From the Nuclear Threat Initiative and The Project on Managing the Atom at Harvard's Belfer Center
Wednesday, September 26, 2007 12:00 AM
Is it really plausible that terrorists could get and use a nuclear bomb?
Yes. Unfortunately, terrorist use of a nuclear bomb is a very real danger. During the 2004 presidential campaign, President George W. Bush and Senator John Kerry (D-Mass.) agreed that nuclear terrorism was the single greatest threat to U.S. national security. Published estimates of the chance that terrorists will detonate a nuclear bomb in a U.S. city over the next ten years range from 1 percent to 50 percent. In a 2005 poll of international security experts taken by Senator Richard Lugar (R-Ind.), the median estimate of the chance of a nuclear attack in the next ten years was 29 percent -- and a strong majority believed that it was more likely that terrorists would launch a nuclear attack than that a state would. Given the horrifying consequences of such an attack, even a 1 percent chance would be enough to call for rapid action to reduce the risk.
What materials could terrorists use to make a nuclear bomb?
To make a nuclear bomb requires either highly enriched uranium (HEU) or plutonium. Neither of these materials occurs in nature, and producing either of them requires expensive facilities using complex technologies, almost certainly beyond the capability of terrorist groups. Hence, if all of the world's stockpiles of nuclear weapons, HEU and plutonium can be effectively protected and kept out of terrorist hands, nuclear terrorism can be prevented: no nuclear material, no bomb, no nuclear terrorism.
How difficult would it be for terrorists to get the materials needed to make a nuclear bomb?
Highly enriched uranium and plutonium are hard to make, but may not be so hard to steal. These raw materials of nuclear terrorism are housed in hundreds of facilities in dozens of countries -- some with excellent security, and some secured by nothing more than an underpaid guard and a chain link fence. There are no binding global standards setting out how well nuclear weapons and the materials needed to make them should be secured.
Theft of the essential ingredients of nuclear weapons is not just a hypothetical worry, it is an ongoing reality. The International Atomic Energy Agency (IAEA) has documented 15 cases of theft of HEU or plutonium confirmed by the countries concerned (and there are additional well-documented cases that the countries involved have not yet been willing to confirm). In many of these cases, the thieves and smugglers were attempting to sell the material to anyone who would buy it -- and terrorist groups have been seeking to buy it.
How much expertise is needed to make a nuclear bomb? Would a large operation be required?
Unfortunately, government studies have concluded that once a terrorist organization had the needed nuclear material, a handful of skilled individuals might be able to make a crude nuclear bomb using commercially available tools and equipment, without any large fixed facilities that might draw attention, and without access to classified nuclear weapons information. Getting nuclear material and making a crude nuclear bomb would be the most complex operation terrorists have ever carried out ¿ but the risk that a sophisticated group could pull it off is very real. Roughly 90 percent of the effort in the Manhattan Project was focused on making nuclear bomb material; getting stolen nuclear material would allow terrorists to skip the hardest part of making a nuclear bomb.
The simplest type of nuclear bomb, known as a "gun-type" bomb, slams two pieces of nuclear material together at high speed. The bomb that destroyed Hiroshima, for example, was a cannon that fired a shell of HEU into rings of HEU. Plutonium cannot be used to make a gun-type bomb with a substantial explosive yield, because the neutrons that all plutonium emits cause the bomb to blow itself apart before the nuclear reactions proceeds very far. To make a bomb from plutonium would require a more complex "implosion-type" bomb, which would be more difficult for terrorists to build -- but government studies have repeatedly concluded that this possibility also cannot be ruled out.
How much nuclear material would terrorists need to make a bomb?
The amount of nuclear material needed to make a bomb depends on the material and the skill of the bomb-maker. A simple gun-type nuclear bomb would require approximately 50 kilograms of HEU -- an amount that would fit in a suitcase. Implosion-type bombs are more efficient, requiring less nuclear material. Unclassified estimates suggest that basic first-generation implosion-type bombs like the Nagasaki bomb can be made with 6 kilograms of plutonium or 15 kilograms of HEU. With these relatively small amounts, a terrorist group could potentially build a bomb with the power of thousands of tons of high explosive. Sophisticated nuclear weapon states can potentially make nuclear bombs with smaller amounts of nuclear material.
Rather than stealing nuclear material and making a bomb, could terrorists steal and use an already assembled nuclear weapon?
Possibly. Nuclear weapons are generally better secured than some stocks of HEU and plutonium are. Nevertheless, the United States is spending hundreds of millions of dollars beefing up security for its own nuclear weapons complex sites, and hundreds of millions more helping Russia improve security for its warhead sites.
