“Iran now has 5,000 kg (11,023 lb.) of low-enriched uranium,” he says. “But they only have 5,000 tons of raw uranium. That is not enough for a nuclear-power reactor, but it is more than enough for nuclear weapons. “They have enough enriched uranium to produce 3-5 weapons,” Asculai says. “The minimum arsenal is four—one for underground testing, a spare and two for a deterrent arsenal.”
“Later it will go very fast, but first they have to set up a different centrifuge cascade and some special containers,” Asculai says. “They will probably do it at the Fordow underground enrichment plant near Qom. This to my mind was the smoking gun when it was revealed in 2009. It has no civilian use. The Iranians are masters of concealment, so I think revealing the Fordow facility was an accident.”
Another detailed analysis by the Institute for Science and International Security (ISIS), issued in early October, concludes that Iran could create a “significant quantity” (SQ) of weapons-grade uranium (WGU)—25 kg, considered the minimum necessary for one device—in 2-4 months in a breakout scenario.
However, there is a catch. To do this, Iran has to deplete its existing stockpile of 2% low-enriched uranium (LEU)—with the result that subsequent SQs take longer, because the process has to start from scratch, with non-enriched material.
ISIS estimates Iran could produce two SQs in 4.6-8.3 months—based on computer simulations of the centrifuge installations at the Natanz plant—and could, with changes to the enrichment sequence, produce up to four SQs in 8.9-12.8 months. But that would deplete LEU stocks to the point where each additional bomb-load of material would take 9.5-17 months at Natanz. The smaller Fordow plant would take at least 21 months to produce a single bomb, according to ISIS.
Iran can put itself in a stronger position to attempt a breakout only by delaying the attempt and concentrating on bulking up its LEU stockpile—but this would mean losing ground against Israeli's improving defenses. And Iran remains burdened by international sanctions.
Moreover, continued Iranian protests about “sabotage”—including allegations that IAEA inspectors are directly involved—suggest that undercover attacks on the nuclear program, including recent alleged bomb attacks on power supplies, are still not under control, following the success of cyberattacks. The ISIS modeling does not take such problems into account.
Neither does 25 kg of WGU equal a bomb, let alone a missile warhead. The bomb itself has to be engineered and tested. And so far, only France, with practical experience of nuclear-weapons design, has declared a warhead operational without a physical test. Finally, the device must be integrated into a reentry vehicle (RV) that protects and powers it and fuzes it reliably at the correct altitude.
Iran also has to determine what constitutes a credible threat in the face of Israeli defenses—in a situation where the balance of attack and defense is the reverse of what prevailed in the Cold War. Unless and until Iran can develop effective penetration aids, such as maneuvering or low-radar-cross-section RVs and decoys (and that is likely to be a long time, since these constituted some of the most difficult projects of the Cold War era), the only available tactic to reduce the effectiveness of the defenses is a costly salvo attack.
Israel, meanwhile, is upgrading its defenses to deal with exactly that threat, including two entirely new interceptors and a major upgrade to the existing Arrow 2 missile. The Arrow System Improvement Program represents the latest evolution of the weapon, capable of intercepting faster targets at longer ranges.