Worst case for nuclear is probably worse than the worst case for coal. The planet might be transformed in unwanted ways due to global warming, but that's better than it becoming irradiated and inhospitable to life.
That being said I still think that nuclear is our best option.
Chernobyl was literally the worst case for nuclear power. The design flaws were myriad and the industry has learned a tremendous amount. It's not going to irradiate the whole planet, full stop.
That being said I still think that nuclear is our best option.