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May 29, 2009 | 1426 GMT
Debunking Myths About Nuclear Weapons and Terrorism
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A warning placard on a container at a decommissioned nuclear facility
Summary

STRATFOR’s Geopolitical Intelligence Report on May 26 generated many questions and responses from our readers concerning various scenarios of nuclear terrorism and nuclear proliferation. We take a closer look at issues of terrorism, loose nukes, unstable and unpredictable world leaders and clandestine delivery in a follow up to our coverage of nuclear weapons in the 21st century.

Analysis

STRATFOR’s Geopolitical Intelligence Report that examined North Korea’s nuclear test elicited many questions from our readers regarding nuclear terrorism and the role that could be played by irrational world leaders in actually using such a weapon or device. STRATFOR examines these issues.

Terrorists and Apocalyptic-Minded Jihadists

Concerns about nuclear terrorism have been a reality since even before Sept. 11, 2001 — though a profound lack of situational awareness in the wake of those attacks spawned a deep concern about what plans al Qaeda might already have in motion for the weeks and months that followed.

In planning the 9/11 attacks, al Qaeda enjoyed financing that included patronage from Saudi royalty and — perhaps even more importantly — sanctuary from which to operate in Afghanistan. Hardened radicals, bent on re-establishing a Caliphate across the Muslim world, al Qaeda had time and resources to consider devoting to potential chemical, biological, radiological or nuclear (CBRN) programs. Their only success (they tinkered unsuccessfully with biological and chemical weapons) was in weaponizing hijacked civilian airliners.

Presently, al Qaeda is a shadow of its former self, and empirical evidence in the years since 2001 has shown a steady erosion — especially after the July 2005 London Underground and March 2004 Madrid bombings — of the apex leadership’s capability to orchestrate global strikes. Al Qaeda’s remaining leadership is on the run and focused only on operations in the Middle East and South Asia. Al Qaeda “franchise” operations have undoubtedly sprung up around the world, but these are far less capable and far more localized than the pre-Sept. 11 al Qaeda phenomenon.

Though al Qaeda is only one example, it is important to note that the immense security, sanctuary, financial backing and time that al Qaeda had was insufficient to begin attempting to produce a crude nuclear device in any meaningful way — the furthest they got was attempting to procure nuclear materials that turned out to be fake, sold to them by con men. Even chemical and biological weapon pursuits (which were certainly explored and experimented with) were not seriously or successfully pursued, given the complexity and cost.

Efforts to clandestinely build a nuclear device require a coherent and consistent investment measuring in the billions (if not tens of billions) of dollars over a period likely spanning a decade or more. They require large, fixed, well-powered and vulnerable installations for a variety of aspects of the effort. These installations represent an enormous risk and opportunity cost for a terrorist organization. The international community closely monitors some of the equipment required, and they will concentrate an enormous investment of intellectual, financial and material resources into just the sort of target that the United States can bring air power to bear upon.

Though the history of the use of CBRN in terrorist attacks is limited, the fact of the matter is that most cases where groups have considered pursuing these capabilities have ultimately led to them being abandoned in favor of more obtainable and efficient tactics. They simply fall well short of the destruction wrought by simpler and more conventional explosive devices. Pound for pound, dollar for dollar and hour for hour of effort, high explosives are far more effective at inflicting massive casualties. The innovation of using hijacked civilian airliners as human-guided cruise missiles is far more in line with al Qaeda operational thinking than concepts of concentrating so much in easily targetable facilities for long periods of time. Doing so runs in the face of basic operational security considerations for any terrorist organization.

For further reading on STRATFOR’s perspective on the full spectrum of weapons of mass destruction, see the following analyses:

Loose Nukes and Clandestine Acquisition

But what about acquiring a nuclear weapon that has already been built? The security of nuclear weapons is and has long been an important concern.

However, the effort involved in actually trying to steal a nuclear weapon would entail a significant dedication of resources and an immense intelligence effort beyond the reach of almost any terrorist organization. Indeed, the odds of a failure are high, no matter how careful and meticulous the planning. Some nuclear weapons facilities around the world are obviously not as hardened as others, but taken as a whole, they are some of the hardest targets on the planet, and the personnel better vetted than almost any other institution.

Even the lightest attempt to begin probing runs the risk of not only failing to acquire a bomb, but setting off a series of alarms and red flags that brings such an aggressive investigative and law enforcement/military response down on the terrorist organization that it could be completely wiped out before it ever attempted to target its true objectives (whatever they might be).

And even if one could be stolen or otherwise acquired, modern nuclear weapons have been designed to include a series of (highly classified) safety features. Though all nuclear weapons are not created equal, these range from permissive action links without which the device cannot be armed (a feature Pakistan is now thought to employ) to configurations that will actually render the fissile core(s) useless if improperly accessed. The security of nuclear weapons in Pakistan has long been something STRATFOR has kept a close eye on, and something we continue to monitor. The Hollywood scenario of a terrorist group stealing away with a nuclear device in the night and automatically being able to arm it at its convenience is not grounded in reality. Furthermore, the theft would be difficult to carry off without setting off the same alarms and red flags that would leave little opportunity for the device to be smuggled particularly far — much less half way around the world.

Nuclear weapons are complex devices that require considerable care and maintenance — especially the small, modern and easily transportable variety. After the collapse of the Soviet Union, fears arose of a series of Soviet suitcases containing sophisticated nuclear devices were somehow lost. These fears persisted into the 21st century, well after the fissile and radioisotope materials in the design would have decayed significantly enough to effect the performance of the weapon, in addition to the diminished functionality of its other components after being handled roughly over the years.

Irrational Actors

One of the questions that arose from our analysis of the North Korean situation was that it was governed by a reliance on rational actors. There was a concern that STRATFOR was too quick to assume that North Korean leader Kim Jong Il or Iranian President Mahmoud Ahmadinejad could be considered rational.

Historically, every leader makes mistakes and missteps. Some are certifiable: Josef Stalin utterly refused to believe his advisers when they insisted that Nazi forces were poised to invade in 1941. Even after the invasion began, he refused to believe it until his most trusted advisers actually traveled to the front lines.

But despite Stalin’s ruthlessness when it came to cracking down on the population of the Soviet Union, he did not throw a nuclear weapon at the United States the moment he got one, even though many in the West feared that he might. Running a country as Stalin ran the Soviet Union for as long as he did requires a certain rationality, and most importantly, a personal nature that clings tenaciously to continued existence. Overseeing the defense of that country against the Nazi onslaught and then implementing an aggressive crash nuclear program takes coordination and focus.

