Iran’s nuclear programme entered a critical phase in 2025, marked by years of covert operations, sabotage, and international diplomacy. Despite recent military strikes and cyber-attacks from Israel and the US, Iran’s nuclear infrastructure remains partly operational. This estimate is an attempt to provide a detailed status update on Iran’s nuclear facilities, enriched uranium stockpile, breakout capabilities, and the possible impact of recent attacks on its nuclear timeline.
Trajectory of the nuclear programme
Iran’s quest has been to design a pure fission type of nuclear weapon based on implosion design using Uranium-235 and plutonium. Iran did not have a plutonium processing plant; therefore, it initially concentrated only on developing a U-235 implosion high explosive assembly without a nuclear core. Towards this end, Iran tested nuclear explosive assemblies without a nuclear core—commonly referred to as “cold tests”. The recent report by the International Atomic Energy Agency (IAEA) lifted the lid on the secretive implosion tests carried out by Iran two decades ago in its four nuclear sites. The tests were carried out at the four nuclear sites—Marivan, Lavisan-Shian, Varamin, and Turquz-Abad.
According to IAEA reports, Iran carried out several implosion tests around 2003 using full-scale hemispherical implosion systems. These tests involved using high explosives to create a spherically inward shock wave, compressing a surrogate core made of natural or depleted uranium rather than weapons-grade material. Such cold tests are a critical step in nuclear weapons development, allowing a country to validate the design and functioning of the explosive assembly without using actual fissile material. As the IAEA confirmed these tests it also reported Iran’s preparations for further cold tests. It remains unclear whether all planned cold tests were completed, as Iran has sanitised relevant test sites in recent years, complicating verification.
Based on current intelligence and available evidence, Iran does not possess nuclear weapons, even though it has accumulated a substantial stockpile of highly enriched uranium. According to estimates in early 2025, Iran has a significant uranium stockpile enriched up to 60 percent. Nuclear weapons cannot be made with this grade of enrichment because it can’t sustain a fast, uncontrolled chain reaction, required for releasing a large amount of energy compared with the other isotopes. Therefore 90 percent enrichment level is required for weapons-grade uranium to attain a sustained nuclear chain reaction for obtaining the desired yield of weapon.
Nonetheless according to IAEA and independent experts, if Iran chose to further enrich its stockpile to weapons-grade, it could produce enough fissile material for multiple nuclear weapons within matter of weeks. These estimates highlight that the period needed to produce enough weapons-grade uranium for a single nuclear weapon—is now estimated to be almost ‘zero’, meaning it could theoretically achieve this in days or weeks if it decided to do so.
Despite its capability, there is no credible evidence that Iran has taken the final steps to build or assemble a nuclear weapon. Experts agree that Iran has not so far moved towards weaponisation, which involves additional complex processes beyond merely enriching uranium, such as designing and building a deliverable warhead with safety locks, fusing system and sensors which could be fitted on long range missiles. This stage could likely take several months or even years to complete. Some of the reasons for this are outlined below.
Plutonium and reprocessing capability
Iran does not produce significant amounts of plutonium for several reasons mainly relating to reactor design and international agreements.
Iran’s main facility for producing plutonium is the Arak (IR-40) heavy water reactor, originally designed to generate enough plutonium for one or two nuclear weapons per year—if operated in its original configuration and paired with a reprocessing facility. Civil works for the project began in October 2004. It was initially planned that the reactor would begin nuclear operations in 2014. However, under the 2015 Joint Comprehensive Plan of Action (JCPOA), Iran agreed to redesign the reactor to minimise plutonium production and to make it proliferation-resistant. As part of this agreement, Iran removed the original reactor core and filled it with concrete, disabling its ability to produce weapons-grade plutonium.
