"I find hope in the work of long-established groups such as the Arms Control Association...[and] I find hope in younger anti-nuclear activists and the movement around the world to formally ban the bomb."

– Vincent Intondi
Professor of History, Montgomery College
July 1, 2020
Section 1: Background and Status of Iran’s Nuclear Program
Share this

Table of Contents

The comprehensive nuclear agreement reached by Iran and the P5+1 (China, France, Germany, Russia, the United Kingdom, and the United States) on July 14 2015, is a breakthrough after over a decade of negotiations to resolve international concerns about Tehran’s nuclear program. 

Prior to this historic agreement, Tehran had been steadily improving its capability to produce fissile material for nuclear weapons. 

Although the U.S. intelligence community assessed that Iran abandoned a coordinated nuclear weapons program in 2003, the 2007 National Intelligence Estimate (NIE) on Iran and more-recent intelligence community testimony assessed that Iran has developed a range of technologies, including uranium enrichment, nuclear warhead mechanics, and delivery systems, that would give it the option to launch a nuclear weapons development effort in a relatively short time frame “if it so chooses.”1

Such an effort is not the same as a crash program designed to construct a nuclear weapon as soon as possible, which would require that Iran eject inspectors and try to produce weapons-grade material at its declared facilities or perhaps at undeclared facilities before such an effort could be detected and disrupted. 

Instead, Tehran appeared to be taking a more deliberate approach, building up as much of its technological base as possible for what is ostensibly a peaceful nuclear energy program while reserving the option to make a political decision to build and deploy nuclear weapons.

As Director of National Intelligence James R. Clapper explained in his 2012 testimony, “We judge Iran’s nuclear decision-making is guided by a cost-benefit approach, which offers the international community opportunities to influence Tehran.”2 A comprehensive deal dramatically increases the costs of pursuing nuclear weapons and decreases the benefits. 

Iran’s Nuclear Ambitions and Capabilities
Iran’s interest in pursuing an ambitious nuclear power program preceded the 1979 revolution. The United States provided a kick-start to Iran’s nuclear program by signing a nuclear cooperation agreement under President Dwight Eisenhower’s Atoms for Peace Program in 1957 and subsequently provided the five-megawatt-thermal (MWt) Tehran Research Reactor. The shah’s government later announced plans for building more than 20 nuclear power reactors for generating electricity.3

Beginning with the first serious discussions with Tehran in the 1970s about helping to construct nuclear power reactors, the U.S. government sought to impose safeguards beyond those required by the nuclear Nonproliferation Treaty (NPT). For his part, the shah pushed hard for domestic development of the full nuclear fuel cycle, in particular the ability to reprocess spent fuel.4 Although Iran claims today that Washington accepted a robust nuclear power program in Iran under the shah, the United States insisted at the time that Iran not possess a reprocessing capability due to fears it would be used to produce plutonium for nuclear weapons.5 

After a brief interregnum following the 1979 revolution, the Iranian government resumed its pursuit of the previous regime’s nuclear aspirations, albeit slowly, as Ayatollah Ruhollah Khomeini initially opposed nuclear development for theological reasons. Following Khomeini’s death in 1989, the new supreme leader, Ayatollah Ali Khamenei, expanded Iran’s undeclared nuclear activities.6 The nuclear capabilities that Iran has been pursuing can be used for a peaceful nuclear energy program and nuclear weapons development, although some of the capabilities on which Iran focused strongly before the July 2015 deal suggest a prior intention to develop the option to build weapons. 

Iran’s interest in developing a nuclear weapons capability was directly aligned with the central priority of its leadership: the survivability of its regime. The Islamic Republic’s revolutionary government has seen itself under threat since it came to power in 1979 because of Tehran’s adversarial relationship with the United States and from the bitter eight-year war with Iraq, which invaded Iran in 1980. 

