Eliminating Nuclear Threats

A Practical Agenda for Global Policymakers



GARETH EVANS and YORIKO KAWAGUCHI CO-CHAIRS                    Commission Members

4. The Threat of Nuclear Terrorism

Possible State and Non-State Actors

4.1     There is a significant and continuing fear internationally of nuclear terrorism – shared by the public and decision-makers alike. The UN Secretary-General has labelled nuclear terrorism “one of the most serious threats of our time”. U.S. President Obama has been equally blunt: “There is no graver danger to global security than the threat of nuclear terrorism, and no more immediate task for the international community than to address that threat.”

4.2     That fear is justified. There are terrorist actors in existence – as the whole world has known since Al Qaeda’s orchestration of 9/11 – who would, if they could, cause massive and indiscriminate havoc in almost any one of the world’s major cities. And there is every reason to fear that they can match that intent with capability. There is quite a high risk that they could produce a “dirty bomb”, combining conventional explosives with radioactive material, to devastating psychological effect. The risk is very much smaller that they could produce a far more physically destructive nuclear explosion, given the scale of the technical and logistical problems that would have to be overcome. But it is not negligible. And the possibility of cyber attacks on nuclear command and control centres is growing ever more significant.

4.3     Possible terrorist actors might either be acting independently of state backing, or have state sponsors. Since 1995, there have been several cases that confirm the danger that either group of actors can have access to – and no scruples about using – devices or substances with the potential for mass killings. The Aum Shinrikyo attacks in Tokyo in 1995 and the unsolved anthrax attacks in the United States in 2001 were the first two. Another was the poisoning of Alexander Litvinenko in London in 2006 with Polonium-210, which reminded the world that individuals can obtain a key material for detonating nuclear weapons and smuggle it undetected through the airports of countries on high alert against terrorist threats.

4.4     In the case of a nuclear weapon, it would require a large, well organized and well funded group to build, let alone buy, such a weapon, maintain security at all stages, and successfully transport it to the intended site for detonation. It is now known that Al Qaeda some years ago attempted to obtain enriched uranium, and that senior members of the group had at least one meeting with two Pakistani nuclear experts. The apparently dispersed and diffuse nature of its current organization and funding, after being under siege for most of the last decade, make the central organization, such as it is, a less likely candidate now than in the past for such a role. But it has offshoots and imitators in many countries.

4.5     The danger posed by any such group would be much enhanced by state backing, whether for nuclear materials or know-how, or simply for the necessary funding. The number of states likely to give deliberate support of this kind would be very small. Even regimes with a long history of, if not irrationality, at least playing by different rules to everyone else, would be unlikely to lend such assistance without first making an assessment of the likely consequences should they be identified – including the possibility of nuclear retaliation (the chances of which would be significantly higher if those states were already nuclear-armed themselves). A more substantial concern is that states with weak or fragile institutions, multiple internal power centres, and imperfect arrangements for securing weapons and dangerous materials, might end up providing such support even in the absence of any explicit government intent or direction to do so.

4.6     It should be borne in mind that the face of terrorism in ten to fifteen years may well be quite different from today’s. The politics of war and peace, and of security, may well shift from religion-based terrorism to eco-terrorism. In this scenario, there may be an even greater prospect that scientific and technical personnel from the richest countries will aid eco-terrorist use of nuclear weapons or materials.

Availability of Weapons and Material

4.7     Designing, building and delivering a nuclear weapon. Unless a terrorist group were to acquire a fully functioning nuclear weapon, it would need to build one. It is widely assessed that such a group would most likely opt for the simpler gun design than the more sophisticated implosion-type (see Box 4-1). The know-how to build a crude nuclear device of the gun-type weapon used to bomb Hiroshima can largely be found on the internet, and the engineering resources required to put it together would not be beyond the capacity of a well-organized and funded group.

