A nuclear weapon uses a fissile material to cause a nuclear chain reaction. The most commonly used materials have been uranium 235 (U-235) and plutonium 239 (Pu-239). Both uranium 233 (U-233) and reactor-grade plutonium have also been used. The amount of uranium or plutonium needed depends on the sophistication of the design, with a simple design requiring approximately 15 kg of uranium or 6 kg of plutonium, and a sophisticated design requiring as little as 9 kg of uranium or 2 kg of plutonium. Plutonium is almost nonexistent in nature, and natural uranium is about 99.3% uranium 238 (U-238) and 0.7% U-235. Therefore, to make a weapon, either uranium must be enriched, or plutonium must be produced. Uranium enrichment is also frequently necessary for nuclear power. For this reason, uranium enrichment is a dual-use technology, a technology which "can be used both for civilian and for military purposes". Key strategies to prevent proliferation of nuclear arms include limiting the number of operating uranium enrichment plants and controlling the export of nuclear technology and fissile material.
Iranian development of nuclear technology began in the 1970s, when the U.S. Atoms for Peace program began providing assistance to Iran, which was then led by the Shah. Iran signed the Treaty on the Non-Proliferation of Nuclear Weapons (NPT) in 1968 as a non-nuclear weapons state and ratified the NPT in 1970.
In 1979 the Iranian Revolution took place, and Iran's nuclear program, which had developed some baseline capacity, fell to disarray as "much of Iran's nuclear talent fled the country in the wake of the Revolution." Furthermore, Ayatollah Ruhollah Khomeini was initially opposed to nuclear technology, and Iran engaged in a costly war with Iraq from 1980 to 1988.
In the late 1980s Iran reinstated its nuclear program, with assistance from Pakistan (which entered into a bilateral agreement with Iran in 1992), China (which did the same in 1990), and Russia (which did the same in 1992 and 1995), and from the A.Q. Khan network. Iran "began pursuing an indigenous nuclear fuel cycle capability by developing a uranium mining infrastructure and experimenting with uranium conversion and enrichment". According to the nonpartisan Nuclear Threat Initiative, " have long suspected Iran of using its civilian nuclear program as a cover for clandestine weapons development." Iran, in contrast, "has always insisted that its nuclear work is peaceful".
In August 2002 the Paris-based National Council of Resistance of Iran, an Iranian dissident group, publicly revealed the existence of two undeclared nuclear facilities, the Arak heavy-water production facility and the Natanz enrichment facility. In February 2003 Iranian President Mohammad Khatami acknowledged the existence of the facilities and asserted that Iran had undertaken "small-scale enrichment experiments" to produce low-enriched uranium for nuclear power plants. In late February International Atomic Energy Agency (IAEA) inspectors visited Natanz. In May 2003 Iran allowed IAEA inspectors to visit the Kalaye Electric Company but refused to allow them to take samples, and an IAEA report the following month concluded that Iran had failed to meet its obligations under the previous agreement.
In June 2003 Iran—faced with the prospect of being referred to the UN Security Council—entered into diplomatic negotiations with France, Germany, and the United Kingdom (the EU 3). The United States refused to be involved in these negotiations. In October 2003 the Tehran Declaration was reached between Iran and the EU 3; under this declaration Iran agreed to cooperate fully with the IAEA, sign the Additional Protocol, and temporarily suspend all uranium enrichment. In September and October 2003 the IAEA conducted several facility inspections. This was followed by the Paris Agreement in November 2004, in which Iran agreed to temporarily suspend enrichment and conversion activities, "including the manufacture, installation, testing, and operation of centrifuges, and committed to working with the EU-3 to find a mutually beneficial long-term diplomatic solution".
In August 2005 Mahmoud Ahmadinejad, a hard-liner, was elected president of Iran. He accused Iranian negotiators who had negotiated the Paris Accords of treason. Over the next two months, the EU 3 agreement fell apart as talks over the EU 3's proposed Long Term Agreement broke down; the Iranian government "felt that the proposal was heavy on demands, light on incentives, did not incorporate Iran's proposals, and violated the Paris Agreement". Iran notified the IAEA that it would resume uranium conversion at Esfahan.
