A solution will also have to address the potential for a plutonium bomb. In May, Iran announced that the heavy-water reactor in Arak would become operational early next year. Some American and European officials claim that Iran could produce weapons-grade plutonium next summer. These two announcements indicate that Iran is making progress on this alternative track. So far, the West has not paid much attention to the potential for a plutonium-fueled weapon. Now it must do so.

A functioning nuclear reactor in Arak could eventually allow Iran to produce sufficient quantities of plutonium for nuclear bombs. Although Iran would need to build a reprocessing facility to separate the plutonium from the uranium in order to produce a bomb, that should not be the West’s primary concern. Western negotiators should instead demand that Iran shut down the Arak reactor.

This is crucial because the West would likely seek to avoid an attack on a “hot” reactor, lest it cause widespread environmental damage. Once Arak is operational, it would effectively be immune from attack and the West would be deprived of its primary “stick” in its efforts to persuade Iran to forgo a military nuclear capability.