Usually talk of the Iran nuclear crisis concerns uranium enrichment. But with a deal reportedly in reach as six world powers and Tehran meeting again in Geneva on November 20, attention turned to Iran's potential to produce weapons-grade plutonium. Why is the completion of Iran's Arak heavy-water research reactor a source of concern?
What is the Arak reactor?
Iran is building a small research reactor in the west of the country that it says will be used to produce medical isotopes and generate up to 40 megawatts of thermal power. But the reactor worries Western powers because one of the byproducts in its spent fuel will be weapons-grade plutonium.
The Western powers, which accuse Iran of using its nuclear program to secretly acquire the ability to make atomic weapons, worry that the plutonium could provide Iran with an alternative to highly enriched uranium for that purpose.
Once operational, the Arak reactor could produce five to 10 kilograms of weapons-grade plutonium a year, enough for one nuclear weapon annually.
Iran has been constructing the Arak reactor since the 1990s and progress has been slow. For this reason, Arak has traditionally taken second place to concerns over Iran's uranium-enrichment track, which is moving ahead quickly.
But the Arak reactor figured highly in the latest talks between Iran and six world powers in Geneva on November 7-9 due to French concerns that a deal might be reached that satisfied fears over uranium enrichment but left open the issue of Arak. That could be dangerous because, once Arak starts operating, a military attack to destroy becomes a particularly complicated option.
"If it were to be attacked during initial startup of operations, there would be some fallout of [radiation] because you have a core with nuclear fission going on inside," says Mark Hibbs, a Berlin-based nuclear-policy expert with the Carnegie Endowment for International Peace. "But [the scale] would not be anything like an attack on a large power reactor. The real fallout would be political and diplomatic because there is an understanding in the international community that operating nuclear installations, particularly reactors where fission is going on, should not be attacked."
How close to completion is Arak?
Iran originally planned for Arak to start operating in the first quarter of 2014. However, the UN's nuclear agency says the reactor has been plagued by delays in construction and is still a long way from completion.
The head of the International Atomic Energy Agency (IAEA), Yukiya Amano, told the Reuters news agency last week that Iran still has "quite a lot to do" to complete the Arak research reactor and it is unclear when it will come into operation.
Once Arak is working, it will not pose an immediate threat. The reactor would have to run 12 to 18 months to produce enough plutonium-containing spent fuel for a bomb. Also, Iran currently does not have any known reprocessing facility for extracting the plutonium from the spent fuel rods.
Is there room for compromise?
Iran and the so-called P5+1 -- the United States, Russia, China, Britain, and France, plus Germany -- were due to meet again in Geneva on November 20. Ahead of those talks, experts suggested the Western powers could be open to accepting Arak if Iran were to agree to strict conditions for operating the plant.
"One of those options could be that once the reactor is operational, the spent fuel is removed from the country," says Kelsey Davenport, a nonproliferation analyst at the Washington-based Arms Control Association. "There is also the possibility that, in the course of a deal, the six countries negotiating with Iran could offer to replace this type of reactor with another type of reactor called a light-water reactor that does not produce that same plutonium that could be used for weapons."
Iran has invested heavily in obtaining a heavy-water reactor, including building a heavy-water production facility nearby. Whether Tehran would now accept redesigning its research reactor -- and risk losing face for capitulating to Western pressure -- is debatable.
France this week listed four conditions
for a deal to be struck with Iran, including the halt of construction on Arak. Iranian President Hassan Rohani responded by warning the West not to make "excessive demands" in negotiations, while Iran's parliament reportedly began drawing up a plan to safeguard the country's nuclear achievements -- including expansion of the Arak reactor.
How badly did Arak derail talks in Geneva this month?
When the two sides last met in Geneva earlier this month, they came closer than ever before to agreeing on a temporary, confidence-building deal that could give them the momentum to reach a later, permanent solution to the Iran nuclear standoff.
Discussions reportedly focused on suspending or rolling back key elements of Iran's nuclear program for six months in exchange for the easing of some sanctions on Tehran. But despite negotiations running a day longer than expected, no deal was reached in part because France objected to the fact that the plan would only commit Iran to not starting up the Arak reactor for half a year, not to suspending all work on it.
According to Hibbs, although Arak proved to be one of the thorniest issues on the table in Geneva, the disagreements over it may yet prove temporary.
"I think when cooler heads prevail what we may see is a suspension [of essential activities] agreed to between Iran and the [world] powers," he says. "That would mean that Iran would agree not to fabricate the fuel [for Arak] and it might mean the Iranians would agree not to build and construct things in areas that the IAEA needs to see to design an effective safeguards system for the reactor. If the Iranians were to agree to suspend these essential activities, the French and others should be satisfied and the powers and Iran can conclude their agreement and move to the next phase."
What happens next?
Since the last round of negotiations in Geneva, Iranian nuclear officials have made one concession that directly involves Arak.
In an agreement last week with the IAEA, Tehran said it would provide "managed access" to two important nuclear facilities that have not been regularly viewed by arms inspectors. One is a uranium mine; the other is the plant that produces heavy water for the Arak reactor.
Davenport sees this as a positive sign.
"The fact that Iran is now letting the IAEA visit the heavy-water production plant is a huge step forward," he says. "The agency has been trying to visit that site since 2011 and has not been able to. So, that's definitely a plus."