Technicians extracted the highly enriched uranium from the apartheid regime’s nuclear weapons in 1990, then melted the fuel down and cast it into ingots. Over the years, some of the cache has been used to make medical isotopes, but roughly 485 pounds remains, and South Africa is keeping a tight grip on it.

That gives this country — which has insisted that the United States and other world powers destroy their nuclear arsenals — a theoretical ability to regain its former status as a nuclear-weapons state. But what really worries the United States is that the nuclear explosives here could be stolen and used by militants to commit the worst terror attack in history.

Available: http://www.washingtonpost.com/world/africa/us-unease-about-nuclear-weapons-fuel-takes-aim-at-a-south-african-vault/2015/03/13/b17389f6-2bc1-4515-962d-03c655d0e62d_story.html