4.8     The two major hurdles to be overcome would be acquiring sufficient fissile material, discussed separately below, and the engineering expertise needed to make the device work. The amount of fissile material required for one 15 kt atomic bomb built to a gun-type design (like that used on Hiroshima) would be around 50 kg of weapons-grade high enriched uranium (90 per cent U-235); an implosion-type weapon of the same yield would require far less fissile material – around 5 kg of plutonium or 15 kg of HEU for a basic design. Engineering the two colliding elements of a gun-type weapon in the exact shape and within the fine tolerances required to produce a super-critical nuclear explosion would be a difficult but not impossible task; building an implosion-type device would be a very much more formidable enterprise.


BOX 4-1


“Gun-assembly” nuclear weapon

“Gun-assembly” nuclear weapon

A gun assembly, which can only work with high enriched uranium (HEU), involves firing one or more shaped pieces of HEU at a shaped HEU target, bringing together enough fissile material to create a super-critical mass. For a proliferator or terrorist, a gun assembly has the advantage of being comparatively easy to design and manufacture, but the disadvantage of requiring much more HEU than an implosion device—depending on the design, around 50 kg.


“Implosion-type” nuclear weapon

“Implosion-type” nuclear weapon

An implosion device involves compressing a sub-critical sphere of fissile material—plutonium and/or HEU—achieving super-criticality through increasing the density of the material. Compared with a gun assembly, an implosion device is more efficient and requires far less fissile material—around 5 kg of plutonium or 15 kg of HEU for a basic design—but design and manufacture are very complicated, requiring precise processing and shaping of the fissile core and precise firing of the high explosive lenses.


4.9     Delivery to target would not be an insuperable problem. Weapons of this kind do not have to be dropped from an aircraft, exploding in mid-air, or carried by missile, to cause horrendous damage. For example, a Hiroshima-sized weapon detonated from inside the back of a large van in Trafalgar Square, London in the middle of a working day would cause what have been estimated as 115,000 fatalities and another 149,000 casualties from a combination of blast, fire and radiation poisoning; detonated in population-dense central Mumbai, the figures would be more like 481,000 fatalities and 709,000 other casualties.

4.10     Maintaining security for an operation as complex as this, for as long as it would take, would obviously be very difficult, and might be a reason for a group building its weapon in a fragile, failing, failed or phantom state where scrutiny might be expected to be less intense than in the target state or city. Air transport would be high risk, but if sea transport to that state were involved, luck might well run in favour of the terrorist group: the U.S. Container Security Initiative is one of many practical demonstrations that it is impossible to exhaustively inspect every container cargo at busy ports. And if truck transport across land borders was involved, rather less luck would probably be needed. Even radiological detection is easier to avoid with nuclear weapons than is the case with “dirty bombs” using (as discussed below), widely available but highly radioactive material.

4.11     Availability of nuclear weapons and materials: “loose nukes”. It is not impossible that fully assembled weapons could be acquired by terrorist groups in some circumstances, depending on the state of affairs of the nuclear-armed country in question, including the internal political situation, the degree of corruption in civilian and military agencies, the general reliability of the security services, and the means for protection and control over nuclear armaments and materials. But for nearly all practical purposes, the concern is more over the huge world stockpile of uranium of significant degrees of enrichment, as well as plutonium for energy, military, and scientific purposes.

4.12     There are a number of estimates for global stocks of high enriched uranium and separated plutonium. For high enriched uranium they range from 1750 to 1850 tonnes in military programs and 20 to 50 tonnes in civil programs, and for separated plutonium from 155 to 260 tonnes in military programs and 165 to 230 tonnes in civil programs. Most of the military materials (more than 90 per cent) are in the stockpiles of the U.S. and Russia, but even a relatively small amount stored in other countries presents a serious danger, taking into account that, as noted above, as little as 50 kg of high enriched uranium may be enough for manufacturing a Hiroshima-yield crude nuclear explosive device by terrorists.


