Centrifuge Nuclear Technology Essay

I wrote about centrifuges a few weeks ago, and have learned some new, interesting things since then. John Krige, a professor at the History, Technology, and Society program at Georgia Tech, has two quite provocative articles  published about interactions between the US and the UK regarding centrifuges in the mid-to-late 1960s. They are worth your attention.

European centrifuges (URENCO)

Krige’s first article is “Hybrid knowledge: the transnational co-production of the gas centrifuge for uranium enrichment in the 1960s,” just published online (and forthcoming in print, I believe) in the British Journal for the History of Science (BJHS).1 As the title may tip you off, this is an article for a primarily history of science/science studies crowd, and speaks in that idiom. Don’t let the jargon scare you off, though: as far as the genre goes, it’s readable and the underlying point is an important one. It concerns the interchanges of centrifuge information between the US and the UK in the early 1960s, which were done under the 1955 US/UK Agreement for Co-operation on the Civil Uses of Atomic Energy, and their consequences when the UK, Netherlands, and Germany decided to go into a cooperative, profitable effort to produce a commercial centrifuge enrichment plant in 1967. (What eventually became URENCO, I believe.)

The US thought this was a somewhat dodgy enterprise — they really didn’t think centrifuges would be as profitable as gaseous diffusion, their chosen enrichment method, but the UK disagreed — but were happy to support it, so long as the UK didn’t give away any “restricted data” that had been produced by the US. And there’s the rub: the UK and US had been exchanging information for a long time, and the UK really thought that it had produced a completely indigenous design (taking off from Gernot Zippe’s unclassified contributions) without any significant US “data” in it. The US disagreed and threatened to cut off all future US-UK exchanges if the latter didn’t let them verify to their satisfaction that there wasn’t any US data in the design. The UK, for its part, thought that it had a really superior centrifuge design compared to the US, and were worried that if the US claimed parts of it were “theirs,” it would completely muddy up their attempts to get clear of the US monopoly on the enrichment of uranium.

In the end, the US decided the UK design was kosher enough, and all was well with them. But it’s a fascinating (and to me, totally unknown) episode in the US-UK “special (nuclear) relationship,” one which really highlights some fundamentally interesting aspects of both US and UK atomic policy, and the fundamentally transnational (as Krige puts it) nature of modern centrifuge development (an Austrian working in the USSR develops technology that he then further works on in the US and the UK which is then turned into a company with the UK, Germany, and Netherlands, etc.). It also gets into some good history of science questions about how one identifies the source of any given piece of design or machinery — and how difficult that can be.

US centrifuges (Piketon)

The second paper by John is “The Proliferation Risks of Gas Centrifuge Enrichment at the Dawn of the NPT: Shedding Light on the Negotiating History,” just published online (and imminently forthcoming in print) in The Nonproliferation Review.2 This essay was a winner of an annual prize by the journal (one of two) and John gave a presentation on it last Thursday at GWU (which you can watch online — John is the first of the two speakers/winners, after the introduction by Stephen Schwartz).

In this paper, John tackles the question of the apparent ambiguity in the 1968 Nuclear Non-Proliferation Treaty (NPT) about whether centrifuge-style enrichment activities (like that currently pursued by Iran) were considered a protected form of “peaceful use” to be allowed and encouraged. It has been speculated that at the time of the treaty’s writing, the risks posed by centrifuge enrichment — which is a lot smaller scale than gaseous diffusion plants, and thus easier to hide or protect — weren’t considered by the NPT drafters, and thus represent an unanticipated “loophole” in the treaty terms.

What John has found is that while centrifuges were not discussed in the official record, they were discussed extensively on the backchannel by the US and the UK.In particular, the UK was extremely worried about the proliferation potential for the gas centrifuge. They, after all, were pursuing the technology themselves, and knew it could be a potent game-changer in breaking the gaseous diffusion monopoly. They wondered if it would not be the angle pursued by a future proliferating state, and conveyed as much to the US.

The US was itself comparatively unworried. It thought that it (and its European allies) could control the spread of centrifuge technology through classification and export controls, and still were dubious that the centrifuge would play a bit role in world affairs anytime soon. I pushed John on this at the talk (you can hear me asking a rambling question about this at the 1:41:24 mark in the video linked above), and he elaborated in a way that I thought was more compelling: the US was weary about getting the treaty signed (they had finally gotten the Soviets on board, and the NPT treaty process was over a decade old at that point), and were worried that any attempt to modify the treaty at that point would bog it down for years to come. Furthermore, the UK was engaging in said partnership with the Dutch and the West Germans, and the US really wanted to make sure the Germans were still on board with the NPT.

(The West Germans were really not too pleased with the NPT and it was a huge hassle to get them to ratify it; like many nations, they appropriately saw it as an infringement on their national sovereignty and their future security options. Of course today the Germans are big supporters of the NPT — it’s interesting how these things switch around, depending on where you are sitting at the time.)

The UK didn’t push the matter, because it didn’t want to rankle the treaty process, either, and because it too wanted to profit off of the centrifuge. So both the US and UK let the matter slide. (I think John’s work highlights something that I’ve been thinking for a short while now: there’s a lot of potential for a “deep” history of the NPT, one that goes beyond the open record.)

