Nuclear Proliferation and the Problem of Terrorism by Francesco Calogero and Carlo Schaerf

Francesco Calogero

Physics Department, University of Rome "La Sapienza"
Carlo Schaerf
Physics Department, University of Rome "Tor Vergata"

Nuclear proliferation

It is in everybody's interest to prevent a breakdown of the nonproliferation regime; in particular, in the interest of the 5 NPT nuclear-weapon countries (USA, Russia, Great Britain, France, China), of the three non-NPT nuclear-weapon countries (Israel, India, Pakistan), and even more so of all the other countries of the world - inasmuch as all these countries, and their citizens, have a stake in survival and the preservation of our civilization. However the leadership - and also many citizens -- of certain non-nuclear-weapon (NNW) countries might consider intolerable the discriminatory aspects of an international regime in which only a few countries -- possibly including countries they consider their enemy -- possess a nuclear arsenal; hence they might be induced to seek a nuclear-weapon capability, or at least, as a first step in this direction, to pursue technological developments that would make it easier and quicker to acquire such a capability if the decision to do so were eventually made. Hence it is difficult to summon a strong universal consensus to impede nuclear-weapon proliferation unless it is clear that the "discriminatory" aspect of the present nonproliferation regime - mainly based on the NPT - is temporary. Conclusion: the alternative futures are either the transition to a nuclear-weapon-free world (NWFW) or a catastrophic breakdown of the overall nonproliferation regime.

The time scale for the bifurcation between the routes leading to one or the other of these two alternative futures is measured in years or perhaps decades, certainly not centuries.

The catastrophic character of the breakdown of the overall nonproliferation regime has two aspects: it refers to its pace, that is likely to have a catastrophic allure after the process begins, with more and more countries getting - more or less willingly - into the act; and to its eventual consequences, the spread of nuclear weapons to many countries will bring about their use "in anger" entailing catastrophic outcomes, death and suffering for millions of individuals indeed the very demise of our civilization.

The establishment and viability of a NWFW have been advocated, and also seriously investigated, by Pugwash [1] (and others) for decades, but tended to be considered utopian by most mainstream politicians and strategic thinkers in the key nuclear-weapon countries - until recently, when an opposite trend is emerging [2], presumably in recognition of the elementary truths mentioned above and as well of the new opportunities provided by the end of the Cold War. Progress towards a NWFW is most desirable and should be the focus of the 2010 NPT Review Conference -in the guise of credible pronouncements about the desirability of this outcome, of genuine commitments by all the 5 NPT nuclear-weapon countries to an early implementation of Article VI of the NPT, of serious studies of the viability of a NWFW (including its verifiability [3]) and of course of additional significant progress in nuclear disarmament and in phasing out strategic doctrines envisaging the actual use of nuclear weaponry under any circumstances other than in response to a nuclear attack.

Nuclear terrorism

The destruction of a city by a nuclear explosion would be a tremendous disaster; there is no need to belabor this point, indeed it is universally agreed that every effort must be made to prevent this from happening (this is also emphasized by those who believe the time has nevertheless come to plan for the aftermath of such a catastrophe [4]) . But to do so it must be recognized, to begin with, that there do exist terroristic groups who would perform such a deed if they could (after 9/11 few doubt this). It is moreover expedient to envision the easiest routes to perform such a terrible act and to bring them to the attention of the authorities who can and should take preventive actions; although reasonable care should also be taken, while doing so, not to provide hints that might be useful to terrorists.

The easiest route for a terroristic group who wants to destroy a city with a nuclear explosion is to build the nuclear explosive device in the target city. Indeed a transportable device is considerably more difficult to realize than one assembled, as it were, on the bench in a rented garage or possibly in an apartment in a high rise residential building downtown. Doing so will be quite easy if the terrorists manage to get hold of a sufficient quantity of "weapon-grade" Highly Enriched Uranium (HEU). It would be quite difficult otherwise.

Indeed, while alternative strategies could be envisaged, for instance using Plutonium rather than Highly Enriched Uranium, or getting hold of a nuclear weapon and carrying it to the target city rather than manufacturing a nuclear explosive device there, each of these alternatives is, from the point of view of the terrorists, substantially more difficult, perhaps even impossible (at least to terrorists without any State support). Hence the prevention of nuclear terrorism should be mainly focused on making sure that a sufficient quantity of "weapon grade" HEU is not acquired by terrorists; although some efforts should obviously also be focused on guaranteeing the physical security of nuclear warheads (especially those more easily transportable, such as certain "tactical" nuclear weapons) and in making them resistant to unauthorized use (for instance by equipping them with Permissive Action Links), and as well on guaranteeing the physical security of Plutonium and on minimizing its usage in the nuclear fuel cycle (especially if such usage is only promoted for parochial motives, being economically unwarranted [5]).

