I have been asked to discuss Iran’s nuclear weapons potential – and I will, but I’m going to take a broader look.
The short answer is that the centrifuge approach that Iran is pursuing is capable (when mature) of producing either low-enriched uranium(LEU), useful for power reactors, or HEU, highly-enriched uranium, which can be used to make a fission bomb, among other things. Just for general information, natural uranium is about 0.7% U-235. LEU means that the fraction of U-235 is somewhere under under 20% (3%-5% in light water reactors) , while HEU is more highly enriched. Typical uranium nuclear weapons are usually >85% U-235, although the real nuclear players use plutonium cores nowadays . You can make a gun-type fission bomb with highly enriched HEU, which is simpler to develop than implosion, although less efficient.
Given sufficient highly enriched HEU, making a gun-type bomb is not too hard. South Africa managed it. Probably Iran could as well. Producing the fissionable material, in the case of HEU, is harder than using it in a bomb. For plutonium, which requires implosion, designing and building the weapon is difficult, possibly more difficult than preparing the fissionable material.
Times have changed. Back in the 1940s, no one had mastered the centrifuge approach, and the US used cumbersome and expensive gaseous diffusion, along with even more expensive calutrons. Enrichment was hard, and it was easier to make LEU and run a breeder reactor to make plutonium, which could separated by chemical processes.
Zippe, confined in a sharashka in Siberia after WWII, made centrifuges work. After his release (and isn’t that a strange thing?), his work was commercialized by a European consortium, Urenco. Zippe further improved the method’s efficiency by switching the rotor material from aluminum to maraging steel: the productivity of these gizmos varies directly as the square of the strength-to-weight ratio. Later, people used carbon-fiber reinforced materials.
Since these centrifuges run at 1500 revolutions per second or more, figuring out how to make them work wasn’t easy. Some bright guys failed before Gernot Zippe. However, assuming that the recipe has already been developed and you have it, developing Zippe-style centrifuges is possible, although still tricky. Abdul Qadeer Khan, a Pakistani engineer who worked for a Uranco subcontractor, got that recipe and took it home, where it became the basis of the successful Pakistani nuclear program. Later, he, or more likely the Pakistani government, traded that recipe to Iran, Libya and North Korea.
At one time, the Bush administration thought, or at any rate claimed, that Iraq had a centrifuge-based atomic program, but that wasn’t the case. I thought the claim of a nuclear program was obviously false before we invaded. My reasoning was as follows. Iraq was broke, except for the oil-for-food program, and we tightly controlled all that money. It was also under pretty tight sanctions, limiting the technical goodies that could be imported even if they had had any money. Iraq wasn’t able to make the goodies locally: they had a very limited technical base. The Baathists also had very limited human resources available: something like 80% of the population was Kurdish or Shiite and thus untrusted, leaving about 4 million Sunni Arabs as potential physicists and nuclear engineers. That was manpower enough for South Africa, and for Israel, but let’s be real. The Arabs are near-zeros in science and engineering and have been so for centuries. Sheesh, a big fraction of Iraqis were illiterate.
And the icing on the cake was that this all had to be done in a way that was invisible to our ‘national technical means’ – which means spy satellites, but other things as well, such as communications intercepts, detecting funny xenon and krypton isotopes, etc. This would also include humint, if we were any good at it, which we’re not.
Everything that the Bush administration said about this was bullshit. There were technical types employed by the Feds in the national labs – Sandia, Livermore and Los Alamos, Oak Ridge, who knew better, but they were ignored. Try to remember that the decision-makers in our government, the elected and appointed people, know nothing. They don’t know anything technical. They don’t know much about history or biology. Silvestre Reyes, who used to be head of the House Intelligence Committee, has no idea whether Al Qaeda was Sunni or Shiite. He was a Democrat: but of course the Republican committee members didn’t know either. Nor did top FBI antiterrorism officials. Or McCain. Or Bush. While the general public still can’t find Iraq or Iran on a map.
But I digress. Can Iran make this work? Sure looks like it. Iran has some money. It has a better technical base than Iraq, basically because they don’t completely live off oil. They make cars, trucks, steel: Iraq didn’t. If you look at available human resources, I would guess that more than half of Iran’s population of 70 million would be clearable on such a program. This is not to say that they are any smarter than Iraqis, but numbers and resources help.
Do I think that Iran is or will become a strategic threat to the US? No.