Iranian centrifuges (Natanz)

Whether this affects one’s interpretations of the NPT today — John thinks that there is basically no real legal argument against Iran being able to develop centrifuges, and certainly no argument that the early NPT drafters had left an unanticipated “loophole” in place that anyone is taking advantage of — seems to me, someone not at all versed in international law, to be unclear. (Do off-the-record conversations between two parties count towards later interpretations of a treaty’s intent?) But either way, it’s a fascinating story. The apparent US lack of concern about specifically centrifuge proliferation has come back to haunt it, these decades later.


Tags: 1960s, Business and industry, Centrifuges, Proliferation, United Kingdom

This entry was posted on Monday, June 25th, 2012 at 9:39 am and is filed under Meditations. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.

Citation: Alex Wellerstein, "More on Centrifuge History," Restricted Data: The Nuclear Secrecy Blog, June 25, 2012, accessed March 11, 2018, http://blog.nuclearsecrecy.com/2012/06/25/more-centrifuge-history/.

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This is a brief history of Iran's progress toward the ability to build a nuclear weapon. The emphasis is on achievements, rather than motives. The achievements presented here have been cataloged primarily by the International Atomic Energy Agency (IAEA).

Following a decade of steady expansion and years of diplomacy to halt the progress of Iran’s nuclear program, Iran agreed to an historic accord with six major world powers on July 14, 2015.  The agreement, known as the Joint Comprehensive Plan of Action (JCPOA), substantially reduced Iran’s known nuclear capability in return for sanctions relief. Under it, Iran has dismantled thousands of uranium-enriching centrifuges, shipped tons of low-enriched uranium to Russia, destroyed the core of a heavy water reactor capable of producing plutonium, and agreed to reconfigure the reactor so as to produce less plutonium.  Before the agreement, Iran might have—by illicit steps—been able to produce the fuel for a nuclear weapon in as little as a few months.  Now Iran would require about a year.  In addition, Iran has promised not to expand its capability beyond its present limit for at least ten years.[1]

The JCPOA was the culmination of years of controversy and diplomatic activity surrounding Iran’s nuclear program.  International interest in Iran was heightened dramatically in the summer of 2002, when the existence of two nuclear sites was revealed by an exiled Iranian resistance group.[2]  Within a year, the world realized that Iran had built or was building everything needed to produce enriched uranium, which could fuel nuclear weapons as well as nuclear reactors. The sites included a uranium mine at Saghand, a yellow cake production plant near Ardakan, a pilot uranium enrichment plant at Natanz, and a commercial-scale enrichment facility on the same site. In addition, Iran was continuing work on a 1,000 megawatt nuclear reactor at Bushehr and was building a heavy water production plant at Arak, next to which Iran planned to build a 40 megawatt heavy water reactor. Beginning in March 2003, following revelations that Iran had concealed nuclear work from the IAEA, the Agency began investigating Iran's nuclear history.[3]  The IAEA now has the responsibility of monitoring and verifying the nuclear-related provisions of the JCPOA.

Iran has long maintained that its nuclear program is benign, legal, and authorized by its membership as a non-nuclear weapon state in the nuclear Non-Proliferation Treaty (NPT), which guarantees its members the right "to develop nuclear energy for peaceful purposes."[4]  However, the United States has countered by contending that Iran has no need for nuclear energy and that its civilian energy program serves only to camouflage a nuclear weapon effort.[5] The JCPOA marks a shift away from this position, as the agreement will allow Iran to develop a commercial-scale uranium enrichment program after the first 10 years of the accord.

Early Nuclear Efforts

Under the Shah, Iran launched a series of ambitious nuclear projects that relied on assistance from the United States and Europe. According to Akbar Etemad, the President of the Atomic Energy Organization of Iran (AEOI), from 1974 through 1978, Iran was already carrying out nuclear research and education at the University of Tehran when the NPT entered into force on March 5, 1970.[6] The work centered on a five megawatt research reactor supplied by the United States, which began operation in 1967.

By the mid-1970s, according to Etemad, Iran had launched an extensive nuclear energy program. In 1974, the Shah set the goal of producing roughly 23,000 megawatts of electrical power from a series of nuclear power stations within twenty years. A host of contracts between Iran and nuclear suppliers in Europe and the United States followed: Iran struck a deal with Kraftwerk Union (KWU, a Siemens subsidiary) of then-West Germany to build two 1,200 megawatt reactors at Bushehr[7] and negotiated with the French company Framatome for two additional 900 megawatt reactors. In 1974, Iran reportedly invested $1 billion in a French uranium enrichment plant owned by Eurodif, a European consortium.[8] Etemad also described Iran's indigenous work on the nuclear fuel cycle in the 1970s, including plans for a new nuclear research center at Isfahan and the exploration of uranium mining and ore processing.

The 1979 Iranian revolution halted this work for a number of years. The war with Iraq, which began in 1980, consumed resources and damaged Iran's existing nuclear infrastructure. The two power reactors under construction at Bushehr were bombed several times,[9] after which Siemens abandoned the project.

