I recommend reading Lenin's Tomb: The Last Days of the Soviet Empire. It is an elaborate attempt to figure out the reasons behind the collapse. According to the author Chernobyl played a major role.
I don't agree with him and the reason is simple. "Major role" implies that if it had not happened then USSR might would not have collapsed, or it's fate had delayed significantly. But the thing is - even if there were no Chernobyl at all, USSR must have collapsed anyway due to a multitude of enormous internal issues. May be just a little later, but it's absolutely not a question if it would collapsed or not. Therefore Chernobyl just can't have a major role in that.