The in-game nuclear aircraft carriers do the same things as the conventional aircraft carriers, but they can carry more aircraft units (8 squadrons max vs. 10) and they move substantially faster (53 kmh max vs. 83 kmh). Note, however, that you must complete the level 6 5 aircraft carrier research AND level 5 nuclear power research before you may begin the nuclear aircraft carrier research.
[Corrected per @King Draza Mihajlovic's comment below.]
