There are 2 categories of atomic weapons: the Nuclear Device and the Thermonuclear Device. They can be built as a city Project in any city and both require the Uranium resource to produce. There is no limit on the number that a player can build.
Once a Nuclear or Thermonuclear Device is created, it is added to the player's inventory and can then be used by any unit or improvement capable of deploying it on the map. This includes bomber aircraft, Nuclear Submarines, and the Missile Silo.
Nuclear Devices have a blast radius of 1. When deployed from a Missile Silo, they have a Range of 12. They cost 14 Gold per turn to maintain.
Thermonuclear Devices have a blast radius of 2. When deployed from a Missile Silo, they have a Range of 15. They cost 16 Gold per turn to maintain.