Anyone who has read Richard Rhodes Pulitzer Prize winning book The Making of the Atomic Bomb knows the awesome technical problems that had to be overcome by the scientists and engineers who worked on America’s Manhattan Project. And while the Iranian’s clearly have something of a head start in that many of the concepts worked out at Los Alamos have since entered the public domain via leaks and through books like Rhodes, the fact is that there are some aspects to building a bomb that are still closely guarded secrets and require a level of technical expertise not readily found in a third world country like Iran.
There are several ways around the technical problems that are being encountered by Iran as they seek to construct a nuclear weapon. Experts from other nuclear powers like China, Pakistan, and especially North Korea have probably already contributed to Iran’s enrichment program. This has been a given since we uncovered the nuclear bazaar being operated by the “Father of the Pakistani bomb” A.Q. Khan. There is little doubt that Dr. Khan was able to greatly assist the mullahs in the 1990’s with both the knowledge and sources for hardware that the Iranians will need to go nuclear. And perhaps most frighteningly (and blessedly least likely) is that the Iranians have been able to secure a quantity of enriched uranium (U-235) that they have already used to construct several crude nuclear devices.
That nightmare scenario cannot be ruled out but is unlikely due to the extraordinary difficulty in extracting the highly enriched (HE) uranium from what is commonly called yellowcake or Uranium Hexafluoride. The conversion process is technically challenging and very expensive which would make it difficult for all nuclear powers with the possible exception of China and Russia to be marketing the material to the Iranians. Countries like India, Pakistan, and North Korea would not have enough U-235 to spare. Since it takes around 125-150 lbs of HE Uranium to build even the crude “gun design” device that the US dropped on Hiroshima and since in order to get that amount of nearly pure U-235 you need to have several hundred tons of yellowcake to work with, it would be highly unlikely for any secondary nuclear power to sell the mullahs what they need to construct a nuclear device.
If we assume the Iranians have the technical expertise to enrich uranium, how long then do we have before Iran gets the bomb? A National Intelligence Estimate leaked to the Washington Post and New York Times (natch!) last summer indicated that our government believes the Iranians are a decade away from being able to explode a nuclear device. Given the history of the CIA’s prognostication abilities with regards to countries going nuclear, that time frame should not give comfort to anyone with an ounce of common sense. The Israeli’s on the other hand believe that Iran could be nuclear capable by the end of this decade (2009). The difference is significant in that the Mossad probably has better in country sources than the CIA.
So unless the Iranians have hidden much more of their nuclear program than anyone is aware – a difficult concept to entertain given that the movement of nuclear materials is carefully watched – it is likely that we still have 3-5 years before we would be forced to act.
Some of the major technical hurdles that Iranians have to overcome in order to build a bomb are outlined in this excellent article by Dr. Jeffrey Lewis of the blog Arms Control Wonk. Lewis is on the board of the Bulletin of Atomic Scientists and an arms control expert. What impressed me most about this article was his patient explanations of the engineering problems the Iranians have already experienced as well as what lies in store for them as they seek to build the infrastructure necessary to enrich uranium:
David Albright and Corey Hinderstein at the Institute for Science and International Security (ISIS) released an estimate that breaks down the steps for Iran to make fissile material for a bomb, along with a nifty satellite image (at right) of Iran’s Fuel Enrichment Plant (FEP) at Natanz.Most references to Iran being “months†away from a bomb are really statements about how close Iran will be once it completes the FEP—something, as you will soon see, that will take a few years.
[snip]
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.
Please note that this would be a “crash” program and that the date 2009 dovetails nicely with the Israeli estimate.
While most experts believe that the Iranians will eventually have 50,000 centrifuges housed in the FEP at Natanz, the best estimate is that they currently only have 1000 – 1500 on hand, hence the long lead time between getting the enrichment plant up and running and converting enough U-235 to build a workable bomb. At full capacity, the plant should be able to enrich enough uranium to make 25-30 bombs a year.