Weapon-grade HEU is Uranium substantially free of impurities and containing a quite high proportion of the isotope U-235, say, more than 90%; while natural Uranium contains only 0.7% of this isotope, the remaining 99.3% consisting essentially of the isotope U-238; and the Low Enriched Uranium (LEU) used as fuel in most electricity-producing nuclear reactors contains from 3% to 5% U-235. The enrichment of Uranium (namely, the increase of the proportion of U-235 in its make-up) is a difficult process that few countries muster and it is certainly beyond the capabilities of terrorists. Hence the prevention must be focused on making sure that terrorists have no chance to acquire HEU - by stealing it, by buying it from someone who stole it (no HEU is freely available for sale), by obtaining it from a country within whose leadership there are powerful elements supportive of the terrorist activity, or via a commando action in a depository where such material is stored (in the latter case the fact that the terrorists got hold of the material would be immediately known; in the others, it might remain undiscovered until the material is used to destroy a city, and then it might not be very easy to trace its origin -- although even after the explosion it should be possible to identify the origin of the Uranium used by investigating its isotopic composition and impurities: nuclear forensics 4).

It is impossible to build an explosive device with LEU enriched 5.4% or less. The critical mass of Uranium enriched 10% is 3800 kg but it could be reduced to 2200 kg with the use of an appropriate reflective layer ("tamper"). A tamper 20 cm thick could reduce the critical mass of Uranium enriched 20% from 700 kg to 330 Kg, corresponding to a ball with a diameter of 32 cm (~1 foot)[6]. The critical mass of a spherical mass of pure U-235 (without any tamper) is 47 kg, corresponding to a ball with the diameter of 17 cm. 47 kg of U-235 could be reduced to 16 kg if surrounded by 10 cm of natural Uranium or to 14 kg with a beryllium (Be) tamper of the same thickness.

Critical mass for uranium-235 as a function of enrichment.

100 (one hundred) kilograms of HEU are more than enough to manufacture easily an explosive nuclear device "of Hiroshima-type" capable to destroy a city. Due to its small volume (approximately five liters or a sphere with a diameter of 22 cm) and minimal radioactive signature, transporting this material (of course, parceled in more than one piece) to any city is an easy job: indeed the attempt to prevent this by creating an impenetrable barrier protecting a country or even just a specific city is, in our opinion, a wasted effort -- yet huge funds are devoted, for instance in the USA, to this rather useless task. Let us re-emphasize that, once the needed quantity of weapon-grade HEU is available, the destruction of a city becomes an easy job: there will be no difficulty to acquire all other needed materials, as well as the required know-how, by any intelligent do-it-yourself bricoleur, who needs not have any previous experience in the manufacture of nuclear weaponry (although of course such experience would be helpful).

The main motive of concern is the fact that, mainly due to the excessive accumulation of nuclear weaponry and materials during the Cold War, the existing world stocks of HEU are enormous, more than one million kilograms; most of this material is in Russia, very large stocks are also in the USA, much lesser quantities (but still amounting to thousands of kilograms) are in several other countries [7]. How to deal with this huge potential for disaster?

Let us outline tersely the main aspects of this problem. Various interlinked questions are significant: how to deal with the stocks of HEU accumulated in view of the manufacture of nuclear weapons whose production was eventually considered unnecessary, or with the HEU recovered from the dismantlement of nuclear weapons now recognized as redundant (and being dismantled in the context of the limited nuclear disarmament now taking place); what are the possible civilian uses of HEU other than to produce nuclear explosive devices and how to deal with this issue; where is HEU still produced and how to stop altogether this development; what to do as soon as possible and instead in the very long run; what can be done by national (or even private) initiatives and what requires instead joint international activities; and what can be done with respect to these issues in the context of the 2010 NPT Review Conference, and/or in other analogous contexts, for instance at the Conference on Disarmament in Geneva.

Let us now proffer in this connection a few facts and observations. [8]

First of all it should be noted that all the 5 NPT nuclear-weapon countries have announced that they have stopped any production by enrichment of additional HEU. But there is no international agreement to consolidate these commitments, and no international verification to confirm that these commitments are indeed respected.

