The continuing nuclear talks with Iran have just entered their most challenging phase. During the next six months, the US and its negotiating partners will try, in the words of President Barack Obama, to persuade Iran to agree on a “peaceful nuclear programme,” including a “modest enrichment capability,” that leaves it short of the ability to produce nuclear weapons.

This task will be far harder to achieve than is generally understood.

A civilian programme to enrich uranium for nuclear power must, by its nature, be many times larger than a bomb programme. That is the opposite of what most people think. In fact, a small-scale enrichment programme for nuclear power does not really exist. To understand why, let us look at some numbers.

Everyone is worried about Iran’s centrifuges, the fast-spinning cylinders that enrich uranium. The cylinders can be used to make fuel for either power reactors or bombs. For comparison, it takes 25 times more enrichment power to fuel a standard-size, 1,000-megawatt reactor such as the one the Russians built in Bushehr, Iran, than it does to fuel a single bomb. Put another way, if Iran had the enrichment power to fuel the Bushehr reactor for a year and instead decided to make bombs, it could produce the fuel for a nuclear warhead every 15-25 days a year. No deal with the US will allow Iran to have such power. Moreover, such capability will be a vast scale-up of Iran’s current programme. Iran now produces about 1.9 metric tonnes of enriched uranium a year. It takes approximately 20 metric tonnes to fuel a 1,000-megawatt reactor. To fuel a smaller, 360-megawatt reactor (which Iran says it will build), Iran would have to produce three times as much enriched uranium as it does now. Either option will allow Iran to fuel several nuclear weapons a year, if it chose to do so.

If Iran cannot be permitted to make the fuel for a power reactor, what good are its centrifuges? Their only possible use will be to fuel a non-power reactor, such as the small research reactor in Tehran. However, Iran has already enriched more uranium than the Tehran reactor needs for the foreseeable future. Iran’s centrifuges do not fit into a peaceful nuclear power programme. There are far too few to fuel a power reactor, but quite enough for nuclear weapon production. This unfortunate fact hangs over the negotiations. So far, Iran’s centrifuges have enriched a stockpile of uranium that is two-thirds of the way to weapons-grade. By enriching its stockpile further, the Iranians could fuel about six nuclear weapons.

How will these numbers affect the talks? Is it possible for Iran to have a “modest enrichment capability” that cannot fuel a weapon?

One solution will be for Iran to keep running its centrifuges and get rid of its stockpile of enriched uranium. In this scenario, Iran’s centrifuges could be fed by natural uranium only. Starting at that level will require more power and time to produce weapons-grade fuel. If using natural uranium, the centrifuges Iran currently operates will need more than six months to enrich enough uranium for a bomb. That will give other countries time to intervene if Iran tries to make a dash for the bomb. The enriched uranium Iran has already produced can be sent to Russia, where it can be fashioned into fuel rods not readily convertible to weaponry. And Iran will have to leave approximately 9,000 of its centrifuges — about half — installed but non-operational.

Another option will be for Iran to keep its enriched uranium, but further scale back the operation of its centrifuges. This will be necessary because, theoretically, the roughly 9,000 operating centrifuges Iran currently has, if fed enriched uranium, will need only about two months to enrich enough uranium for a bomb. Because Iran has never enriched uranium to weapons-grade, the real timeline will be longer, but it is difficult to know how much. To theoretically extend the enrichment time to six months, Iran can operate no more than 3,000 centrifuges, leaving some 15,000 dormant.

For either option to work, Iran will have to allow inspectors unfettered access to its nuclear programme, to guard against cheating. It also will have to dismantle or modify the large, plutonium-producing research reactor it is building in Arak, relinquish and stop expanding its small stockpile of uranium enriched to 20 per cent and agree to not operate additional centrifuges.

Will the Iranians agree? So far, the odds seem long. Iran has trumpeted its plans to expand, not contract, its supply of centrifuges. Nevertheless, the US must insist upon one of these options. Otherwise, Iran will be left with centrifuges that contribute nothing to civilian nuclear energy, but provide a clear path to the bomb.

— Washington Post

Gary Milhollin is president of the Wisconsin Project on Nuclear Arms Control, which publishes IranWatch.org; Valerie Lincy is executive director of the Wisconsin Project.