Chernobyl is the only nuclear accident that resulted in a major loss of life. It was also caused by issues that have been addressed by every major country using nuclear power as an energy source. Safety concerns that came up and were addressed due to Chernobyl probably even went into the much smaller loss of life and the better (if not well done) response to Fukushima.
Even TMI led to major changes in the nuclear power rules/regulations in the US (at the very least) which help us run our plants much more safely.
We have been using nuclear power for over 55 years now, and in that time, there have only been 2 major disasters. For the US, we have lost very few lives due to nuclear power accidents (I think the number is 3 known for actual US nuclear power accidents being the primary cause, but there could be some obscure ones I'm not aware of).