The situation in the other 3 countries possessing a nuclear arsenal (Israel, India and Pakistan) is less clear. Israel has a deliberate policy of opacity regarding all nuclear matters. In India the main route to a nuclear-weapon capability has been Plutonium rather than HEU, but a capability to enrich Uranium has also been developed. In Pakistan the acquisition of nuclear weapons has been instead based on an indigenous capability to enrich Uranium, via centrifuge technology, that was also, for some time, proliferated around the world by the network organized by A. Q. Khan. This individual -- considered "the father of the nuclear-weapon capability of Pakistan" and therefore regarded by many in Pakistan as a national hero -- was instrumental in developing in Pakistan an indigenous capability to enrich Uranium on the basis of blueprints and other data he stole while working at the URENCO European Consortium in the Netherlands. He is now under house-arrest (perhaps more symbolic than effective [9]) for his criminal activity in proliferating clandestinely this capability around the world: while this endeavor was certainly largely motivated by greed (indeed Khan lives now as a rich man in his house), it is not clear whether this activity was also supported by certain sectors of the Pakistani official establishment for geopolitical reasons, grounded on anti-American feelings (motivating exports to North Korea) and/or solidarity with other Islamic regimes (motivating exports to Libya, Iran, perhaps Syria). Hopefully these developments have been now all identified and brought under some sort of control.

It must be kept in mind that the enrichment of Uranium to produce LEU is a legitimate activity that can be motivated by "peaceful" applications, since LEU is the standard fuel for electricity-producing nuclear reactors. But the same technology allows the transformation of natural Uranium to LEU and then of LEU to HEU, the second step being indeed easier (less energy consuming) than the first. Hence quite intrusive verification techniques are required to make sure that an establishment producing LEU does not produce HEU. The International Atomic Energy Agency (IAEA) based in Vienna is capable to administer such an effective verification, especially in the context of a cooperative environment: and indeed it does so, as required by the NPT, in the few NPT non-nuclear-weapon countries that produce LEU (and to some extent also in the NPT nuclear-weapon-countries that have voluntarily submitted some of their Uranium-enrichment installations to IAEA verification).

Clearly the natural context to make progress towards a universal termination of the production of HEU is the Conference on Disarmament in Geneva, where a Fissile Materials Cut-off Treaty (FMCT) is one of the two main items that awaits consideration by this institution, whose activity has been stalled for too many years (the other main item is the Prevention of an Arms Race On Space); but this matter shall also be discussed at the 2010 NPT Review Conference.

Clearly it is difficult to envisage that a civilization like ours (I refer here mainly to that prevailing in reasonably "democratic" countries) can survive if a very small group of individuals - possibly including crazies or fanatics; without any checks to constrain their actions - can acquire clandestinely the capability to destroy one or more cities. Hence it seems to me that in the long run HEU should be completely eliminated. It is important to realize that this does not necessarily entail the elimination of nuclear energy, that can be based on LEU (which cannot be used to manufacture nuclear explosive devices). Of course it will then be necessary to make sure, through appropriate verification, that the facilities that produce LEU do not produce any HEU. It will also be necessary to phase out all "peaceful" uses of HEU.

The "peaceful" uses of HEU are mainly of two kinds: "research" reactors and reactors for naval propulsion (mainly submarines, and some Russian icebreakers).

In the case of research reactors (whose energy output is generally much smaller than that of "power" reactors for the production of electricity) the motivation for using HEU as fuel rather than LEU is generally in order to have a more compact geometry and to achieve higher neutron fluxes which might be more convenient for certain experiments. But the use of HEU is not indispensable: there is now significant progress in the development of much more compact and efficient types of LEU fuel. Indeed the transition of research reactors hitherto fueled by HEU (those not in the process of being altogether phased out) to being fueled by this new kind of compact LEU is in progress. Clearly it is desirable that this transition be effected as quickly and universally as possible, and allocation of funds to this end should be made by all "affluent" countries (especially those that manufactured, and possibly exported, these research reactors to begin with). In the meantime of course the accounting and physical security should be strengthened worldwide of the unused [10] HEU fuel stocked at all research reactors (many of which are located in "low-security" environments such as University campuses). International agreements to promote these developments now exist, but their effectiveness is far from satisfactory (see for instance the analysis provided in the paper by Matthew Bunn and Micah Zenko quoted above, in footnote 6). Indeed sometimes interventions by private initiatives (such as NTI) have been instrumental to correct dangerous situations. Attention to these issues should become part of the 2010 NPT Review Conference, to stimulate all countries to take actions commensurate to the potential risks.

