Zero risk of nuclear terrorism

Manufacturing a nuclear weapon. To accomplish this, a terrorist group would have to obtain an appropriate amount of one of the two most popular materials for nuclear weapons, highly enriched uranium (HEU) or plutonium separated from fuel used in a production reactor or a power reactor. Weapon-grade plutonium is found in weapon manufacturing facilities in nuclear weapon states and is very highly protected until it is inserted in a weapon. Reactor-grade plutonium, although still capable of being weaponized, is less protected, and in that sense is a more attractive target for a terrorist, especially since it has been produced and stored in prodigious quantities in a number of nuclear weapon states and non-weapon states, particularly Japan.

But terrorist use of plutonium for a nuclear explosive device would require the construction of an implosion weapon, requiring the fashioning of an appropriate explosive lens of TNT, a notoriously difficult technical problem. And if a high nuclear yield (much greater than 1 kiloton) is desired, the use of reactor-grade plutonium would require a still more sophisticated design. Moreover, if the plutonium is only available through chemical separation from some (presumably stolen) spent fuel rods, additional technical complications present themselves. There is at least one study showing that a small team of people with the appropriate technical skills and equipment could, in principle, build a plutonium-based nuclear explosive device (Mark et al., 1986). But even if one discounts the high probability that the plan would be discovered at some stage (missing plutonium or spent fuel rods would put the authorities and intelligence operations under high alert), translating this into a real-world situation suggests an extremely low probability of technical success. More likely, according to one well-known weapon designer,4 would be the death of the person or persons in the attempt to build the device.

There is the possibility of an insider threat; in one example, a team of people working at a reactor or reprocessing site could conspire to steal some material and try to hide the diversion as MUF (materials unaccounted for) within the nuclear safeguards system. But this scenario would require intimate knowledge of the materials accounting system on which safeguards in that state are based and adds another layer of complexity to an operation with low probability of success.