Enriched uranium can be used in power plants; or, if more highly enriched, in a bomb.© Punchstock

Tensions have run high in the past week over Iran's nuclear ambitions. And today, Iranians restarted work at their uranium production plant, ending an agreement they had to put such activity on hold. The UN's nuclear watchdog, the International Atomic Energy Agency (IAEA), has monitored the country for some years, and this week installed cameras in the production plant to watch over proceedings.

Tehran says that its uranium production is geared towards a civilian nuclear programme, but the United States fears that they intend to develop nuclear warheads. news@nature.com takes a look at what's going on.

What happens at Iran's uranium plant in Isfahan?

The Isfahan plant is a chemical refinery, which takes purified uranium oxide (U₃O₈) ore, known as yellowcake, and turns it into uranium hexafluoride (UF₆). This is just one stage in the complicated process of delivering uranium that can undergo fission in nuclear power plants and some nuclear weapons. "The uranium conversion facility in Isfahan has started its activities under IAEA supervision," Mohammad Saeedi, deputy head of Iran's Atomic Energy Organization, told reporters at the plant today.

Where does Iran get its uranium ores?

Iran has one of the largest deposits of uranium ore in the Middle East, and has mined it at Saghand since February 2003. Yellowcake will be extracted from the ore at a plant in Bandar Abbas once it begins operating this year.

What will they do with the refined uranium?

The only reason for producing uranium hexafluoride is that it can be enriched to boost the proportion of uranium-235, the isotope responsible for fission reactions. This involves turning the chemical into a gas, and feeding it through a series of centrifuges that spins the chemical to separate uranium-235 from its heavier and less fissile cousin, uranium-238.

Natural uranium ore contains about 0.7% uranium-235. Reactor-grade uranium needs a few percent. Nuclear weapons need more than 80%.

At the moment, Iran says it has no immediate plans to enrich the uranium hexafluoride produced at Isfahan, which will contain no more uranium-235 than raw uranium ore.

But Iran also says it would like to develop a nuclear energy programme, to help meet rising electricity demands; they say they would prefer to export their oil for profit, rather than burning it at home. The country is about a year away from finishing a 1,000-megawatt reactor being built at Bushehr. This reactor is specifically designed to use enriched uranium fuel, so it is presumed they will aim to enrich their uranium at some point in the future.

Does Iran have the capacity to enrich uranium?

An enrichment plant at Nantanz already houses a few hundred centrifuges, and several thousand more are planned. But large-scale enrichment is not yet possible in Iran, says IAEA spokesman Peter Rickwood. Enriching to weapons-grade uranium-235 requires many thousands of centrifuges, which poses serious engineering challenges.

But Paul Leventhal, founder of the Nuclear Control Institute, a Washington DC-based group that lobbies to prevent nuclear proliferation, notes that the IAEA's assessment may not be the whole story. "The IAEA doesn't have a very good track record for finding undisclosed nuclear facilities," he says.

Why is the International Atomic Energy Agency so worried?

There are few short-term worries. But in the long term, the same technology used to develop a civilian nuclear programme would give Iran access to the material needed for a nuclear bomb.

The country has concealed details of its nuclear activities from the IAEA in the past. So the authority has now installed cameras in the Isfahan factory to see how much uranium comes into the factory, how much goes out, and whether any goes missing along the way.

If Iran did start enriching its own uranium sometime in the future, the IAEA would like to monitor that too, just as it does in many other countries with civilian nuclear power programmes but no weapons. Uranium enriched to a few percent is fine - a few tens of percent is not.

How easily could this material be used to make a bomb?

Not easily at all. Several kilograms of uranium-235 are needed to reach the critical mass for a nuclear explosion, which would come from processing several tonnes of uranium hexafluoride using machinery that the country doesn't yet have.

Leventhal agrees with recent US security service assessments that Iran could still be a decade away from having a nuclear weapon. But he adds that many think it is a case of when, rather than if, Iran pursues nuclear weapons, and so he argues that the country should not be allowed to develop nuclear energy. "My bottom line is that this regime should not be allowed to go nuclear," says Leventhal. 

Nuclear Control Institute