Ariane Tabatabai in Bulletin of the Atomic Scientists:
Amid the thorny nuclear negotiations between Iran and six world powers, most observers have recognized two main sticking points: How much to limit Tehran’s ability to enrich uranium, and how sanctions will be lifted. But as meetings resume between Iran and its negotiating partners—the United States, the United Kingdom, France, Russia, China, and Germany, also known as the P5+1— an issue once thought settled is anything but.
The Arak Heavy Water Reactor, also known as IR-40, almost derailed the initial rounds of talks in 2013. Following the conclusion of the interim deal in November of that year, French Foreign Minister Laurent Fabius expressed his concerns over the reactor, telling the French newspaperLe Monde (link in French) that “Arak, the most proliferation-prone facility, the one producing the most plutonium, is not necessary for civilian use. But once it goes online, we cannot destroy it.”