During Akbar Hashemi Rafsanjani's presidency, beginning in the late 1980s, Iran's nuclear program revived. By the early 1990s, as Iran recovered from the war with Iraq, its nuclear program was once again moving forward, based on assistance from Russia, China and Pakistan. With China, Iran signed two nuclear cooperation protocols, in 1985 and again in 1990. And in 1995, Iran concluded a protocol of cooperation with Russia to complete the construction of the reactor at Bushehr and possibly supply a uranium enrichment plant.[10] Some of the items originally contemplated in these deals, like the enrichment plant, were never delivered as a result of pressure from the United States. Others, like Bushehr, served as a screen behind which Iran obtained sensitive equipment that would not be sold on its own because of its bomb-making potential. Throughout the 1990s, entities in Russia and China continued to help Iran, despite occasional pledges from their governments to curtail nuclear assistance. During this period, Iran is also believed to have received uranium enrichment technology through the black market network run by Pakistani scientist A. Q. Khan.[11]

The deals-official and illicit-struck by Iran in the 1990s allowed it to make important progress in its indigenous nuclear effort. By 2003, when the scope of its nuclear program became clear, Iran had already made progress towards mastering the technology needed to make enriched uranium[12], one of the materials that can be used to fuel a nuclear weapon. Because many of its nuclear experiments were conducted in violation of its inspection agreement with the IAEA, Iran was forced to provide new information on this work and to explain its purpose. Iran's explanations, along with the results of the IAEA's inspections, were published in a series of Agency reports beginning in June 2003.[13]

Seeking Nuclear Fuel

Iran's pursuit of nuclear expertise has taken it down two differnt pathways to nuclear weapon fuel: uranium enrichment and spent fuel reprocessing to recover plutonium.  These materials are "fissile" because they are unstable and fission, or split, when struck by neutrons. Both can fuel a nuclear bomb or be used as fuel in a nuclear power reactor. However, producing nuclear fuel, regardless of its ultimate use, is a difficult task.

The Uranium Path

The difficulty in producing a concentrated amount of uranium 235-the fissile form of uranium needed to fuel a nuclear weapon-is that natural uranium contains only a small amount (.7%) of this isotope. Producing a concentrated amount of U-235 requires a series of steps that begins at the mine and ends with the production of enriched uranium fuel. Iran has sought to master each step in this process.

Mining and milling

Before uranium can be refined to fuel a reactor or a bomb, it must be mined. This is the first step in what is referred to as the "front end" of the nuclear fuel cycle. On February 9th, 2003, Iranian President Mohammad Khatami declared that his government intended to extract uranium from a mine at Saghand, in the province of Yazd.[14] The mine is a key part of Iran's plan to produce nuclear fuel indigenously. According to Dr. Ghannadi-Maragh, the Vice President of Iran's Atomic Energy Organization, the mine site consists of two deposits, with a combined reserve of 1,580,000 tons of uranium ore and an average grade of 553 g/tonne.[15]  The Saghand mine has an estimated annual production capacity of 50 tonnes of uranium, according to the IAEA.[16] The Gchine mine, located in the south of Iran near Bandar Abbas, has an estimated production capacity of 21 tonnes of uranium per year.  Iran reported that mining operations at Gchine started in July 2004.[17]  The reserve at Gchine is estimated at 40 tonnes of low but variable grade uranium.[18]

Once mined, uranium ore must be processed into a uranium concentrate called yellowcake. In February 2003, Iranian authorities admitted to producing yellowcake at a milling plant in Ardakan in Yazd Province.[19] The AEOI had approved the construction of a yellowcake production plant in 1994 and contracted with an Iranian company to build the plant in 1999.[20] The Ardakan Yellowcake Production Plant has a design capacity that corresponds to that of its associated mine at Saghand, 50 tonnes of uranium per year.[21]

China is believed to have been the source of the Saghand mining technology. Iran has admitted that Chinese experts participated in detailed exploration work for the mine. Experts from China's Beijing Research Institute of Uranium Geology have conducted scientific exchanges with Iranian nuclear scientists and have explored in Iran in the past.


Once mined and concentrated into yellowcake, the uranium must be converted to a gas. This gaseous form of uranium, called uranium hexafluoride (UF6), serves as the feedstock for centrifuges, which then enrich uranium to a form suitable for either reactor fuel or nuclear weapons. In 2000, the Iranian government informed the IAEA that a plant for uranium conversion was being constructed at Esfahan (Isfahan).[22]  In a speech to the IAEA in May 2003, Gholamreza Aghazadeh, head of the AEOI, said that the conversion facility, which is located at the Esfahan (Isfahan) Nuclear Technology Center (ENTC), would be used to convert yellowcake into UF6.[23]

The IAEA received preliminary design inforatmion on the Uranium Conversion Facility (UCF) at Esfahan in July 2000 and updated design information in April 2003.

According to the design information provided by Iran, the conversion plant was intended to have a number of process lines for transforming uranium compounds.  The planned process lines included steps for converting uranium ore concentrate into UF6 (yielding 200 t annually of UF6 ); converting low enriched UF6 into UO2 (yielding 30 t annually of UO2 enriched to 5% U-235); converting depleted UF6 into uranium tetrafluoride (UF4) (yielding 170 t annually of depleted UF4); converting low enriched UF6 into low enriched uranium metal (yielding 30 kg annually of uranium metal enriched to 19.7% U-235); and converting depleted UF4 into depleted uranium metal (yielding 50 t annually of depleted uranium metal).[24]

Iran’s activities at UCF have focused on the first two of these process lines: the conversion of uranium ore concentrate into UF6 and the production of UO2.  The other process lines are still planned.[25] Iran began conducting hot tests at UCF in May and June 2004, generating about 30-35 kg of UF6.[26] Since the start of conversion activities at UCF, Iran has produced 550 tonnes of natural UF6 at UCF, of which 185 tonnes have been transferred to the Fuel Enrichment Plant at Natanz.  Iran has also produced 13.8 tonnes of natural uranium in the form of UO2 at UCF, of which 13.2 tonnes have been transferred to the Fuel Manufacturing Plant (FMP) at Esfahan.  In November 2015, the IAEA reported that Iran has neither produced UO2 at UCF nor transferred any UO2 from UCF to FMP since January 2014.  Iran is continuing R&D activities at UCF on the recovery of uranium from scrap generated from conversion activities.[27]