Analogous observations are also applicable to the HEU-fueled reactors used for naval propulsion (the need for the relevant nuclear reactors to be as compact as possible is rather obvious, especially for submarines). Indeed the French nuclear-propelled submarines are now being converted from HEU to LEU fuel. On the other hand a very large quantity of HEU (hundreds of tons) has been set aside in the USA, sufficient to provide fuel for nuclear propelled submarines for many decades. Inasmuch as some of these submarines are equipped with long-range nuclear-armed missiles, constituting an important component of the nuclear-weapon arsenal of the USA, this fact is clearly a negative indication regarding the eventual willingness of the USA - rather, of those who made such decisions in the USA -- to ever proceed towards complete nuclear disarmament.

But the main risk is presumably entailed by the enormous quantities of HEU stocked in Russia, and to a lesser (but still quite large) extent in the USA. In the aftermath of the dissolution of the Soviet Union the concern about the security of the HEU stocked in the former Soviet Union was certainly justified, given the difficult economic and societal circumstances then prevailing there. Now the accounting and physical security of the HEU has substantially improved, also thanks to cooperative activities conducted with other States, primarily with the USA; but much remains to be done.

Some progress has also been made in eliminating HEU: indeed the oversized stocks of HEU left over after the end of the Cold War make the elimination of large quantities of it -- hundreds of tons -- insignificant from a military-strategic point of view (except as regards the risk of its use by terrorists!); while the down-blending transformation of HEU into LEU can be performed easily hence cheaply. (Let us re-emphasize that LEU cannot be used to manufacture nuclear explosive devices, and that transforming LEU back to HEU is a task beyond the capabilities of most States, let alone a terrorist group). The most important development of this kind is the so-called "HEU Deal", agreed at the beginning of the 1990's, that regulates the down-blending to LEU in Russia of 500 tons (half a million kilograms) of Russian HEU and the sale of this LEU to American utilities via the United States Enrichment Corporation (USEC). Unfortunately, mainly for commercial reasons (namely, not to affect adversely the market price of LEU), this deal has been spread over a quite long time period (20 years) -- hardly consistently with a proper appreciation of the danger entailed by the prospects of nuclear terrorism based on the availability of HEU. Moreover, again for commercial reasons, this program suffered various delays.

Anyway so far the HEU Deal caused the elimination by down-blending of over 300 tons of Russian HEU (estimated by USEC to correspond to the elimination of over twelve thousand nuclear warheads), and it seems to proceed now at a steady rate entailing the elimination of 30 tons of HEU per year. For the 300 tons of HEU already eliminated, $4.6 billion have been paid to Russia; it is expected that, when all the 500 tons will be eliminated, $7.6 billion shall be altogether paid: the envisaged date is 2013 (provided a new round of haggling about costs does not once more delay the process). The elimination of 500 tons (half a million kilograms) of HEU is of course a very positive result; but much more could have been and should be done, indeed a faster rate of elimination (by as much as a factor of five) would have been feasible - certainly technologically and also in terms of Russian willingness - provided adequate funds were immediately available to support an acceleration of the elimination of the 500 tons of HEU declared excess by Russia. An extension of the project so as to eliminate additional quantities of Russian HEU can also be envisaged, perhaps via a different sort of financial arrangement; although the willingness of Russia to proceed in this direction has in the mean time decreased, due to nationalistic feelings that consider HEU as a crucial strategic asset -- in spite of its redundancy with respect to any reasonably conceivable military needs. Unfortunately - and in my opinion most unwisely -- the USA and other affluent countries do not seem as committed to address this question as it should be implied by the lip service paid to the risk of nuclear terrorism, for instance at the meeting of the G8 group of nations (or G7+1: Canada, France, Germany, Italy, Japan, UK, USA + Russia) held at Kananaskis in 2002, where the formula 10+10/10 (ten plus ten over ten) was advertised, meaning an agreement "in principle" to devote 10 billion US dollars by the USA, plus 10 billion US dollarsby the other countries, over the next 10 years, to promote various developments meant to alleviate the risk of the use by terrorists of means of mass destruction. But these commitments have not been and are not being fully implemented.

A study advocating faster progress in the elimination of HEU and suggesting political and financial arrangements to this end has been completed some years ago. It originated in the Pugwash context, and it was eventually commissioned by the Swedish government and performed by an international expert group.[11] The main idea of that study is to offer financial incentives to Russia (and possibly to other countries of the former Soviet Union; but most of the HEU is in Russia) to promote additional elimination of HEU besides that already agreed with the USA. Analogous ideas have been aired in other contexts. Perhaps some developments in this direction - at least in the bilateral USA-Russia context - are now in progress; this is in the interest of these two countries and the rest of the world.