No one can run a country alone. Leaders require loyal and competent administrators. A certifiable and apocalyptic-minded leader is simply unlikely to rise so far — and is even less likely to command the respect and loyalty of those necessary to actually run the country for any length of time.

Kim Jong Il undoubtedly ranks very high among the world’s most idiosyncratic world leaders. But he has deftly transferred and consolidated control over a country that was run by a single individual, his father, for nearly 50 years. By balancing various groups and interests, he has both maintained internal control and loyalty and kept the attention of some of the world’s most powerful countries focused on North Korea for more than 15 years. Indeed, he has overseen the allocation of resources necessary to build both crude intercontinental ballistic missiles and crude nuclear devices while faced with crushing international sanctions. This is the track record of a competent (if annoying) leader, not a crazy one.

If Kim was merely suicidal, he has had the artillery, artillery rockets and short-range ballistic missiles at hand to destroy Seoul and invite a new Korean War since before his father died — a choice that would be far quicker, cheaper and even more complete than the prototype nuclear devices that North Korea has so far demonstrated. Rather, his actions have consistently shown that his foremost goal has been the survival of his regime. Indeed, he has actually curtailed much of the more aggressive activity that occurred during his father’s reign, such as attempting to assassinate South Korea’s president.

While Kim’s actions may seem unstable (and, indeed, they are designed to seem that way in order to induce an element of uncertainty at the negotiating table), Pyongyang regularly uses ballistic missile tests and even its nuclear tests as part of a larger strategy to not only keep itself relevant, but to ensure regime survival.

As for Ahmadinejad and his fiery rhetoric denying the Holocaust, calling for the destruction of Israel and defying the United States, he has not lost steam in recent months before the country’s next presidential election in June. This rhetoric has a role. Not only is it populist, and intended for domestic consumption, but it is also a strategy, similar to North Korea’s, to cultivate perceptions and influence behaviors by making Tehran appear crazy and unpredictable. Regardless, even if he is reelected, the true power in the country is the clerical leadership, not the country’s highly-visible president. Although the executive in Iran does indeed wield considerable power, the complexity of the Iranian political system allows for several layers of oversight.

Furthermore, the Supreme Leader Ayatollah Ali Khamenei — the true leader in Tehran — has consistently relied upon consensus when it comes to policy- and decision-making. Under his direction and authority, the various institutions — the executive, Parliament, the Expediency Council, the Supreme National Security Council, the Assembly of Experts, the Guardians Council, the Islamic Revolutionary Guards Corps (IRGC) and others all have a say in the final policy on a given matter. Though there are extremist elements within some of these institutions (such as the IRGC), Tehran’s senior leadership has consistently demonstrated itself to be far more rational than Ahmadinejad’s rhetoric suggests. In short, even if Iran did have nuclear weapons, it would not be Ahmadinejad — or any potentially like-minded successor — with his finger on the proverbial button.

Furthermore, any fears associated with Iran’s possession of nuclear weapons must be balanced against the policies of Israel, which is not known for its subtlety or half measures. The Israelis deploy a fully functional nuclear triad, and have a variety of survivable means for delivering a decisive retaliatory blow against Tehran if nuclear weapons were ever used against them. This is not doubted by anyone in Tehran.

Truly crazy and suicidal leaders have a difficult time becoming leaders of a country even capable of considering trying to developing a nuclear weapon, much less being able to see the process through to the end over the course of a decade. But the leader of a country has worked to get to that position. They may have taken risks, but they were generally calculated and they want to enjoy the fruits of that labor. The consequences for miscalculating with nuclear weapons is annihilation — not only for themselves, their family and the power base that they have toiled to build, but for the entire society.

Nuclear Weapons and Proxies

Another concern is that North Korea, Iran or Pakistan might hand off a nuclear weapon to a non-state actor or proxy of some sort — one that would detonate it at a mutually-agreeable target as soon as possible. Subsets of this same issue are whether one of these countries might not use a shipping container or some other clandestine means to carry out an attack on the United States or another target — the deniable use of nuclear weapons.

Three factors must be considered when addressing the above concern. The first is an issue of trust and control. Non-state, militant proxies like Hezbollah rely on patrons like Iran for support and training. But they have their own interests as well — and they hold those close. Despite its own rhetoric about Israel, for example, Hezbollah’s senior leadership often owns property in Beirut and elsewhere in Lebanon, and has grown wealthy off the proceeds. They are no more interested in seeing their livelihood and retirement destroyed in the Israeli retaliation than Tehran. This older generation does not have complete control over the organization (nor is it a monolithic, unified entity), and there is certainly no shortage of young, ideologically motivated militants in Lebanon.

But that assumes Tehran would ever hand over a nuke to Hezbollah in the first place. Proxies must be kept dependent, otherwise they cease to be proxies. They do not share some deep bond of trust. Though there may be some shared ideological affinities (like their hatred of all things Israeli), they attempt to maintain control over their proxies. Handing over even a crude nuclear device is anathema to that relationship and would destroy the dynamics by which the country enforces its will as a patron. It would have provided an organization that it can never fully trust with the one true guarantor of sovereignty.

Second, the nuclear device is the product of an immense, expensive national effort. Each individual weapon or device — especially early on — represents an enormous investment of national resources. By handing one over to an outside group, the country not only has no assurance of it being employed in the way they want, but opens itself to the prospect of that immense investment being wasted or misused. Because a meaningful nuclear deterrent rests on not one weapon, but many, the incentive will be for the country to consolidate its stockpile and deploy it to multiple locations that it has strong control over in order to work towards establishing that deterrent.

Finally, there is the issue of risk. A nuclear weapon used in a terrorist attack — not just against the United States or Israel, but anywhere in the world — will be followed by the most intense, broad and meticulous investigation in human history. The idea that because a bomb was involved in a terrorist attack that the fissile material that made it possible will not be traced ruthlessly to its source simply does not hold water. The necessary investigative processes are not only possible and well understood, but work to improve and further refine them has only intensified and received additional funding after 9/11. Indeed, a country providing a nuclear weapon to a non-state group could not have even reasonable assurances that it would not come back to haunt them, either through investigation or interrogation of those that carried out the attack.

Far from being able to carry out a nuclear strike clandestinely or deniably, Tehran would be opening itself up to responsibility and accountability for Hezbollah’s actions. Again, the material will almost certainly be traced back to Tehran. And it would be Tehran that suffered the consequences.

