The International Atomic Energy Agency (IAEA) has reported that Iran has doubled its production rate of 20 percent enriched uranium-235. This has provoked a significant amount of public discussion of when it might be determined that Iran has crossed a "red line" defining its nuclear effort conclusively as a nuclear weapon, rather than a power-reactor program, and whether any threat represented by this program should be considered imminent.
As to whether the Iranian effort is a bomb program or not, the answer is straightforward. Since commercial reactors require only 3 percent-enriched uranium-235, a factory producing 20 percent-enriched fissile material is clearly part of a nuclear-weapons program.
But is the Iranian bomb imminent? According to a number of commentators, it is not, since the manufacture of an atomic bomb built to American standards would require further uranium enrichment, to better than 90 percent purity. This misses an important point. While optimal, 93 percent-enriched "bomb grade" material is not necessary for producing a nuclear bomb. The bomb that devastated Hiroshima was 80 percent-enriched. In fact, bombs can be made out of material with enrichments as low as 6 percent, albeit at some cost in increased weapon weight. The accompanying table from Oak Ridge National Laboratory shows the relationship between required critical mass and enrichment for naked spheres of uranium metal.
While using enrichment levels inferior to the official 93 percent uranium-235 "bomb grade" imposes a weight penalty, 20 percent-enriched uranium-235 is definitely "bomb usable" and is, accordingly, classified as such. Furthermore, the figures in the table cite the critical mass required for naked uranium-metal spheres. If instead the spheres are surrounded by a neutron reflector, such as 10 centimeters of beryllium, the required critical mass can be reduced by as much as a factor of three. Thus, instead of 746 kilograms of 20 percent-enriched uranium-235 being required to make a bomb, about 250 kilograms would be sufficient to do the job, without any further enrichment.
According to IAEA, Iran already has 190 kilograms of 20 percent-enriched uranium-235, of which 120 kilograms is available for bomb production, and is now producing more material at a rate of 13 kilograms per month. Assuming that the IAEA is correct in its figures, it would only take Iran another 10 months to have enough 20 percent-enriched uranium-235 material to build a bomb. However, if the IAEA has underestimated Iran's production rate, or if Iran continues to step up the pace, sufficient material for a bomb could be available much sooner.
According to David Sanger and Eric Schmitt, writing in the New York Times on Sept. 2, the Obama administration is currently trying to "calm Israel," so as to dissuade it from undertaking a military strike to stop the Iranian bomb program. In addition, Mr. Sanger and Mr. Schmitt report that the president has ruled out any U.S. military action that might "harm ordinary Iranians," or even inconvenience them by damaging the electric power grid that powers the bomb-making plants. Such action should be avoided, say administration representatives, "in order to give sanctions time to work."
However, as the IAEA report makes clear, it is not sanctions, but bomb-makers, who are being given time to do their work. Indeed, it is quite clear that, even if strong sanctions might work in principle, no policy that forbears from imposing economic difficulties on ordinary Iranians could ever include measures that might effectively dissuade the regime -- and obviously, they haven't. So one must wonder, exactly what outcome does the Obama administration have in mind?
In any case, one point should be clear: The red line has already been crossed.
Robert Zubrin is a fellow with the Center for Security Policy and author of "Merchants of Despair: Radical Environmentalists, Criminal Pseudo-Scientists, and the Fatal Cult of Antihumanism" (Encounter Books, 2012).