Iran's nuclear programme explained: uranium enrichment, IAEA stockpile and the path to talks

The proposed ceasefire between the United States and Iran is being held up by one central issue — Iran's nuclear programme. For nearly three decades, Washington has argued that Tehran is close to building a nuclear bomb. Iran has consistently denied this, saying its programme is meant only for civilian purposes such as electricity generation and medical research. The US strikes of June 2025 hit several Iranian nuclear sites, but a large part of Iran's highly enriched uranium is believed to have survived. As fresh nuclear talks are being prepared, here is an explainer of how the technology works and what is actually at stake.

Uranium is the most common fissile material used in both civilian reactors and nuclear weapons. In its natural form, uranium is mostly the heavier U-238 isotope (more than 99 per cent). Only a small share (about 0.7 per cent) is the lighter U-235 isotope, which is much easier to split (fissile). To make uranium useful as fuel or as a weapon, the proportion of U-235 must be raised — a process called enrichment. Enrichment is done in centrifuges, which spin very fast and separate the two isotopes.

Different uses require different levels of enrichment. A nuclear power plant typically needs uranium enriched to between 3 and 5 per cent. Uranium becomes "highly enriched" at 20 per cent purity. Nuclear weapons normally need enrichment of 90 per cent or more. The reactors that power US nuclear submarines are also reported to use such weapons-grade fuel. An important physics point is that the higher the enrichment level, the easier it becomes to push it up further — so going from 60 per cent to 90 per cent is a much shorter step than going from natural uranium to 5 per cent.

According to International Atomic Energy Agency (IAEA) estimates cited just before the Israeli strikes of June 13, 2025, Iran had stockpiles of uranium enriched at various levels. Iran has officially said it has capped enrichment at 60 per cent and has not aimed for the 90 per cent weapons-grade level. The worry is that there is almost no civilian use for uranium between 20 per cent and 90 per cent — most reactors only need 3-5 per cent. The IAEA has stated that the 60 per cent stockpile, if pushed further, would be enough material for about 10 nuclear weapons. After the June 2025 strikes, IAEA Director General Rafael Grossi said "a bit more than 200 kg" of the 60 per cent material is believed to be intact at a tunnel complex in Isfahan and at Natanz.

The diplomatic backdrop is the 2015 Joint Comprehensive Plan of Action (JCPOA), commonly called the Iran nuclear deal. Signed by Iran, the United States, the United Kingdom, France, Germany, Russia, China and the European Union, the JCPOA capped Iran's enrichment at 3.67 per cent and gave the IAEA wide inspection rights, in return for sanctions relief. The first Trump administration withdrew the US from the deal in 2018, arguing it did not cover Iran's ballistic missile programme or its support to regional militant groups. Iran then gradually expanded enrichment.

Before the 2026 war, according to Omani Foreign Minister Badr al-Busaidi, Iran had signalled willingness to stop stockpiling, to "down-blend" its 60 per cent material into reactor-grade fuel and to allow US inspectors. The June 2025 strikes interrupted that process. Iran has since used the Strait of Hormuz — through which a fifth of the world's oil normally moves — as leverage. The current ceasefire is fragile and Trump has said Iran must end its Hormuz chokehold and dismantle its bomb-making capacity, terms that Tehran has not yet accepted.

Reports suggest a possible compromise. Iran may agree to send about half of its 60 per cent enriched stockpile to a third country in exchange for 5 per cent reactor-grade material, and dilute the rest inside Iran. Kazakhstan has reportedly indicated willingness to receive the material — a procedure that was used in a limited form under the 2015 deal as well.

For India, the issue matters on three counts — energy security (Iran's role and the Strait of Hormuz), regional stability in West Asia where about nine million Indian citizens live and work, and India's principled stand at the IAEA Board of Governors and the United Nations. India has consistently supported a diplomatic resolution to the Iran nuclear issue.

For exam preparation, this story is a good case study of nuclear physics basics, the working of the IAEA, the JCPOA and India's West Asia policy.