There has been much public discussion recently about the Iranian nuclear program, particularly the question of when it might be determined that it had crossed a “red line” defining it conclusively as a nuclear-weapons, rather than a power-reactor, program. An analysis of Iran’s actual production suggests that the line has already been crossed.
Some of the discussion has been quite absurd. For example, page 1 of the February 25 New York Times features a story entitled “U.S. Agencies See No Move by Iran to Build a Bomb.” Meanwhile, on page 8 of the very same edition, David Sanger and William Broad report that International Atomic Energy Agency inspectors have determined that Iran is now producing large quantities of 20-percent–enriched uranium-235 in a facility located under 250 feet of granite protection. 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.
So perhaps the CIA did not read the IAEA report featured on page 8. That said, most of those who are aware of it have drawn the conclusion that Iran is well on its way towards producing “bomb-grade” (93-percent–enriched) material. This is true, but it misses an important point. While optimal, 93-percent–enriched “bomb grade” material is not necessary for producing a nuclear bomb. The weapon that devastated Hiroshima was only 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 following data from Oak Ridge National Laboratory Publication ORNL/TM-13517, Table 2, page B-5, 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 above 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.
According to the IAEA report, Iran already has 74 kilograms of 20-percent–enriched uranium-235, and is producing more material at a rate of 6.8 kilograms per month. Assuming that the IAEA is correct in its figures, it would take Iran another 26 months to have enough 20-percent–enriched uranium-235 material to build a bomb. But 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.
In any case, one point should be clear: The red line has already been crossed.