Technical Difficulties: IR-1 and IR-2 Centrifuges
IR-1 or P1 Centrifuges
During a March 2008 visit to the underground plant in Natanz, President Ahmadinejad, accompanied by officials and journalists, walked past rows of IR-1 type centrifuges. These first-generation centrifuges were developed in Iran based on a Pakistani model known as the P1. The centrifuges consist of a tube about 2 meters high containing an aluminum rotor spinning at extremely high speeds, into which uranium hexafluoride is introduced. By spring 2009, 7,000 of these centrifuges had been installed and had enriched 1.2 tons of uranium to 4%.
© Photo: Iran’s Presidency Office/European Pressphoto Agency
Uranium enrichment requires extensive expertise and high-quality materials. Iran did not choose the easiest or fastest route if its aim is to build a bomb.
The Iranian program relies on two types of centrifuges, known as IR-1 and IR-2. The first-generation IR-1 centrifuges, operating in Natanz, were developed from a Pakistani model. The development of these centrifuges was laborious: 7,000 were installed by spring 2009, compared to 3,000 in 2007, far fewer than the 54,000 planned in 2006. Iranian engineers encountered numerous setbacks in developing these centrifuges because the material used for the rotors had to withstand forces tens of thousands of times greater than gravity.
IR-2 Centrifuges: Carbon Fiber Rotors
At the pilot enrichment facility in Natanz, located in non-underground buildings, Mr. Ahmadinejad examines the carbon fiber tube that forms the rotor of a new generation of domestically manufactured centrifuges, called IR-2 (Iranian second generation). The rotor of these centrifuges is about 1 meter long—half the length of the IR-1 centrifuges—but is said to spin twice as fast. The carbon fiber rotor is reportedly much more resistant to centrifugal forces than the special steel initially considered.
© Photo: Iran’s Presidency Office/European Pressphoto Agency/NY_Times
Gholamreza Aghazadeh, the former head of the Iranian Atomic Energy Organization, recounts: “Our machines were breaking down frequently in the early days of the program. A study showed that clusters of microbes inadvertently left by the hands of technicians assembling the centrifuges were the cause. This tiny amount of microbes was enough to unbalance the rotation and destroy the machine. By destruction, we mean that the machine was reduced to powder.”
These difficulties led Iran to develop a new type of centrifuge, known as the IR-2, based on the second-generation Pakistani P2 centrifuge model. An ultra-resistant steel rotor made it possible to increase enrichment capacity by spinning faster while reducing the risk of destruction. But such steel was difficult to produce. Iran then developed its own model by replacing the steel rotor with carbon fiber—a material incredibly strong for its weight.
In September 2009, the Iranian Atomic Energy Organization (IAEO) announced that its scientists had succeeded in producing a new, more efficient generation of centrifuges.
Slowed Production
By the end of February 2010, during a White House briefing, senior administration officials declared they had evidence that Iran was struggling to keep its enrichment equipment operational. Thousands of centrifuges installed at Natanz, its main enrichment site, were not spinning. The Obama administration stated that Iran was producing only 100 grams of enriched uranium per day and that even if this capacity were quadrupled, it would still take years to produce enough material for a weapon.
Technical difficulties or sabotage? In 2008, President George Bush, after rejecting a secret Israeli request for bunker-buster bombs capable of destroying the underground Natanz complex, reportedly told interlocutors—according to senior U.S. and foreign officials—that he had authorized covert sabotage operations to derail Iran’s alleged development of nuclear weapons.
The possibility of sabotage was reinforced in November 2010 when reports emerged of a computer virus called STUXNET, allegedly designed to disrupt the operation of the centrifuges by altering their spinning speeds. The IAEA noted that Iran had suspended enrichment for several days following electrical malfunctions, although it was unclear to what extent these incidents were linked to the virus. Shortly afterward, on November 29, two nuclear scientists were targeted by bomb attacks from motorcycle-riding assailants on their way to work. One scientist was killed (the third in two years) and the other injured. Authorities suspected Mossad and the CIA were behind the attacks.
Despite the expertise gained by Iranian engineers, months of difficult research and development were still needed before these centrifuges could be used on a large scale, which was expected to quadruple enrichment capacity.
In January 2013, Tehran informed the International Atomic Energy Agency (IAEA) of its intention to use IR-2m type centrifuges in Unit A-22 of the Natanz enrichment facility. This new generation of more modern centrifuges, designed for low-level enrichment below 5%, was not intended for the Fordo site. The installation was to be gradual. A first batch of 180 IR-2m centrifuges was reportedly installed in February 2013.
Before stepping down after the election of Hassan Rouhani as the new president, Mr. Fereydoun Abbasi Davani, head of Iran’s nuclear program, stated on August 17, 2013, that there were approximately 18,000 centrifuges, with more than 10,000 in operation—figures confirmed by the IAEA. Among the 18,000, about 1,000 second-generation centrifuges were far more efficient.
After the Iran Nuclear Deal of July 14, 2015
One clause of the agreement imposed a significant limitation on Iran’s enrichment capacity, requiring it to stop using its most advanced centrifuges. For four years, IAEA inspections confirmed that these obligations were respected. This has no longer been the case since August 2019. In response to severe economic sanctions imposed by the Trump administration, which withdrew from the agreement, Iran announced it was reactivating advanced centrifuges, though it remained under IAEA oversight and claimed the breach was reversible.
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