Iran’s tritium puzzle: The final ingredient in a nuclear bomb?

By Shyam Bhatia

London, July 6. With international attention fixated on uranium enrichment at Natanz and Fordow, a quieter but arguably more significant question is gaining traction among nuclear experts: Has Iran mastered tritium production?

Tritium – an unstable isotope of hydrogen used to boost the yield and efficiency of nuclear weapons – is notoriously difficult to produce and even harder to store.

Its presence would indicate that Tehran is not merely building a bomb, but preparing to miniaturise it for missile delivery.

“Tritium and deuterium gas can be used as fusion fuel in boosted nuclear weapons, making the warhead smaller, lighter, and more powerful,” according to Dr David Albright, founder of the Institute for Science and International Security (ISIS), in a 2022 technical briefing. “That capability represents a significant advance beyond just enriched uranium.”

Unlike uranium, which can be stockpiled for decades, tritium decays relatively quickly, with a half-life of 12.3 years. Any indication that Iran has tritium on hand implies ongoing production or recent acquisition.

In 2019, then head of Iran’s Atomic Energy Organization, Ali Akbar Salehi, acknowledged publicly that Tehran had misled international partners over the redesign of the Arak heavy water reactor.

“We had bought tubes, but we didn’t tell the other side,” Salehi told Iran’s IRIB news.

“We told them the tubes were filled with cement. But we had not disposed of all of them.”

According to Olli Heinonen, former deputy director-general of the IAEA, Iran’s old Arak design could have produced plutonium and tritium if a deuterium target was inserted. While the reactor was to be modified under the JCPOA, that redesign remains incomplete.

As far back as 2015, he warned a Foundation for Defence of Democracies (FDD) panel: “Arak is a classic plutonium production reactor. And yes, if you insert lithium or deuterium targets, you could also produce tritium.”

The 2020 revelation of the so-called “Rainbow” site – near the Khojir missile complex – by the National Council of Resistance of Iran (NCRI) added fresh urgency to the tritium question. NCRI previously exposed Iran’s nuclear enrichment facilities at Natanz and Arak in 2002, a disclosure later verified by the IAEA.

“We believe this site is being used to work on nuclear weapon triggers and advanced warhead design,” said Mehdi Abrishamchi, a senior NCRI figure, during a Paris press conference in September 2020. “The Iranian regime is now focusing on weaponisation.”

Western governments have treated NCRI disclosures with caution, but acknowledge their past accuracy. The US State Department noted in a 2021 background briefing that “certain NCRI claims have proven credible over time”.

The National Council of Resistance of Iran (NCRI) is an exiled Iranian opposition group that functions as the political umbrella for the Mujahedin-e Khalq (MEK), a formerly armed resistance group once classified as a terrorist organisation by the US, UK, and EU – but no longer.

Founded in 1981, the NCRI is headquartered in Auvers-sur-Oise, near Paris. It claims to be a secular, democratic alternative to the Islamic Republic and regularly engages Western policymakers.

Maryam Rajavi serves as the group’s president-elect. She is the widow of Massoud Rajavi, the long-time MEK leader who disappeared from public view in 2003 and is presumed dead or in hiding.

The MEK began as an Islamist-Marxist guerrilla group in the 1960s and fought both the Shah and the post-revolution clerical regime. During the Iran-Iraq War, it controversially allied with Saddam Hussein, establishing Camp Ashraf in Iraq. This alliance damaged its credibility among many Iranians.

NCRI gained global notice in August 2002, when it revealed the secret nuclear facilities at Natanz and Arak – a disclosure later confirmed by the IAEA. Since then, it has continued releasing satellite imagery and dossiers on Iran’s covert activities, including the “Rainbow” site.

While Iran dismisses the NCRI as a front for “traitors and terrorists”, the group remains a key source for dissident information. The US State Department acknowledges that some of its revelations have proven accurate.

Multiple expert assessments – including from the International Institute for Strategic Studies (IISS) – have suggested that Iran likely received tritium-related documentation from Pakistan’s AQ Khan network, including blueprints for neutron initiators.

In a 2009 IISS report titled Nuclear Black Markets, the authors stated: “Some of the materials offered by Khan’s associates included Chinese-supplied designs for nuclear weapons that contained references to tritium-boosted fission triggers.”

Although the Iranian government has denied any such involvement, former Pakistani investigators confirmed that Iran was among the recipients of the Khan network’s assistance prior to 2003.

North Korea is another suspected source. According to a 2015 Mossad assessment, reported in the British media, Iran had obtained “information related to nuclear triggering mechanisms consistent with those tested by North Korea”. While no direct tritium transfer was cited, the implication was that cooperation may have extended beyond blueprints.

Former US State Department non-proliferation official Mark Fitzpatrick has noted in public interviews that “Iran’s nuclear programme has certainly benefited from outside help – whether from Pakistan or indirectly from North Korea.” He added that “the tritium question remains open”.

The renewed interest in tritium is not merely academic. Experts fear that if Iran has secured a tritium supply – or the means to produce it domestically – it could signal the regime’s readiness to build a deliverable nuclear weapon, as opposed to simply maintaining a breakout threshold.

David Albright wrote in a 2023 ISIS report: “Tritium is a final-stage ingredient. Its presence suggests weaponization planning is advanced, not theoretical.”

In the mid-1990s, the Natanz site was still a patch of desert, but NCRI insiders were already whispering its name to selected reporters.

Some, including myself, were guided – blindfolded at times – toward unnamed facilities near Isfahan and Parchin, where underground chambers, high-voltage cables, and sealed concrete bunkers hinted at projects far removed from peaceful energy.

That was before Arak. Before Rainbow. Before the IAEA found uranium particles in places Iran said inspectors had no business being.

And now, there is tritium.

(Shyam Bhatia is author of Nuclear Rivals in the Middle East, published by Routledge).