Overview of Iran's Nuclear Program

Table of contents

Current Status

Nuclear Application

Component One: Fissile Material

Component Two: Weaponization

Component Three: Delivery Vehicles

In February 2009, U.S. Director of National Intelligence Dennis C. Blair defined a nuclear weapons capability as the sum of three components: 1) fissile material production, 2) “design, weaponization, and testing” of a warhead, and 3) a delivery vehicle.[1]  In the context of this definition, the American intelligence community concluded in 2007 that Iran “halted its nuclear weapons program,” including covert fissile material production related activities, in 2003.[2]  The estimate assumed that an active nuclear weapons program satisfies all three of the components (uranium enrichment, weapons design, and delivery systems) comprising a nuclear weapons capability.

The director of national intelligence later clarified the 2007 intelligence estimate to point out that Iran only halted the “least significant” component of its nuclear program—weapons design.[3] Indeed, in the annual threat assessment presented to the U.S. Senate Select Committee on Intelligence in February 2009, Director Blair confirmed Iran’s active pursuit of the two more significant components necessary for a nuclear weapons capability—the production of fissile material and delivery systems.[4]

In December 2008, nuclear proliferation control expert Gary Samore said of the current state of Iran’s nuclear program:

"At this point, Iran has mastered the P-1 centrifuge technology that it acquired from Pakistan some 20 years ago and is now embarked on building up its bank of centrifuge machines and stocks of low enriched uranium. Eventually, this will create an option for Iran to produce enough highly enriched uranium quickly enough to support a nuclear weapons program – so called nuclear break out."[5]  

This uranium enrichment activity forms the core of Iran’s nuclear program. Uranium enrichment, particularly its dual-use application for military purposes, is also central to concerns regarding a potential nuclear weapons program. Iran’s stated purpose for its program is to generate nuclear fuel for civilian application, invoking its rights under the Nuclear Nonproliferation Treaty (NPT), of which it is a signatory.[6]

Indeed, Article IV of the NPT does afford signatories the right to pursue nuclear energy for peaceful purposes. Signatories of the NPT have the right to develop nuclear energy under the condition that they bear responsibility for meeting certain obligations. Under Article III of the NPT, signatories must adhere to specific safeguards established by the International Atomic Energy Agency (IAEA) and verifiably prevent the “diversion of nuclear energy from peaceful uses to nuclear weapons or other nuclear explosive devices.”[7]

Iran has violated its obligations under the NPT over the course of several decades.[8] Iran’s noncompliance led to the United Nations Security Council’s adoption of multiple binding resolutions demanding that Iran cease its uranium enrichment activities and allow for an objective verification of its nuclear program. The inherent relationship between uranium enrichment and a nuclear weapons capability concerns the international community and creates the basis for targeted measures toward Iran.

The production of fissile material in the form of uranium enrichment establishes the foundation for Iran’s potential nuclear weapons capability. Iran’s ongoing uranium enrichment activity allows it to produce low-enriched uranium (LEU) from natural uranium ore. A centrifuge method converts uranium ore, in the form of a gas, to LEU:  

"The process uses a large number of rotating cylinders interconnected to form cascades. The UF6 gas is placed in the cylinder, which is then rotated at a high speed. The rotation creates a strong centrifugal force that draws more of the heavier gas molecules…toward the wall of the cylinder, while the lighter gas molecules (containing the U-235) tend to collect closer to the center. The stream that is slightly enriched in U-235 is withdrawn and fed into the next higher stage, while the slightly depleted stream is recycled back into the next lower stage."[9]

The resulting LEU acquired from the gas centrifuge process serves as the basic material necessary to produce high-enriched uranium (HEU)—or weapons-grade uranium. The degree of concentration of the uranium isotope U-235 sets LEU and HEU apart.  Conversion of LEU to HEU requires an additional adequate stock of LEU for proper enrichment.  Enriched uranium is suitable for use in a nuclear weapon once the concentration U-235 reaches 90 percent.[10]  

Alternatively, another uranium enrichment method known as laser enrichment can produce HEU. This process is both more efficient and more difficult than gas centrifuge enrichment[11] Iran experimented with laser enrichment technology between 1991 and 2003.[12]  Iran’s pilot laser facility at Lashkar Abad was shut down in 2003.[13]  The IAEA reported in 2008 that a private company, whose management claims it is not currently conducting nor planning to enrich uranium, now runs the Abad laboratories..[14]