Is this how the CIA calculated that it would take the Iranians a decade to produce a bomb? It would certainly take years to install 50,000 centrifuges and get them synced up so that they would work properly. If this is the case, it is interesting that they left the fact out of their leaks that the Iranians could engage in a crash program in enrichment that would cut the lead time for bomb building almost in half.
That said, as Dr. Lewis points out, even a crash program in enrichment would not guarantee an Iranian bomb in 3 years:
The interesting question is what technical problems the US IC expects Iran to encounter. The thing about a crash program is that things, well, crash.
The engineering tolerances necessary to spin a centrifuge at supersonic speed in order to separate isotopes are extremely difficult to achieve. And each centrifuge must act in concert with the others so that all 1500 machines are working together. Called a “cascade,” Lewis points out that this may be just one of several technical hurdles the Iranians must overcome even in a crash program.
If all this is true, the good news is we have time – time to get serious about working with dissident groups in Iran to affect regime change. Because in the end, no other option seems viable at this point. The fact is that the Iranians could hurt us in retaliation far more than we could hurt them by taking out their nuclear capability. And with not much prospect of European cooperation on meaningful sanctions, the regime change route may be our best bet to thwart the murderous designs of the mullahs.
UPDATE
Dr. Lewis has published Part II of his 3 part series “Iran and the Bomb” which deals with the difficulties in warhead development for Iranian missiles.
UPDATE II
Aziz P. at Dean’s World nails it:
The analysis by ArmsControlWonk is thorough and detailed and goes into the specifics of nuclear production – including a very relevant discussion of lead. I urge everyone to read the full post. The bottom line: Iran is at least three years away from the bomb, even with the unrealistic assumption that the engineering is flawless enough to avoid even a single technical problem.It is deeply troubling that instead of discussing how we might facilitate the birth of a new Iran, we are instead talking about “Hobbesian choices” and hinting darkly at 100 million potential dead in the middle east – by our hands. How noble of us! How monstrous. Preemptive war is one thing; preemptive genocide another.
And as Aziz makes clear in his own post (read the whole thing), it would betray our new found sense of mission to spread democracy in the Middle East if we were to bomb the Iranians with all the misery that would entail for the Iranian people – who would surely rally around the mullahs – as well as expose our own vulnerabilities to Iranian countermeasures.
The point I was trying to make is that we have time. Let’s put it to good use.
See also Demosophists analysis of a piece from Stratfor by George Friedman at the Jawa Report that is well worth your time.
2:10 pm
Israel Hints At Military Preparation Against Iran
AP
Israel’s defense minister hinted Saturday that the Jewish state is preparing for military action to stop Iran’s nuclear program, but said international diplomacy must be the first course of action.
“Israel will not be able to ac…
2:48 pm
The debate on Iran continues
There’s more discussion of the situation in Iran going on in the blogosphere:
This discussion on Blue Force has some good resources for coming to a better understanding of the situation.
Aziz at Dean’s World comes to a position not unlik…
2:52 pm
Thanks for airing this.
A couple of further points:
1) I’ve never know whether to believe the 60 kilograms figure always cited for a hiroshima-style gun-bomb. Is it true or misinformation?
2) Part 2 of the article aludes to the tradeoffs between a testing required and bomb design – a HEU implosion design is substantially more frugal with HEU but riskier (than gun style design) technically especially without testing. It’s unclear to me how much use of an implosion design reduces the time-to-first-device in a crash program. At any rate the 3 year figure seems to cover this.
3:54 pm
You say …
> Since it takes around 125-150 lbs of HE Uranium to build even the crude “gun designâ€
Then you quote Lewis
> 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).
From what I remember reading I think Lewis’ number is more accurate.
> Bill Arnold Says:
January 22nd, 2006 at 2:52 pm
> 2) Part 2 of the article aludes to the tradeoffs between a testing required and bomb design – a HEU implosion design is substantially more frugal with HEU but riskier (than gun style design) technically especially without testing. It’s unclear to me how much use of an implosion design reduces the time-to-first-device in a crash program.
