The end result can be the same. The disaster at Chernobyl wasn't the uncontrolled chain reaction - if that had been all that happened, the town of Chernobyl would still be considered inhabitable. The ionisation plume was pretty, but not dangerous to anyone who wasn't in it. The disaster at Chernobyl was that the building blew up (because of the chain reaction) and the explosion spread radioactive stuff for miles. Fukushima was also going to blow up, due to hydrogen gas IIRC, but they prevented it from blowing up.