China is widely acknowledged to be the source of information for the conversion plant. As part of a 1997 agreement with the United States to prevent new cooperation and to halt all existing projects with Iran in the nuclear field, China pledged to cancel a project to help Iran build a conversion plant. Despite this promise, however, China appears to have provided Iran with a blueprint for the plant. Iran admits that the conversion plant is based on a design provided by a foreign supplier in the mid-1990s. China is also believed to have given Iran design information and test reports for equipment.[28]

In addition, China supplied uranium compounds in 1991, which Iran did not declare to the IAEA and which allowed Iran to conduct laboratory tests of the processes to be used in the conversion plant. These compounds included 1000 kg of UF6, 400 kg of UF4 and about 400 kg of natural UO2.[29]


After uranium is mined and converted into a gaseous form, the U-235 isotope must be separated from the more abundant U-238 isotope in a process called enrichment. But because these two uranium isotopes are identical chemically, they cannot be readily separated by a simple chemical reaction. They must be parted by exploiting the slight difference in their weights. Uranium enriched to between three and five percent U-235 is typically used to fuel power reactors of the type Iran is constructing at Bushehr; uranium enriched to 90% or more U-235 can be used to fuel nuclear weapons.

There are a number of different ways to enrich uranium. Iran has focused on gas centrifuge enrichment and has also experimented with laser isotopic separation.


Centrifuge separation works by passing UF6 through high-speed rotational machines called centrifuges. The different weights of the uranium isotopes cause them to separate, with the heavier U-238 being thrown to the outside of the centrifuge and the lighter U-235 staying nearer the inside. Centrifuges require several repetitions with the enriched product to reach the desired level of concentration; more repetitions are required to obtain a higher concentration of U-235, which is necessary to produce weapon-grade fuel.

Iran's centrifuge program was launched in 1985 at facilities controlled by the AEOI in Tehran.[30]  Around 1987, Iran received a centrifuge design through what the IAEA has termed a "foreign intermediary."[31]  During this first phase of Iran's centrifuge effort, Iran also obtained about 2,000 components from abroad.[32] According to a February 2004 Malaysian police report, Iran received two containers of centrifuge parts, worth $3 million, through the Khan network.[33]  This transfer allegedly took place between 1994 and 1995.[34]

In 1997, Iran moved its centrifuge development effort to the Kalaye Electric Company in Tehran.[35]  According to Iranian authorities, from 1997 through 2002, Kalaye was used to test and assemble centrifuges for uranium enrichment.[36]  In October 2003, after initial denials, Iran admitted that it had used 1.9 kg of UF6, allegedly imported from China in 1991, to test centrifuges at Kalaye.[37] This work took place between 1998 and 2002 and, according to Iranian officials, achieved an enrichment level of 1.2% U-235.[38]  The IAEA first visited parts of Kalaye in March 2003 and Agency inspectors were allowed to take environmental samples at the site during a follow-up visit in August 2003.[39] During this visit, inspectors noted that "considerable modification" had been made to the facility since their visit in March.[40]

Beginning in 2002, Iran's centrifuge enrichment program was moved to Natanz,[41] the location chosen for a 1,000 centrifuge pilot plant and a commercial-scale facility intended to house over 50,000 centrifuges. According to Iran, the Natanz site will produce nuclear fuel for power plants using uranium enriched from three to five percent U-235.

The Natanz site was revealed publicly in August 2002 by the NCRI[42] and first visited by the IAEA in February 2003. In his report to the IAEA Board of Governors in March 2003, IAEA Director General Mohamed ElBaradei stated that the site included a pilot plant that was "nearly ready for operation, and a much larger enrichment facility still under construction."[43]

Iran first used UF6 to test a centrifuge at the pilot plant in June 2003, and in August 2003 tested a ten-machine cascade using UF6.[44] Enrichment work at the pilot plant was suspended beginning in November 2003, following an agreement between Iran and Britain, France and Germany. However, Iran continued to manufacture centrifuge parts and assemble centrifuges at a number of workshops.[45]

The machines at Natanz are of an early European design, similar to the P-1 centrifuge that has been under the control of the Khan Research Laboratories (KRL) in Pakistan, and which was stolen from Western Europe's Urenco program during the1970s and 1980s. According to a paper presented by France at a Nuclear Suppliers Group meeting in May 2003, Iran was believed to have improved on the Pakistani design and achieved "a model effective enough to consider enrichment on an industrial scale."[46] Iran's first-generation centrifuge is referred to as the IR-1.

