Can Terrorists Build the Bomb?

It's the ultimate nightmare: a nuclear attack in the U.S. masterminded by terrorists. Here's how that could happen-- and how we can prevent it

Last fall, the race to stop terrorists from acquiring a nuclear bomb passed through Tashkent, Uzbekistan. There, on the morning of September 19, a Russian Antonov 12 cargo plane touched down carrying two nearly indestructible steel canisters. Under the watch of elite security forces armed with machine guns, Uzbek officials unloaded the canisters and drove them to a remote, wooded area about 20 miles from the Central Asian capital. Waiting there at the Institute of Nuclear Physics, which houses a small nuclear reactor used for scientific research, was a team of Americans, Russians and officials from the International Atomic Energy Agency. With extreme care, they filled the canisters with 24 pounds of reactor fuel containing highly enriched uranium, the ideal ingredient for a terrorist nuke. Area roads were closed off as an armed convoy rushed the cargo back to the airport. The canisters were loaded back onto the Antonov 12 and flown to Russia, where their contents were sent to a secure facility and blended with less-potent materials to create a mixture that is of little use to aspiring terrorists.

Amid the conflict in Iraq and the hunt for Osama bin Laden, this is a side of the war on terrorism you rarely hear about: the drive to prevent terrorists from acquiring the ingredients for a nuclear bomb. In recent years, operations similar to the one in Uzbekistan have been conducted in Libya, Serbia, Romania and Bulgaria. These efforts reflect an intense and growing concern within the U.S. government about the specter of nuclear terrorism. It is one of the few issues on which President George W. Bush agreed with his former rival, John Kerry, who called nuclear terrorism the greatest threat that we face in the world today.

That threat comes not just from suspected weapons programs in Iran and North Korea, but also from Al Qaeda
and other terrorist groups. Last year Michael Scheuer, who ran the CIA’s Osama bin Laden unit for several years in the late 1990s, wrote a letter to the Senate Intelligence Committee warning of the “careful, professional manner in which al-Qaeda was seeking nuclear weapons . . . in deadly earnest.” More than a decade ago, bin Laden allegedly tried to buy a canister of uranium in Sudan for $1.5 million. (He appears to have been scammed.) In August 2001, he met with two Pakistani nuclear scientists. And later that year, crude sketches of nuclear weapons were found in Al Qaeda training camps in Afghanistan. Scheuer told CBS’s 60 Minutes last year that bin Laden even sought a religious edict from a Saudi cleric on whether he could use a nuclear weapon against America. The cleric’s answer: Go for it.

Intent isn’t the same as capability, of course. But of more than a dozen nuclear-arms experts I interviewed, almost all agreed that assembling a crude nuclear bomb, though extremely difficult, is by no means impossible.

Just ask Graham Allison. In his recent book Nuclear Terrorism: The Ultimate Preventable Catastrophe, he concludes that a terrorist nuke attack is “inevitable” unless the U.S. works much harder and faster to safeguard nuclear material. A former assistant secretary of defense who served under President Bill Clinton and now teaches government at Harvard University, Allison is actually taking small bets from colleagues that terrorists will detonate a crude nuclear bomb in a U.S. city within a decade. “If this happened tomorrow,” he says, “I could almost explain it more easily than I could explain why it hasn’t happened.”

Not everyone is as alarmist as Allison. Most experts with whom I spoke said that a nuclear terror attack is plausible but not inevitable, and that there’s no way to precisely gauge the odds. “I don’t think the public ought to lose a lot of sleep over the issue,” says nuclear physicist Tom Cochran of the Natural Resources Defense Council.

There is a consensus, though, about how such a nightmare would unfold. What follows is an examination of each step a terrorist organization would need to take to pull off a nuclear attack, and what is being done to raise the hurdles.


Buying or stealing an entire bomb would be extremely difficult, because most countries guard their nuclear weapons zealously and outfit them with mechanical locks or electronic codes to prevent tampering. Nuclear material, on the other hand, is at least in theory a lot easier to get. And, says Laura Holgate of the nonprofit Nuclear Threat Initiative in Washington, D.C., “Once you have material, everything is easier. Our mantra is, â€It’s the material, stupid.'”

Two metals can produce a mushroom cloud: uranium and plutonium. Uranium can be found in nature, though not in bomb-grade form. Uranium ore mined from the earth consists almost entirely of the relatively stable isotope U-238 and has only tiny amounts of the isotope
U-235, which is highly fissile–it splits easily, releasing large amounts of energy.