I think an implosion design requires Plutonium instead of U-235.
———————————
Ref the 3 year estimate
>The point I was trying to make is that we have time. Let’s put it to good use.
Since it’s unclear how MUCH time wouldn’t it be better to solve the problem a year too early than a day too late?
4:54 pm
Bill:
My figure of 125-150 comes from this site:
http://www.buzzle.com/editorials/3-11-2004-51554.asp
The minimum amount to start a chain reaction as described above is known as SuperCritical Mass. The actual mass needed to facilitate this chain reaction depends upon the purity of the material, but for pure U-235, it is 110 pounds (50 kilograms), but no Uranium is never quite pure, so in reality more will be needed.
That jogged my memory from the Rhodes book where he stated that the Hiroshima bomb used 150 lbs of U-235. I trust Lewis’ number since he’s an expert and I’m not but it could be that something as crude as the “gun design” may need more – I don’t know.
Basically, the gun design as a just barely subcritical mass of U-235 at one end of a long barrel and a “plug” of U-235 at the other end. Fire the plug down the barrel and when it comes into contact with the larger mass, it goes critical and sets off the device.
As I said, very crude but still a pretty big bang. And that design may indeed require a larger amount of HEU.
Anrold:
You are correct about the implosion device using Plutonium. That design is technologically beyond Iran for the forseeable future as it requires shaped charges being set off around a sphere of Plutonium with extremely precise timing – microseconds apart as I recall – because the Plutonium must be “squeezed” from a ball the size of a cantelope to one the size of an orange. Any mistakes and all you get is a fizzle.
There are other ways to get HEU to supercriticality like bombarding the mass with neutrons from some neutron rich source (usually polonium) but these designs are technically beyond all but the most sophisticated nuclear program.
The real worry is that Iran will get its hands on a supply of U-235 from North Korea or Pakistan (China would be nuts to give the mullahs anything). As I tried to point out, those countries are barely making enough U-235 for their own programs to contemplate letting the precious material be sold to anyone else. That’s not to say it won’t happen or hasn’t happened already. It’s just not likely.
11:24 am
Another great article Rick.
There are several important challenges when attempting to figure out what the Iranians are doing. First is our lack of data. What we know is like moutain peaks that rise above a layer of clouds – it’s an incomplete picture at best. Some of the reason for the various predictions on capability come from the differing assumptions one is forced to make because critical information simply isn’t available. That said, I tend to agree with a 2-3 year timeline based on what we know, but it’s always possible the Iranians have a separate, covert enrichment program that uses centrifuges or another enrichment technology that may have already given them a crude bomb, or perhaps one this year.
The second, and in my mind, largest, factor in determining the state of the Iranian program is intent. We simply don’t have a good idea what Iran’s true goals are. I think it is safe to assume that Iran wants a nuclear weapon, but that is only the minimum we need to know. What is their ultimate goal? Do they simply want a handful of weapons to guard against their nuclear neighbors Pakistan, Russia and Israel? Or do they want 30 weapons with a capability to produce several a year? What capacity for production do they want – there is a big difference in how they will prosecute their program depending on these goals.
Another important consideration is how they intend to weaponize these bombs. It’s assumed that Iran eventually intends to put weapons on their ballistic missiles, but that goal is a very difficult engineering problem that will take them some time to overcome. Is that their ultimate goal? Or will they limit themselves to another, less challenging (from an engineering perspective) method of delivery. Their options in this area are limited, since their Air Force lacks the capability to reliably deliver a weapon to a target in another country.
The answers to these unknowns will determine how the Iranian’s program will manifest, because they will determine the technical aspects of the program.
I’m short on time at the moment and will try to go into greater detail later.
11:25 am
Formation of Radical Islam
The mission inside the preformation of Radical Islamofascism is but a loop… playing out the synchronicities of former regimes. This time, the stakes are higher with nuclear weaponry.