BOX 4-2

Impact of Terrorist nuclear explosions IN London and Mumbai

Diagram box 4-2Detonation of
Hiroshima-size (15 KT)
nuclear weapon in Trafalgar Square, London, on a working day.
Estimated Fatalities:115,000
Estimated Casualties: 149,000










Diagram box 4-2Detonation of Hiroshima-size (15 KT)
nuclear weapon in central Mumbai
on a working day.
Estimated Fatalities: 481,000
Estimated Casualties: 709,000











Diagram box 4-2







4.13     These huge stocks of nuclear materials are maintained using extremely varied accounting systems, and the conditions for storing and protecting them from hijacking or sale to criminal elements are far from reliable. It is commonly assumed that the safest are nuclear warheads on deployed strategic forces and centralized storages of the five original nuclear-weapon states. Tactical munitions are less secure when stored at armed forces depots. Weapons grade uranium and plutonium of the five is considered sufficiently well preserved and guarded. Less secure is unirradiated low enriched uranium and civilian plutonium, used in power plants and for other peaceful purposes. Irradiated nuclear fuel containing uranium, plutonium and many other radioactive materials will generally be “self-protecting” against unauthorized removal due to its high radiation level.

4.14     It is harder to make a judgment about the military nuclear stockpiles of the nuclear-armed states outside the NPT. Most probably they are quite safe in India and Israel, but some doubts exist about the situation in Pakistan. As for civilian nuclear materials, their safety differs greatly from state to state, the most secure being non-nuclear-armed states of NATO and the EU, and Japan.

4.15     Access to know-how is clearly no less indispensable than the ability to acquire the necessary material. There have clearly been those willing to trade in nuclear knowledge, such as the A.Q. Khan network in Pakistan and the associated Swiss Tinner family. North Korea has also made its weapons-related know-how available to friendly regimes. International efforts to stem a possible outflow of nuclear scientists and technicians following the break-up of the Soviet Union have been judged largely successful, but this is an area which will require serious ongoing vigilance.

4.16     “Dirty bombs”. Radiological weapons, or “dirty bombs” are those which use conventional explosives to disperse radioactive materials. No great sophistication is needed to design, build and deliver them. Depending on the amount of explosives, considerable localized damage could be caused by their detonation, and on the nature and quantity of radioactive material used, an extensive area could be rendered inaccessible for an extended period, or require extremely expensive clean-up. The psychological shock experienced by the public from such an attack would no doubt be enormous, and achieve the fundamental terrorist aim of creating widespread terror.

4.17     Much smaller quantities of radioactive materials could be used for a dirty bomb – grams, not kilograms. There is also an enormously wide pool of potential sources to be found in the tens of thousands of hospitals and research schools around the world, not least in countries with less than exacting security and accounting procedures for radiological materials. Apart from in the nuclear fuel cycle (where highly radioactive material abounds, especially in the form of spent reactor fuel rods, but is closely secured, very dangerous to work with, and hard to hide), such materials are found in the civilian sphere in two main applications: as unsealed radiopharmaceutical material, used for the diagnosis and treatment of a range of diseases; and as sealed sources for a wide range of medical, agricultural, industrial and research applications.

4.18     The vast majority of such sources in use around the world are of relatively low radioactivity (e.g. smoke detectors) and do not pose a safety or security threat. However, some applications (such as radiotherapy, or sterilization of medical instruments), require sources of higher activity, and there have been a number of serious radiation accidents where high activity sources have been lost, stolen or abandoned: for example in Brazil, in 1987, when the accidental rupture in a building demolition of the source capsule of an abandoned caesium-137 radiotherapy unit resulted in several deaths, required the monitoring of some 112,000 persons, contaminated some 85 houses, and required a massive cleanup producing some 3,500 cubic metres of waste. Recently the theft was reported in Argentina of a canister of caesium-137 from an oil-drilling operations base, with two armed men overcoming a lone security guard and breaking into an underground bunker.

4.19     One downside for terrorists proposing to use dirty bombs is that, while they may be easier to acquire, assemble and detonate than nuclear weapons, they may be rather more difficult to transport and deploy in terms of avoiding radiological detection. Under the auspices of the Global Initiative to Combat Nuclear Terrorism, spearheaded by the U.S. and Russia, there has been a substantial effort to improve global radiological as well as nuclear detection architecture, including the installation of radiation detection equipment at many major international ports and airports around the world. That said, certain materials – such as the isotope used in the Litvinenko case – are effectively impossible to detect if contained within a minimal form of shielding.

