An Unpleasant Subject

Probably for no particular reason other than the generally tremulous state of the zeitgeist, there are a lot of rumors, speculation and theories floating around to the effect that non-state actors, presumably Jihadists of one stripe or another, already possess one or more functional nuclear weapons. That would certainly be bad news. A semi-related issue, obviously, is the question of Iran's alleged pursuit of nuclear weapons, and nuclear proliferation more generally.

It occurs to me that this is a field of the greatest public concern in which most people don't understand the basic scientific issues. I expect my readers are pretty sophisticated, but I'd like to know -- did you know all or most of what I'm about to explain, or is any of it news? (If I'm boring you with stuff you already know, you can go check out Today in Iraq, where I did the post today.)

In order to make a nuclear weapon, you need a sufficient amount of either the element plutonium -- any isotope will work, but it's easier to use material consisting predominantly of Pu239 -- or so-called highly enriched uranium (HEU). Naturally occuring uranium consists mostly of the istope U238, but you need at least 20% U235, and preferably a higher proportion, to make a bomb. For nuclear reactor fuel, you only need enrichment to 3% or so.

Plutonium is almost non-existent in nature, but it builds up in nuclear reactor fuel as it is "burned" for power. It can be extracted chemically from used fuel rods, but they are highly radioactive and dangerous to handle. It is also considerably more difficult to make a functional plutonium bomb than it is to make a bomb from HEU.

HEU has low radioactivity and can be handled without special precautions. Even worse, if you have less than 400 Kg of 20% U235, or as little as 20Kg of 90% or more U235, it is astonishingly easy to make a bomb. No high technology is needed. A nuclear explosion occurs when a sufficient mass of weapons-grade fissionable material is aggregated. To make an HEU bomb, all you need is a gun with a closed barrel. Put a lump of HEU of more than 50% critical mass in the closed end, and a similar lump in the chamber, then fire the gun. The lump in the chamber will smash into the lump at the other end, and goodbye Peoria. Such devices are so simple to build and so reliable that it is thought that a terrorist could confidently make and deploy one, even though testing would obviously be impossible.

Making a plutonium bomb requires a much more sophisticated device in which a hollow ball of plutonium is forcefully imploded. Sophisticated industrial facilities would be necessary, and a manufacturer would probably not be confident that it worked without being able to test the design.

Fortunately, it is very difficult to enrich uranium. The isotopes can only be separated by taking advantage of the difference in their atomic weights, which is tiny. Enriching uranium requires huge industrial plants with large amounts of precision machinery. It is only feasible for states.

Used nuclear fuel rods are "too hot to handle" at first, but after 25 years or so they cool down to the point where a relatively sophisticated non-state actor could conceivably extract the plutonium.

So there are three conceivable ways for a non-state actor to obtain a working nuclear weapon, without the cooperation of a state:

a) Steal an actual, working nuclear weapon from a national arsenal;
b) Steal enough HEU, and make your own bomb;
c) Either steal plutonium, or steal some decades-old used nuclear fuel rods and extract the plutonium, and then somehow obtain sophisticated design information and hardware.

At present, any scenario under (c) seems implausible. However, in the fuel-recycling/breeder reactor future proposed by the Bush administration, there will be far more used nuclear fuel and plutonium in circulation. Used reactor fuel also makes a fabulous "dirty bomb," so there will be very serious security concerns with any such nuclear economy.

The HEU scenario, unfortunately, is more plausible. After the collapse of the Soviet Union, many security guards and scientists at nuclear weapon and research sites went unpaid and facilities were left unsecured. An engineer at one facility actually did steal 1.5 Kg of HEU, hoping to sell it for profit. He was caught, but nobody can rule out that other thefts were not thwarted. Since 1993, U.S.-Russian cooperation has resulted in great improvements in the security of former soviet nuclear sites, but it's hard to know how good security really is presently. There are also substantial stockpiles of HEU in Kazakhstan, Uzbekistan, Belarus, Ukraine, and other places whose political stability and national security competence may be uncertain.

As for someone stealing an intact weapon, most U.S. and Soviet/Russian weapons have fail-safe devices that make them impossible to detonate without access to security codes. (I'm not sure why it wouldn't be possible to extract HEU from a device and build your own detonator for it, but evidently they are booby-trapped to make this extremely difficult.) However, so-called tactical (i.e., comparatively small) nuclear weapons in the former Soviet arsenal have been reported to lack these fail-safe devices. The Russians claim that all Soviet weapons are accounted for, but it's impossible to know if they are telling the truth, or even whether they really know.

The bottom line is, it seems unlikely, but it is not impossible, that there are one or more loose nukes out there somewhere. If so, they are bulky -- the idea of a "suitcase bomb" is unrealistic, we're talking something more like a steamer trunk, at least. You can't smuggle it in your checked luggage, but you could ship it.

What to do? Collect as much HEU as possible, from military and research sites around the world. Dilute it with U238. Then it can be used as reactor fuel. Think twice and three times about a future plutonium economy. Stop further nuclear weapons proliferation, but that can only happen if the present nuclear powers get serious about disarmament. Why should Iran or other regional powers agree to give up uranium enrichment and the prospect of acquiring nuclear weapons if it's perfectly alright for Israel, Pakistan, India, the U.S., Russia, China, France and the UK to have them? Obviously they won't and there isn't any moral case to be made why they should.

The human and political consequences of any sort of attack using a nuclear explosive weapon, anywhere, are incalculable. One can easily think of some prospects that are far too painful to contemplate. The one thing that Kerry and Bush agreed on in their "debates" was that this is what worries them the most. But Mr. Bush hasn't actually done anything about it, because it requires diplomacy, international cooperation, and humility on the part of the United States, not bullying and U.S. exceptionalism.