According to a 2010 Pentagon report on Iran’s military power, “Iran’s nuclear program and its willingness to keep open the possibility of developing nuclear weapons is a central part of its deterrent strategy.”7 Subsequent reports found that Iran “is developing a range of technical capabilities that could be applied to the production of nuclear weapons if the decision is made to do so.”8

Iran’s nuclear ambitions also are rooted in the country’s goal of exerting influence throughout the region. Tehran’s military power is not proportionate to its economic power, however, and its conventional military capabilities are limited by lack of training and modern weaponry. 

Any decision by Iran’s leadership to pursue nuclear weapons development would need to overcome significant political and technical hurdles, even more so after a deal is implemented. Iran has long said that its nuclear program is exclusively for peaceful purposes. Additionally, there is religious opposition to the development of weapons of mass destruction. Khamenei has called nuclear weapons a “grave sin,” claiming that Iran “has never pursued and will never pursue” them.9 

Iran’s apparent work on developing a nuclear warhead, at least prior to 2004, undermines Khamenei’s declarations; Iran would need to find some way to explain the reversal of its stated policy to Iranian domestic audiences and the international community.

The comprehensive nuclear deal limits the most relevant aspects of Iran’s nuclear program that could be used to build nuclear weapons. The deal restricts Iran’s uranium-enrichment-related activities, modifies its heavy-water reactor activities, and puts in place a stringent monitoring and verification regime to ensure that Tehran abides by the agreement and does not pursue a covert program.  

Uranium Enrichment
For more than a decade, Iran’s uranium-enrichment program was the focus of international concern about Iran’s nuclear aspirations. Iran’s enrichment program provides it with the ability to produce one form of fissile material for nuclear weapons: weapons-grade highly enriched uranium (HEU). 

The uranium pathway is the most likely route that Iran would use to produce fissile material for nuclear weapons, if the decision was made to pursue them. Iran enriches uranium using a machine called the gas centrifuge, which spins at very high speeds to increase the concentration, or percentage, of the fissionable isotope uranium-235 (U-235). 

Centrifuges are organized in groups called cascades, which generally contain either 164 or 174 machines and produce uranium enriched to different levels. Uranium enriched to less than 5 percent U-235 is typically used to fuel nuclear power plants. Research reactors, such as the Tehran Research Reactor, often run on uranium enriched to 20 percent. Uranium enriched to less than 20 percent is referred to as low-enriched uranium (LEU). Nuclear weapons require HEU, which typically has greater than 90 percent U-235.

Beginning in the mid-1980s, Iran acquired gas centrifuge technology through the nuclear smuggling network led by former Pakistani nuclear official Abdul Qadeer Khan, who provided similar assistance to Libya and North Korea. The centrifuge model that Iran is using to enrich uranium, the IR-1, is based on a Pakistani design, the P-1. The P-1 design was originally smuggled by the Khan network from the European enrichment consortium URENCO in the 1970s.

Iran currently enriches uranium at two sites, Natanz and Fordow. Iran has manufactured more than 20,000 centrifuges domestically for these facilities, but is unlikely to be able to produce indigenously all of the materials, such as high-quality carbon fiber and maraging steel, necessary to expand its nuclear program. Tehran relied on illicit networks to bypass international sanctions prohibiting the purchase of these materials. This dependency on foreign suppliers slowed Iran’s production of centrifuges. 

The Natanz plant is Iran’s primary uranium-enrichment facility. An Iranian opposition group, the National Council of Resistance of Iran, revealed in August 2002 that Iran was building the facility. In February 2003, Iran officially acknowledged the existence of Natanz and allowed the International Atomic Energy Agency (IAEA) to visit the facility. At that time, Iran had about 100 centrifuges installed in a pilot cascade. 

The Natanz site comprises an industrial-scale enrichment facility, the Fuel Enrichment Plant, which is intended to eventually house about 50,000 centrifuges, and the Pilot Fuel Enrichment Plant. The Pilot Fuel Enrichment Plant is a research and development facility where Iran is testing more-advanced models of centrifuges, including the IR-2M, IR-4, IR-5, IR-6, and IR-6S, to replace the crash-prone IR-1 models. An IR-8 machine is partially installed.  Progress on the advanced machines has been slow and it is unclear how efficient these machines are. 

