underwear! Meanwhile the concrete is cracking cables are breaking, switch boards are on fire and the tiles are falling off the roof all the safety valves have lifted and your ear drums are bursting.

Do you remember the Towering inferno? Some people watched it a dozen times but was anyone prepared for 9/11. No not one! Human beings are clever but not infallible, and you should be now have figured you are living in the age of destruction and that there is more to come. I kid you not!

They said the back up generators were not working so they probably did not keep up maintenance on this very important equipment. They didn't need it in the past..so there you go. This is an assumption but I guess we will know the answers later on. They now say they have had a meltdown!!