- By Bethany Bell and David Gritten
- BBC News, in Vienna and London
The global nuclear watchdog has found uranium particles enriched to 83.7% purity – very close to weapons grade – at Iran’s underground Fordo site.
In a report seen by the BBC, the International Atomic Energy Agency (IAEA) said it was holding discussions with Iran “to clarify the matter”.
Iran has said that “unintended fluctuations” in enrichment levels may have occurred.
It has openly enriched uranium to 60% purity for two years in violation of a 2015 nuclear deal with world powers.
The deal, which was aimed at preventing Iran from developing nuclear weapons, saw the country limit its nuclear activities and allow monitoring by IAEA inspectors in return for relief from crippling economic sanctions.
However, it has been close to collapse since US President Donald Trump unilaterally withdrew and reimposed sanctions in 2018, and Iran retaliated by increasingly violating restrictions.
Uranium is a naturally occurring element that can have nuclear-related uses when it has been refined or enriched. This is achieved by using centrifuges – machines that spin at supersonic speeds – to separate out the most suitable isotope for nuclear fission, called U-235.
Low-enriched uranium, which typically has a concentration of 3-5% of U-235, can be used to produce fuel for commercial nuclear power plants.
Highly enriched uranium has a purity of 20% or more and is used in research reactors. Weapons grade uranium is 90% enriched or more.
After the US reimposed sanctions, it first resumed enrichment to 20% and then began producing smaller amounts of 60% enriched material as well – a significantly higher level than it had reached before.
The IAEA’s latest quarterly report to member states said inspectors found the 83.7% enriched uranium particles in samples taken at Fordo in late January.
The head of the Atomic Energy Organization of Iran downplayed the significance of the discovery, saying he expected it would soon be “put to rest”.
Mohammad Eslami told reporters on Wednesday that the sample was “just a particle that cannot even be seen with a microscope” and insisted that “the important thing is the volume of the product stored” after enrichment, according to the official Irna news agency.
Iran insists its nuclear activities are entirely peaceful, but experts have warned that the breaches have theoretically reduced the time it would take it to obtain enough weapons-grade uranium for one bomb if it decided to do so.
The top US Defense Department official, Colin Kahl, told a congressional committee hearing on Tuesday that this so-called “breakout time” had been shortened from 12 months to “about 12 days”.
Experts estimate that “weaponization” – producing a nuclear warhead for a missile – will still take another one to two years.