According to IAEA sample tests, Iran’s uranium appears to be of the low-enriched (LEU), or non-weapons grade, variety with a U-235 concentration of less than five percent.[15] A narrow focus on this current lack of weapons-grade uranium (HEU), however, does not consider LEU’s broader significance to a weapons capability.  That is, the potential weapons diversion of enriched uranium remains a timely concern because obtaining an adequate stock of LEU “consumes approximately 70 percent of the work and time required to enrich it to HEU.”[16] Similarly, obtaining enough HEU takes more time than finishing the “weaponization” portion, which is “unlikely to be a significant bottleneck” on the path to a nuclear weapon.[17]   

Iran’s main enrichment facilities, the principal Fuel Enrichment Plant (FEP) and the test Pilot Fuel Enrichment Plant (PFEP), both at Natanz, form the core of the uranium enrichment program. As of November 2008, the International Atomic Energy Agency confirmed that enrichment activities, including advanced component testing and expansion of centrifuges, continued at these two facilities.[18]

The November 2008 IAEA estimates indicate Iran is operating a module with 3,000 first-generation centrifuges and building out a second module of with 3,000 additional centrifuges.[19]  According to the June 2009 International Atomic Energy Agency (IAEA) report, Iran’s Natanz enrichment facility now houses more than 7,000 total centrifuges – 5,000 of which actively enrich uranium.[20]  In November 2008, according to an Iranian media report, the head of Iran’s Atomic Energy Organization (IAEO) claimed that Iran had a plan to “install 50,000 centrifuges in the next five years.”[21]   

A weapons program does not need necessarily need enriched uranium, however: plutonium can serve as an alternative source of the fissile material necessary for a nuclear weapon. A reprocessing plant must separate plutonium from a nuclear reactor’s spent fuel to make the material usable in a weapon. The American intelligence community assesses with high confidence “that Iran will not be technically capable of producing and reprocessing enough plutonium for a weapon before 2015.”[22]

The heavy water production plant and heavy water reactor currently under construction at Iran’s Arak facility could support plutonium reprocessing activities. The ostensible purpose of the site—production of medical isotopes—is difficult to verify.  Burton Richter, a Nobel Laureate physicist and Department of Energy Nuclear Energy Advisory Committee member, notes that the facility under construction at Arak is far more complex than what is necessary for producing medical isotopes and, further, that there is relatively little demand for medical isotopes in Iran and the Middle East.[23]

The use of heavy water at Arak makes the reactor a potential source of the plutonium needed for building a nuclear weapon.  A heavy water reactor, fueled with natural uranium, uses the deuterium isotope instead of the hydrogen isotope used with light water reactors.[24]  A heavy water reactor’s deuterium is significant because of its use in a “boost gas” which produces a more efficient plutonium-fueled nuclear warhead.[25]  A light water research reactor, on the other hand, makes more sense for the type of civilian use Iran claims as being Arak’s purpose. In June 2006, Iran rebuffed an offer by the U.K., France and Germany to help it construct a light water research reactor as an alternative to the heavy water reactor.[26]

The IAEA resolved concerns regarding Iran’s past plutonium separation experiments in that the IAEA findings vindicated Iran’s statements regarding plutonium activities.[27]  Iran’s future activities at the Arak facility, and their potential application toward a nuclear weapons program, remain open-ended. Upon completion, the Arak reactor could potentially produce enough fissile material for nearly two nuclear weapons every year—depending on the facility’s operating conditions and whether Iran undertakes reprocessing activities.[28]  

As of June 2009, the heavy water production plant at Arak “appears to have been operating intermittently” since the February report.[29] The IAEA’s current knowledge regarding the reactor remains limited given Iran's repeated denial of IAEA inspectors' requests to conduct design inspections of the heavy water research reactor at the Arak facility.[30]

Weaponization—the design, testing and preparation of a nuclear warhead—follows enrichment as the second phase of a nuclear weapons program. One study defines weaponization as the “process of moving from an initial design of a nuclear explosive device to a warhead which is safe to handle, can be stockpiled for long periods of time and can survive the journey from its storage area to a target.”[31]