Indeed, the closest Pyongyang has come to this is an attempt to share some civilian technology with Syria — its trial run with the idea of low-level proliferation of some civilian (though inherently dual-use) precursor technologies. It quickly decided that the entire idea was too risky and sold Syria out to Israel and the United States, resulting in Israeli airstrikes in Western Syria in 2007. So while the concern about technology sharing is real (and validated by the now infamous network of A.Q. Khan), there are also limitations to how much one country is willing to risk for another. The Israeli bombing and North Korea’s betrayal of Syria will not be soon forgotten.

And if countries like Syria and North Korea cannot trust each other when it comes to such high stakes, the idea that a country would be willing to trust a non-state actor is even more problematic.

Ultimately, such doomsday scenarios cannot ever be completely ruled out, and continual, ever-improving efforts to further secure global nuclear stockpiles and vigilance over them are certainly warranted from a security standpoint. But man has controlled nuclear weapons for more than half a century, and we do not see the latest nuclear crisis playing out any differently than every other nuclear crisis that has come before it. Furthermore, STRATFOR does not subscribe to the idea that countries build nuclear weapons in order to use them immediately, thereby triggering nuclear war, or freely hand them off to non-state actors that would.

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Po 210

Posted: October 26, 2010 in Nuclear Weapons, Po 210, Suitcase Nukes, Terrorism 101

Po-210 is a terrible choice for a poison. Extremely toxic, radioactive, and is extremely difficult to handle. It emits alpha particles and becomes lead. It has a half life of 138.4 days. This means half of the original amount of Po-210 turns into lead every 138 days. It has a short shelf life, which limits it industrial usefulness.

Po-210’s main military application is a neutron source, a polonium-beryllium “nuclear trigger.” This type of nuclear trigger was used in all early nuclear weapons, and is probably used in the missing Soviet suitcase nukes. If the Po-210 has turned into lead, the suitcase nukes will not work. It has been reported al-Qaeda is offering $3 million dollars for a gram of Po210.

Speculation: a courier was transporting Po-210, packaged in small foil packages about the size of the little red or blue sweetener packages, and one or more of the packages leaked. The fine powder would be tracked by the courier’s feet, and spread by contact with his clothes. This explains the multiple contaminated sites. Po-210 is only a threat if ingested or inhaled. Litvinenko could have touched a contaminated surface and then contaminated his food. Once inside the body, it only takes a microscopic particle to kill.

Polonium-beryllium neutron sources is accurately described in The Rings of Allan. More information can be found on http://www.canadafreepress.com/2006/paul-williams120606.htm

Could the next chapter of our national nightmare be a nuclear one? How hard would it be for operatives of Osama bin Laden to deliver a “suitcase nuke” to our doorstep?

INTERACTIVE GRAPHICS
Map: Hunting Osama
Map: Nukes Pipeline
Interactive: Taliban P.O.W. Revolt
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Latest news: War Against Terror


RECENT COVER STORY
Closing In
Dec. 24, 2001
Past Issues Taliban Last Days Dec. 17, 2001 —————– Lifting the Veil Dec. 3, 2001 —————– Hunt for bin Laden Nov. 26, 2001 —————– Thanksgiving 2001 Nov. 19, 2001 —————– Inside Al-Qaeda Nov. 12, 2001 —————– Defender In Chief Nov. 5, 2001 —————– Going In Oct. 29, 2001 —————– The Fear Factor Oct. 22, 2001 —————– Facing the Fury Oct. 15, 2001 —————– How Real Is the Threat? Oct. 8, 2001 —————– Life on the Home Front Oct. 1, 2001 —————– One Nation, Indivisible Sept. 24, 2001 —————– Day of Infamy Sept. 14, 2001


PHOTO ESSAYS
Kabul Unveiled
Taliban on the Run


MORE STORIES
Where’s OBL: Letter from Tora Bora
Anthrax: Where the Investigation Stands
TIME/CNN POLL: Americans Standing By Bush’s War

The technical answer is that the threat is still considered to be remote; there is no hard evidence that any terrorist group, including bin Laden’s, has a finished nuclear weapon in its arsenal. But not long ago, anthrax seemed a distant threat. And it is possible for the bad guys to assemble an atom bomb with contraband uranium and off-the-shelf parts. “It’s not particularly probable, but it’s possible,'” says Anthony Cordesman, a senior fellow at the Center for Strategic and International Studies in Washington. “The difficulty is that we are dealing with a wide range of low-probability cases. We can’t be afraid of any one, but we have to be concerned about all of them.” Among those probabilities: “dirty” conventional bombs loaded with radioactive garbage and attacks on nuclear plants that cause massive radiation leaks.

For years, cloak-and-dagger stories have circulated that Soviet suitcase nukes (also known as atomic demolition munitions, or ADMs) had gone unaccounted for and presumably ended up on the Russian black market. The Russians have offered confusing and conflicting statements about the disposition of their ADMs, leading some to suspect the worst. The ADMs weigh from 60 lbs. to 100 lbs., according to Bruce Blair, a former U.S. Air Force officer and expert on Soviet nuclear weapons. They could be carried in a case 8 in. by 16 in. by 24 in. The fissile material inside the mini-nukes degrades over time, though, and it’s unlikely that the Russians maintained them or that their new owners could. “There’s no good evidence that any rebel group or terrorist has these,” says John Lepingwell, a nuclear expert with the Monterey Institute of International Studies.

If terrorists can’t buy portable nukes, they would have to make them. And in a frightening study done by the Nuclear Control Institute, a nonproliferation group in Washington, a panel of nuclear-explosives experts concluded that a group of dedicated terrorists without nuclear backgrounds could assemble a bomb if it had the right materials (such as plutonium 239, uranium 235, plutonium oxide and uranium oxide). It would take about a year to complete the job. “There’s little question that the only remaining obstacle is the acquisition of the material,” says Paul Leventhal, the institute’s president. Less than 110 kg of active ingredients could yield 10 kilotons of explosive power–a Hiroshima-size weapon. Even if the terrorists didn’t get the recipe quite right, a 1-kiloton yield could still devastate a city. And forget the suitcase: a truck will do, or a container ship to float the bomb into an American port.

Where would bin Laden get the material? Again, the most common answer is Russia, with its reputation as a fissile flea market. And a bin Laden associate has told authorities that the mastermind is shopping for nuclear ingredients. Adds Leventhal: “My feeling is that the prudent assumption is that bin Laden is nuclear capable in some fashion.” Other experts are less certain that any terrorist group could pull off a nuke. A 1999 Rand study on terrorism noted somewhat reassuringly that “building a nuclear device capable of producing mass destruction presents Herculean challenges for terrorists and indeed even for states with well-funded and sophisticated programs.”