In addition to the IR-1 centrifuge, Iran has a program to develop more advanced models. Iran received a design for the P-2 in 1994 from what the IAEA termed "foreign sources."[47] The IAEA has concluded that Iran received the same drawings for the P-2 as Libya,[48]  which received the design, along with P-2 components, through the Khan network. The P-2 uses a maraging steel rotor with bellows and is similar to another early European centrifuge design.[49] According to Iran, mechanical testing of the P-2 rotors began in 2002,[50]  using carbon composite rotors manufactured domestically rather than rotors made with maraging steel, which Iran was unable to produce.[51] The AEOI contracted with a private company based in Tehran to produce the rotors and to conduct the tests, allegedly without using nuclear material.[52] Iran has procured magnets useful in the P-2 from Asian suppliers and has sought to acquire about 4,000 magnets suitable for the P-2 through a European intermediary.[53]

These investments in equipment and know-how  paid off. By the end of 2007, Iran had commenced feeding uranium hexafluoride gas into approximately 3,000 centrifuges it had installed at its site at Natanz. All were of the IR-1 variety. The number of these centrifuges then rose steadily. By late 2008 Iran had installed almost 5,000 centrifuges, and by August 2015, Iran had installed over 15,000 centrifuges and was feeding gas into more than 9,000 of them.  In February 2013, Iran began installing a more advanced centrifuge model at Natanz, referred to as the IR-2m.  By August 2015, 1,008 IR-2m centrifuges had been installed, though none had been fed with uranium gas. During this same period Iran made great strides in producing uranium hexafluoride at its Uranium Conversion Facility (UCF) in Isfahan. From March 2004 through February 2011, Iran produced a total of 371 tons of this material.[54]

The result was to enable Iran to produce, by November 2015, a stockpile of 8.3 tons of low-enriched uranium (enriched to 3.5% U-235), an amount sufficient to fuel seven nuclear weapons if further enriched to weapon grade.  Under the terms of the JCPOA, Iran was required to reduce its stockpile of low-enriched uranium to no more than 300 kilograms, a requirement Iran fulfilled by shipping most of its stockpile to Russia in December 2015.[55]

For the first 10 years of the JCPOA, Iran will be permitted to maintain no more than 5,060 IR-1 centrifuges at Natanz and will not be permitted to enrich uranium above 3.67 percent for the first 15 years.  All excess centrifuges were dismantled and stored at Natanz under IAEA monitoring.

Work at Natanz also included experiments at a pilot plant. These have concentrated on the development of more advanced centrifuges, including the IR-2m, IR-4, IR-5, IR-6, IR-6s, IR-7, and IR-8. Some of these machines have been tested with UF6. According to the terms of the JCPOA, Iran is permitted limited research and development activities and testing of these advanced centrifuge models for the first ten years of the agreement.  After ten years, Iran will be permitted to manufacture complete models of advanced centrifuges and begin installing and operating them at the Natanz facility.  After 15 years, Iran will be allowed to install and operate any type of centrifuge at any of its declared uranium enrichment facilities.  Iran’s aim is to make centrifuge operations entirely indigenous, developing not only centrifuge components but also measuring equipment and vacuum pumps.

The most sensitive endeavor at the Natanz pilot plant was  to increase the enrichment level of low-enriched uranium, an essential step to being able to fuel a nuclear weapon. Iran justified this action by claiming that the higher enrichment (to 20% U-235) is necessary to fuel a small  research reactor.  The interim nuclear accord struck with Iran in November 2013 halted this work.  By that date, Iran had produced 450 kg of this material.  According to calculations by the Wisconsin Project, Iran would theoretically need 120 kg of this 20 percent material in order to produce a bomb.

Until halting production in January 2014, Iran was using an experimental cascade of 328 centrifuges at Natanz to produce some 4.4 kg each month of 20 percent enriched uranium hexafluoride -- a level of enrichment which accomplishes 90 percent of the work needed to process natural uranium to weapons grade. 

Iran had also been making this 20 percent material at the Fordow Fuel Enrichment Plant.  Of the nearly 3,000 IR-1 centrifuges installed at the plant, about 700 were contributing to the production of 20 percent enriched uranium before this activity was halted in January 2014.[56]

Fordow was considered a troubling choice for this work. It consists of a series of chambers built into a mountain and fortified against air attack. The plant was built secretly and its existence was only revealed by President Obama in 2009.  Under the JCPOA, Fordow will be converted into a nuclear research center, and no uranium enrichment or enrichment-related research and development will be permitted in the facility for the first 15 years of the agreement. 

-Laser Isotopic Separation

Because isotopes of different masses absorb different wavelengths of light, uranium isotopes can be separated by lasers precisely tuned to excite or ionize only the U-235. The U-235 is then separated out using a chemical reaction or magnetic forces that attract the excited atoms and leave behind the neutral ones. Iran has pursued two types of laser enrichment technology: the first, atomic vapor laser isotope separation (AVLIS), has achieved the greatest success; the second, molecular laser isotope separation (MLIS), appears not to have progressed as far.

Iran's laser enrichment program began before the 1979 revolution and relied on assistance from at least four foreign sources.[57]  In 1975, Iran contracted with a foreign supplier for a laboratory to study uranium metal. The laboratory, which was established at the Tehran Nuclear Research Center (TNRC), contained two mass spectrometers. In the late 1970s, Iran contracted with a second supplier for help with the study of MLIS technology.[58]

Then, in 1991, Iran ordered a Laser Spectroscopy Laboratory (LSL) and a Comprehensive Separation Laboratory (CSL) from a third supplier.[59] Iran received 50 kg of natural uranium metal from the same supplier in 1993. Both laboratories were originally set up at the TNRC,[60] where, between 1999 and 2000, eight kilograms of uranium metal were used in AVLIS enrichment experiments.[61] The labs were then relocated to Lashkar Ab'ad in October 2002,[62] where further AVLIS enrichment experiments were carried out using 22 kg of the uranium metal.[63] Iran had previously established a pilot plant for laser enrichment at Lashkar Ab'ad.[64] According to Iranian laboratory reports supplied to the IAEA, the average level of enrichment in these experiments was between eight and nine percent, and occasionally as high as 15%.[65] This is above the level of three percent Iran had originally claimed.[66] The IAEA has estimated that Iran's AVLIS installation at Lashkar Ab'ad had the capacity to produce one gram of uranium per hour, but could not operate continuously.[67]