Before it can be used in a bomb, uranium must be “enriched,” a process that sifts out nonfissile U-238 to increase the proportion of fissile U-235. The more the uranium has been enriched, the more fissile it becomes and the less is required to make a bomb. Scientists generally consider uranium consisting of more than 20 percent U-235 to be “highly enriched” and suitable for a bomb, although uranium used in advanced nuclear-weapons programs and some nuclear reactors is enriched as much as 90 percent.

Enriching uranium is a vastly complicated and expensive process well beyond a terrorist group’s reach. It requires the use of expensive centrifuges whose production and export is closely monitored and which require sophisticated expertise to operate. Iraq tried in vain for years to enrich uranium, and Iran is approaching success only after decades of effort. “Iran has poured hundreds of millions–some would say billions–into their program, and as far as we know, they’re not there yet,” says Charles Ferguson, a science
and technology fellow at the Council on
Foreign Relations. Manufacturing plutonium is even more daunting. Plutonium is produced by irradiating uranium in
a nuclear reactor–hardly a practical option for most terrorists.

But while Iran and other nations are seeking full-fledged production capabilities, a terrorist group simply has to get its hands on enough material for a single bomb. All the next Mohammed Atta would need to make a bomb big enough to instantly obliterate everything within a third of a mile is about 100 pounds of uranium enriched to 90 percent: a lump about the size of a bowling ball, or a
bigger lump if the enrichment level is lower. It takes even less plutonium, which is far more fissile than uranium, to build an equally destructive bomb: about 35 pounds, a grapefruit-size hunk.

Given its greater potency, you might expect terrorists to covet plutonium for their bomb. Plutonium is so radioactive, though–far more so than uranium–that handling it can be quickly fatal. For the same reason, it makes radiation detectors go wild. Detonating plutonium requires a complex bomb design, with multiple explosive charges timed to exquisite precision. Finally, it tends to be stored at military installations and commercial power reactors, where security is generally very tight.

Uranium is an easier target. “Highly enriched uranium is more plentiful and more dispersed,” Cochran explains.
“It’s less well-guarded in the commercial
sector. It’s easier to handle in terms of toxicity.” Even prolonged exposure to uranium brings no short-term health effects. It can increase long-term cancer risks, but that wouldn’t deter a sui-
cide jihadist. Uranium’s relatively low
radioactivity also makes it harder to detect than plutonium. And crucially, Cochran says, “it’s easier to construct a crude [nuclear] device” from uranium.

That makes highly enriched uranium the ultimate attainment for a nuke-
building terrorist. Unfortunately, there are about two thousand tons of it stored worldwide. “Russia is the mother lode,” Holgate says. Huge military budget cuts in post-Soviet Russia allowed nuclear safeguards to lapse badly in the 1990s. The U.S. has been working with Russia to improve security at its nuclear facilities, but less than a quarter of Russia’s sites have been upgraded to meet standards set by investigators from the U.S. Government Accountability Office who visited several Russian nuclear facilities
in 2000 and 2001. At one site, they
discovered a gate to the main nuclear-
storage area wide open and unattended. At another, no guards responded when the visitors set off metal detectors. Not much nuclear material seems to have leaked from Russian military facilities, however, and although there have been numerous reports of attempted sales of stolen material, most have been frauds or “involve extremely small quantities of material,” Cochran says.

A more worrisome source of nuclear material is the civilian world, including research reactors such as the one at the Institute of Nuclear Physics in Uzbekistan. Some 130 reactors powered by highly enriched uranium operate in more than 40 countries, the product of an early Cold War-era program in which the U.S. and U.S.S.R. helped their allies obtain nuclear technology. Several more reactors are shuttered but may still
keep fuel onsite. Collectively, the world’s research reactors contain 22 tons of
highly enriched uranium, enough to build hundreds of nuclear bombs.

Research-reactor fuel tends to be stored under notoriously light security.
A later GAO report, published last year, found that “the fence surrounding the [unnamed foreign research reactor] facility was in poor condition, security guards at the front gate were unarmed, and there were no guards at the reactor building, which we entered without escort.” And security often amounts to little more than a couple of lightly armed guards–no match for a team of terrorists like the group that seized an elementary school in Beslan, Russia, last summer.

