Nuclear Iran

The hard part of building a nuclear weapon is obtaining the requisite quantity of suitable fissile material - highly enriched uranium or plutonium. Plutonium can be produced from uranium in nuclear reactors, but Iran doesn't yet have any reactors big enough to produce worthwhile amounts of plutonium - and the reactors themselves require somewhat enriched uranium. Consequently, the key choke point for Iranian nuclear capability is the capability to produce enriched uranium, especially highly enriched uranium. There are a few possible ways to enrich uranium (separate fissile U235 from the more common U 238 isotope). The method of choice today is a cascade of high speed gas centrifuges, but it takes a lot of them to produce a bomb's worth.

So how close is Iran to getting nukes? Via Josh Marshall, we have some informed or otherwise guesses opinions. Let's start with a well known idiot:

Instead of being years away from the point of no return for an Iranian bomb, as we were before we allowed Europe to divert anti-proliferation efforts into transparently useless talks, Iran is probably just months away.

Jeffrey Lewis and others over at armscontrolwonk.com have some more reality based estimates in a series of several posts. Some highlights:

What would a Strike on Iran’s Nuclear Facilities Look Like?

Conventional wisdom states that Iran’s facilities are too dispersed to permit a strike like the one Israel conducted against Iraq’s Osiraq nuclear reactor in 1981. (The Osiraq story is quite a bit more complicated than you might think.)

Iran’s facilities are more dispersed, but some key assets are probably quite vulnerable to an airstrike.

The Atlantic Monthly conducted a wargame that including plans for a strike. The Atlantic Monthly game envisioned a strike against “125 targets associated with nuclear and chemical and biological storage/production facilities” in Iran including “10 nuclear R&D site targets.” The total was about 300 aim points requiring about 20 penetrating weapons.

They have labelled satellite pictures and powerpoint slides. Much of Iran's nuclear capability is known from the International Atomic Energy Authority (IAEA) inspections. The most dangerous capability being developed is the uranium enrichment facility. They show a picture of the Natanz uranium enrichment facility, designed to hold 50,000 centrifuges.

Destroying this facility should not be difficult. Although the bunkers are buried, the exact locations are well know from images captured during construction.

According to reporters who visited the facility, the bunkers are about 18 m underground. That’s deep, but not so deep that the facility would withstand a GBU 28.[deep penetrating "bunker-buster" warhead]
Incidentally, Israel is in the process of buying 100 GBU 28s from the United States. A coincidence, I am sure.

The problem with hitting the Natanz facility is that, at this point, it is basically a pair of empty bunkers—Iran’s centrifuge components are stored elsewhere and would probably be moved in the event of an impending airstrike.

Jeffrey Lewis has his own ideas on the timeline:

When some moron like Charles Krauthammer claims Iran is now just “months” away from a bomb, you can pretty much ignore him: He has no idea what he is talking about.

Overall, Iran is probably a little less than a decade away from developing a nuclear weapon. The key question here is how long it will take Iran to enrich a few tens of kilograms of uranium to more than 90 percent U-235.

In a worst case scenario, Iran might make enough highly enriched uranium for a bomb fairly quickly:

So, the real question, however, is how quickly Iran could assemble and operate 1,500 centrifuges in a crash program to make enough HEU for one bomb (say 15-20 kg).

Albright and Hinderstein have created a notional timeline for such a program:

Assemble 1,300-1,600 centrifuges. Assuming Iran starts assembling centrifuges at a rate of 70-100/month, Iran will have enough centrifuges in 6-9 months.
Combine centrifuges into cascades, install control equipment, building feed and withdrawal systems, and test the Fuel Enrichment Plant. 1 year
Enrich enough HEU for a nuclear weapon. 1 year
Weaponize the HEU. A “few” months.
Total time to the bomb—about three years.

Lewis thinks that there are a lot of technical obstacles that will make the process quite a bit slower.

Another post looks at how difficult it might be for Iran to build a bomb that could be delivered by one of their missiles. There a plent of problems there too. The missiles have limited carrying capacity and it takes considerable sophistication to design a small bomb.

UPDATE: According to this Federation of American Scientists article, the GBU-28 (and presumably it's GPS guided cousin, the GBU-37) can destroy hardened targets up to 50 feet deep. By my arithmetic, that puts an 18 meter (60 feet) deep target close to the limit of the GBU-28 capabilities. But Lewis knows this stuff pretty well, so I doubt that he would be wrong on this.