Which is why the greater danger may lie in dirty bombs, conventional weapons used to spray radioactive material–anything from used reactor rods to contaminated clothing–over wide areas. Although the death toll wouldn’t be great, the contamination and the public panic could be widespread. “The ultimate dirty bomb is a nuclear power reactor,” says NCI’s Leventhal. That someone will run a jet into a cooling tower isn’t the only risk. Periodically the Nuclear Regulatory Commission has staged mock attacks against facilities, and the faux intruders won half the time–meaning they were in a position to cause severe damage. It’s a target-rich environment: not only is the core vulnerable, but one NRC study also concluded that if terrorists blew up the cooling pool that holds the spent fuel, the radiation could kill 6% of the people living within 10 miles of the plant.

Read more: http://www.time.com/time/magazine/article/0,9171,1101011029-180495,00.html#ixzz13Q3ECd1H

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Can Terrorists Build Nuclear Weapons?

Carson Mark, Theodore Taylor, Eugene Eyster, William Maraman, Jacob Wechsler

J. Carson Mark is a member of the Nuclear Regulatory Commission’s Ad visory Committee on Reactor Safeguards and of the Foreign Weapons Eval uation Group of the U.S. Air Force. He is a former division leader of Los Alamos National Laboratories’ Theoretical Division and serves as a consultant to Los Alamos and a number of governmental agencies.Theodore Taylor is chairman of the board of Nova, Inc., which specializes in solar energy applications. He is a nuclear physicist who once designed the United States’ smallest and largest atomic (fission) bombs. He also designed nuclear research reactors. He has served as deputy director (Scientific) of the Defense Atomic Support Agency and as an independent consultant to the U.S. Atomic Energy Commission. He is coauthor (with Mason Willrich) of Nuclear Theft: Risks and Safeguards and is the subject of John McPhee’s The Curve of Binding Energy.

Eugene Eyster is a former leader of Los Alamos National Laboratories’ WX Division, which is responsible for the explosive components of nuclear weap ons. A specialist in chemical explosives, he participated in the Manhattan Project.

William Maraman, a specialist in chemical and metallurgical processing of plutonium and uranium, is director of TRU Engineering Co., which does consulting work on transuranic elements. He was at Los Alamos National Laboratories for thirtyseven years, where he was leader of the Plutonium, Chemistry and Metallurgy Group and of the Material Sciences Division.

Jacob Wechsler is a physicist specializing in nuclear explosives. He was a member of the Manhattan Project and was leader of Los Alamos National Laboratories’ WX Division, which is responsible for the explosive components of nuclear weapons.

General Observations

Two options for nuclear devices to be built by terrorists are considered here: that of using the earliest design principles in a so-called crude design and that of using more advanced principles in a so-called sophisticated design.

A crude design is one in which either of the methods successfully dem onstrated in 1945—the gun type and the implosion type—is applied. In the gun type, a subcritical piece of fissile material (the projectile) is fired rapidly into another subcritical piece (the target) such that the final assembly is supercritical without a change in the density of the material. In the implosion type, a near-critical piece of fissile material is compressed by a converging shock wave resulting from the detonation of a surrounding layer of high explosive and becomes supercritical because of its increase in density.

A small, sophisticated design is one with a diameter of about 1 or 2 feet and a weight of one hundred to a few hundred pounds, so that it is readily transportable (for example, in the trunk of a standard car). Its size and weight may be compared with that of a crude design, which would be on the order of a ton or more and require a larger vehicle. It would also be possible, in about the same size and weight as a crude model but using a more sophis ticated design, to build a device requiring a smaller amount of fissile material to achieve similar effects.

For a finished implosion device using a crude design, terrorists would need something like a critical mass of uranium (U) or plutonium (Pu) or, possibly, UO2 (uranium oxide) or Pu02 (plutonium oxide). For a gun type device, substantially more than a critical mass of uranium is needed, and plutonium cannot be used. It may be assumed that the terrorists would have acquired (or plan to acquire) such an amount either in the form of oxide powder (such as might be found in a fuel fabrication plant), in the form of finished fuel elements for a reactor—whether power, research, or breeder— or as spent fuel.

For a small, sophisticated design, the terrorists may need a similar amount of fissile material since practically all the presumed reductions in size and weight have to be taken from the assembly mechanism, and, with a less powerful assembly, not only will it be important to have the active material in its most effective form, but its amount will have to be sufficient to achieve supercriticality. Alternatively, a smaller amount could be used in a sophis ticated design with a more powerful and heavier assembly mechanism.

Conceivably oxide powder might be used as is, although terrorists might choose to go through the chemical operation of reducing it to metal. Such a process would take a number of days and would require specialized equip ment and techniques, but these could certainly be within the reach of a dedicated technical team.

Fuel elements of any type will have to be subjected to chemical pro cessing to separate the fissile material they may contain from the inert clad ding material or other diluents. This process would also require specialized equipment, a supply of appropriate reagents, well-developed techniques spe cific to the materials handled, and at least a few days to conduct the operation. Spent fuel from power reactors would contain some plutonium but at such low concentrations that it would have to be separated from the other materials in the fuel. It would also contain enough radioactive fission fragments that the chemical separation process would have to be carried out by remote operation, a very complicated undertaking requiring months to set up and check out, as well as many days for the processing itself. The fresh fuel for almost all power reactors would be of no use, since the uranium enrichment is too low to provide an explosive chain reaction.

The terrorists would need something like a critical mass of the material they propose to use. For a particular fissile material, the amount that con stitutes a critical mass can vary widely depending on its density, the char acteristics (thickness and material) of the reflector employed, and the nature and fractional quantity of any inert diluents present (such as the oxygen in uranium oxide, the uranium 238 in partially enriched uranium 235, or chem ical impurities).

For comparison purposes, it is convenient to note the critical masses with no reflector present (the “bare crit”) of a few representative materials at some standard density. For this discussion, the following examples of bare critical masses have been chosen:

10 Kilograms (kg) of Pu 239, alpha-phase metal (density = 19.86 grams per cubic centimeter [gm/cc]).

52 kg of 94% U-235 (6% U-238) metal (density = 18.7 gm/cc).

approximately 110 kg of U02 (94% U-235) at full crystal density (density = 1I gm/cc). approximately 35 kg of Pu02 at full crystal density (density = 11.4 gm/cc).