Prior to the November 24 Joint Plan of Action, Iran had installed 15,420 IR-1 centrifuges at the Fuel Enrichment Plant, of which approximately 9,200 are operational in 54 cascades. The IR-1 machines are currently enriching uranium to 3.5 percent. Another 328 IR-1s enriched uranium to 20 percent at the Pilot Plant until the November 2013 interim deal dropped the enrichment level to 3.5 percent. 

In January 2013, Iran informed the IAEA that it planned to install IR-2M machines in production-scale cascades at the Natanz Fuel Enrichment Plant. Prior to the November 2013 agreement, Iran had installed 1,008 advanced IR-2M centrifuges, but these machines never enriched uranium.

Experts assess that, when operational, the IR-2M centrifuges will be three to five times more efficient than the IR-1 centrifuges. 

The Fordow facility is located inside a mountain bunker and was built in secrecy, until September 2009, when France, the UK, and the United States publicly revealed its existence. Iran is believed to have informed the IAEA about the plant’s existence only after discovering that Western intelligence agencies had learned of it. 

Iran enriched uranium to 20 percent at that facility using 696 IR-1 centrifuges. After the November 2013 interim deal, these machines produced uranium enriched to 3.5 percent. An additional 11 cascades containing approximately 2,000 IR-1 centrifuges were installed at Fordow, but are not operating, bringing the facility to nearly full design capacity of about 2,800 machines. 

Iran was ostensibly enriching uranium to 20 percent to provide fuel for the Tehran Research Reactor, which produces medical isotopes, and for similar research reactors Iran claims it will build in the future.11 Although enriching uranium to 20 percent is not necessarily indicative of an intention to make a nuclear weapon, stockpiling uranium at this level was worrisome because if Iran attempted to produce weapons-grade uranium, it could do so much faster using 20 percent-enriched uranium than by starting with 3.5 percent-enriched material. Enriching uranium to 20 percent constitutes about 90 percent of the work needed to enrich uranium to weapons-grade levels. 

Moreover, the rationale behind Iran’s production of 20 percent-enriched uranium was dubious, particularly as experts assess that current stockpiles “exceed any realistic assessment of [Iran’s] need.”12 

Heavy-Water Reactor Project
Another potential path to the construction of nuclear weapons is to separate weapons-grade plutonium from spent nuclear fuel. Iran began construction of a reactor, the IR-40, in 2004 at its Arak site. This reactor, if completed as originally designed, would have provided enough plutonium annually for up to two nuclear weapons. Iran claimed the reactor was intended to produce medical isotopes, but it was poorly suited for that function. 

 Construction was beset by delays, due in part to proliferation-related sanctions, which have prevented Iran from obtaining some of the materials required. 

However, by November 2013, Iran had made considerable progress, including installing the upper containment vessel and the reactor vessel and testing prototype uranium fuel assemblies for the reactor in the Tehran Research Reactor. 

In order to use plutonium from a reactor such as the IR-40, Iran would have needed a reprocessing facility to separate the plutonium from the reactor’s spent fuel. In 2004, Iran revised its declaration to the IAEA regarding the Arak site and eliminated plans for constructing a reprocessing facility. Iran currently is not known to be working on such a capability, although Tehran admitted to the IAEA in 2003 that it had carried out reprocessing experiments during 1988-1993 without informing the agency.13 

IAEA Safeguards
For nearly 20 years, Iran pursued much of its sensitive nuclear work in secret without informing the IAEA of its activities. It was not until Iran’s facilities at Natanz and Arak were publicly revealed in the fall of 2002 that the agency was able to begin carrying out a thorough accounting of work Iran performed on uranium enrichment and other programs with possible weapons purposes. 

Since 2003, many key Iranian facilities (now 18) have been under IAEA safeguards. From 2004 until early 2006, Iran voluntarily agreed to implement an additional protocol to its IAEA safeguards agreement, which expanded inspector access to facilities. 