A stolen nuclear weapon might be very difficult for a terrorist group to detonate. Many nuclear weapons are equipped with electronic locks making it impossible to set off the weapon without putting in the appropriate code or figuring out a way to bypass the lock. Unfortunately, on older Russian tactical nuclear weapons, such locks are thought to be absent in some cases and relatively easily bypassed in others. U.S. strategic nuclear weapons also do not incorporate such locks, and some other countries' weapons may also lack them. In addition, modern nuclear weapons are typically equipped with devices that prevent the weapon from going off until it has passed through its expected flight sequence ¿ such as a period of rocket-powered flight followed by coasting through space and reentering the atmosphere, in the case of a long-range ballistic missile. While designed more for safety than security, these devices would also make it more difficult to detonate most stolen weapons. If terrorists could not figure out how to detonate a stolen weapon, they might choose to cut it open and use the nuclear material inside to try to make a bomb of their own.
Are there "suitcase nukes" on the loose?
Probably not. In the 1990s, Gen. Alexander Lebed, then the national security advisor to Russian President Boris Yeltsin, said that more than 100 nuclear weapons designed to be carried by one person ¿ so-called "suitcase nukes" ¿ could not be accounted for and might be missing. The Russian Ministry of Defense firmly denied that any weapons were missing, and Lebed ultimately backed off from his initial statements. Ultimately enough information was released to make a reasonably convincing case that none of these man-portable nuclear weapons were missing. It is clear, however, that both the United States and the Soviet Union did in fact manufacture nuclear weapons designed to be carried and used by one or two people. In the United States, all such weapons have been dismantled, and some Russian statements indicate that the same is now true in Russia.
Once a nuclear bomb or nuclear material has been stolen, could we stop it from being smuggled?
The chances would not be very good, unfortunately. The amounts of HEU or plutonium needed for a bomb are small and easy to smuggle. These materials are not radioactive enough to require any special equipment to carry them, or to make them easy to detect. After they have left the site where they are supposed to be, they could be anywhere, and all the later lines of defense are variations on searching for needles in haystacks. With hundreds of millions of people and vehicles crossing U.S. borders every year, making sure no one gets in with a suitcase of potential bomb material is an immense challenge. Even if governments screened every container coming across their borders with a radiation detector, terrorists would not be likely to send their nuclear bomb material through one of the readily-observable radiation detectors, but would use one of the many other possible routes to avoid inspection. Moreover, if HEU was shielded with lead, detectors now being deployed would not be able to detect the weak radiation it emits (unless it was contaminated with the isotope U-232, and the detector was designed to look for the gamma rays from that decay chain). If the United States cannot stop the flow of illegal drugs and illegal immigrants across its borders, it is unlikely that it will succeed in stopping nuclear material. Even an assembled nuclear bomb might fit in the hold of a yacht, in a truck, or in a small plane.
What would happen if terrorists set off a nuclear bomb in a major city?
Terrorist use of a nuclear bomb would be an historic catastrophe. If a crude nuclear bomb with an explosive equivalent of 10,000 tons of TNT (10 "kilotons" in the language of nuclear weapons) were set off at Grand Central Station on a typical work-day, some 500,000 people might be killed, and hundreds of thousands more would be injured, burned, and irradiated. The direct economic damage would likely be in the range of $1 trillion, and the reverberating economic effects throughout the United States and the world would come to several times that figure. In 2005, then-UN Secretary General Kofi Annan warned that such an attack "would stagger the world economy and thrust tens of millions of people into dire poverty," causing "a second death toll throughout the developing world." The terrorists would surely claim they had more bombs already hidden in U.S. cities, potentially provoking widespread panic and economic disruption. In short, America and the world would be changed forever.
What terrorist groups are known to be seeking nuclear weapons? What do we know about their attempts?
Al Qaeda has been seeking nuclear weapons and the material needed to make them for more than a decade. Osama bin Laden and his followers have repeatedly attempted to acquire stolen nuclear material and to recruit nuclear expertise. In 2001, for example, bin Laden and his deputy Ayman al-Zawahiri met at length with two senior Pakistani nuclear scientists and discussed nuclear weapons. As early as 1993, al Qaeda attempted to purchase what it believed was HEU in the Sudan. In the 1990s, the Japanese terror cult Aum Shinrikyo, which launched the nerve gas attack in the Tokyo subway, also attempted to get nuclear weapons. Russian officials have confirmed that Chechen terrorist teams have carried out reconnaissance at Russian nuclear warhead storage sites, and in 2005, the Russian Minister of the Interior warned that Russia had intelligence that Chechen groups were planning "attacks against nuclear and power industry installation" intended to "seize nuclear materials and use them to build weapons of mass destruction." Some Chechen factions are closely linked to al Qaeda.