In all cases (others as well as these), the mass required for a bare crit varies inversely as the square of the density. Thus, the bare crit of delta-phase plutonium metal (density = 15.6 gm/cc ) is about 16 kg. Similarly, at densities the square root of two times larger than those above, the bare crit masses would be one-half those indicated. If any reflector is present, the mass re quired to constitute a critical assembly would be smaller than those above. With a reflector several inches thick, made of any of several fairly readily available materials (such as uranium, iron, or graphite, for example), the critical mass would be about half the bare crit. Thicker reflectors would further reduce the mass but would be more awkward without providing much more of a reduction. Although beryllium is particularly effective in this respect—providing critical masses as low as one-third the bare crit—it is not readily available in the form needed and is not considered further.) It is consequently assumed here that a mass of half the bare crit is what terrorists would require to complete a near-critical (crude) assembly.

With respect to the effects of dilution by isotopes of heavy elements, only the two most obvious cases need be considered. One is that of reactor- grade plutonium. This material is not uniquely specified, since the fractional amount of the Pu-240 depends on the level of exposure of the fuel in the reactor before it is discharged. However, at burn-up levels somewhat higher than present practice, the bare crit of plutonium would be only some 25-35 percent higher than that for pure Pu-239. Because of spontaneous fission, the effect of the Pu-240 on the neutron source in the material is thus likely to be more important than its effect on the critical mass. Nevertheless, nuclear weapons can be made with reactor-grade plutonium.

The other obvious dilution case is that of uranium at enrichments lower than 94 percent. Here the effect on critical mass, and consequently on the amount of material that must be acquired and moved by the assembly system, is quite appreciable. For example, the bare crit of 50 percent enriched ura nium is about 160 kg (~3 times that of 94 percent material) and for 20 percent material about 800 kg ( ~15 times that for 94 percent). Similar factors will apply for uranium oxide as a function of enrichment. In this same con nection, it may be noted that the mixed oxide fuel once considered for the Clinch River Breeder Reactor (~22 percent plutonium oxide plus ~78 per cent uranium oxide) would correspond to uranium at an enrichment of somewhat less than 40 percent and have a critical mass a little more than four times larger than 94 percent uranium oxide.

As a final general observation, for a crude design, terrorists would need something like 5 or 6 kg of plutonium or 25 kg of very highly enriched uranium (and more for a gun-type device), even if they planned to use metal. They would have to acquire more material than is to go into the device, since with metal considerably more material is required to work with than will appear in the finished pieces. The amounts they would need can be compared with the formula quantities identified in federal regulations for the protection of nuclear materials: 5 kg U-235, or 2 kg plutonium. Sites at which more than a formula quantity is present are required to take measures to cope with a determined, violent assault by a dedicated, well-trained, and well-armed group with the ability to operate as two or more teams. Trans port vehicles that carry more than a formula quantity must be accompanied by armed escort teams and have secure communications with their base. Transport vehicles carrying smaller amounts are not so heavily guarded, but there are provisions intended to ensure that in the aggregate no more than a formula quantity is on the road at one time. For terrorists having to acquire at least several formula quantities, there are formidable barriers to overcome.

 

Crude Designs

Crude designs are discussed primarily in the context of the problems facing a terrorist group. Schematic drawings of fission explosive devices of the earliest types showing in a qualitative way the principles used in achieving the first fission explosions are widely available. However, the detailed design drawings and specifications that are essential before it is possible to plan the fabrication of actual parts are not available. The preparation of these drawings requires a large number of man-hours and the direct participation of indi viduals thoroughly informed in several quite distinct areas: the physical, chemical, and metallurgical properties of the various materials to be used, as well as the characteristics affecting their fabrication; neutronic properties; radiation effects, both nuclear and biological; technology concerning high explosives and/or chemical propellants; some hydrodynamics; electrical cir cuitry; and others.

It is exceedingly unlikely that any single individual, even after years of assiduous preparation, could equip himself to proceed confidently in each part of this diverse range of necessary knowledge and skills, so that it may be assumed that a team would have to be involved. The number of specialists required would depend on the background and experience of those enlisted, but their number could scarcely be fewer than three or four and might well have to be more. The members of the team would have to be chosen not only on the basis of their technical knowledge, experience, and skills but also on their willingness to apply their talents to such a project, although their susceptibility to coercion or considerations of personal gain could be factors. In any event, the necessary attributes would be quite distinct from the paramilitary capability most often supposed to typify terrorists.

Assuming the existence of a subnational group equipped for the activist role of acquiring the necessary fissile material and the technical role of making effective use of it, the question arises as to the time they might need to get ready. The period would depend on a number of factors, such as the form and nature of the material acquired and the form in which the terrorists proposed to use it; the most important factor would be the extent of the preparation and practice that the group had carried out before the actual acquisition of the material. To minimize the time interval between acquisition and readiness, the whole team would be required to prepare for a consid erable number of weeks (or, more probably, months) prior to acquisition. With respect to uranium, most of the necessary preparation and practice could be worked through using natural uranium as a stand-in.

The time intervals might range from a modest number of hours, on the supposition that enriched uranium oxide powder could be used as is, to a number of days in the event that uranium oxide powder or highly enriched (unirradiated) uranium reactor fuel elements were to be converted to ura nium metal. The time could be much longer if the specifications of the device had to be revised after the material was in hand. For plutonium, the time intervals would be longer because of the greatly increased hazards involved (and the absolute need of foreseeing, preparing for, and observing all the necessary precautions). in addition, although uranium could be used as a stand-in for plutonium in practice efforts, there would be no opportunity to try out some of the processes required for handling plutonium until a suf ficient supply was available.

To achieve a minimum turnaround time, the terrorists would, before acquisition, have to decide whether to use the material as is or to convert it to metal. They would have to make the decision in part in order to proceed with the design considerations, in part because the amounts needed would be different in the two cases, and in part to obtain and set up any required equipment.

For the first option—using oxides without conversion to metal—the terrorists would need accurate information in advance concerning the phys ical state, isotopic composition, and chemical constituents of the material to be used. Although they would save time by avoiding the need for chemical processing, one disadvantage (among others) is the requirement for more fissile material than would be needed were metal to be used. This larger amount of fissile (and associated) material would require a larger weight in the assembly mechanism to bring the material into an explosive configuration.

As to the second option—converting the materials to metal—a smaller amount of fissile material could be used. However, more time would be needed and quite specialized equipment and techniques—whether merely to reduce an oxide to the metal or to separate the fissile material from the cladding layers in which it is pressed or sintered in the nuclear fuel elements of a research reactor, for example. The necessary chemical operations, as well as the methods of casting and machining the nuclear materials, can be (and have been) described in a straightforward manner, but their conduct is most unlikely to proceed smoothly unless in the hands of someone with experience in the particular techniques involved, and even then substantial problems could arise.