Unlike the bulky, extremely radioactive fuel rods used in commercial nuclear power plants, research-reactor fuel usually consists of small pellets that weigh only a few pounds each and aren’t too hot to handle. “[A] thief could easily put several of them at a time into a backpack,” wrote Matthew Bunn, a nuclear-proliferation expert who works with Graham Allison at Harvard, in a 2004 report.

Despite all this potential, virtually no nuclear material is known to have been smuggled out of research reactors. Which raises the question: If highly enriched uranium is so poorly protected, why
hasn’t more material gone missing? Proliferation experts cite two reasons for this happy surprise. In Russia, they say, the loyalty of underpaid military officials and nuclear scientists appears to be stronger than expected. Second, fears that organized crime syndicates would try to reap huge profits through nuclear smuggling have not yet been borne out, Holgate says. Why not? “Other activities of organized crime are way less hassle,” she suggests.

Fortunately, it’s only getting harder
for terrorists to steal nuclear material. During the 1990s, a joint U.S.-Russian program upgraded security at dozens of former Soviet nuclear installations. And in recent months, security has been improving at many civilian research reactors. With the Global Threat Reduction Initiative (GTRI), a program begun by the Energy Department last year with a budget of $450 million over 10 years, the U.S. hopes to secure vulnerable nuclear material around the globe. That means cataloguing nuclear material, increasing security at research reactors and, in some cases, removing uranium from places like Uzbekistan’s Institute of Nuclear Physics. Also under the GTRI, the U.S. is working to convert research reactors to run on uranium with an enrichment level below 20 percent, which is virtually useless for bomb-making.


If a terrorist does manage to acquire fuel from a research reactor, preparing it for use in a bomb requires expertise, chemicals, industrial equipment, explosives and a clandestine workspace. None of these, however, is beyond the reach of a well-organized and well-funded terrorist group such as Al Qaeda.

Assembling a bomb requires metallurgy and engineering skills, as well as some familiarity with conventional explosives. A terrorist group would surely love the help of a nuclear scientist, but such expertise is not a prerequisite. No stage of the process requires classified knowledge. The relevant chemistry formulas, for instance, are in graduate-school textbooks. It might not even take a big team. A study done by the federal Office of Technology Assessment in
1977 concluded that such a project could be done with “at a minimum, one person capable of researching the literature in several fields, and a jack- of-all-trades technician.”

The first step in building a bomb is to process reactor fuel–typically a uranium-aluminum alloy –into pure uranium. (Terrorists could skip this part if they managed to get hold of bomb-ready uranium from a military installation.) “You can use nitric acid,” Ferguson explains, which is cheap and available even in high-school labs. A terrorist chemist would cut up the fuel and dissolve it in a vat of boiling acid, then use an organic compound to isolate the uranium. Ferguson says the ideal compound for this is
tributyl phosphate (TBP), although other compounds may also do the job. TBP has commercial uses, such as the production of plastics and ink, which might provide cover for a
terrorist ordering large quantities (probably in the hundreds of gallons.)

If all goes well, the TBP should attach itself to the uranium and, like oil and water, separate from the acid. “You stir, and you have TBP and uranium floating on top. The bottom is acid and aluminum. So you basically just skim [the top] off,” Ferguson explains. All that’s left is to wash away the TBP. Given uranium’s low radioactivity, this work could be done in lab coats and goggles in a small warehouse.

Regulators can’t do much to make this step more difficult. One possibility is to restrict the sale of TBP. “Some countries track it, some don’t,” says Michael Levi, a nuclear-terrorism expert at King’s College at the University of London.

If a terrorist group obtained the necessary chemicals, extracting enough uranium for a bomb could take only a few weeks. The bomb-makers could then get down to the grunt work of construction. “I think the hardest step in the process is the extraction of uranium,” Ferguson says. “Once they do that, then it becomes very simple.”


The nuclear weapons stockpiled by the U.S. and Russian governments are far more sophisticated and lethal than anything a terrorist could build. Instead a
terrorist would most likely opt for the simplest nuclear weapon, called a gun bomb. Like a rifle, a gun bomb uses a conventional explosive charge to fire a bullet. But in this case, the bullet is a lump of uranium that slams into a second piece of uranium at the other end of the barrel. The impact compresses the two pieces, creating a “supercritical mass” that sets off a nuclear chain reaction. It’s a simple but proven method. “The Hiroshima bomb was literally a cannon barrel that slammed two pieces of highly enriched uranium together,” Bunn explains.

