If tomorrow every coal plant was shut down and replace with nuclear, total greenhouse gas emissions would go down 25%, most environmental toxin emissions (mercury,etc) could go down 50% or more, particulate emissions would go down a lot. It would be great for the environment.
It'd be great if you ignore the issue of nuclear waste, as well as security issues. Anyway, it's possible that fission is a necessary evil until nuclear fusion and renewable sources are fully developed, but the governments should better invest in the latter instead of wasting billions in funding power plants based on nuclear fission, which common sense indicates that is condemned to disappear in the future.
There's no reason to expect nuclear fission plants will be obsolete in 50 years. Nobody has come close to creating a workable model of a nuclear fusion power station.
With renewables, sure, you should also invest there. But, you can't have an electricity grid powered exclusively by wind and solar.
And, sure, nuclear waste is a problem. But, I'd rather worry about where to dispose of nuclear waste safely than know I was spewing pollution into the air.