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Nuclear capabilities may eludeterrorists, experts say

Of all the clues that Osama bin Laden is after a nuclear weapon, perhaps the most significant came in intelligence reports indicating that he received fresh approval last year from a Saudi cleric for the use of a doomsday bomb against the United States.
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Of all the clues that Osama bin Laden is after a nuclear weapon, perhaps the most significant came in intelligence reports indicating that he received fresh approval last year from a Saudi cleric for the use of a doomsday bomb against the United States.

For bin Laden, the religious ruling was a milestone in a long quest for an atomic weapon. For U.S. officials and others, it was a frightening reminder of what many consider the ultimate mass-casualty threat posed by modern terrorists. Even a small nuclear weapon detonated in a major American population center would be among history's most lethal acts of war, potentially rivaling the atomic destruction of Hiroshima and Nagasaki.

Despite the obvious gravity of the threat, however, counterterrorism and nuclear experts in and out of government say they consider the danger more distant than immediate.

They point to enormous technical and logistical obstacles confronting would-be nuclear terrorists, and to the fact that neither al Qaeda nor any other group has come close to demonstrating the means to overcome them.

So difficult are the challenges that senior officials on President Bush's national security team believe al Qaeda has shifted its attention to other efforts, at least for now.

"I would say that from the perspective of terrorism, the overwhelming bulk of the evidence we have is that their efforts are focused on biological and chemical" weapons, said John R. Bolton, undersecretary of state for arms control and international security. "Not to say there aren't any dealings with radiological materials, but the technology for bio and chem is comparatively so much easier that that's where their efforts are concentrating."

Still, the sheer magnitude of the danger posed by a nuclear weapon in terrorist hands -- and classified intelligence assessments that deem such a scenario plausible -- has spurred intelligence and military operations to combat a threat once dismissed as all but nonexistent. The effort includes billions of dollars spent on attempts to secure borders, retrain weapons scientists in other countries and lock up dangerous materials and stockpiles.

"The thing to keep in mind is that while it is extremely difficult, we have highly motivated and intelligent people who would like to do it," said Daniel Benjamin, a former National Security Council staff member and senior fellow at the Center for Strategic and International Studies. Each type of weapon of mass destruction -- nuclear, biological and chemical -- presents special challenges for the groups seeking to acquire them, but also opportunities that can be exploited by people determined to unleash their awesome destructive powers. This is the first of three articles aimed at exploring those risks and challenges.

Difficult course
Without sophisticated laboratories, expensive technology and years of scientific experience, al Qaeda has two primary options for getting a bomb, experts say, both of which rely on theft -- either of an existing weapon or one of its key ingredients, plutonium or highly enriched uranium.

Nuclear scientists tend to believe the most plausible route for terrorists would be to build a crude device using stolen uranium from the former Soviet Union. Counterterrorism officials think bin Laden would prefer to buy a ready-made weapon stolen in Russia or Pakistan, and to obtain inside help in detonating it.

Last month, Michael Scheuer, who ran the CIA's bin Laden unit, first disclosed in an interview on CBS's "60 Minutes" that bin Laden's nuclear efforts had been blessed by the Saudi cleric in May 2003, a statement other sources later corroborated. As early as 1998, bin Laden had publicly labeled acquisition of nuclear or chemical weapons a "religious duty," and U.S. officials had reports around that time that al Qaeda leaders were discussing attacks they likened to the one on Hiroshima.

A week after his CBS appearance, Scheuer said at breakfast with reporters in Washington that he believed al Qaeda would probably seek to buy a nuclear device from Russian gangsters, rather than build its own.

There were as many as a dozen types of nuclear weapons in the hands of the Soviet Union at the end of the Cold War, but Russian officials have said that several kinds have since been destroyed and that the country has secured the remainder of its arsenal. The nature and scope of nuclear caches are among the most tightly held national security secrets in Russia and Pakistan.

It is unclear how quickly either country could detect a theft, but experts said it would be very difficult for terrorists to figure out on their own how to work a Russian or Pakistani bomb.

Newer Russian weapons, for example, are equipped with heat- and time-sensitive locking systems, known as permissive action links, that experts say would be extremely difficult to defeat without help from insiders.

"You'd have to run it through a specific sequence of events, including changes in temperature, pressure and environmental conditions before the weapon would allow itself to be armed, for the fuses to fall into place and then for it to allow itself to be fired," said Charles D. Ferguson, science and technology fellow at the Council on Foreign Relations. "You don't get it off the shelf, enter a code and have it go off."

The strategy would require help from facility guards, employees with knowledge of the security and arming features of the weapons, not to mention access to a launching system.

Older Russian nuclear weapons have simpler protection mechanisms and could be easier to obtain on the black market. But nuclear experts said even the simplest device has some security features that would have to be defeated before it could be used.

"There is a whole generation of weapons designed for artillery shells, manufactured in the 1950s, that aren't going to have sophisticated locking devices," said Laura Holgate, who ran nonproliferation programs at the Pentagon and the Energy Department from 1995 to 2001 . "But it is a tougher task to take a weapon created by a country, even the 1950s version, a tougher job for a group of even highly qualified Chechen terrorists to make it go boom."