Casting the bomb’s uranium into two separate pieces is a relatively straightforward machine-tool task. Slightly more complicated is devising the cannon that will fire the uranium. Terrorists could either fashion their own cannon or acquire a military cannon like a Howitzer. This choice would depend somewhat on the quality of uranium they had acquired. The more highly enriched the uranium, the less powerful the cannon that would be required to create a chain reaction. Although you can’t buy a modern Howitzer on eBay, it’s not impossible to get heavy conventional military equipment. As the NRDC’s Tom Cochran notes, military hardware of every type is currently “lying around all over Iraq.”

Actually detonating such a bomb may be the easiest step of all. Basic gunpowder is ideal for firing the cannon, Levi explains. The bomb could be triggered with a cellphone or a garage door opener
–technology no more sophisticated than that used in Iraqi roadside bombs.

Last year Senator Joseph Biden asked scientists at three national laboratories to see if they could assemble the mechanical components of a gun-style bomb with commercially available equipment alone. A few months later, they reported back that they had done it.

The process of building a crude bomb is made even easier by the fact that–unlike state-run nuclear programs, which are typically held to strict safety standards–terrorists can afford to make mistakes. A bomb made from 100 pounds of 90 percent highly enriched uranium could deliver an explosive yield of about 10 kilotons, or slightly less than the force of the 1945 Hiroshima blast. A smaller blast would occur if the uranium were of a lower enrichment grade or if the cannon misfired because of design flaws. But even a one-kiloton explosion would level a city block, killing everyone in the vicinity and igniting huge fires. Radiation would kill perhaps thousands more. Mass panic would ensue. In other words, even a relative dud would be an absolute catastrophe.


Of course, terrorists couldn’t simply air-mail their bomb to the White House mailroom. Transporting it would be
the final challenge. And depending on
its design, a crude nuke might weigh between half a ton and a few tons. Delivering the bomb to its target is “not trivial,” Levi says. “It’s one thing to smuggle a small piece of uranium into the country. It’s another thing to smuggle a fully built several-ton hunk of steel.”

Nevertheless, a huge cannon would still fit easily into a cargo-shipping
container, more than 23 million of which arrive in the U.S. every year. Approximately 5 percent of these
are inspected by customs officials on arrival. All customs workers now wear radiation detectors clipped to their belts, which sniff the air for gamma rays given off by uranium and plutonium. A uranium bomb, however, would be hard to detect. A 2002 GAO report found that the belt detectors had “limited range” and “may be inappropriate for the task.” What’s more, simple lead shielding can block gamma rays. More sophisticated radiation detectors are being installed at all ports of entry, though these might miss a lead-shielded bomb. The limitations of these scanners are one reason that the federal government gave up on a “Ring around Washington” project, which would have placed radiation sensors on major land and water approaches to the capital.

Even efficacious scanners might overlook nuclear materials that were smuggled into the U.S. in small amounts and then assembled into a weapon in the very city that the terrorists had targeted. That’s why most experts strongly agree that the best strategy is to stop terrorists at step one, by preventing nuclear material from being stolen in the first place.

After years of relative inattention, September 11 made this mission a
higher priority for the federal government. In the past three years, Congress has increased funding for the Nunn-Lugar Cooperative Threat Reduction program, which now spends more than $1 billion a year upgrading security
at former Soviet nuclear sites such
as weapons factories and nuclear
submarine bases, reprocessing Russian nuclear material into a form that can’t readily be used for bombs, and employing 40,000 nuclear scientists who might otherwise work for “states of concern” or terrorists. The Global Threat Reduction Initiative and operations such as the one in Uzbekistan signal a new aggressiveness by policymakers who, like the president, are all too aware of the threat of nuclear terrorism.

Critics insist that these programs aren’t moving with enough urgency. At the current speed, Bunn notes, our efforts to secure Russian nuclear material will take close to a decade. The GTRI’s mandate is to remove unused uranium fuel from the world’s most worrisome research reactors by the end of 2005. But given that each operation has taken months to plan, that date seems overly optimistic. And the Energy Department doesn’t expect to retrieve spent fuel–which can also just as easily be made into a bomb–until 2010.

The good news is that, given enough time and resources, sensitive material can be secured. “Nuclear terrorism is preventable,” says Graham Allison. “If you don’t have highly enriched uranium or plutonium, you can’t make a bomb. No highly enriched uranium, no mushroom cloud, no nuclear explosion, that’s it. Locking down things that we don’t want people to steal is not brain surgery.” Unfortunately, neither is building a nuclear bomb.