Has any terrorist group succeeded in acquiring nuclear material?
Despite various terrorist claims, there is no convincing evidence that any terrorist group has yet succeeded in getting a nuclear bomb or the HEU or plutonium needed to make one.
What has been done to reduce the risk of nuclear theft and terrorism?
A wide range of programs in the United States and elsewhere are making real progress in reducing the global danger of nuclear terrorism -- but much more remains to be done. Through Nunn-Lugar cooperative threat reduction programs and related efforts, security has been dramatically improved at scores of buildings and bunkers with either nuclear weapons or the materials needed to make them in the former Soviet Union and in other countries around the world. Hundreds of kilograms of HEU have been removed from potentially vulnerable nuclear sites around the world. HEU-fueled research reactors are being converted to run on low-enriched uranium (LEU) fuel that cannot be used in a nuclear bomb, and their HEU is being removed. As a second line of defense, radiation detectors are being installed at key ports and border crossings around the world -- and at U.S. border crossings and elsewhere within the United States. Hundreds of tons of potential nuclear bomb material are actually being destroyed (for example, by blending HEU with other uranium to produce LEU reactor fuel that cannot be used in a bomb); remarkably, roughly one of every 10 light bulbs in the United States is powered with fuel from dismantled Russian nuclear weapons. These programs continue to be excellent investments in U.S. and world security.
But important gaps remain. Security upgrades have not yet been completed for scores of nuclear material buildings and warhead sites in Russia -- and for some, there is no agreement to cooperate on security upgrades. Upgrades in China are just beginning, and India has not yet agreed to cooperate on nuclear security improvements. Only a small fraction of the world's HEU-fueled research reactors have had all their HEU removed. Most of the HEU the United States itself shipped to countries around the world for use as research reactor fuel is not yet eligible for the U.S. offer to take it back. A dangerous gap remains between the urgency of the threat and the scope and pace of the U.S. and international response.
What is highly enriched uranium? What is enrichment?
Highly enriched uranium is uranium that contains 20 percent or more of the isotope uranium-235 (U-235 for short). Because it easily fissions, uranium-235 is useful in powering nuclear reactors or nuclear bombs.
Natural uranium mined from the ground contains only 0.7 percent U-235 and cannot sustain the explosive nuclear chain reaction needed for a nuclear bomb. To make HEU, the uranium has to be "enriched" ¿ that is, the concentration of U-235 has to be increased. Separating the atoms of U-235 from the atoms of U-238 (which make up more than 99 percent of natural uranium) requires complex and difficult technology, since these atoms have the same chemical properties and differ only slightly in weight. Terrorist groups would almost certainly not have the technical or financial means to enrich their own uranium. Unfortunately, the same technologies used to make LEU for peaceful reactor fuel can also be used to make HEU for nuclear weapons -- which is why Iran's pursuit of uranium enrichment technology is raising international concern.
What is plutonium and where is it found?
Plutonium is a man-made radioactive element that can be used in nuclear fuel or nuclear weapons. It is extremely heavy, with 94 protons in its nucleus. Plutonium is produced when an atom of U-238 absorbs a neutron, typically in a nuclear reactor. All current nuclear power reactors produce plutonium in their spent fuel, though this plutonium cannot be used in nuclear weapons until it has been chemically separated from the uranium and the intensely radioactive fission products in the spent fuel, a step known as reprocessing. As with uranium enrichment, it is extremely unlikely that terrorists could build and operate their own nuclear reactor and reprocessing facility to produce plutonium for a bomb. Plutonium-239, the most common isotope and the one most useful in nuclear weapons, has a half-life of 24,000 years (meaning that half of it will have decayed after that time, half of the remainder after another 24,000 years, and so on). Over geologic time, therefore, plutonium has decayed away and little of it exists in nature.
What are weapons-grade uranium and weapons-grade plutonium?
In principle, any HEU can fuel a nuclear bomb. However, the greater the concentration of U-235, the less HEU is needed for the bomb. Weapons-grade uranium consists of 90 percent or greater U-235. Despite this definition, however, nuclear bombs can be and have been made with less enriched material. The average enrichment of the HEU used in the Hiroshima bomb was roughly 80 percent.
Weapon-grade plutonium typically contains 93 percent or more plutonium-239 (Pu-239), the isotope most useful in nuclear weapons. The plutonium in the spent fuel discharged from typical power reactors is "reactor-grade," containing larger concentrations of Pu-240 and Pu-241, which are more troublesome for weapons designers. Nevertheless, government studies have concluded that any state or group that could make a bomb from weapon-grade plutonium could also make a bomb from reactor-grade plutonium.
