Seizure of almost three kilograms (6.6 pounds) of highly-enriched uranium (HEU) from nuclear smugglers arrested December 14 in the Czech Republic dramatically illustrates the breakdown in controls over weapon-usable nuclear material in the former Soviet Union, the suspected source of the material. It also makes clear that the risk of nuclear terrorism is growing.
A number of other incidents have pointed to an emerging black market in weapons-usable nuclear materials. This past summer, three seizures of plutonium and one of HEU in Germany---all in gram quantities or less---were seen as the tip of an iceberg of bomb material beginning to be smuggled out of the former Soviet Union.2 Larger seizures of HEU were also reported to have taken place: one involving six pounds in St. Petersburg in March 1994;3 one of three pounds near Moscow in October 1992; and one of about four and a half pounds in Lithuania in 1992.4
This paper answers some frequently asked questions about the nature of the materials and the extent of the danger involved.
1. Isn't the uranium seized in the Czech Republic too low a grade to be made into a nuclear weapon?
Some statements by government and International Atomic Energy Agency (IAEA) officials have tended to understate the weapons potential of the uranium seized in Prague. Preliminary tests by Czech authorities reportedly indicate that the HEU consists of 87.5 percent of the uranium-235 isotope, the fissile isotope of uranium which sustains the explosive chain reaction in nuclear bombs.5
Statements by the Czech Interior Ministry that the HEU was just short of weapons-grade,6 and by an IAEA spokesman that "over 90 percent [enrichment in U-235] is the kind of material bombmakers like,"7 are misleading in that they imply the HEU could not be used to fashion a workable nuclear bomb. In fact, the bomb used to destroy Hiroshima, a gun-type fission device, contained HEU with an average enrichment of about 80 percent, somewhat lower than the HEU seized last week.8 Terry Hawkins, deputy director for nonproliferation at Los Alamos National Laboratory, stated that 87.5 percent HEU could be used to make a nuclear bomb, and added, "If these materials in these quantities are coming through, it should be of major concern to the U.S. government."9
2. Isn't the three kilograms of HEU seized far less than the amount needed to make a nuclear bomb?
Reports on the Czech HEU seizure have emphasized that three kilograms of HEU are not enough to make a bomb. Several statements made to support this point substantially overstate the amount of HEU that would be needed. One press report cited unnamed "American government officials" as stating that "about 44 pounds (20 kilograms) of highly enriched uranium are needed to make a bomb ..."10 The IAEA defines a "significant quantity" (SQ) of HEU, the amount needed to make a nuclear bomb, as 25 kilograms.11
However, Carson Mark, former chief of nuclear-weapons design at Los Alamos, estimated that Iraq could have built a nuclear bomb using about 12.3 kilograms of HEU, or half the official SQ.12 Thomas Cochran, senior scientist at the Natural Resources Defense Council (NRDC), stated that "a low-technology bomb in the 10- to 20-kiloton range would require about 10 kilograms of highly enriched uranium."13
A research team at the University of California (Santa Cruz) found that three kilograms, in fact, would be sufficient to produce a nuclear bomb. By means of computer modeling of a simple fission weapon design, they found a nuclear yield equivalent to more than 100 tons of high explosives could be achieved with only one kilogram of HEU and "a yield half that of the Hiroshima bomb" with five kilograms.14 The authors concluded that "one can make an atomic weapon with much less nuclear material than generally thought," and they proposed "that the use of HEU should be eliminated in applications in order to prevent the spread of small-scale atomic weapons."15
Moreover, sophisticated terrorists would not need to build an actual nuclear bomb in order to cause nuclear violence. Less than three kilograms of HEU would be sufficient to construct an easily transportable and concealable "chain-reacting radiological weapon," according to a former U.S. nuclear weapons designer. While not producing a nuclear explosive yield, such a device could be made to go "super-critical" and disperse lethal amounts of radioactivity over a radius of hundreds of yards.16
3. Can HEU be used on its own to make nuclear bombs, or is it strictly a triggering material for hydrogen bombs?
A spokesman for the Interior Ministry of the Czech Republic, stated that
"uranium enriched with the 235 isotope to the degree of 80 to 90 percent is used---like plutonium-239---as the trigger for igniting the thermonuclear part of a nuclear warhead."17While true, this statement and others like it convey the impression that HEU can be used only to trigger a sophisticated thermonuclear or hydrogen bomb, rather than be used on its own to fuel a first-generation nuclear weapon. That impression is incorrect.
As noted above, the Hiroshima bomb was a fission weapon fueled solely with HEU. Iraq, Pakistan, and South Africa chose to base their covert nuclear weapons programs on HEU.18 Thus, HEU's significance is as a fuel for first-generation nuclear weapons, as well as a potential triggering material for more advanced thermonuclear weapons.
