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How Close Is Iran to Exploding Its First Nuclear Bomb?

The most worrisome scenario would be for it to “sneak out”
iran, nuclear bomb, graham t. allison, low-enriched uranium


Over the past decade Iran has been cautiously, but steadily, putting in place all the elements it needs to construct a nuclear weapon in short order. But as James R. Clapper, director of National Intelligence, told the U.S. Senate in January, while the Iranians are “moving on that path ... we don’t believe they have actually made the decision to go ahead with a nuclear weapon.”

For several years experts have debated the possibility of a “breakout” scenario in which Iran makes a mad dash to complete and test its first bomb before other nations can act to stop it. That would require doing as much as possible to prepare for bomb making without tripping the alarms of the International Atomic Energy Agency (IAEA), the source of most good intelligence about Iran’s declared program. From that point, Iran would then race to conduct a test quickly, perhaps in as little as several weeks. How close is Iran to achieving such an option?

Let us start with what we know. Since 2006 Iran has accumulated a stockpile of low-enriched uranium (LEU), containing 5 percent of the uranium 235 isotope, putatively to fuel future civilian nuclear reactors. If Iran were to enrich this material further, to the point at which 90 percent of it was uranium 235, it would provide the core of four nuclear bombs. Since February 2010 it has also been enriching uranium to 20 percent and has recently tripled the production rates of this material. It has also experimented with centrifuges that are three to six times more efficient than the first-generation centrifuges it is currently operating (the designs for which it got from Pakistan’s nuclear god­father A. Q. Khan). These are significant steps toward making a bomb. Producing 20 percent enriched uranium requires nine tenths of the time and effort needed to make bomb-usable uranium. The IAEA suspects that although Iran may well have suspended its dedicated nuclear weapon research program in 2003, by that time it had already learned enough to be able to make such uranium into a simple, testable nuclear weapon.

The state of Iran’s declared stockpile and production capabilities is fairly well known. But it may well have undeclared capabilities, materials and know-how. In addition to the facilities at Natanz and Fordow that the IAEA inspects regularly, it is reasonable to assume that Iran has invested in hidden enrichment facilities because both Israel and the U.S. have been threatening air strikes on these targets for many years. Although no one has reported evidence that Iran has bought nuclear weapons or material from the former arsenal of the Soviet Union or from North Korea, Iran’s leaders must have considered this option as well. We know that more than one bomb’s worth of fissile material went missing after the Soviet Union collapsed.

With the centrifuges now known to be operating, from where Iran stands today it would take at least five months to produce enough material for one bomb. As more centrifuges come online and production rates improve, this timeline will shorten. But any scenario that requires months between tripping the IAEA’s alarm and testing a bomb would mean taking a huge risk of being attacked, something Iran’s supreme leader Sayyid Ali Khamenei has so far assiduously avoided.

How then could Iran produce a nuclear bomb without getting bombed? The most worrisome scenario would be for it to “sneak out.” Iran would complete the conversion of its low-enriched uranium stockpile to 20 percent at declared facilities, as it is now doing. Simultaneously, it would install advanced centrifuges at a secret facility. At the chosen moment, it would stage an incident—say, an explosion at Fordow—that it would claim had dispersed such high levels of radioactivity that the area had to be quarantined for several weeks, making inspections impossible. (It could even blame the incident on an Israeli covert attack.) Under this cover, Iran would move the 20 percent uranium to the secret facility and complete the enrichment to weapons-grade levels. Because the U.S., Israel and the IAEA would be unable to determine whether declared stockpiles had been moved or where they had been moved to, they might find themselves unable to act. In this scenario, Iran could produce enough weapons-usable uranium to conduct a test in as little as a few weeks.

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