History of the nuclear program of Iran

Iran's nuclear program began under Shah Mohammad Reza Pahlavi in the 1950s as part of the U.S. Atoms for Peace initiative. In 1967, Iran established the Tehran Nuclear Research Center with a U.S.-supplied 5 MW research reactor. During the 1970s, Iran pursued ambitious plans for up to 20 nuclear power plants (starting the Bushehr reactors with German assistance), but progress halted after the 1979 Islamic Revolution and the Iran–Iraq War. Iraq's use of chemical weapons during that war influenced Iran's post-revolution leaders to secretly revive a weapons-related nuclear program in the mid-1980s. By the 1990s, Iran was rebuilding its nuclear infrastructure: it sought a nuclear fuel cycle (mining, conversion, enrichment) and covertly obtained centrifuge designs from the Pakistani Abdul Qadeer Khan network. Construction of the Bushehr 1000 MWe power reactor resumed with Russian help and was completed in 2011 under IAEA safeguards.

Iran's nuclear activities remained mostly clandestine until 2002, when dissidents revealed undeclared facilities at Natanz (uranium enrichment) and Arak (heavy water reactor). This sparked an international crisis. Under pressure, Iran agreed in late 2003 to suspend enrichment and signed the IAEA Additional Protocol, amid an EU-3 (UK, France, Germany) negotiation effort. However, these voluntary limits collapsed after the election of Mahmoud Ahmadinejad in 2005, and Iran resumed enrichment, leading the IAEA Board of Governors to find Iran in non-compliance and the United Nations Security Council to impose sanctions starting in 2006. Throughout the late 2000s, Tehran steadily expanded its enrichment capacity, including the secret construction of the Fordow underground enrichment plant, revealed in 2009, and accumulated low-enriched uranium, at one point reducing its estimated nuclear breakout time to a few months. Covert actions sought to slow Iran's progress (for example, the Stuxnet cyber-attack in 2010 targeted Iran's centrifuges), but the program continued to advance.

A diplomatic breakthrough came in 2015, when Iran and the P5+1 (US, UK, France, China, Russia, and Germany) reached the Joint Comprehensive Plan of Action (JCPOA). This agreement imposed strict limits on Iran's nuclear program, capping uranium enrichment at 3.67% U-235, shrinking Iran's enriched uranium stockpile to 300 kg, and requiring the Arak heavy-water reactor to be redesigned, in exchange for broad sanctions relief. The JCPOA was implemented in 2016 with the IAEA verifying Iran's compliance. However, in May 2018 the United States unilaterally withdrew from the accord, citing Iran's missile program, support of proxies, and aggressive regional policies; US sanctions were reimposed, and Iran responded from 2019 onward by violating JCPOA limits. By 2020–2021, Iran ended its enrichment restraint and began enriching to higher levels than allowed. As of 2025, Iran's nuclear program is far more advanced than a decade earlier, having expanded significantly in both scope and scale. In June 2025, the International Atomic Energy Agency (IAEA) found Iran non-compliant with its nuclear obligations for the first time in 20 years.^[1] Iran retaliated by launching a new enrichment site and installing advanced centrifuges.^[2]