The time factor enters the picture in a quite different way. In the event of timely detection of a theft of a significant amount of fissile material— whether well suited for use in an explosive device or not—all relevant branches of a country’s security forces would immediately mount an intensive response. In addition to all the usual intelligence methods, the most sensitive technical detection equipment available would be at their disposal. As long as thirty-five years ago, airborne radiation detectors proved effective in prospecting for uranium ore. Great improvements in such equipment have been realized since. A terrorist group would therefore have to proceed deliberately and with caution to have a good chance of avoiding any mishap in handling the material, while at the same time proceeding with all possible speed to reduce their chance of detection.

In sum, several conclusions concerning crude devices based on early design principles can be made.

I . Such a device could be constructed by a group not previously engaged in designing or building nuclear weapons, providing a number of requirements were adequately met.

2. Successful execution would require the efforts of a team having knowledge and skills additional to those usually associated with a group engaged in hijacking a transport or conducting a raid on a plant.

3. To achieve rapid turnaround (that is, the device would be ready within a day or so after obtaining the material), careful preparations extending over a considerable period would have to have been carried out, and the materials acquired would have to be in the form prepared for.

4. The amounts of fissile material necessary would tend to be large— certainly several, and possibly ten times, the so-called formula quantities.

5. The weight of the complete device would also be large—not as large as the first atomic weapons (~10,000 pounds), since these required aero dynamic cases to enable them to be handled as bombs, but probably more than a ton.

6. The conceivable option of using oxide powder (whether of uranium or plutonium) directly, with no postacquisition processing or fabrication, would seem to be the simplest and most rapid way to make a bomb. However, the amount of material required would be considerably greater than if metal were used. Even at full cyrstal density, the amounts are large enough to appear troublesome: ~55 kg (half bare crit) for 94 percent uranium oxide and ~17.5 kg for plutonium oxide. However, the density of the powder as acquired is nowhere close to crystal density. To approach crystal density would require a large and special press, and the attempt to acquire such apparatus would constitute the sort of public event that might blow the cover of a clandestine operation. Besides, the time required for processing with such a press would preclude a rapid turnaround. Even to achieve densities a little above half of crystal would require some pressing apparatus (not as conspicuous as a large press and conceivably obtainable quietly), but time would again be required to process material quantities of perhaps three or four times those above. The densities available in powder without pressing are not well determined but are quite low, probably in the range of 3 to 4 gm/Cc, although possibly lower.

Within the confines of the crude design category—that of a device guar anteed to work without the need for extensive theoretical or experimental demonstration—an implosion device could be constructed with reactor- Brade plutonium or highly enriched uranium in metal or possibly even oxide form. The option of using low-density powder directly in a gun-type assembly should probably be excluded on the basis of the large material requirements.

There remains the possibility of using a rather large amount of oxide powder (tens of kilograms or possibly more) at low density in an implosion- type assembly and simply counting on the applied pressure to increase the density sufficiently to achieve a nuclear explosion. Some sort of workable device could certainly be achieved in that way. However, obtaining a per suasive determination of the actual densities that would be realized in a porous material under shock pressure (and hence of the precise amount of material required) would be a very difficult theoretical (and experimental) problem for a terrorist team. In fact, solving this problem does not belong in the crude design category. Still, a workable device could be built without the need for extensive theoretical or experimental demonstration.

The amount of low-density oxide powder required for a small, crude, implosion-type device is far larger than previously suggested by Theodore Taylor; his view has changed only as to the feasibility of a small, crude device such as terrorists might attempt to build with a single small container of plutonium oxide powder seized from a fuel fabrication plant. We agree, however, that a crude implosion device could be constructed with reactor-grade plutonium or highly enriched uranium in metal or possibly even in oxide form.

7. Devices employing metal in a crude design could certainly be con structed so as to have nominal yields in the 10 kiloton range—witness the devices used in 1945. By nominal yield is meant the yield realized if the neutron chain starts after the assembly is complete and the fissile material is at or near its most supercritical configuration: projectile fully seated in the target for the gun-type device or all the material compressed in the implosion device. In all such systems, there is an interval between the moment when the fissile material first becomes critical (projectile still on its way to its destination, or only a small part of the material compressed) and the time it reaches its intended state. During this interval, the degree of supercriticality is building up toward its final value. If a chain reaction were initiated by neutrons from some source during this period, the yield realized would be smaller—possibly a great deal smaller—than the nominal yield. Such an event is referred to as preinitiation (or sometimespredetonation). Obviously, the longer is this interval or the greater is the neutron source in the active material, the larger is the probability of experiencing a preinitiation. The neutron source in even the best plutonium available (lowest Pu-240 content) is so large and the time interval for a gun-type assembly with available pro jectile velocities (~1000 ft./sec.) is so long that predetonation early in this time interval is essentially guaranteed. For this reason, plutonium cannot be used effectively in a gun-type assembly. The neutron source in enriched uranium is several thousand times smaller than in the plutonium referred to, so that uranium can be used in a gun-type assembly (with available projectile velocities) and have a tolerable preinitiation probability. For this to be true, it is necessary to have rather pure uranium metal, since even small amounts of some chemical impurities can add appreciably to the neutron source. The source in uranium oxide, for example, may be ten or so times larger than in pure metal; the source in reactor-grade plutonium may be ten or more times larger than in weapons-grade plutonium. However, reactor-grade plutonium can be used for making nuclear weapons.

If the assembly velocities (of the projectile or material driven by an implosion) are quite low, the earliest possible preinitiation could lead to an energy release (equivalent weight of high explosive) not many times larger than the weight of the device. If the velocities are quite high (so that the degree of supercriticality increases appreciably during the very short time it takes the neutron chain to build up), the lowest preinitiation yield may still be in the 100 ton range, even in a crude design. Reductions in the weight of the assembly-driving mechanism (whether gun-firing apparatus or amount of high explosive) will, other things being equal, tend to result in lower assembly velocities. The considerations outlined will put some limits on what may be decided to be desirable in connection with a crude design.

8. There are a number of obvious potential hazards in any such operation, among them those arising in the handling of a high explosive; the possibility of inadvertently inducing a critical configuration of the fissile material at some stage in the procedure; and the chemical toxicity or radiological hazards inherent in the materials used. Failure to foresee all the needs on these points could bring the operation to a close; however, all the problems posed can be dealt with successfully provided appropriate provisions have been made.

9. There are a number of other matters that will require thoughtful planning, as well as care and skill in execution. Among these are the need to initiate the chain reaction at a suitable time and for some reliable means to detonate the high explosive when and as intended.

