Reactor is encased inside of a concrete sarcophagus.
If it gets blown up, the entire earth is SCREWED.
It
was encased inside the sarcophagus, but there's a great big hole in the top, and the reactor lid's at a funny angle against the wall so it could fall over and send a load of radioactive dust up and out. They're planning on making a new one in 2012 though.