You suggested:

I’m just wondering if the IC’s dates do not assume an overt breakout.

What I think your positing is that fitting out a clandestine plant and then creating bomb fuel is the source for the quite extended timeline for Iran to be bomb-ready.

Definitely a possiblity. What I have read, tho, implies that the time is based on Iran’s overt declared facilities.

I just checked an article that was repeatedly cited at ACW:

From WaPo:

Iran Is Judged 10 Years From Nuclear Bomb
U.S. Intelligence Review Contrasts With Administration Statements

By Dafna Linzer
Tuesday, August 2, 2005
…
The new estimate extends the timeline, judging that Iran will be unlikely to produce a sufficient quantity of highly enriched uranium, the key ingredient for an atomic weapon, before “early to mid-next decade,” according to four sources familiar with that finding. The sources said the shift, based on a better understanding of Iran’s technical limitations, puts the timeline closer to 2015 and in line with recently revised British and Israeli figures.

The estimate is for acquisition of fissile material, but there is no firm view expressed on whether Iran would be ready by then with an implosion device, sources said.

The timeline is portrayed as a minimum designed to reflect a program moving full speed ahead without major technical obstacles.
…
Sources said the new timeline also reflects a fading of suspicions that Iran’s military has been running its own separate and covert enrichment effort.“

Another technical question for you: I understand that most of the separative work takes place going from natural to LEU in terms of the absolute amount of U238 removed. However, as U-238 is removed, do diminishing returns kick in at some point? In other words, as the ratio of U235-U238 goes up, does it become more difficult to remove the U238 as it diminishes in relative quantity?

Altho a clandestine operation is a possibility, my calcs do not have to assume that.

The nightmare of possessing ANY enrichment capability is that one can stay “kosher” (and even intend on staying kosher) indefinitely, produce “harmless” LEU.

The terrible danger is the possession of LEU, whether homegrown or imported, and ANY enrichment tools (calutrons, AVLIS, centrifuges, vortex tubes, supersonic nozzles, thermal diffusion columns, whatever)

Consider my calcs another way. The Iranians could produce ONLY LEU till they have accumulated the SWUs (about 4-5,000). At no time do they need to produce one smidge of HEU (nor even desire to.)

But…
Any time after that, Iran can either overtly breakout and re-jigger the cascades to upgrade the innocent LEU to HEU or they can divert the LEU feedstock to a clandestine plant (or trickle the LEU gas out gradually). Remember much more that 3/4 of the required enchichment work is already stored in the LEU. (That’s the counterintuitive aspect of enrichment)

At that time, my second calc kicks in, the 3 months LEU to a bomb.

Bottom line is

show clear intent to weaponize

does not necessarily obtain.

Analogously (sp?) consider Germany’s bomber development pre-war. A fleet of high quality airliners and cargo planes were developed, staying within treaty obligations.

When war came, the planes were rapidly modded as bombers.

It seems to me both those scenarios would show the world exactly what Iran was up to. Since only part of the NIE’s have been leaked/released, I’m beginning to wonder if the IC figures assume a clandestine program and not one that relies on safeguarded facilities and material.

Although I don’t dispute your figures, I think the chance that Iran would actually pursue such courses of action would be minimal since doing so would show clear intent to weaponize and give the US and others ample cause and opportunity to destroy the facilities before that 20kg HEU is produced.

Also assume that the 2100 centrifuges at the FEP, running or under constuction, are all that they can muster. Let us finally assume that they can only run them 75% of the time on average.

What is the proliferation bottom line?

It takes 4000 SWU to produce 20 kilograms of 90% enriched uranium. 20kg of HEU is suficient for one very conservative 1st generation atomic bomb, or several higher tech bombs.

The Iranium FEP would (using my parameters) produce a bombs worth by December of 2008. Compare that to the ‘official” estimates of 2012-2015.

Remember my calculations are biased heavily towards poor perfomance from the Iranian operations.

Just for giggles (altho I am sure the Israelis have done the math, and are not amused), let us assume that the Iranians decide to screw the UN and divert the fresh fuel the Russians will deliver for Bushehr.

With the performance I specified, Iran, with only 2100 centrifuges, produce a bomb in just 3 months.