Progress in preventing nuclear terrorism
Terrorists who wanted to kill 100,000 people and destroy a city could build a simple nuclear bomb, without much difficulty, by obtaining some Highly Enriched Uranium (HEU). As little as 20 kg of HEU would provide the fuel for a possible bomb to even a fairly unsophisticated terrorist group. I probably could do it myself with the help of a few engineers and someone who understands how to use explosives.
The simplest way to get access to HEU is to steal the stuff from a research reactor or a reactor that makes isotopes for medical use. Many of these reactors are guarded by a couple of guys with semiautomatic rifles, who could be overpowered or bribed. Obtaining fuel in this way would more likely lead to a usable weapon than stealing a bomb, which could not be made to work without codes and, usually, a critical gadget for ignition.
In these research and commercial reactors, HEU generally exists in handy packages of 10 or 20 kg. It is easy to carry, and the radiation, though harmful, is not lethal.
Many experts have been worried for years that terrorist groups would make use of this relatively easy way to manufacture a nuclear weapon. About thirty years ago, an agreement was reached to do away with all this HEU and, instead, use Low Enriched Uranium (LEU) in the reactors or produce the isotopes in a cyclotron. LEU cannot be used to make the Bomb. Little was done to implement this agreement for many years, but gradually the USA has been retrieving and repatriating much of the HEU it has sold over the years to countries all over the world. The US National Nuclear Security Administration has recovered more than one ton of HEU. The US program has also supported the repatriation to Russia of another two tons of HEU and plutonium.
The following nations have now been relieved of their HEU: Brazil, Bulgaria, Chile, Colombia, Denmark, Greece, Latvia, Libya, Mexico, the Philippines, Portugal, Romania, Serbia, Slovenia, South Korea, Spain, Sweden, Taiwan, Thailand, Turkey and Ukraine. Removal of HEU is going on in other countries but is not yet finished. A few non-cooperating countries need to understand what is at stake and close down this road to a terrorist nuclear bomb before our luck runs out.