What are the nuclear sites at the heart of Iran's controversial programme?

Regime's main bases feature uranium enrichment plants, nuclear power plants and research reactors

An Iranian technician at work at Isfahan, where uranium is converted. AFP

Iran's nuclear programme began taking shape in the 1950s under the former shah, Mohammad Reza Pahlavi. In a far cry from today’s tension, it did so with US backing, under Washington’s Atoms for Peace drive, aimed at promoting peaceful use of nuclear technology and helping develop civilian nuclear power in allied nations.

The Tehran Nuclear Research Centre was created and after a small research reactor arrived from the US, Iran's nuclear programme was under way.

Iran has stepped up its nuclear programme in recent years, after a landmark deal with world powers – the UK, US, Germany, France, Russia and the EU – curbing its nuclear activities in exchange for sanction relief, began to unravel in 2018 when the US unilaterally withdrew.

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A number of nuclear sites have been built that Tehran says are used for peaceful reasons only. Five round of talks with the US to renew a nuclear agreement this year have failed to produce any substantial results.

A day after the International Atomic Energy Agency (IAEA), the UN's nuclear watchdog, passed a resolution declaring Iran in breach of its non-proliferation obligations for the first time in almost 20 years, Israel launched an attack on Iranian nuclear and military sites on Friday, killing some senior military commanders.

Here is a look at some of the major nuclear sites and their importance to Tehran’s programme.

Uranium enrichment plants

Natanz

The country’s main enrichment site lies about 220 kilometres south-east of Tehran, outside the holy city of Qom. Part of the complex is underground to defend nuclear infrastructure from potential air strikes. Here, groups of centrifuges work together to enrich uranium quickly.

Natanz features two main branches: the vast underground fuel enrichment plant (FEP) and the pilot enrichment plant (PFP).

An exiled Iranian opposition group revealed in 2002 that Iran was secretly building Natanz, igniting a diplomatic stand-off between the West and Iran over its nuclear intentions that continues today.

The FEP, built for enrichment on a commercial scale, has the capacity for 50,000 centrifuges. Around 16,000 are currently installed, 13,000 of which are in operation, refining uranium to up to 5 per cent purity.

Natanz was targeted by the malicious Stuxnet computer virus, believed to have been an Israeli-US creation, which destroyed some centrifuges. Two separate sabotage attacks, attributed to Israel, also have struck the site.

Israel’s Prime Minister Benjamin Netanyahu on Friday said the Israeli attack had “struck at the heart of Iran’s nuclear enrichment programme”, in a televised address. “We targeted Iran’s main enrichment facility in Natanz."

IAEA director general Rafael Grossi confirmed the Natanz site was "among targets".

A view of the Isfahan enrichment complex in Iran. Maxar Technologies / AFP

Fordow enrichment site

Secretly built in breach of UN resolutions under a mountain near Qom, Fordow is protected by anti-aircraft batteries which means it is better protected from potential bombardment than the Natanz FEP.

Fordow is 100km south-west of Tehran and also houses centrifuge cascades, but it smaller than Natanz. Construction began in 2007, the IAEA estimates, although Iran informed the watchdog about the plant as late as 2009 after the US and allied western intelligence agencies became aware of it. US president at the time, Barack Obama, said: "The size and configuration of this facility is inconsistent with a peaceful programme."

The 2015 deal with major powers did not allow Iran to enrich uranium at Fordow. There are now about 2,000 centrifuges there, most of them advanced IR-6 machines, of which up to 350 are enriching by to up to 60 per cent.

In 2023, uranium particles enriched up to 83.7 per cent were discovered at the Fordo plant, which Iran claimed were the product of "unintended fluctuations" during the enrichment process.

Nuclear power plant

Bushehr

Iran's only operating nuclear power plant, on the Gulf coast, is 750km south of Tehran. Construction began under Iran’s Shah Mohammad Reza Pahlavi in the mid-1970s. After the 1979 Islamic Revolution, the complex was repeatedly targeted in the Iran-Iraq war.

A German company began the building project, which was halted by the revolution and later completed by Russians. Bushehr began operating at a lower capacity in 2011 before being plugged into the national power grid in 2012. It is fuelled by uranium produced in Russia, not Iran, and is monitored by the IAEA. Iran is in the process of building two similar reactors on the site.

Towers at the Arak heavy water nuclear reactor loom into view in central Iran. AP

Uranium conversion and research reactors

Arak heavy water reactor

Work on the Arak heavy-water research reactor on the outskirts of the village of Khondab began in the 2000s but stopped under the terms of the 2015 deal.

Iran has since informed the IAEA of plans to commission the reactor by 2026.

The research reactor was officially intended to produce plutonium for medical research and the site, 250km south-west of Tehran, features a production plant for heavy water, which helps cool nuclear reactors but produces plutonium as a by-product that can be used in nuclear weapons. That could provide Iran another path to the bomb beyond enriched uranium.

Iran had agreed under its 2015 nuclear deal to redesign the Arak plant to allay proliferation concerns.

Isfahan houses a nuclear fuel fabrication site that produces low-enriched fuel for power plants. AFP

Isfahan Nuclear Technology Centre

The complex in Isfahan, 350km south-east of Tehran, employs thousands of nuclear scientists. It is home to three Chinese research reactors and laboratories associated with Iran’s atomic programme. The plant was industrially tested in 2004 after completion.

The Isfahan centre also houses a nuclear fuel fabrication site, which opened in 2009 and produces low-enriched fuel for power plants.

The Tehran Research Reactor is stationed at the headquarters of the Atomic Energy Organisation of Iran, the civilian body overseeing the country’s atomic programme. The US provided Iran with the reactor in 1967 as part of America’s “Atoms for Peace” programme during the Cold War. It initially required highly enriched uranium but was later retrofitted to use low-enriched uranium after proliferation concerns.

In July 2022, Iran announced plans to construct a new research reactor at the site.