"Is nucular power efficient?" Well, compared to what? Compared to buring coal, yes, it's vastly efficient. Compared to fusion (should we ever be able to create and sustain a fusion reaction) no, it isn't.
It also depends on how you define "efficient." Fission reactors today still create radioactive waste, which no one wants to deal with. Compare that to, say, photovoltaics, or wind generation, and you could argue which is cleaner, and which is less dangerous.
There will be, no doubt, new sources of energy available in the future. Matter/anti-matter is one possibility, zero point energy is another, geo thermal, orbiting powersats, tidal, helium 3 reactors...
Or if republicans keep running things the way they are, the survivors will heat their homes with burning wood, and/or Llama dung.
Number Two: Conform, Number Six! Conform!
Number Six: I will not be stamped, filed, indexed, briefed, debriefed, or numbered! I am a person.