In any case the risk entailed by the prospect that terrorists get hold of enough HEU to destroy one or more cities shall have to be faced by the international community more seriously than it has been done hitherto, in spite of the lip service paid to this danger in a number of context and by a number of speakers. An important international forum where cooperative initiatives to face this danger shall hopefully be discussed and agreed upon is the 2010 NPT Review Conference.

Avoiding the acquisition by terrorists - whichever their backgrounds and motivations - of the capability to destroy cities and thereby cause enormous casualties, sufferings and damage, must clearly be a shared interest of the international community, inasmuch as it is made up of States which, in spite of geopolitical economic ideological differences, do all belong to a common civilization. Let us hope that an understanding of the impending character of this danger will motivate all relevant decision makers to address this issue with the real commitment that is appropriate to it.

[1] See, for instance, the Pugwash Monograph entitled A Nuclear Weapon Free World: Desirable? Feasible?, edited by J. Rotblat, J. Steinberger and B. Udgaonkar, published in English (Westview, 1993) and then translated in many other languages (Russian, Japanese, Chinese, Korean, Spanish, Swedish, French).

[2] See, for instance, the two op-ed papers by George Shultz , Bill Perry , Henry Kissinger and Sam Nunn (Wall Street Journal, January 4, 2007 and January 15, 2008), and related activities and endorsements.

[3] An interesting step in this direction has been recently (5 February 2008) proposed at the Geneva Conference on Disarmament by Des Browne, British Minister of Defense: 'Laying the Foundations for Multilateral Disarmament', see:

[4] See for instance the recent Report by Ashton Carter, Michael May and Bill Perry entitled " The Day After: Action in the 24 Hours Following a Nuclear Blast",

[5] See for instance: Frank von Hippel, "Nuclear Fuel Recycling: More Trouble than It's Worth", Scientific American, April 2008, available at:


Wu Jun and Zhang Songbai: Analysis of the Risk of Nuclear terrorism. Presented to the XVII Amaldi Conference, DESY 14-16 March 2008

[7] For data on the available stocks worldwide of fissile materials including HEU see for instance the paper by Matthew Bunn and Micah Zenko in the web site of NTI ( and the extensive bibliography (papers and web sites) reported there.

[8] Much more detailed information on all these matters than can be reported in this paper can be easily googled; key websites are those of the Arms Control Association (ACA:, of the James Martin Center for Nonproliferation Studies (formerly called Monterey Institute for International Security:, of the National Resources Defense Council (NRDC:, of the Nuclear Threat Initiative ( , of the Institute for Science and International Security (ISIS: ), of the Bulletin of Atomic Scientists (BAS:, of the Pugwash Conferences on Science and World Affairs (; key American authors are David Albright, Matthew Bunn, Tom Cochran, Richard Garwin, John Holdren, Bill Potter, Frank von Hippel, as well as their collaborators. Examples of non-American sources are the Stockholm International Peace Research Institute (SIPRI: ), the Peace Research Institute Frankfurt (PRIF:, the PIR Center in Moscow (PIR:, the Chinese Academy of Engineering Physics in Beijing (CAEP:; and of significant authors are Alexey G. Arbatov, Anatoly Dyakov, Viktor N. Mikhailov, Li Bin, Shen Dingli, Hu Side. Many additional relevant institutions and authors can be easily found via the web starting from these.

[9] See the item "A. Q. Khan" in Wikipedia.

[10] The used fuel rods represent less of a security risk because generally their high radioactivity makes it extremely difficult, perhaps impossible, for terrorists who might get hold of them to utilize them in order to manufacture a nuclear explosive device. They might be used by terrorists to manufacture a radiation dispersive device (RDD: sometimes called "dirty nuclear bomb"), but this danger is relatively minor when compared with the capability to destroy a city with a "Hiroshima-type" nuclear explosion. And it is not so easy to manufacture such an RDD, because of the difficulty to disperse widely the radioactive material, which in fact cannot be too radioactive, otherwise the terrorists handling it would become incapacitated before being able to disperse it. Indeed the main impact of an RDD is likely to be caused by the panic it might produce, and by its economic consequences -- including the cost of a clean-up operation bringing the levels of radioactivity below the stringent standards of normal life, of the order of the natural radioactive background.

[11] G. Arbman, F. Calogero, Paolo Cotta-Ramusino, Lars van Dassen, M. Martellini, M. Bremer Maerli, A. Nikitin, J. Prawitz, L. Wredberg, "Eliminating Stockpiles of Highly Enriched Uranium: Options for an Action Agenda in Co-operation with the Russian Federation", Report submitted to the Swedish Ministry for Foreign Affairs, SKI Report 2004: 15, ISSN 1104-1374, available on and on the Pugwash website: .