Coal is a limited resource, and regardless of whether it's in 80 years or 300, we will run out, necessitating a change in the infrastructure anyway.
Changing to a nuclear power plant requires building one, as well as arranging for waste transport and management (not to mention a P.R. campaign of epic proportions to get public approval in the first place).
All these are expensive, and all will be projects that one government is going to have to commit to, with the knowledge that any payoff from it will most likely land during the opposition's reign, while having to deal with a huge public furore. In short, far too much effort for most politicians to deal with.
Compare this to switching to alternate, primarily decentralised, power generation. As I said earlier, there will need to be large infrastructure changes, and I'll happily admit it may come to more, in total, than switching to nuclear would.
HOWEVER, switching to decentralised power can be done gradually, spreading the cost out over multiple terms of government. For example, legislating that all new buildings generate at least X MW of power for every Y MW of predicted usage would be a good way to begin. Further on that legislation tack, requiring more energy efficient construction styles would also increase the relative value of every Watt generated.
Regarding cost of the actual equipment, you could use federal funding to construct manufacturing facilites to produce solar cells etc for both domestic and foreign consumption, providing both local jobs and an additional export revenue stream from the increasingly environmentally conscious world.
It is far more likely to garner public support, as even the staunchest denier of global warming cannot argue against a pollution free method of power generation with far greater redundancy and likely lower end costs for individual consumers over long term use.
Finally, it already aligns with existing government policy; in short, it is far more likely to be taken up by the government now.
tl;dr? I'm not saying switching to alternative energy generation is the only viable option. I'm not even saying it is definately the best (I honestly have neither the information, time, nor inclination to do a complete cost benefit analysis of all possible methods), all I'm saying is don't write it off. It's not impossible, nor even that improbable that 50 years hence we all produce our own power and nuclear or coal-fired power is a fading memory.