Wednesday, April 12, 2006

Iranian Nuclear Speculations

I will have to somewhat disagree with Juan Cole's Informed Comment

I don't know Iran; I don't have access to any classified information on nuclear weapons.
I do know something about physics...

First of all, Iran is clearly been working on putting together a full nuclear cycle for about 20 years

That means they want to be able to do it all in-house: mining, enrichment, burning, plutonium extraction, power generation and bomb production.

It is clear that they did the science in the early-to-mid-90s, they tested centrifuges, built small high neutron flux reactors and got small amounts of plutonium extracted.

So, they learned Pu chemistry, what isotopes you get with different burns, and maybe some metallurgy.

They then set up centrifuge halls and played with an AVLIS (laser isotope separator).

They also ordered a 1GW reactor from the russians, and refined uranium oxide (aka "yellowcake") into both uranium tetrafluoride, uranium hexafluoride and uranium metal.
Supposedly several tons of uranium oxide were processed.

Now: there are two ways to make bombs, at the basic level.
Get highly refined uranium-235 metal; or, fairly pure plutonium-239. In kilogram quantities.
U-235 bombs are simple and need not be tested. "A grad student could make one of those".
Pu-239 bombs are notoriously fickle and are said to need testing (although maybe not so much any more...)

If you want to go on to thermonuclear weapons, then you want Pu-239 production, and either some genuis level physicists assisted by good engineers (of which Iran has plenty), or help from someone who already figured it.

So... the claim is that Iran is about a decade away from having a nuclear bomb.
This is not necessarily true for several reasons.
What is probably true is that Iran is about a decade away from having a totally in-house bomb production line capable of providing everything for "many" bombs per year.
For that you want lots of yellowcake, a high power reactor to breed plutonium, and a refining facility to supply the reactor.
You use the U-238 rejected from the enriched U-235 to breed plutonium in a neutron absorbing blanket around the reactor,
and you use the enriched U-235 to keep the reactor going. You can spin off some power either through dual use reactors (what the USSR and UK did) or purpose built faciltiies.

What could Iran do quicker:

1) they could have bought one-to-few bombs as insurance while they get production going.
These would be vulnerable, last reserve and well kept secrets unless a demo is required, until they could make their own replacements; they might even work if they tried them.

2) they could have partially enriched uranium as starting materal for their enrichment pipeline.
Well, we know they do, because the russian power reactor was supposed to come with a few tons for power production. This can be enriched much faster than native ore to bomb levels, and you only need to enrich a little bit of it (and add some unenriched back into the bulk, so enrichment levels appear high, just not as high as they used to be). This gets you a few U-235 bombs earlier than full processing, with much fewer centrifuges.

3) they could have small operational reactors (which they do) doing lab batch production of Pu-239 through U-238 irradiation between IAEA visits. Gets you small amounts, but doable, maybe, without IAEA catching you. Maybe enough for two bombs, one to test, one to save. Eventually.

4) Busherhr reactior is by various accounts either 80% complete, or been up and running for 1-3 years.
If they left the exterior partly built, but the core is running without several hundred MW of electricity coming out, then it
is probably in plutonium breeding mode.
It takes a few months to cycle the Pu out, so they could have done one-few production batches, enough for several untested bombs to be assembled. If it is up and running for 1+ year.

PS: 5) Iran built a heavy water production facility, if they successfully built a hidden small heavy water reactor burning unenriched or low enriched uranium, then they could have been doing small scale Pu production for a few years. Big If.

The last option is the worst-case scenario.
If Israel or US has half-decent human or technical intelligence they know whether Bushehr is running, and someone within the government still knows what that could do, I think. At least over in Israel.
Israel is getting very antsy about this whole thing.

I'm thinking > 50% odds of a large airstrike in late April or early May this year.
It will be telegraphed, but "we" collectively will not believe they're actually going to do it, 'cause it is "completely nuts".

Either way Iran will be a nuclear power by 2015 and quite possibly much earlier.
They may become a very irate nuclear power, or merely just a paranoid one. Depends.

PS: argh, double post. Bad blogger...

IAEA has Bushehr-1 connecting to the grid in October 2006
If they are really planning to hook-up by Oct, then the fuel is either being delivered no later than, er, now; or, it is already there. News reports conflict about whether the fuel of enriched uranium was shipped or held up last year. Which is the case is very important for Iran's status.
If I were an Iranian engineer, I would have no-load runs several months before planning to go on the grid.
If I were an Iranian weapons designer I would do short burns and reprocess the blankets in those months, which means Iran could have started extracting Pu sometime between late 2005 and Real Soon Now.
If I were a Russian engineer I would go home now.


Anonymous Anonymous said...

About 65 kg of HEU is needed for a rudimentary gun-type design, 20kg of HEU with a primitive implosion design and 8-10kg with advanced implosion design.

For a good weapon-grade Pu, the numbers are 7kg and 1-3kg (for advanced implosion design, depending on required yield).

If they can manufacture tritium (in a reactor), adding about 0.5g of T2 as D+T mix into the cavity of the Pu-core could raise the yield of implosion bomb from 20 to 60kt.

I don't expect any country to start with thermonuclear weapon right of the bat - design of a thermonuclear weapon requires detailed radioopacity studies and small+powerful thermonuclear primary (=optimised implosion design, preferably boosted)

if they use reactor-grade Pu obtained from light water-moderated reactor, they would need about 10kg and the bomb would be heavier, heat-producing and radioactive but they could still get full yield (20kt) out of it if they know what design changes to do. Without them, the yield would be somewhere in single kilotonns.

2:13 PM  
Blogger JasonSpalding said...

The Iranian President Mahmoud Ahmadinejad said “I declare here that the laboratory-scale nuclear fuel cycle has been completed and young scientists produced enriched uranium”. What was his definition of laboratory-scale? Laboratory scale characterization, small scale and pilot scale test method development.

2:14 PM  
Anonymous Anonymous said...

Nice post. Really impressive actually. I'm leaving more knowledgable regarding nuclear capacity. Also much more convinced there will be an attack in some form.

11:10 AM  
Blogger Steinn said...

the secret milkshake comments are the sort which can not be answered...
cf this cryptic link

But, yes. If Bushehr goes online, then 3 months later they should be able to pull out tens of kg of adequate purity plutonium through lab chemistry they have already tested.

My interpretation of "lab scale" is gram quantities.
As opposed to kilograms for production.
If you have many patient small labs you get somewhere interesting eventually, if you want to.

I am quite worried that the US will launch an airstrike either before Bushehr is fueled or before the fuel elements can be pulled out for reprocessing.

Strangely enough both sides are being "rational" when considering only their own perspective. Looking at them from the outside, the irrationality seems apparent.
The World War I parallel are worrying, with cascading ultimata and posturing for internal consumption leading to unavoidable conflict.

4:03 PM  
Blogger Stephen said...

I got here from

From what they appear to have, assuming they don't worry about compact delivery mechanisms, they probably have the capacity to build a bomb (low single digits) now.

I think you've hit the nail on the head with the rest of the analysis.

8:02 AM  
Anonymous Anonymous said...

You forget the option of going the Thorium way.
Simply put: By lowering Thorium down a reactor the neutron radiation with transform it into U-233, that is 40x as energy-rich as U-235 and you get pure quality out of the reactor. No further enrichment or refinement needed and you only need approx 7-8 kg to make a Hiroshima size nuke, that's almost as good as Plutonium. You can also use U-233 as reactorfuel in lightwater-reactors to breed Plutonium or even more U-233 out of Thorium. And Thorium 3-4x as abundened in nature as Uranium.

11:47 AM  

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