4.20     Cyber attacks. Producing and detonating radiological or full-scale nuclear weapons would not necessarily exhaust the would-be nuclear terrorist’s repertoire: cyber attacks on the command and control centres of nuclear-armed states must now be acknowledged as a significant threat, notwithstanding the major effort continuing to be made by governments to anticipate and defend against such threats. Jujitsu – turning the opponent’s own effort or resources into the lever of his overthrow – has always had great appeal to sophisticated terrorists, and the risks here, sometimes exaggerated but not impossibly far-fetched, include faking a nuclear attack, faking a command signal to launch an attack, posting false claims of claims of responsibility on accessible government websites, disrupting or corrupting with false information emergency communications within and between governments (including on hotlines established between governments to deal with tense or ambiguous situations), and in the event of a warhead actually being launched, massively disrupting disaster relief operations.

4.21     Nuclear command and control has an inherent weakness in relation to cyber warfare, in that states must retain the capability to launch nuclear weapons in the event of a decapitating strike, which requires in turn mobility and redundancy, i.e., having nuclear weapons spread out in multiple locations. All computers in any way connected to the internet are inherently susceptible to infiltration and remote control. Computers which operate on a closed network may also be compromised by various hacker methods, such as privilege escalation, roaming notebooks, wireless access points, embedded exploits in software and hardware, and maintenance entry points. It is known that multiple attempts have been made in the past to penetrate military systems – for example, by hackers to compromise the extremely low radio frequency once used by the U.S. Navy to send nuclear launch approval to submerged submarines. It simply cannot be assumed that such attempts will never be successful in the future.

4.22     Reflecting the importance this issue is assuming, the UN General Assembly in December 2008 approved creation of an intergovernmental panel of experts on information and telecommunications security. The panel will report to the First Committee of the UN General Assembly in 2010.

Assessing the Risk of Nuclear Terrorist Attack

4.23     Given the enormous range of variables involved, it is virtually impossible to make any reliable estimate of how likely it is that a terrorist group may acquire and use a nuclear weapon, or even a much more readily put together and delivered radiological one, or the timeframe in which this might happen.

4.24     The most pessimistic, and often cited, estimates have been those by Harvard’s Graham Allison, who has been arguing since the mid-1990s that a major terrorist nuclear incident is more likely than not, or at least significantly likely, within a foreseeably short time frame, “by end of the decade” or “within the next ten years” as the case may be. He is supported by many influential and knowledgeable figures like the former head of the Los Alamos National Laboratory, Siegfried Hecker, who says that “the general consensus of nuclear weapons experts is that terrorists would face significant but not insurmountable challenges to build a primitive but devastating nuclear device and that it would most likely be delivered to the intended target by truck, boat, or light airplane.”

4.25     Others are much more sceptical, including John Mueller, who concludes that “the likelihood that a terrorist group will come up with an atomic bomb seems to be vanishingly small – perhaps very substantially less than one in a million.” A midway position is that of Cass Sunstein, who notes that if there is a yearly probability of one in 100,000 that terrorists could launch a nuclear or massive biological attack, the risk would cumulate to one in 10,000 over ten years and to one in 5,000 over twenty, suggesting that these odds are “not the most comforting.”

4.26     Trying to make any credible arithmetical assessment of the odds of a major terrorist nuclear attack is clearly a fruitless exercise. But that does not mean that, because the odds are obviously small, there is no real cause for concern: we are all now familiar, in the aftermath of the global financial crisis, with what are variously called “black swan”, “fat tail” or “long tail” events – those which seem impossibly unlikely, but have nonetheless happened. Because the consequences of the event occurring in this case are so catastrophically large, every possible preventive step that can sensibly be taken must be taken. And in doing so it is worth recalling the conclusion of another analyst of the probability of such attacks, Michael Levi, that “It has often been said that defense against terrorism must succeed every time, but that terrorists must succeed only once. This is true from plot to plot, but within each plot, the logic is reversed. Terrorists must succeed at every stage, but the defense needs to succeed only once.”

4.27     Strategies to respond to the threat of nuclear terrorism are discussed in Section 13.



Next: 5. The Risks Associated with Peaceful Uses of Nuclear Energy