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Israeli officials have reportedly laid down a concrete red line that they will not allow Iran to cross: Accumulation of 161 kilograms of solid near-20% enriched uranium (the equivalent of 240 kilograms of near-20% enriched uranium gas). They believe the Iranians would need this quantity to produce weapons-grade uranium for a nuclear warhead. What does this mean in real terms and how definitive is the line?
How much near-20% enriched uranium have the Iranians produced?
Iran had produced about 127 kilograms of this material as of mid-August, according to the International Atomic Energy Agency (IAEA). It has likely produced an additional 24 kg of near-20% enriched uranium since August, assuming a steady production rate. Thus, the estimated total near-20% enriched uranium produced is about 151 kilograms, or just 10 kilograms shy of the Israeli red line (incidentally, a report over the weekend suggesting Iran had suspended enrichment at this level was refuted in Iranian state media and attributed to a misquote).
How long before the Iranians reach this red line?
Approximately 6 months (May 2013)…or 1.5 months (mid-December 2012). Why the range? In one word: assumptions. Iran has allocated a portion of its near-20% enriched uranium for producing fuel plates used in the Tehran Research Reactor (TRR). The IAEA reported in August that Iran has fed about 47 kilograms of near-20% enriched uranium into a process for conversion to uranium oxide used in producing fuel plates and assemblies for the TRR. This allocation has led some, including apparently the Israelis, to assume that that portion is unusable in a breakout scenario for producing weapons-grade uranium and, thus, to subtract that figure from the available stockpile. Iran is about 6 months away from crossing the red line under this assumption.
This assumption, however, is false from a technical standpoint: Near-20% enriched uranium in uranium oxide form can, in fact, be converted back into a gas for further enrichment to weapons-grade. It would not take long to do so theoretically with the use of specialized facilities (days to weeks). The material can only be considered as unusable for a rapid breakout once it is inserted into and irradiated in the reactor core. The Iranians have only irradiated a small fraction of the allocated 47 kilograms—about 4 kilograms—as of August. The majority of the 47 kilograms, therefore, is recoverable in short order for diversion to a breakout. Iran is about 1.5 months away from crossing the red line if the technically false assumption is discarded.
Are these timelines set in stone?
No. Iran now has more than 2,000 centrifuges installed at Fordow that were not enriching according to the last IAEA report (as compared to the 696 that were enriching). Both timelines above assume Iran continues to enrich at current production rates and does not use any of these installed centrifuges. Iran could cross the red lines well before the timelines above if it “surges” online this capacity at Fordow. The current near-20% enriched uranium production rate is approximately 10 kilograms per month. If Iran began enriching in all the centrifuges installed at Fordow today, it would triple monthly production to about 30 kilograms per month. Iran would reach the red line in 2 months or 2 weeks under this scenario.
Is the reported red line quantity (161 kg of near-20% enriched uranium) a definitive figure?
No. It is based on a series of optimistic assumptions. The exact amount of near-20% enriched uranium the Iranians would need to produce weapons-grade uranium for a warhead is determined by the efficiency of the enrichment process going from near-20% to weapons-grade levels, their level of technical proficiency in designing a bomb, and the size of the warhead. The 161 kilograms reportedly includes a cushion of unknown quantity “allowing for the excess that normally goes to make an initial warhead.” Another built-in assumption is that the Iranians, with a lower level of technical proficiency, would need about 25 kilograms of weapons-grade uranium (produced after converting the 161 kilograms near-20% material) with which to build an implosion-type atomic weapon. Weapons designed with a higher level of proficiency can be built using much less material. There are plausible reasons to assume that the process of an Iranian breakout would be inefficient and that it would require more enriched material; there are also plausible reasons to question those assumptions.
What is the bottom line?
It sounds as though the Israelis have articulated what appears to be a very precise figure, presumably based on granular assessments and fine technical considerations. The complexities outlined above, however, suggest that the figure and corresponding timeline are only valid under certain assumptions about Iranian policies and intentions. If those assumptions—about which we should have very little confidence—are wrong, then the Israeli “red line” could move forward, and rapidly.
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