10. Some problems that have required a great deal of attention in the nuclear-weapons program would not seem important to terrorists. One of these would be the requirement (necessary in connection with a weapons stockpile) that devices have precisely known yields that are highly repro ducible. Terrorists would not be in a position to know even the nominal yield of their device with any precision. They would not have to meet the extremely tight specifications and tolerances usual in the weapons business, although quite demanding requirements on these points would still be nec essary. Similarly, in connection with a stockpile of weapons, much attention has been given to one-point safety: the assurance that no nuclear yield would be realized in the event of an unplanned detonation of the high explosive, such as might occur in the case of an accident or fire. To ensure the safety of bystanders, this requirement has been deemed important in the context of a large number of devices widely deployed and subject to movement from place to place by a variety of transport modes and by a series of handling teams. Terrorists would not be concerned with this problem, although they would still have a great interest in the safe handling of their device.

11. Throughout the discussion, it has been supposed that the terrorists were home grown. It is conceivable that such an operation could be spon sored by another country, in which case some of the motivation, technical experts, and muscle men might be brought in from outside. This difference would not change the problems that would have to be addressed or the operations required, but it could increase the assurance that important points are not overlooked. It might also provide the basis for considering a sophis ticated design rather than a crude type.

 

More Sophisticated Devices

Most of the schematic drawings that are available relate to the earliest, most straightforward designs and indicate in principle how to achieve a fission explosion, without, however, providing the details of construction. Since 1945, notable reductions in size and weight, as well as increases in yield, have been realized. Schematic drawings of an entirely qualitative sort are also available that indicate the nature of some of the principles involved in these improvements.

Merely on the basis of the fact that sophisticated devices are known to be feasible, it cannot be asserted that by stealing only a small amount of fissile material a terrorist would be able to produce a device with a reliable multikiloton yield in such a small size and weight as to be easy to transport and conceal. Such an assertion ignores at least a significant fraction of the problems that weapons laboratories have had to face and resolve over the past forty years. It is relevant to recall that today’s impressively tidy weapons came about only at the end of a long series of tests that provided the basis for proceeding further. For some of these steps, full-scale nuclear tests were essential. In retrospect, not every incremental step taken would now seem necessary. Indeed, knowing only that much smaller and lighter weapons are feasible, it is possible at least to imagine going straight from the state of understanding in 1945 to a project to build a greatly improved device. The mere fact of knowing it is possible, even without knowing exactly how, would focus terrorists’ attention and efforts.

The fundamental question, however, would still remain: that of whether the object designed and built would or would not actually behave as pre dicted. Even with their tremendous experience, the weapons laboratories find on occasion that their efforts are flawed. Admittedly, weapons designers are now striving to impose refinements on an already highly refined product, but they have had to digest surprises and disappointments at many points along the way.

For persons new to this business, as it may be supposed a terrorist group is, there is a great deal to learn before they could entertain any confidence that some small, sophisticated device they might build would perform as desired. To build the device would require a long course of study and a long course of hydrodynamic experimentation. To achieve the size and weight of a modern weapon while maintaining performance and confidence in perfor mance would require one or more full-scale nuclear tests, although consid erable progress in that direction could be made on the basis of nonnuclear experiments.

In connection with an effort to reduce overall size and weight as far as possible, it would be necessary to use fissile material in its most effectiveform, plutonium metal. Moreover, while reducing the weight of the assembly mechanism, which implies reducing the amount of energy available to bring the fissile material into a supercritical configuration, it would not be possible at the same time to reduce the amount of fissile material employed very much. In this case, the amount of fissile material required in the finished pieces would be significantly larger than the formula quantity. Alternatively, in an implosion device without a reduction in weight and size, it would be possible to reduce the amount of nuclear materials required by using more effective implosion designs than that associated with the crude design.

In either case—a small or a large sophisticated device—the design and building would require a base or installation at which experiments could be carried out over many months, results could be assessed, and, as necessary, the effects of corrections or improvements could be observed in follow-on experiments. Similar considerations would apply with respect to the chem ical, fabrication, and other aspects of the program.

The production of sophisticated devices therefore should not be consid ered to be a possible activity for a fly-by-night terrorist group. It is, however, conceivable in the context of a nationally supported program able to provide the necessary resources and facilities and an established working place over the time required. It could be further imagined that under the sponsorship of some malevolent regime, a team schooled and prepared in such a setting could be dispatched anywhere to acquire material and produce a device. In such a case, although the needs of the preparation program might have been met, the terrorists would still have to obtain and set up the equipment needed for the reduction to metal and its subsequent handling and to spend the time necessary to go through those operations.

In summary, the main concern with respect to terrorists should be fo cused on those in a position to build, and bring with them, their own devices, as well as on those able to steal an operable weapon.

Sources: http://www.nci.org/k-m/makeab.htm

Are Suitcase Bombs Possible?

By Carey Sublette

Last changed 18 May 2002


It is impossible to verify at the time of this writing whether nuclear devices sized to fit in side a suitcase were actually manufactured by the former Soviet Union, as alleged by Alexander Lebed in September 1997. It is certainly possibel to assess the technicial plausibility of such a claim and to provide a analysis of the likely characteristics of the weapons Lebed described.

A suitcase bomb with dimensions of 60 x 40 x 20 centimeters is by any standard a very compact nuclear weapon. Information is lacking on compact Soviet weapons, but a fair amount of information is available on compact US designs which provides a good basis for comparison.

The smallest possible bomb-like object would be a single critical mass of plutonium (or U-233) at maximum density under normal conditions. An unreflected spherical alpha-phase critical mass of Pu-239 weighs 10.5 kg and is 10.1 cm across.

A single critical mass cannot cause an explosion however since it does not cause fission multiplication, somewhat more than a critical mass is required for that. But it does not take much more than a single critical mass to cause significant explosions. As little an excess as 10% (1.1 critical masses) can produce explosions of 10-20 tons. This low yield seems trivial compared to weapons with yields in the kilotons or megatons, but it is actually far more dangerous than conventional explosives of equivalent yield due to the intense radiation emitted. A 20 ton fission explosion, for example, produces a very dangerous 500 rem radiation exposure at 400 meters from burst point, and a 100% lethal 1350 rem exposure at 300 meters. A yield of 10-20 tons is also equal to the yield of the lowest yield nuclear warhead ever deployed by the US — the W-54 used in the Davy Crockett recoilless rifle.

A mere 1.2 critical masses can produce explosive yield of 100 tons, and 1.35 critical masses can reach 250 tons. At this point a nation with sophisticated weapons technology can employ fusion boosting to raise the yield well into the kiloton range without requiring additional fissile material.

The amount of fissile material that constitutes a “critical mass” varies with the material density and the type of neutron reflector present (if any). A high explosive implosion can compress fissile material to greater than normal density, thus reducing the critical mass. A neutron reflector reduces neutron loss and reduces the critical mass at a constant density. However generally speaking, adding explosives or neutron reflectors to a core adds considerably more mass to the whole system than it saves.

