Iran’s next move at the Fordow enrichment site (updated)

Following up on my last post about US and Israeli redlines for an attack on Iran, I wanted to take a closer look at the issue of advanced centrifuges being moved to the Fordow facility near Qom.

If you recall, Matthew Kroenig and Colin Kahl, both recently-departed Obama administration officials, noted that if Iran were to install advanced centrifuge designs in the deeply-buried Fordow facility, then Western officials would need to consider taking military action against that site.  Kroenig said such a move by Iran would mean “the United States must strike immediately or forfeit its last opportunity to prevent Iran from joining the nuclear club.”

I viewed this as an unreasonable redline to draw, since Iran is already operating next-generation centrifuges at its other enrichment facility and that moving IR-2m or IR-4 machines into Fordow wouldn’t fundamentally alter the nature of Iran’s nuclear weapons potential in the same way that, say, a decision to start stockpiling weapons-grade uranium would.  But I then got to thinking: wouldn’t more advanced centrifuges at the Qom site mean Iran could breakout quicker — possibly even in the 2-3 months between IAEA inspections?  That would, after all, fundamentally alter the state of play on the nuclear issue, and probably would necessitate some deep thinking in Washington and Tel Aviv.

So let’s figure out what we’re really dealing with here. (Warning: math ahead).

According to the latest IAEA report, Iran intends to use the Fordow facility for two purposes: production of 20% enriched uranium and R&D, which has usually meant research and design on next-generation centrifuge technology.  This is an important starting point, because it makes it clear that Iran plans to install next-generation centrifuges at Fordow already.  So we’re not talking about some unlikely event over which we’re willing to go to war; this is part of the plan as of today — meaning there’s a lot at stake if we get things wrong.

At present, no advanced centrifuge designs are installed or are being installed at Fordow, though that could happen anytime.  There are two cascades of IR-2m and IR-4 machines installed at the Pilot Fuel Enrichment Plant at Natanz.  (If you recall, the PFEP served as the testing grounds for 20% enrichment before that process was moved to Fordow in 2011.  So again, it’s likely those machines will someday be moved to Fordow.)

According to most estimates, the IR-2m and IR-4 machines are nearly 4 times as efficient as Iran’s IR-1 centrifuges, meaning their separative work capacity has been estimated at about 3-4 SWU/year.  Assuming standard feed, tails, and 25kg of 90%U235 for a bomb, a conservative estimate of 4SWU/year/centrifuge would mean Iran would need roughly 815 centrifuges to produce one bomb’s worth of material in a year.  Shrink that timeline down to a fast breakout of 3 months, and Iran would need 3261 machines — or about the entire capacity of the Fordow facility packed to the gills.

But all that assumes Iran feeds natural uranium into the machines.  IF Iran wanted to breakout using next-gen machines at Fordow, and IF it tried to do so between IAEA visits, it would likely use its stockpile of 3.5% or, more likely, 20% material.

So using a feed of 3.5%U235, one bomb’s worth of material requires 4821SWUs for a 3-month breakout, or about 1205 centrifuges.  Using a feed of 20%U235, that number shrinks drastically to 312 centrifuges — well within Iran’s current capability.

From there, it is easy to see why some Obama administration officials would be concerned about the presence of advanced centrifuges at Fordow: without round-the-clock inspections, Iran could theoretically produce enough fissile material for one bomb using 2 cascades of advanced centrifuges with a relatively high likelihood of escaping detection until it is too late.  Obviously, this would cut it pretty close, and IAEA inspectors would undoubtedly discover the diversion on their next visit, so Iran would need to weaponize the material and potentially even perform a test detonation in a matter of days in order to truly catch the world by surprise.  That’s unlikely, but not something we can easily ignore.

Thus, it becomes clear from this examination just how important it is for the next round of nuclear negotiations to convince Iran to relinquish its stockpile of 20% enriched material.  Without this stockpile, the fast 3-month breakout scenario would require feeding 3.5%uranium into nearly 7 cascades of advanced centrifuges — far too many for Iran to manufacture at present, given the Western campaign of sanctions and sabotage that have choked off Iran’s supply line.  This would also create space for the West to declare a very clear redline after Iran establishes the reality of next-generation machines at Fordow: 2 cascades won’t keep us up at night, but any more than that and we start getting itchy trigger fingers.

For my money, all this is an argument for a real concerted push at the next P5+1 meeting to take the deal offered by Ahmadinejad last September, so long as it can be expanded a bit to cover the existing stockpile of 20% uranium.  It’s a bit of a stretch to say that it should be a redline for the West when Iran starts installing next-generation machines at Fordow, though I know you can’t just wait until everything’s installed since the facility is nearly invulnerable to airstrikes.  Kroenig and Colin Kahl left off some nuance here, for which they can largely be forgiven.  But there are few things which require more absolute crystal clarity than Western redlines for Iran’s nuclear activities — this is one which might deserve a more detailed explanation from US policymakers.

Update: Josh Pollack informs me that the Fordow enrichment facility is under a much stricter IAEA safeguards regime than I initially thought.  Rather than having a window of 2-3 months between site inspections, the IAEA averages one Design Information Verification (DIV) visit per month, in addition to various other types of near-continuous monitoring, both remote and on-site.  Thus, a breakout scenario that depends on the rapid enrichment of weapons-usable material under the nose of IAEA inspectors strains even further the limits of Iran’s technical capability.