2:16 pm
While the points are laid out in a well thought out manner, it is very dangerous to assume anything with Iran. As to the “don’t worry, they won’t have a bomb for three to five years†thoughts, Fred Kaplan brings about the point as to why it is of utmost importance now (especially to Israel). Source: http://www.slate.com/id/2134497/
“First, it’s worth emphasizing that enriching uranium and spinning gas centrifuge machines are necessary but not sufficient steps toward making A-bombs. The Iranians have to operate a cascade of machines. As David Albright of the Institute for Science and International Security points out in a paper published this month, the Iranians tried this once before, in 2003, but failed miserably and broke about a third of their centrifuges in the process. Repairing the damage and getting the machines running again will take at least six months to a year. And it will take another two years beyond that before the plant starts churning out bombs. In other words, if diplomacy has a chance to work, there is some time to make it work.
How will we know, at what point can we judge, whether diplomacy is feasible or fantasy? Several Israeli officials have said publicly that, once the Iranians successfully operate a cascade of centrifuges, even in small numbers, they will know how to operate cascades in large numbers; they will be self-sufficient in the art and science of building A-bombs; they will have crossed a “red line” or, as some ominously put it, a “point of no return.” In other words, from the viewpoint of many Israelis, the question—can diplomacy work?—will be decided in 2006.â€
3:45 pm
IRAN: HOW LONG DO WE REALLY HAVE?
Niall Fegurson is betting on 2007.
4:33 pm
If Iran is still 3-5 years away from acquiring a nuclear weapon, why are they going out of their way to stage a confrontation with the West? It could all be a bluff to buy more time, but it would be dangerous to assume that. In any event, I’m not comforted by the thought that the Iranians won’t acquire nukes for 3-5 years. By then George Bush will be out of office, and possibly the Republicans, too. I shudder to think how a future Democratic president might deal with an Iranian nuke crisis.
10:05 pm
Author, no, implosion devices can be done with either plutonium 239 or HEU-235.
From a nice simple intro on weapon design at american federation of scientists,
“Implosion systems can be built using either Pu-239 or U-235 but the gun assembly only works for uranium. Implosion weapons are more difficult to build than gun weapons, but they are also more efficient, requiring less SNM and producing larger yields.” (I believe SNM here is “special nuclear material”)
Rick, I see the 65 kilogram figure all over the place on the web (the south african gun-design weapons were supposedly slightly more frugal (more highly enriched) at 50 kilograms) – “The device [hiroshima bomb] contained 64.1 kg of highly enriched uranium, with an average enrichment of 80%. The six bombs built by the Republic of South Africa were gun-assembled and used 50kg of uranium enriched to between 80 percent and 93 percent in the isotope U-235.”
(I realize now I am woefully ignorant of weapon design.) The same article has a simple table:
Uranium-235 Plutonium-239
Bare sphere:56 kg 11 kg
Thick Tamper:15 kg 5 kg
Where a tamper serves the dual purpose of neutron reflection and increasing the time the unit stays assembled before blowing apart.
11:28 pm
Bill:
Thanks for the additional info. My metric conversion table gives me about 144 lbs for 65 Kg’s.
Of course, the polonium (or cadmium is another neutron tamper used) has to be set a precise distance from the mass and then brought in closer proximity in order to bombard it with the neutron bath. That kind of design takes many months of testing in order to come up with the proper distances.
2:39 am
Submitted for Your Approval
First off… any spambots reading this should immediately go here, here, here, and here. Die spambots, die! And now… here are all the links submitted by members of the Watcher’s Council for this week’s vote. Council li…
2:27 pm
The Council Has Spoken!
First off… any spambots reading this should immediately go here, here, here, and here. Die spambots, die! And now… the winning entries in the Watcher’s Council vote for this week are Chaos or Community by Done With Mi…
3:48 pm
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