4. Aren't nuclear weapons too complex to be built by terrorist groups?
An anonymous "nonproliferation expert" has been cited as claiming that "while assembling enough fissile material is the most expensive and difficult part of constructing a bomb, those seeking to produce their own nuclear weapons must also secretly develop an effective detonation system and a delivery means, such as a missile or special aircraft."19 The first part of the statement is true, and a point worth emphasizing. Fissile materials comprise the sine qua non of nuclear weapons-making. Without HEU or plutonium, building a nuclear weapon is impossible. Construction of nuclear weapons should be assumed to be relatively straight-forward for sophisticated terrorists or proliferating states once these materials are in hand.
A panel of five former U.S. nuclear weapons designers reported to the International Task Force on the Prevention of Nuclear Terrorism that a workable nuclear bomb "could be constructed by a group not previously engaged in designing or building nuclear weapons, providing a number of requirements were adequately met,"20 and that even such a crude design could produce a nominal yield in the 10 kiloton range. Even if the bomb "fizzled"--- that is, did not achieve full yield because of design flaws---"the lowest preinitiation yield may still be in the 100 ton range, even in a crude design."21
College undergraduate students, with no access to classified information, have been found to produce workable designs for nuclear fission weapons,22 and even thermonuclear weapons.23 The particular properties of HEU greatly simplify the weapon design process. Luis Alvarez, a physicist with the Manhattan Project, noted in his memoir that "with modern weapons-grade uranium, the background neutron rate is so low that terrorists, if they had such material, would have a good chance of setting off a high-yield explosion simply by dropping one half of the material onto the other half. Most people seem unaware that if separated U-235 is at hand it's a trivial job to set off a nuclear explosion . . . (E)ven a high school kid could make a bomb in short order."24
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1. Steven Dolley is research director and Paul Leventhal is president of the Nuclear Control Institute. Back to document
2. Mark Nelson, "Another Seizure of Plutonium Adds to Fears," Wall Street Journal, August 17, 1994, p. A8. Back to document
3. Michael Gordon, "Russian Aide Says Gangsters Try to Steal Atom Material," New York Times, May 26, 1994, p. A5.Back to document
4. Michael Gordon, "Czech Cache of Nuclear Material Being Tested for Bomb Potential," New York Times, December 21, 1994, p. A8. Back to document
5. Rick Atkinson, "Prague Says Uranium Found in Czech Auto Could Trigger Bomb," Washington Post, December 21, 1994, p. A27. Back to document
6. Robert McLean, "Czech Uranium was Near Weapons Grade," UP wire service story, December 20, 1994. Back to document
7. David Kyd, IAEA, quoted in David Stamp, "Uranium Haul Confirmed as Nuclear Trigger Material," Reuter wire service story, December 20, 1994.Back to document
8. J. Carson Mark, "Some Remarks on Iraq's Possible Nuclear Weapon Capability in Light of Some of the Known Facts Concerning Nuclear Weapons," Nuclear Control Institute, May 16, 1991, p. 11. Dr. Mark is the former head of the theoretical division at Los Alamos National Laboratory and worked on the Manhattan Project. Back to document
9. Quoted in Atkinson, 1994, op cit. Back to document
10. Gordon, "Czech Cache," 1994, op cit. Back to document
11. IAEA, IAEA Safeguards Glossary, IAEA/SG/INF/1, 1980, p. 22.Back to document
12. Mark, 1991, op cit. Back to document
13. Quoted in Gordon, "Czech Cache," 1994, op cit. Earlier this year, Cochran and Christopher Paine released a study urging the IAEA to lower its SQ amounts and strengthen its safeguards. Thomas Cochran and Christopher Paine, "The Amount of Plutonium and Highly Enriched Uranium Needed for Pure Fission Nuclear Weapons," Natural Resources Defense Council, August 22, 1994.A HREF=#ENDBACK12>Back to document
14. D. G. Korycansky, D. Hirsch, & W. G. Matthews, "Estimate of Minimum Quantity of Highly Enriched Uranium Necessary for an Implosion Weapon," unpublished paper, University of California, Santa Cruz, n.d. Back to document
15. Ibid, p. 24. Back to document
16. Personal communication with Theodore B. Taylor, December 21, 1994. Back to document
17. Quoted in Atkinson, 1994, op cit. Back to document
18. Joel Ullum, "Enriched Uranium Versus Plutonium: Proliferant Preferences in the Choice of Fissile Material," Nonproliferation Review, Fall 1994, p. 12. Back to document
19. Atkinson, 1994, op cit., p. A30. Back to document
20. J. Carson Mark et al., "Can Terrorists Build Nuclear Weapons?," in Preventing Nuclear Terrorism, The Report and Papers of the International Task Force on Prevention of Nuclear Terrorism, Ed. Paul Leventhal & Yonah Alexander, Lexington, MA: Lexington Books, DC Heath, 1987, pp. 60-61. Back to document
21. Ibid, p. 62. Back to document
22. Charles Panati, "A Do-It-Yourself Bomb," Newsweek, March 10, 1975, p. 40. Back to document
23. Howard Morland, The Secret That Exploded, New York: Random House, 1981. Back to document
Alvarez, Alvarez: Adventures of a Physicist, New York: Basic Books, 1987,
p. 125. Back to document