A limited exception to this is that a thin beryllium reflector (thickness no more than the core radius) can actually reduce the total mass of the system, although it increases its overall diameter. For beryllium thicknesses of a few centimeters, the radius of a plutonium core is reduced by 40-60% of the reflector thickness. Since the density difference between these materials is on the order of 10:1, substantial mass savings (a couple of kilograms) can be achieved. At some point though increasing the thickness of the reflector begins to add more mass than it saves since volume increases with the cube of the radius. This marks the point of minimum total mass for the reflector/core system.

A low yield minimum mass or minimum volume weapon would thus use an efficient fissile material (plutonium or U-233), a limited amount of high explosives (sufficient only to assembly the core, not to compress it to greater than normal density), and a thin beryllium reflector.

We can now try to estimated the absolute minimum possible mass for a bomb with a significant yield. Since the critical mass for alpha-phase plutonium is 10.5 kg, and an additional 20-30% of mass is needed to make a significant explosion, this implies 13 kg or so. A thin beryllium reflector can reduce this by a couple of kilograms, but the necessary high explosive, packaging, triggering system, etc. will add mass, so the true absolute minimum probably lies in the range of 11-15 kg (and is probably closer to 15 than 11).

This is probably a fair description of the W-54 Davy Crockett warhead. This warhead was the lightest ever deployed by the US, with a minimum mass of about 23 kg (it also came in heavier packages) and had yields ranging from 10 tons up to 1 Kt in various versions. The warhead was basically egg-shaped with the minor axis of 27.3 cm and a major axis of 40 cm. The test devices for this design fired in Hardtack Phase II (shots Hamilton and Humboldt on 15 October and 29 October 1958) weighed only 16 kg, impressively close to the minimum mass estimated above. These devices were 28 cm by 30 cm.

Davy CrockettW-54 Davy Crockett (38 K)

The W-54 design probably approaches the minimum size for a spherical implosion device (the US has conducted tests of a 25.4 cm implosion systems however).

The W-54 nuclear package is certainly light enough by itself to be used in a “suitcase bomb” but the closest equivalent to such a device that US has ever deployed was a man-carried version called the Mk-54 SADM (Small Atomic Demolition Munition). This used a version of the W-54, but the whole package was much larger and heavier. It was a cylinder 40 cm by 60 cm, and weighed 68 kg (the actual warhead portion weighed only 27 kg). Although the Mk-54 SADM has itself been called a “suitcase bomb” it is more like a “steamer trunk” bomb, especially considering its weight.

Minimum mass and minimum volume are not the only design criteria of interest of course, since even 25.4 cm (10 inches) is rather thick even for a suitcase and is wider than the reported 20 cm thickness of Alexander Lebed’s suitcase bomb. Another approach is to instead develop a minimum diameter or minimum thickness design.

Minimizing nuclear weapon diameters has been a subject of intense interest for developing nuclear artillery shells, since the largest field artillery is typically the 208 mm (8.2 inch) caliber, with 155 mm (6.1 inches) artillery being the workhorse. Nuclear artillery shell designs with diameters as small as 105 mm have been studied. Packaging a nuclear artillery shell in a suitcase is an obvious route for creating a compact man-portable device.

The US has developed several nuclear artillery shells in the 155 mm caliber. The only one to be deployed was the W-48 nuclear warhead developed by UCRL, packaged in the M-45 AFAP (artillery fired atomic projectile) shell. The W-48 nuclear warhead measured 86 cm (34″) long and weighed 53.5-58 kg (118-128 lbs). Its yield was on the order of 70 to 100 tons (it was tested in the Hardtack II Tamalpais shot with a yield of 72 tons, predicted yield was 100-300 tons).

The smallest diameter US test device publicly known was the UCRL Swift device fired in the Redwing Yuma shot on 28 May 1956 . It had a 5″ (12.7 cm) diameter, a length of 62.2 cm (24.5 inches) and weighed 43.5 kg (96 lb). The test had a yield of 190 tons, but was intended to be fusion boosted (and thus would probably have had a yield in the kiloton range) but its yield was insufficient to ignite the fusion reaction and it failed to boost in this test. This test may have been a predecessor to the W-48 design.

Later and lighter 155 mm designs were also developed — the W74 (canceled early in development), and the W-82/XM-785 shell. The W82 had a yield of up to 2 kilotons and weighed 43 kg (95 lb), but included a number of sophisticated additional features within this weight. Since it was capable of being fielded with a “neutron bomb” (enhanced radiation) option, which is intrinsically more complex than a basic nuclear warhead, and was in addition rocket boosted, the actual minimum nuclear package was substantially lighter than the weight of the complete round. Its overall length was 86 cm (34″).

It is reported that designs least as small as 105 mm (4.1 inches) are possible. A hypothetical 105 mm system developed for use in an artillery shell would be about 50 cm (20 inches) long and weigh around 20 kg.

Compact nuclear artillery shells (208 mm and under) are based on a design approach called linear implosion. The linear implosion concept is that an elongated (football shaped) lower density subcritical mass of material can be compressed and deformed into a critical higher density spherical configuration by embedding it in a cylinder of explosives which are initiated at each end. As the detonation progresses from each direction towards the middle, the fissile mass is squeezed into a supercritical shape. The Swift device is known to have been a linear implosion design.

Linear Implosion System

It is quite likely, that should the suitcase bombs described by Lebed actually exist, that they would use this technology. It is clear that any of the 155 mm artillery shells, if shortened by omitting the non-essential conical ogive and fuze would fit diagonally in the package that Lebed describes, and the Swift device would fit easily. If the yield is as much as 10 kilotons, then the device would have to be fusion boosted.

A somewhat more sophisticated variation would extend the linear implosion concept to cylindrical implosion, in this case an oblate (squashed) spheroid, roughly discus-shaped, of plutonium would be embedded in a cylinder of high explosive which is initiated simultaneously around its perimeter. The cylindrically converging detonation would compress and deform the fissile mass into a sphere, that could be wider than the original thickness of the system. This type of design would make the flattest possible bomb design, perhaps as little as 5 cm. The only obvious application for such a device would be briefcase bomb, and would require a special development effort to create it.

See Section 4.2 of the Nuclear Weapons FAQ for more details.

Source of weapon and test details The Swords of Armageddon, by Chuck Hansen, Chuckelea Publishing, 1995.

Source: http://nuclearweaponarchive.org/News/DoSuitcaseNukesExist.html