Chernobyl and Fukushima created exclusion zones in the thousands of square kilometers that displaced hundreds of thousands of people. Building them in the middle of nowhere isn't an option either, these plants require access to large amounts of fresh water, and such zones tend to be highly populated. Tbh I don't understand how anyone can look at the effects of the previous nuclear catastrophes and conclude that it is a good idea to continue building more.
Fossils are not the alternative to nuclear power, everybody agrees that they have to go. When you include all the costs of nuclear power, instead of ignoring them as externalities as capitalism allows them to do, it is not cost competitive with renewables such as wind and solar.