Iran contracted with a fourth supplier in the late 1990s for information and equipment related to laser enrichment but secured only some of the equipment it had requested, which was delivered to Lashkar Ab'ad. This equipment was suitable for use in AVLIS experiments.[68]

After conducting this laboratory-scale work, and before informing the IAEA of it, Iran dismantled the relevant equipment and moved it to a storage facility at Karaj.[69]

The Plutonium Path

Iran has also sought the ability to produce plutonium, a second fissile material that can be used to fuel nuclear weapons. But because plutonium exists naturally only in trace amounts, it must be manufactured in a nuclear reactor. This is done by bombarding U-238 reactor fuel with slow neutrons. When the U-238 captures a neutron, the U-239 isotope is produced, which decays into plutonium 239.

Tehran Research Reactor (TRR)

In the late 1960s, the United States supplied the TNRC with a five megawatt research reactor, hot cells and 93% enriched uranium reactor fuel.[70]  The United States stopped the fuel supply after the revolution. In the late 1980s, Argentina reportedly helped Iran reconfigure the reactor's core and later provided about 115 kg of uranium enriched to 20% U-235.[71] This fuel was delivered in 1992.

In October 2003, Iran acknowledged that between 1988 and 1992 it had irradiated depleted uranium dioxide targets (UO2) in the reactor and then conducted plutonium separation experiments in hot cells in a nearby building.[72] According to Iran, seven kilograms of UO2 were irradiated, three kilograms of which were processed into separated plutonium.[73]  The separated plutonium was presented to inspectors from the IAEA in November 2003 at the Jabr Ibn Hayan Laboratories, located at the TNRC.[74]  Iran estimated that it had produced 200 micrograms.[75]  However, the inspectors concluded that Iran understated the amount of plutonium and that the age of the plutonium was less than the 12-16 years Iran declared.[76]

Light-water reactor at Bushehr

Russia has constructed a 1,000 megawatt pressurized light-water reactor at the Iranian port of Bushehr. Russia took over the project in 1995, after Germany halted its construction of the plant. The plant is capable of contributing about four percent of Iran's total electricity output to the national power grid.[77]  The facility is also capable of providing Iran with enough weapon-grade plutonium to construct approximately 35 nuclear weapons annually. This assessment is based on an estimate of the plutonium output from a typical 1,000 megawatt pressurized light-water power reactor.

To use the plutonium from Bushehr in a nuclear weapon, however, Iran would have to construct a plant to extract plutonium from the spent reactor fuel. Iran would also have to keep the spent fuel. Russia has an agreement with Iran to provide low-enriched uranium fuel through the first decade of the Bushehr plant's operation, and the spent fuel will be returned to Russia in accordance with a protocol signed in February 2005. Iran has also agreed to allow the reactor and its fuel to be inspected by the IAEA, so any unauthorized use of the fuel would violate Iran's obligations under the Nuclear Nonproliferation Treaty.

After years of delay, the billion dollar reactor has reached completion. Preliminary testing began in late February 2009 and delivery of the reactor fuel needed for start-up, some 82 tons, was completed in January 2008. The reactor was connected to Iran's national grid on September 12, 2011, and commissioning for the reactor began in January 2012.  Iran took control of the Bushehr reactor from Russia in September 2013.

Despite Iran's promises to return the spent fuel, Iran has made purchasing attempts that indicate it seeks a capacity to reprocess and manipulate spent fuel. According to a May 2003 French paper submitted to the Nuclear Suppliers Group, Iran has sought to acquire high density radiation shielding windows for hot cells and 28 remote manipulators from the French nuclear industry.[78] Such equipment is expressly designed for the extraction of plutonium from spent reactor fuel.

Heavy water technology

Iran has also sought to master heavy water technology. Iran decided to  develop a heavy water production plant and a heavy water research reactor at a site in the Khondab area near Arak, approximately 150 miles southwest of Tehran,. The existence of the heavy water production plant was first revealed by the NCRI in August 2002[79] and verified by commercial satellite imagery in December 2002.[80] The heavy water plant was inaugurated in August 2006 and, using satellite imagery, the IAEA has judged the plant to be operational.  Iran informed the IAEA that the two heavy water production lines at Arak would produce about 16 tons of heavy water annually.

On May 5, 2003, Iran also announced plans to build a 40 megawatt thermal heavy water research reactor, called the Iran Nuclear Research Reactor (IR-40), at the same site.[81] The reactor, fueled by natural UO2, was designed to use heavy water as both coolant and moderator.[82]  Iran has admitted that it received some foreign assistance for the design of the reactor; the United States suspects that Russia provided the help.