How much HEU and plutonium exists in the world?
World stockpiles of separated plutonium and HEU, the essential ingredients of nuclear weapons, amount to well over 2,300 tons -- enough to manufacture over 200,000 nuclear weapons. These materials exist in more than 40 countries, though Russia and the United States have by far the largest stockpiles. The global HEU stockpile is overwhelmingly military, but the 65 tons of the HEU stockpile that is in civilian use is enough for hundreds of nuclear bombs. The global stockpile of plutonium for military uses is in the range of 250 tons, and there are now more than 250 tons of separated plutonium in the civilian sector worldwide as well.
How many states have nuclear weapons?
Nine. Eight countries have demonstrated nuclear weapons capability by having conducted one or more nuclear tests. These states are China, France, India, North Korea, Pakistan, Russia, the United States, and the United Kingdom. In addition, Israel is widely believed to possess an arsenal of nuclear weapons.
How many states have abandoned nuclear weapons?
South Africa is the only state to have built its own nuclear arsenal and then completely dismantled it -- the first case of real nuclear disarmament. The last apartheid government under President F. W. de Klerk made this dismantlement decision and completed the dismantlement before handing over power to African National Congress led by Nelson Mandela in the early 1990s. Also in the mid-1990s, Belarus, Kazakhstan and Ukraine agreed to relinquish nuclear weapons left on their soil when the Soviet Union collapsed (though these states never had complete control of these weapons).
Many other states have started nuclear weapons programs and then verifiably abandoned them, concluding that it was in their national interest not to have nuclear weapons. Indeed, there are more states that have started nuclear weapons programs and given them up than there are states with nuclear weapons -- so efforts to stop the spread of nuclear weapons succeed more often than they fail.
How many nuclear weapons are there in the world?
While there is no official census of the total number of nuclear weapons, the Natural Resources Defense Council (NRDC) compiles some of the best unofficial estimates. According to the NRDC, nine states possess about 26,000 intact nuclear weapons. Russia and the United States have 97 percent of the world's nuclear weapons. About 12,500 of the world's nuclear weapons are considered operational, with the rest in reserve or awaiting dismantlement. In the United States, NRDC estimates that there are nearly 10,000 total intact warheads, of which just over 5,700 are operational. Russia has been very guarded about revealing the size of its stockpile but is believed to have something in the range of 15,000 intact warheads, with over 5,600 operational. The United Kingdom has about 200 warheads. France holds about 350 warheads. China is thought to possess around 200 warheads. NRDC estimates that India has roughly 85 warheads, and Pakistan in the range of 60 warheads. For Israel, NRDC cites a Defense Intelligence Agency estimate of 60 to 80 warheads. Finally, NRDC estimates that North Korea may have roughly ten warheads, though no one knows for sure.
What about a "dirty bomb"? How is that different from a nuclear bomb?
A "dirty bomb" simply spreads radioactive material over an area, to create panic and force people to evacuate. In most dirty bomb scenarios, there would be few if any immediate deaths from radiation -- most of the impact would be from economic disruption, if many blocks of a city had to be evacuated for an extended time. This stands in stark contrast to an actual nuclear bomb, whose blast and fire could incinerate the heart of any major city and kill tens or hundreds of thousands of people.
A dirty bomb -- more formally known as a radioactive dispersal device (RDD) -- would be far easier for terrorists to make, potentially as simple as putting radioactive material in a box with conventional explosives and setting it off. Unlike the plutonium or HEU needed for a nuclear bomb, radioactive materials that might be used in a dirty bomb exist at tens of thousands of locations all over the world: many hospitals, for example, use large radioactive sources. In other words, the probability of a dirty bomb attack is substantially higher than the probability of a terrorist attack with a nuclear bomb, but the consequences of a dirty bomb attack would be far lower.
What about sabotage of a major nuclear facility?
Terrorists might attempt to sabotage a nuclear facility in any number of ways, from attack by a group of outsiders on the ground, to insider sabotage, to attempting to crash a plane into the facility. In most countries, nuclear facilities that would have major consequences if sabotaged are guarded and equipped with strong buildings and containment vessels and redundant safety systems. Although most nuclear power plants were not specifically designed against the possibility of a large plane crash, government and industry studies have concluded that most types of possible crashes would not lead to radioactive releases. Nevertheless, if terrorists managed to overcome these protections, they could potentially cause a devastating radioactive release, which might cause hundreds of fatalities in the weeks after an attack, thousands of longer-term deaths, and contamination of a wide area. Sabotage of a major nuclear facility is probably in between nuclear bombs and dirty bombs in both probability and consequences.