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Many experts believe that the most likely way for terrorists to acquire a nuclear explosive would be to obtain HEU and use this material to make a crude nuclear bomb, known more formally as an improvised nuclear device (IND). According to the
9/11 Commission Report, a trained nuclear engineer with an amount of fissile material about the size of a grapefruit or a
large orange, together with commercially available material, could build an IND that would fit in a van or SUV. Such a bomb would level much of Lower Manhattan.
Although an IND generally is associated with the simplest design for a nuclear explosive, it could be more sophisticated if the terrorist organization had access to individuals with expertise in nuclear engineering, nuclear physics, electronics, metallurgy, chemical processing, and explosives (probably the equivalent of an advanced degree in each of these disciplines but not necessarily actual weapons design or manufacturing experience, though such experience would be helpful). Assembling such a team would in itself be a significant challenge, and small and poorly-funded terrorist groups are not likely to have access to all these skills. A large, well-funded organization, however, might be able to recruit individuals with the required capabilities.
A number of terrorist groups, including some affiliated with Al Qaeda, are known to recruit scientists, engineers, and other specialists with the skills needed to improvise nuclear, chemical, or biological weapons.
Al Qaeda nuclear bomb design. |
By far the most difficult step for terrorists seeking to build an IND would be acquiring a sufficient amount of fissile material. In general, the lower the enrichment in U-235, the larger amount of HEU is required to make an IND.
The International Atomic Energy Agency defines the significant quantities of fissile material as 25 kg of weapons-grade (90 percent or more) HEU equivalent and 8 kg of plutonium. These values constitute the quantity of fissile material needed to form a nuclear weapon. Technically sophisticated nuclear weapons states are able to build nuclear weapons of this explosive power with less fissile material, employing as little as 3-4 kg of plutonium. While terrorists would only need small amounts of fissile material for an IND, hundreds of tons of these fissile materials have been produced and are in military and civilian stockpiles around the globe. As the next section discusses in more detail, much of these fissile materials are inadequately secured or held in countries at risk of political instability.
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