The Atomic Power Mod adds a nuclear power source to the game. The reactor is extremely productive, producing 12,000 KW and unlike other generators can be comfortably constructed well within the confines of your base.
Unlike the other power sources though, it is somewhat unstable. The reactor slowly wears down with use and if permitted to go too long without routine maintenance may suffer a catastrophic containment failure. The reactor also produces a great deal of hard radiation when active which can injure and demoralize your colonists.
Highly productive, extremely conveniently, highly unstable, and very dangerous. Such is the nature of Atomic Power.