Nomad,

Attainable enrichment levels are not related with the size of the centrifuges but with how many of them are cascaded. A chain to produce 4% U235 uranium can produce 98% HEU by recirculation. It "just" takes longer (much longer). Ideally, you want more centrifuges, a bigger cascade to maintain acceptable processing times.

The centrifuges are one of the warning signals coming from Iran. The official explanation is that Iran desires to control its own fuel cycle. But this is a huge investment for a very dubious return. Iran's uranium resources are very modest - nowhere near what they need to cover a large scale deployment of nuclear power plants - so they will have to go abroad to buy natural uranium to put in their enrichment cascades. They may as well buy large quantities of reactor-grade lightly enriched uranium to protect themselves from any foreseeable embargo and concentrate on things like fuel conditioning and post-processing.

So, it just doesn't make any sense except if they want to control the level of enrichment, not targeting lightly enriched uranium for light-water reactors, but ultra-high enriched uranium for nukes.


In my opinion, the real give-away is what's going on in Arak. Iran is building a 40 MW heavy water reactor outside the IAEA control.

A slow-burn heavy water reactor has no interest for energy production and doesn't help Iran to design reactors for energy production. There is only one civilian reactor technology using heavy water - the CANDU reactors - and the very point of that type of reactors is that it can use natural uranium as fuel. So, for civilian purposes, it's either heavy water or enrichment but not both. In addition, CANDU-like reactors are technically pretty complex and this is not what a third-world country would start with for an indigenous design. Iran has nothing to learn from a slow-burn reactor which is not already widely available in open literature.

Slow-burn reactors have only 2 uses:

• As a neutron source for various usages: radionuclide production, material tests, etc.
High purity Pu239 production

Iran claimed that the Arak reactor is for medical radioisotope production. The issue is that Iran already has a zero-power research reactor in Esfahan under IAEA control but is not using it actively, so their claim about the Arak reactor doesn't hold. Let's be very broadminded and assume that Iran has legitimate uses for plutonium, such as MOX fuel for light water reactors and get more bang for their fuel buck. That same type of light water reactor, like the 1000W reactor in Bushser, is a good source of plutonium suitable for MOX cycle and, on top, actually produces useful energy. No need for a slow-burn reactor.

But plutonium produced (and used as MOX) by those light water reactors with a normal fuel cycle is not just Pu239 but a mixture of Pu239, Pu240 with bits of Pu241. Those isotopes are produced when Pu239 absorbs more neutrons. Pu240 and Pu241 are horribly radioactive, including spontaneous neutron decay. So, while it still possible to use reactor-grade plutonium to build nukes, those nukes are very dangerous and have serious issues:

• Explosive yield is very hard to predict and the risk of a complete or partial dude is high.
Those weapons are very dangerous to store and manipulate because of radioactive decay heat and radiation exposure to personnel.
There is a non-negligible risk of auto-ignition, which would certainly not generate the full yield but still make a fine mess of your cherished nuclear weapon storage facility.

That's where slow-burn reactors kick in. They run on natural uranium (no need for enrichment) and it's the only way to produce high purity Pu239, which is easy to extract from the reactor fuel by chemical process (easy as compared to U235 enrichment).

The enrichment capacity and the heavy water reactor are consistent with a diversified, dual-track uranium/plutonium military nuclear program, similar to the North Korean program, and nothing else.

With the highly-enriched uranium track, the issue is the uranium enrichment, slow and expensive, but the weapon assembly can be very simple, safe and very reliable. The weapon can as simple as a gun assembly, similar to the Little Boy bomb dropped on Hiroshima. There is no need to test those weapons. They work. Period.

For the plutonium track, producing the Pu239 nuke fuel is fairly easy and only involves slow-burn reactors running on natural uranium and a bit of weird heavy metal chemistry for separating the plutonium from the uranium fuel rods. The issue lies with the weapon itself, which must be a implosion assembly, a very complex design. Incidentally, it is that type of weapon the US tested at Trinity before dropping one, Fat Man, on Nagasaki. They weren't sure at all it would work, while the Hiroshima bomb wasn't tested beforehand as the Manhattan folks knew it would work.

Iran is full of shit when it proclaims that its nuclear program is all nice and peacefull. It's plain false (or the Iranians have really no clue what they are putting their money into). Their program is for military use.

Those who proclaim that the sky is falling are also full of shit. Iran is nowhere near having a bomb. At least 10 years away, or, assuming that it throws at it every bit of money and resources it has (and starve its population to death), makes no attempt to hide the program from the rest of the planet and get every technical detail right on first try, a strict minimum of 5 years.