Plutonium may be deadly, but uranium is much more dangerous
I sincerely believe that because of its utterly devastating and game-changing implications, nuclear terrorism is one of the greatest threats the world faces. Even a crude nuclear weapon detonated in Mumbai, London, Tokyo or Los Angeles will cause the kind of destruction and havoc that would be every citizen's worst nightmare. Such an event will significantly change the political and social landscape of a country for a long time to come, and probably for the worse. That's all everybody would talk about. In case of nuclear terrorism, the adage about us having to succeed every single time while them having to succeed just once rings resoundingly true.
A recent Nature article emphasizes the steps that President-elect (for only 5 more days) Obama should take to keep nuclear weapons from falling into the hands of terrorists. According to the article, something like only 0.2% of US defence spending is devoted to practical non-proliferation, an amount that has remained virtually unchanged for a decade. The new President's chief science advisor John Holdren has worked on these issues, having already alerted the non-proliferation community to them back in 2002.
What needs to be paid very close attention to is highly-enriched uranium (HEU) and not plutonium. Building a plutonium implosion weapon involves many intricate steps and would likely be beyond the reach of a terrorist outfit. Plutonium is a hideous element that is extremely difficult to work with. The explosives arrangement around it needs to be machined to the finest dimensions in order to work as expected. By contrast, simple firing mechanisms can be used to detonate a uranium bomb (although I don't share the article's predilection for calling it "child's play"). One of the topics of discussion between Pakistani scientists and Osama Bin Laden in August 2001 apparently involved such firing mechanisms. As the article correctly notes, even a uranium weapon fizzle that delivers 1-5 kT in a place like Manhattan would be devastating.
Given this scenario, it is more than disconcerting that some 272 HEU reactors in 56 countries remain unsecured. Feedstock balances for many of these reactors are not meticulously accounted for. Some uranium can even be scraped from the insides of centrifuges or gaseous diffusion tubes and declared as wasted or not produced. Quiet and gradual extraction of tiny amounts could lead to the accumulation of tens of kilograms, a quantity sufficient for a crude explosive device.
Clearly the focus of the new administration should be to try to secure such reactors in hot spots; in Pakistan, Iran and the former Soviet Union. Fortunately, one of the foremost policy actions that Barack Obama was involved in as a Senator was non-proliferation. He worked with Senator Richard Lugar to continue securing nuclear material from the former Soviet Union. Non-proliferation was always one of Senator Obama's special concerns. Let's hope it stays that way.