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NuclearIran FAQ

How many centrifuges are currently operating in Iran?

As of August 2008, Iran has installed some 4,000 centrifuges of the early generation P-1 type at the main Natanz Fuel Enrichment Plant and is operating approximately 3,800 with uranium hexafluoride (UF6). It is experimenting with more advanced centrifuges at the Natanz Pilot Fuel Enrichment Plant.

How much uranium has Iran enriched?

Iran has produced limited quantities of low enriched uranium (LEU), the type suitable for being fabricated into fuel for a reactor. Iran has not produced any weapons usable or high enriched uranium (HEU). As of August 2008, it has accumulated approximately 225-250 kg of LEU, and is believed to be accumulating LEU at a rate of approximately 1 to 1.2 kg per day. This is well below the stated capacity of Iran's centrifuges at Natanz and indicates that Iran has encountered technical difficulties in operating the centrifuges. It also reflects, however, gradual improvement in centrifuge operations since the start of enrichment in early 2006.

What's the difference between a P-1 and P-2 or IR-2 centrifuge?

A P-1 centrifuge is essentially a replica of Pakistan's first centrifuge design. Consisting of a two meter-long aluminum rotor, it can rotate at peripheral speeds of up to 350 meters per second. A P-2 or IR-2 centrifuge is a more advanced Pakistani design, consisting a one meter-long maraging steel rotor capable of peripheral speeds of up to 485 meters per second. The IR-2 designation refers to the second generation of Iranian centrifuges currently under development at the Natanz Pilot Fuel Enrichment Plant and are modified from the original P-2 design, which were made with maraging steel rotors. Iran's IR-2 centrifuges are shorter, consisting of one meter-long carbon composite rotors with no bellows.

What is a SWU?

Separative Work Units or SWU are a unit of measurement given to a centrifuge's ability to separate the fissile U-235 isotope from the U-238 isotope. In a spinning centrifuge, the lighter U-235 isotope will separate from the heavier U-238 isotope, with the U-235 gravitating toward the center of the rotor tube. The capacity of a machine to accomplish this separative work is expressed as SWU. According to the late Stanford physicist Robert Mozley, a centrifuge’s separative power is theoretically linearly dependent on the centrifuge rotor’s length and dependent on the fourth power of the rotor’s peripheral velocity (in practice, the degree of these relationships somewhat vary). Iran's P-1 centrifiges are estimated to have a maximum SWU of 3, and appear to be working at a level of between 1 and 2 SWU per year. For comparison, state-of-the-art centrifuges in operation in the United States and Europe boast SWU of between 40 and several hundred.

Not to overly complicate the explanation, but it is important to understand the relationship between SWU and the "tails" or waste remaining after enrichment, in particular how much U-235 remains in the waste stream. Tails are the centrifuge's waste stream of U-238-rich gas that concentrates around the outside walls of the centrifuge and is withdrawn from the bottom of the machine. This stream contains trace quantities of U-235. A "tails assay" refers to a measurement of the percentage of U-235 remaining. By shifting the feed levels and tails assay, a centrifuge cascade operator can decide how much SWU to expend (within the limits of the actual centrifuge).

Canadian-based Cameco provides a very helpful illustration of SWU and how operators vary SWU to their advantage using an orange juice analogy:

"Let's assume you are in the freshly squeezed orange juice business. By deciding first how much juice you are prepared to leave behind in the pulp, you can then decide the optimum balance between the number of oranges you require and the effort required to squeeze them. If oranges are cheap and the cost of squeezing is high you are less concerned with how many oranges you use, but you want to make your orange juice with the least amount of squeezing. If oranges are relatively expensive and the squeezing process is cheap, you will minimize costs by squeezing fewer oranges more times to get the same amount of juice.

Now think of the oranges as uranium and the effort to squeeze them as SWU. If the price of uranium is relatively low, then you will use more uranium and less SWU to enrich the UF6. If the price of uranium is high and SWU is relatively cheaper, you will use more SWU and less uranium. Enrichment is measured both as the percentage of U-235 in the product and in the depletion. So the percentage of U-235 left behind in the tails assay is critical to the calculation of enrichment. The reactor operator always starts with the tails assay to find the best combination of UF6 feed and SWU."

If the 2007 NIE says that Iran no longer has a nuclear weapons program, why is is still an issue for the UN Security Council?

A copy of the 2007 National Intelligence Estimate on Iran's Key Judgments can be found here. The NIE finds "with high confidence" that in the fall 2003, Tehran halted its nuclear weapons program and assesses with "moderate confidence" that Tehran has not restarted its nuclear weapons program as of mid-2007, while acknowledging it does not know Iran's current intentions. The NIE appears to define narrowly the issue a nuclear weapons program in terms of weapon design and fabrication, and concludes reasonably that there is scant evidence such a program is currently underway.

United Nations Security Council actions have been in response to reports that Iran violated its IAEA safeguards obligations. Its initial resolution in July 2006, was precipitated by an IAEA Governing Board resolution raising doubts about the "exclusively peaceful nature" of Iran's nuclear program, along with its decision to abandon implemnetation of the Additional Protocol and restart work at the Natanz enrichment plant. A summary of Iran's safeguards violations can be found in the November 2004 IAEA report (see paragraph 86). Iran argues that these violations are in the past and that outstanding issues have now largely been addressed through the process established in an IAEA-Iran workplan. This is true in part, but as of September 2008, Iran had still to account for and explain a series of documents detailed in the annex of the May 2008 IAEA report pointing to nuclear weapons-related research. These outstanding issues, in addition to Iran's continued refusal to suspend uranium enrichment and construction of the heavy water reactor, and adhere to the Additional protocol, form the basis of continued UN Security Council action.

What is the Additional Protocol? If it's voluntary, why should Iran be penalized for not adhering to it?

Our friends at the Arms Control Association have an excellent fact sheet explaining the 1997 Additional Protocol, which was born in the aftermath of North Korean and Iraqi nuclear revelations and a desire to expand the IAEA's ability to detect safeguards violations, improve monitoring capabilities and inspection access. While true that the Additional Protocol is voluntary, it is adhered to by the vast majority of NPT members and widely viewed as establishing a new norm in establishing the peaceful nature of nuclear programs. As of May 2008, 88 NPT members have concluded additional protocols that are now in force while another 28 have signed them and are awaiting ratification. A current list of signatories and parties to the AP can be found on the IaEA's website here.