Transporting a weapon out of Russia would provide another formidable obstacle for terrorists.

Most of the ready-made bombs that could be stolen would be those made with plutonium, which emits far higher levels of radiation and is therefore more easily detected by passive sensors at ports than is highly enriched uranium, or HEU.

"I wouldn't rule out plutonium altogether, but if one were a terrorist bent upon demonstrating a nuclear explosion, the HEU route is technically much easier," said William C. Potter, director of the Center for Nonproliferation Studies at the Monterey Institute of International Studies in California.

Building a bomb
Such difficulties have led some nuclear experts to believe bin Laden would be more likely to try to build an improvised nuclear weapon using a combination of uranium and conventional explosives. That design, known as a gun-type device, was used in the atomic bomb over Hiroshima.

While the technology is relatively simple and has been described in dozens of published scientific studies and policy journals, the path to development is filled with technological and logistical challenges -- the most significant of which is obtaining at least 50 kilograms of bomb-grade uranium. That amount would yield a slightly smaller device than "Little Boy," the code name for the Hiroshima bomb, but would be enough to obliterate any life or structure within a half-mile radius of the blast zone.

"If they got less material than that, it would be really dicey that they could build such a bomb," said Ferguson, at the Council on Foreign Relations.

According to a database maintained by the United Nations' International Atomic Energy Agency, there have been 10 known incidents of HEU theft in the past 10 years, each involving a few grams or less. Added up, the stolen goods total less than eight kilograms and could not be easily combined because of varying levels of enrichment. Most important, the thieves -- none of whom was connected to al Qaeda -- had no buyers lined up, and nearly all were caught while trying to peddle their acquisitions.

"Making the connection between buyer and seller has proved to be one of the most substantial hurdles for terrorists," said Matthew Bunn, a senior researcher at Harvard University's Project on Managing the Atom. Of the few known attempts by al Qaeda to obtain HEU, each allegedly stumbled because there was either no seller or the material on offer was fake. "Each time they tried, they got scammed," said Bruce Hoffman, a counterterrorism expert at the Rand Corporation who has tracked al Qaeda for years.

A September report on terrorism by the Congressional Research Service warned that terrorists could "obtain HEU from the more than 130 research reactors worldwide that use HEU as fuel." The report noted that the nations of "greatest concern as potential sources of weapons or fissile material are widely thought to be Russia and Pakistan."

The largest stocks outside the United States are in Russia and around the former Soviet Union, some in facilities with notoriously weak security and safety procedures.

"Once you have the fissile material, it's a matter of basic chemistry, basic machinery and a truck," said Holgate, now a vice president at the nonprofit Nuclear Threat Initiative. "You have to have some technical capability, but once you have those skills, it's certainly within the grasp of the kind of sophisticated, planning-capable terror organizations out there."

Even so, there are a great many steps between obtaining the material and setting off an explosion. That may account for why such an attack has not materialized, despite intelligence warnings.

The uranium would have to be smuggled out of the facility and then transferred, possibly across several borders, seaports and airports, to a location where the device could be assembled. As described in unclassified literature, the gun-type bomb works when one mass of uranium is shot into another inside a tube. Such a device would be small enough to hide in a corner of a shipping container, but that would mean getting it to a port, onto a container and probably bribing a shipper or cargo crew to transport it.

An oil shipment would be optimal for a ready-made device, according to the congressional report, because the "size of the supertanker and thickness of the steel, especially with the use of double hulls," renders some detection equipment unusable.

But HEU emits low levels of radioactivity anyway, and that could be masked with lead shielding. A primitive device could be assembled in a small garage using machine tools readily available at an auto shop and concealed in a lead-plated delivery truck about the size of a delivery van, experts said.

It is also unclear how a terrorist group would know if its weapons development effort was on the right track. Nations with nuclear bombs conduct tests, including explosions that can be detected by scientists and governments. Bunn, who has published two studies on nuclear terrorism, said terrorists would not necessarily need to conduct such tests, but doing without them would increase chances that human error would foil plans or delay progress.

The most elaborate known effort by a terrorist group to develop a nuclear program was undertaken by the Japanese cult Aum Shinrikyo, which instead of stealing enriched uranium planned to mine and enrich the material itself.

Members of Aum Shinrikyo, intent on world destruction when it began its 1993 quest for a nuclear weapon, had all the means to pull it off, on paper at least: money, expertise, a remote haven in which to work, and most important, a private uranium mine.

But the group made dozens of mistakes in judgment, planning and execution. It shifted course, launching its chemical attack on the Tokyo subway in 1995.

"There are valuable lessons in Aum's experience, and there are false lessons," said Benjamin, co-author of "The Age of Sacred Terror." "The valuable lesson is that WMD terrorism is hard to do," he said. "But given that they didn't try what would be the most efficient way to put together a nuclear bomb, we shouldn't overrate their example as a reason why it's not going to happen."

Al Qaeda has been on the run since the United States deprived it of a haven in Afghanistan, making it more difficult for the group to operate on such an ambitious scale.

"At this moment, they are less capable of carrying out an operation like this because it would require so many different experts and operatives," Benjamin said. "But even a depleted group could do it if they got the right breaks."