The heavy water reactorwas the subject of a visit by the IAEA in November 2010. The IAEA inspectors confirmed that civil construction at the site was “almost complete” and that some major equipment, including the pressurizer for the reactor cooling system and the main crane in the reactor building, had been installed. In May 2013, the IAEA confirmed that the reactor vessel had arrived at Arak and that major components had been installed at the reactor.  In June 2013, Iran installed the main reactor vessel at Arak.[83]

Under the terms of the JCPOA, Iran was required to remove the calandria from the reactor at Arak and fill it with concrete, rendering it inoperable.  The IAEA verified that Iran had fulfilled this requirement in January 2016..[84] Under the terms of the JCPOA, Iran is prohibited from pursuing the construction of the IR-40 reactor based on its original design.  Instead, with the assistance of an international consortium, Iran will redesign and rebuild the reactor to minimize the production of plutonium.  The nominal power of the redesigned reactor will not exceed 20 MWth.[85]

Iran has always claimed that the IR-40 is intended for civilian research and development and for the production of radioisotopes for medical and industrial use. However, most states that have built this type of reactor, which is widely considered larger than necessary for research, have used it to produce bombs. The well-known precedents are Israel's Dimona reactor, supplied by France and Norway, and India's Cirus reactor, supplied by Canada and the United States.

Some fuel for the original IR-40 reactor had been produced at the Fuel Manufacturing Plant at Esfahan.  On May 23, 2009, IAEA inspectors were able to visit the facility.  It was operational and had produced natural uranium pellets to fuel the heavy water reactor at Arak.  Iran ceased the production of fuel assemblies for the Arak reactor after the implementation of the Joint Plan of Action in January 2014.  All previously produced fuel assemblies remained at the Fuel Manufacturing Plant.


Every country trying to develop a nuclear weapon has faced two challenges. First came the need to produce a critical mass of fissile material-uranium 235 or plutonium-the metals needed to fuel a first-generation bomb. The second challenge was to produce a device that could cause the uranium or plutonium to explode in a nuclear chain reaction. This second process is called weaponization.

A number of the activities and experiments Iran has undertaken, when coupled with its concealment efforts and its firm commitment to mastering the production of fissile material, suggest that Iran could be trying to make a nuclear device.

In September 2003, the IAEA discovered that Iran had produced polonium-210, a radioisotope with a half-life of 138 days.[86] Iran conducted Po-210 production experiments in the Tehran Research Reactor (TRR) between 1989 and 1993 by irradiating bismuth metal.[87] One of the best-known uses for Po-210 is as a neutron initiator in nuclear weapons.[88] It also has civilian applications, such as in nuclear batteries.[89] However, the IAEA considers the applications of Po-210-based nuclear batteries to be extremely limited.[90] Iran has said that the experiments were part of a study on neutron sources, but has been unable to provide documentation supporting this purported intent.[91]

There have also been reports that Iran has sought deuterium gas from Russia.[92] According to an intelligence report citing Russian sources that was circulated at the IAEA in July 2004, Iranian middlemen negotiated with companies in Russia to purchase deuterium gas after failing to produce it domestically. Deuterium gas is used, in conjunction with tritium, to boost the yield of fission bombs. Deuterium and tritium are hydrogen isotopes that release neutrons and energy when they fuse in thermonuclear explosions.

In addition, French intelligence services have reported that Iran has sought items useful for nuclear tests and simulation, including documentation on flash radiography equipment and pulse generators.[93] Iran has also tried to purchase machines that can be used to shape uranium or plutonium metal, such as isostatic presses and vacuum furnaces.[94] And according to a May 2003 media report, a Swede of Iranian origin arranged the purchase of 44 high-voltage switches for Iran from Behlke Electronic GmbH, a German company. The switches, which were reportedly seized by German customs agents, could be used to trigger nuclear weapons.[95][96][97]

Beyond its procurement efforts, the way in which Iran has organized and delegated its nuclear work to entities related to the defense ministry could suggest a military purpose. According to the IAEA, seven of the 13 workshops dedicated to the domestic production of centrifuge components are located on sites controlled by the ministry of defense.[98]

Moreover, if Iran received the same package of nuclear goods from the Khan network as did Libya-an eventuality that is widely suspected-then it could have received the same Chinese-origin bomb design. China is believed to have supplied Pakistan with a tested nuclear bomb design in the early 1980s. It is reportedly this design that the Khan network resold to Libya, along with documents in Chinese containing detailed instructions on how to manufacture parts for and assemble an implosion-type device.

Suspicions about Iran's intentions have also been increased by Iran's refusal to cooperate with the IAEA. In early February 2008, the IAEA presented member states, including Iran, with specific evidence that Iran had pursued work related to nuclear weapons. In its May 2008 report, the Agency listed eighteen documents supporting these allegations. Iran has called the documents "forged" or "fabricated," and refuses to help the Agency investigate their validity by providing access to individuals, records and sites. For instance, it has barred IAEA inspectors from interviewing Mohsen Fakhrizadeh, former head of the Physics Research Center who was reportedly described by the IAEA as the Iranian military official in charge of Iran's nuclear effort.

In 2011, the IAEA consolidated all of its outstanding questions about Iran’s alleged efforts to pursue nuclear weaponization research: the so-called “possible military dimensions to Iran’s nuclear program.” The analysis in the report was based on information that the Agency received from IAEA member states, from the Agency’s own investigative efforts, and from information provided by Iran.  The IAEA judged the allegations of work on nuclear weapons “to be, overall, credible” and “consistent in terms of technical content, individuals and organizations involved, and time frames.”[99]

The 2011 IAEA report contained detailed information about Iran’s effort to develop a nuclear weapon, including:

  • computer modeling of implosion, compression, and nuclear yield, as recently as 2009;
  • high explosive tests simulating a nuclear explosion but using non-nuclear material in order to see whether an implosion device would work;
  • the construction of at least one containment vessel at a military site, in which to conduct such high explosive tests;
  • studies on detonation of high explosive charges, in order to ensure uniform compression in an implosion device, including at least one large scale experiment in 2003, and experimental research after 2003;
  • support from a foreign expert, reportedly a former Soviet weapon scientist named Vyacheslav Danilenko, in developing a detonation system suitable for nuclear weapons and a diagnostic system needed to monitor the detonation experiments;
  • manufacture of a neutron initiator, which is placed in the core of an implosion device and, when compressed, generates neutrons to start a nuclear chain reaction, along with validation studies on the initiator design from 2006 onward;
  • the development of exploding bridgewire detonators (EBWs) used in simultaneous detonation, which are needed to initiate an implosive shock wave in fission bombs;
  • the development of high voltage firing equipment that would enable detonation in the air, above a target, in a fashion only making sense for a nuclear payload;
  • testing of high voltage firing equipment to ensure that it could fire EBWs over the long distance needed for nuclear weapon testing, when a device might be located down a deep shaft;
  • a program to integrate a new spherical payload onto Iran’s Shahab-3 missile, enabling the missile to accommodate the detonation package described above.[100]

Between 2011 and 2015, the IAEA regularly reported that the Iran was evading questions related to the Agency’s investigation of Iran’s alleged weaponization efforts.  When the JCPOA was agreed to in July 2015, Iran and the IAEA also signed a “Road-Map” agreement intended to resolve all of the IAEA’s outstanding questions related to this investigation.  As part of a separate agreement, the IAEA received environmental samples from the Parchin military base, which was a suspected site of nuclear weapons experimentation.  The samples were reportedly collected by Iranians under IAEA monitoring by video and still cameras and GPS tracking.[101]

On December 2, 2015, the IAEA issued its final report on Iran’s alleged weaponization efforts, concluding that Iran had a coordinated nuclear weapon-related program until 2003, and that some weapon-related activities continued through 2009.[102]  The IAEA report disclosed that Iran did not provide new information or meaningful information for most of the 12 outstanding issues in the IAEA’s investigation.  To many of the Agency’s questions, Iran offered no new information, or made denials without explanation, or gave explanations contradicted by other information available to the Agency.  Nonetheless, the IAEA Board of Governors voted unanimously to close the Agency’s investigation on December 15, 2015.[103]

Safeguards Violations

Under the NPT, Iran must allow the IAEA to inspect its nuclear-related material so that the Agency can verify its peaceful use. This includes what the NPT calls all "source or special fissionable material" and all facilities where such materials are being used, processed or produced anywhere on Iran's territory or anywhere under its control. Iran must also tell the IAEA about changes to its nuclear material inventory and submit inventory change reports when necessary.[104] Finally, Iran is required to provide updated design information on its nuclear facilities and information on facilities where nuclear material is held or stored.[105]

In a report to the IAEA Board of Governors in June 2003, following four months of Agency inspections in Iran, IAEA Director General Mohamed ElBaradei concluded that Iran "has failed to meet its obligations under its Safeguards Agreement with respect to the reporting of nuclear material, the subsequent processing and use of that material and the declaration of facilities where the material was stored and processed.”[106]  Following that conclusion, the IAEA has documented a number of instances in which Iran violated its safeguards agreement by failing to report:

  • The import of nearly 2,000 kg of uranium compounds (1,000 kg of UF6, 400 kg of UF4 and 400 kg of UO2) in 1991,[107] allegedly from China;
  • The processing of 1.9 kg of UF6 (imported in 1991) in centrifuges at the Kalaye Electric Company, which produced 1.2% enriched uranium;[108]
  • The conversion of 9.43 kg of the UF4 imported in 1991 into UF6 in a laboratory at the TNRC;[109]
  • The production of uranium metal in a laboratory at the TNRC in the 1990s using 376.6 kg of UF4 imported in 1991;[111]
  • The production of 2.5 kg of UF4 using UO2 imported in 1991;[111]
  • The irradiation of several grams of UO2 in the TRR and its subsequent processing in a laboratory at the TNRC;[112]
  • The irradiation of 3 kg of depleted UO2 targets in the TRR and subsequent plutonium separation experiments carried out in hot cells at the TNRC, in which about 200 micrograms of plutonium were produced;[113]
  • The import of 50 kg of natural uranium metal in 1993;[114]
  • The processing of 30 kg of the uranium metal imported in 1993 in two series of AVLIS enrichment experiments: first between 1999 and 2000 at the TNRC using 8 kg of uranium, and second at Lashkar Ab'ad between October 2002 and February 2003 using 22 kg of uranium metal;[115]
  • Pilot-scale laser enrichment operations at the TNRC and Lashkar Ab'ad using imported equipment and failing to provide design information on these sites;[116]
  • The transfer of nuclear equipment and material used in laser experiments to a waste storage facility at Karaj, and failing to provide design information on this new site;[117]
  • The use of uranium compounds imported in 1977 and exempted from inspection (U3O8 and depleted UO2) and yellowcake imported in 1982 in experiments at two laboratories at the Esfahan (Isfahan) Nuclear Technology Center;[118]
  • The use of depleted UO2, which Iran had originally declared as material lost during experiments, to produce UF4 in a laboratory at the TNRC;[119]
  • Research and development work on a more advanced centrifuge, known as the P-2, which should have been disclosed to the IAEA in Iran's October 2003 full nuclear report to the Agency. This omission violated Iran's obligations under the IAEA's Additional Protocol, which Iran had agreed to honor, pending ratification in the Iranian parliament.[120]

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