Not only does it go wrong, we have absolutely no way to stop it. It's literally out of our control.
I was a supporter of Nuclear, though Fukushima taught me a very important lesson.
When things went bad there, we literally stood back and said "well, damn. There is nothing we can do" and watched it melt for weeks and weeks. Nobody could go in, and we had no robots that could go in and do a thing. It was lucky it's close enough to just pump endless water into it. Then a few weeks later the experts said "oh, all that highly contaminated water is going straight into the ocean. We wondered where it was going". As it were the Japanese had elderly people volunteering to go in, essentially committing suicide.
It's also worth remembering that at Chernobyl there was also nothing we could do - other than force people to commit suicide by going in where it was deadly. That won't fly today.
While the chances of things going that wrong are very low (it's only happened twice, maybe three times in history) I think the consequences are too great to justify it. We can't even control it when it goes bad!