A March 2008 technical briefing conducted for diplomats by the IAEA deputy director general questioned the extent of Iran’s weaponization activities.  According to a participant at the meeting, the IAEA had gathered evidence from several foreign intelligence agencies corroborating Iranian documents that indicated Iran had undertaken “sophisticated research into some key technologies needed to build and deliver a nuclear bomb,” including “studies on modifying Iran’s Shahab missile to allow it to accommodate a large warhead, which would detonate 600 meters above its target.”[32]

To weaponize a warhead, one needs approximately 20-25 kilograms of HEU for use in a “controlled fission reaction.”[33]  Based on information provided in the IAEA’s November 2008 report, Iran’s stock of LEU:

"…is on average about four percent enriched, meaning that about four percent of Iran’s LEU (U-mass) is the isotope uranium 235, the most important isotope for fueling a power reactor or building a weapon. Thus, the 425 kilograms of uranium contains approximately 17 kilograms of uranium 235. This quantity appears insufficient for Iran to make a nuclear weapon, when inevitable losses in the Iranian enrichment and potential weaponization processes are included."[34]

Based on this estimate, Iran is near the threshold of possessing enough fissile material, which if further enriched, would afford it the capability to weaponize a nuclear package.  ISIS nuclear nonproliferation experts estimated that Iran will acquire enough enriched uranium for a potential weapons application sometime in 2009—the exact month depending on the operational efficiency and expansion of Iran’s enrichment facilities at Natanz.[35]

After reaching this threshold, nonproliferation expert Mark Fitzpatrick estimates that Iran would need at least one year to further enrich its uranium to obtain weapons-grade fissile material—assuming that Iran overcomes certain technical challenges associated with maintaining centrifuge machines.[36] [37]  The weaponization of fissile material faces technical challenges deemed “within Iran’s reach”:

"Among the technical challenges of weaponisation would be the reconfiguring of existing LEU production facilities, or the building of clandestine facilities, the mastery of the HEU production process and the reconversion of HEU to metal, the shaping of the uranium metal into pits, the design of a weapon small enough to fit onto a warhead of a delivery vehicle, the fashioning of the nuclear triggering device and (in the case of implosion devices) of the spherical explosive lenses and reflector, learning how to sustain the nuclear reaction with an additional source of neutrons, and the construction of the device."[38]

To this end, the American intelligence community believes that Iran possesses the “scientific, technical, and industrial capacity” to eventually build a weapon.[39]

As a former National Security Council nonproliferation expert explains, “just as the bomb making is easier than getting the HEU, the delivery is much easier than making the bomb.”[40]

Delivery vehicles allow a country to fire a potential nuclear warhead against a target.  Following the production of fissile material and its subsequent weaponization, a delivery vehicle would need to incorporate a nuclear warhead to constitute a nuclear weapon. Countries most commonly use ballistic missiles as delivery vehicles.  Ballistic missiles deploy in the following manner:

"After an initial powered phase of flight, a ballistic missile leaves the atmosphere (about 100 kilometers) and follows an unpowered trajectory or flight path before reentering the atmosphere toward a predetermined target. Ballistic missile ranges can vary from a hundred or so kilometers to more than 10,000 kilometers."[41]

According to national intelligence director Blair, “Iran continues to deploy and improve ballistic missiles inherently capable of delivering nuclear weapons.”[42]  Official Iranian media reports, publicizing ballistic missile tests and military parades showcasing Iran’s hardware, give outsiders the primary source of information on Iran’s missile capabilities—despite the fact that the reports often produce conflicting information and lack independent verification.

As noted by the head of the U.S. Missile Defense Agency, Iran currently pursues “newer and longer-range missile systems and advanced warhead designs.”[43]  Iranian officials claim that Iran’s ballistic missiles are defensive deterrents and are not related to Iran’s nuclear program.[44] Ballistic missiles like the Shahab-3, with a range of 1,250 miles, do have a potential nuclear weapons capability.  Iran could use the Shahab-3, for example, to deploy a nuclear warhead with slight modifications.[45]  The payload capacity for a Shahab-3, nearly one ton, can also support a nuclear warhead.[46]