The International Atomic Energy Agency (IAEA)

Question

1. controls nuclear weapons stockpiles.
2. inspects nuclear power plants.
3. tests nuclear weapons.
4. builds nuclear power stations.

I think it's number 4

Answer 1

http://www.google.com/search?q=IAEA&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a

Answer 2

The International Atomic Energy Agency (IAEA) is an international organization that seeks to promote the peaceful use of nuclear energy, and to inhibit its use for any military purpose, including nuclear weapons.

copied from wiki

4. builds nuclear power stations.
seems to be the only acceptable answer