Brian Ross at ABC News reports that “Iran has more than tripled its ability to produce enriched uranium in the last three months, adding some 1,000 centrifuges …” and adds that “Iran could have enough material for a nuclear bomb by 2009.”
Hang on there.
The US intelligence community, on the other hand, is sticking by its 2012-2015 estimate. Sheila MacVicar at CBS News reports that “neither the CIA, the Defense Intelligence Agency, nor the Director of National Intelligence have changed their estimates of when Iran could have a nuclear weapon. The time frame most often mentioned is 2012-2015.”
So what’s up?
They Have to Actually Work To Be Scary
Well, Iran may have installed 1,000 centrifuges, but that doesn’t mean Iran can operate them.
David Albright, the expert that Brian Ross quoted, was actually much less alarmist than the ABC story. “If … they get the centrifuges to work and actually enrich uranium on a distinct basis,” Albright said, “then you’re looking at them having, potentially having enough highly enriched uranium for a nuclear weapon in 2009.”
That is a pretty big “if” and the subject of today’s blog post.
Iran still cannot operate its current cascades on a continuous basis. Instead, the IAEA reports that Iran continues to feed UF6 “intermittently” into single, 10-, 24- and 164 machine cascades.
David and Jackie Shire recently did a really cool calculation based on Iran’s UF6 consumption to show that the centrifuges are only operating about 20 percent of the time (say 5 hours a day).
So cool, I decided to do it myself.
The IAEA has published detailed data about how much UF6 Iran has consumed during various operating periods for its 164 centrifuge cascades (the amount of UF6 introduced into single machines and 10- and 20- machine cascades is probably trivial):
- “Since 6 June 2006, centrifuges in the single machine test stand and in the 10-machine and 20-machine cascades have been run mostly under vacuum, but with the feeding of UF6 into single machines of the 20-machine cascade for short periods of time. Between 6 and 8 June 2006, the 164-machine cascade was also tested with UF6. Further testing of the 164-machine cascade with UF6 was carried out between 23 June and 8 July 2006. During these tests, a total of approximately 6 kg of UF6 was fed into the machines and enriched to various levels of U-235. The feeding of UF6 into the 164-machine cascade was resumed on 24 August 2006.”
- “Since 31 August 2006, centrifuges in the single machine test stand, and the 10-machine, 20- machine and first 164-machine cascades at the Pilot Fuel Enrichment Plant (PFEP) have been run, mostly under vacuum, with UF6 being fed during intermittent periods. The installation of the second 164-machine cascade was completed and, on 13 October 2006, testing of the cascade with UF6 gas was begun. Between 13 August and 2 November 2006, a total of approximately 34 kg of UF6 was reported by Iran as having been fed into the centrifuges and enriched to levels below 5% U-235.”
- “Between 2 November 2006 and 17 February 2007, a total of approximately 66 kg of UF6 was declared by Iran as having been fed into the process and enriched to levels below 5% U-235. The environmental sample results thus far indicate a maximum enrichment of 4.2% U-235 in the first 164-machine cascade.”
You can combine this with the technical information provided by Iran Atomic Energy Organization Director Gholam-Reza Aqazadeh:
In the 164 chain, the maximum amount of material that we can feed the system is 70 grams an hour, with a 10 percent product of 7 grams. The product is 7 grams. Some 93 grams remain. When a series is operating 24 hours you have to multiply 24 by 70 grams. This is the total product of one series.
To recap. We have the dates of operation, the amount of hex consumed and the feed rate.
Let’s put that in a chart!
|Dates of Operation||#||Hours||UF6 Consumed (kg)||Operating Time (%)|
|6-8 Jun/23 Jun – 8 Jul||1||456||32||6||18|
|24 Aug – 2 Nov||1||1752||158||35||22|
|13 Oct – 2 Nov||2||504|
|3 Nov – 16 Feb||1||2,568||360||66||18|
”#” indicates whether the cascade is Iran’s first or second 164-centrifuge cascade.
I made slightly different assumptions that David and Jackie about the dates of operation, but the result is the same. Iran operates is centrifuges about 20 percent of the time, on average about 6 days a month (or, again on average, five hours a day).
Workin’ Hard or Hardly Workin’?
One hypothesis is that Iran runs the centrifuges for awhile, they crash, Iran fixes them, rinse, repeat. We know that Iran had a big crash back in April 2006. Maybe that wasn’t the last.
A second possibility is that Iran is deliberately limiting the operations, keeping the centrifuges spinning empty in a vacuum. One reason might be to diffuse diplomatic pressure. Another explanation, which intrigues me, is that Iran is husbanding a limited supply of Chinese hex (UF6).
China sold Iran about 1000 kg of hex in 1991. China was also building Iran an uranium conversion plant at Esfahan, before the Clinton Administration—in a very good bit of diplomacy—stepped in to convince the Chinese to cut-off assistance. (One result is that the Iranians rely on a crap indigenous pulse columns. More on pulse columns.)
Iran has, apparently, been using the Chinese hex because their own UF6 contains impurities such as molybdenum that “plate out” (or collect on the walls) while the centrifuges spin, causing them to become unbalanced and crash. In fact, McVicar quotes a “Western diplomat” describing Iran’s “yellowcake” as “crap” and “full of impurities”. One wonders if that diplomat meant the hex?
As one can see from the table above, two continuously operating 164 centrifuge cascades would exhaust 1 ton of UF6 in about 10 months. So, if Iran still can’t make clean UF6, then they’ve got to be very careful with that supply of Chinese hex. And perhaps that explains why the IC is sticking with the 2012-2015 date.
Anyway, I don’t have any inside information, just a guess.
(Hat tip to SPK for kicking my butt to write this.)
Update Andrew Foland is understandably appalled by the opening jibberish that centrifuges “separate radioactive particles from the raw material.”