In February 2006 Iran ended its voluntary implementation of the Additional Protocol and resumed enrichment at Natanz, prompting the IAEA Board of Governors to refer Iran to the UN Security Council. After the vote, Iran announced it would resume enrichment of uranium. In April 2006 Ahmadinejad announced that Iran had nuclear technology but said that it was purely for power generation, not weapons. In June 2006 the EU 3 joined China, Russia, and the United States, to form the P5+1. The following month, July 2006, the UN Security Council passed its first resolution demanding Iran stop uranium enrichment and processing. Altogether, from 2006 to 2010, the UN Security Council subsequently adopted six resolutions concerning Iran's nuclear program: 1696 (July 2006), 1737 (December 2006), 1747 (March 2007), 1803 (March 2008), 1835 (September 2008), and 1929 (June 2010). The legal authority for the IAEA Board of Governors referral and the Security Council resolutions derived from the IAEA Statute and the United Nations Charter. The resolutions demanded that Iran cease enrichment activities and imposed sanctions on Iran, including bans on the transfer of nuclear and missile technology to the country and freezes on the assets of certain Iranian individuals and entities, in order to pressure the country. But in Resolution 1803 and elsewhere the Security Council also acknowledged Iran's rights under Article IV of the NPT, which provides for "the inalienable right ... to develop research, production and use of nuclear energy for peaceful purposes".[b]
In July 2006 Iran opened the Arak heavy water production plant, which led to one of the Security Council resolutions. In September 2009 U.S. President Barack Obama revealed the existence of an underground enrichment facility in Fordow, near Qom, saying, "Iran's decision to build yet another nuclear facility without notifying the IAEA represents a direct challenge to the basic compact at the center of the non-proliferation regime." Israel threatened to take military action against Iran.
In a February 2007 interview with the Financial Times, IAEA director general Mohamed ElBaradei said that military action against Iran "would be catastrophic, counterproductive" and called for negotiations between the international community and Iran over the Iranian nuclear program. ElBaradei specifically proposed a "double, simultaneous suspension, a time out" as "a confidence-building measure", under which the international sanctions would be suspended and Iran would suspend enrichment. ElBaradei also said, "if I look at it from a weapons perspective there are much more important issues to me than the suspension of [enrichment]," naming his top priorities as preventing Iran from "go[ing] to industrial capacity until the issues are settled"; building confidence, with "full inspection" involving Iranian adoption of the Additional Protocol; and "at all costs" preventing Iran from "moving out of the [treaty-based non-proliferation] system".
A November 2007 U.S. National Intelligence Estimate assessed that Iran "halted its nuclear weapons program" in 2003; that estimate and subsequent U.S. Intelligence Community statements also assessed that the Iranian government at the time had was "keeping open the 'option' to develop nuclear weapons" in the future. A July 2015 Congressional Research Service report said, "statements from the U.S. intelligence community indicate that Iran has the technological and industrial capacity to produce nuclear weapons at some point, but the U.S. government assesses that Tehran has not mastered all of the necessary technologies for building a nuclear weapon."
U.S. Secretary of State John Kerry
shakes hands with Iranian Foreign Minister Javad Zarif
after the P5+1 and Iran concluded negotiations about Iran's nuclear capabilities on November 24, 2013
In March 2013 the United States began a series of secret bilateral talks with Iranian officials in Oman, led by William Joseph Burns and Jake Sullivan on the American side and Ali Asghar Khaji on the Iranian side. In June 2013 Hassan Rouhani was elected president of Iran. Rouhani has been described as "more moderate, pragmatic and willing to negotiate than Ahmadinejad". But in a 2006 nuclear negotiation with European powers, Rouhani said that Iran had used the negotiations to dupe the Europeans, saying that during the negotiations, Iran managed to master the conversion of uranium yellowcake at Isfahan. The conversion of yellowcake is an important step in the nuclear fuel process. In August 2013, three days after his inauguration, Rouhani called for a resumption of serious negotiations with the P5+1 on the Iranian nuclear program. In September 2013 Obama and Rouhani spoke by telephone, the first high-level contact between U.S. and Iranian leaders since 1979, and U.S. Secretary of State John Kerry met with Iranian foreign minister Mohammad Javad Zarif, signaling that the two countries were open to cooperation. Former officials alleged that, in order to advance the deal, the Obama administration shielded Hezbollah from the Drug Enforcement Administration's Project Cassandra investigation regarding drug smuggling and from the Central Intelligence Agency. As a result of the Politico report, Attorney General Jeff Sessions ordered an investigation to determine the veracity of the allegations.
After several rounds of negotiations, on 24 November 2013 the Joint Plan of Action, an interim agreement on the Iranian nuclear program, was signed between Iran and the P5+1 countries in Geneva, Switzerland. It consisted of a short-term freeze of portions of Iran's nuclear program in exchange for decreased economic sanctions on Iran, as the countries work towards a long-term agreement. The IAEA began "more intrusive and frequent inspections" under this interim agreement. The agreement was formally activated on 20 January 2014. On that day, the IAEA issued a report stating that Iran was adhering to the terms of the interim agreement, including stopping enrichment of uranium to 20 percent, beginning the dilution process (to reduce half of the stockpile of 20 percent enriched uranium to 3.5 percent), and halting work on the Arak heavy-water reactor.
A major focus on the negotiations was limitations on Iran's key nuclear facilities: the Arak IR-40 heavy water reactor and production plant (which was under construction, but never became operational, as Iran agreed as part of the November 2013 Joint Plan of Action (interim agreement) not to commission or fuel the reactor); the Bushehr Nuclear Power Plant; the Gachin uranium mine; the Fordow Fuel Enrichment Plant; the Isfahan uranium-conversion plant; the Natanz uranium enrichment plant; and the Parchin military research and development complex.