WITH the March 24th deadline for reaching agreement looming, and Israel’s prime minister, Binyamin Netanyahu, kicking up a fuss in Washington (see article), the outlines of a deal to constrain Iran’s nuclear programme are in place. But as another round of negotiations between Iran and the P5+1 countries—America, Britain, China, France, Germany and Russia—wrapped up in Montreux, Switzerland, on March 4th, there were still gaps between the parties.

The aim of the negotiators is to increase by at least a year the “breakout” time it would take Iran to create enough weapons-grade material to make a bomb—currently estimated to be about three months. To that end, in return for an easing of sanctions, Iran should reduce both the capacity of its uranium-enrichment facilities and its stocks of low-enriched uranium. According to the London-based International Institute for Strategic Studies the shape of the deal may be like this:

• Iran would cut the number of centrifuges it is using for enrichment from the 9,500 in service today to about 7,000. Most would be at Natanz; perhaps only a few hundred would be in the deep underground hard-to-bomb facility at Fordow (see map). Its other centrifuges, including 9,000 that are installed but not operating, would be placed in secure stores under the seal of the International Atomic Energy Agency.

• Much of Iran’s 8,000kg stockpile of low-enriched uranium would be either exported to Russia or converted into uranium oxide, which cannot easily be used for further enrichment.

• The way in which material passes between the remaining centrifuges would be changed so as to make it harder to get up to high levels of enrichment.

• Because bombs can also be made from plutonium, Iran’s reactor at Arak would be reconfigured to produce only around 1kg of plutonium a month.

These measures would remain in force for ten years, after which there would be a staged relaxation and the time taken for a bomb’s worth of enrichment would start to reduce again. The rate at which it might do so is a continuing concern for the P5+1 negotiators, especially as Iran wants to develop faster centrifuges between now and then.