Between 2006 and the November 2013 interim agreement, Iran kept many activities out of the inspections process. For example, Iran’s centrifuge manufacturing and development work was not safeguarded after 2006, when Iran stopped implementation of its additional protocol. This was preceded by the IAEA finding Iran in noncompliance with its safeguards agreement in September 2005 and the agency’s decision to refer Iran to the UN Security Council in February 2006. 

In 2007, Iran stopped sharing early access and design information for its nuclear facilities with the IAEA, as it is obligated to do under the so-called modified Code 3.1 of its safeguards agreement. Although Iran announced it would revert to the original arrangement, the agency said the modified arrangement cannot be unilaterally altered and that Iran was still required to provide the notifications required by Code 3.1.14

As a result, the agency did not have regular access to the heavy-water reactor under construction at Arak, and Iran refused to share plans regarding the construction of any additional nuclear facilities. Tehran also refused IAEA requests to install real-time camera monitoring at its enrichment facilities, a measure that would provide the earliest indication of any Iranian move to begin producing weapons-grade material. 

Until 2013, Iranian officials argued that their actions were justified because the IAEA and the UN Security Council were trying to deprive Iran of the inherent rights to which all NPT members are entitled. In fact, Iran was reneging on the terms of the safeguards agreement it concluded with the IAEA, one of its core NPT responsibilities on which its rights to nuclear technology is conditioned. Within the construct of the final deal, reapplication of Iran’s additional protocol and Code 3.1 assists the agency in exercising due diligence in monitoring Iran’s program so that it can determine whether the program encompasses weapons-related activities.


1. James R. Clapper, “Unclassified Statement for the Record on the Worldwide Threat Assessment of the U.S. Intelligence Community for the Senate Select Committee on Intelligence,” Office of the Director of National Intelligence, January 31, 2012, p. 6, http://www.intelligence.senate.gov/120131/clapper.pdf. 

2. Ibid.

3. International Institute for Strategic Studies (IISS), “Iran’s Nuclear, Chemical, and Biological Capabilities: A Net Assessment,” February 3, 2011. 

4. Abbas Milani, “The Shah’s Atomic Dreams,” Foreign Policy, December 29, 2010.

5. IISS, “Iran’s Nuclear, Chemical, and Biological Capabilities.”

6. Ibid.

7. U.S. Department of Defense, “Unclassified Report on Military Power of Iran,” April 2010. 

8. U.S. Department of Defense, “Unclassified Report on Military Power of Iran,” April 2012.

9. “Iran Will Never Seek Nuclear Weapons: Leader,” Press TV, February 22, 2012. 

10. International Atomic Energy Agency Board of Governors, “Implementation of the NPT Safeguards Agreement and Relevant Provisions of Security Council Resolutions in the Islamic Republic of Iran: Report by the Director-General,” GOV/2014/28, May 23, 2014; David Albright et al., “ISIS Analysis of the IAEA Iran Safeguards Report,” ISIS Report, May 23, 2014, http://isis-online.org/uploads/isis-reports/documents/ISIS_Analysis_IAEA_Safeguards_Report_23May2014-finaldoc.pdf.

11. The United States originally supplied Iran with the Tehran Research Reactor in 1967. At that time, the reactor operated using highly enriched uranium fuel enriched to more than 90 percent uranium-235. In 1993, conversion of the reactor to use fuel targets enriched to just under 20 percent was completed. Argentina facilitated the conversion and provided 115 kilograms of 20 percent-enriched uranium for the reactor. IISS, “Iran’s Nuclear, Chemical, and Biological Capabilities.” 

12. William C. Witt et al., “Iran’s Evolving Breakout Potential,” ISIS Report, October 8, 2012, http://isis-online.org/uploads/isis-reports/documents/Irans_Evolving_Breakout_Potential.pdf. 

13. IISS, “Iran’s Nuclear, Chemical, and Biological Capabilities.”

14. Ibid.