Technical elements of Iran deal put the brakes on nuclear breakout

A once-secret nuclear facility deep under a mountain near Iran’s holy city of Qom is slated to become one of the world’s most unusual international research centers. A plutonium-producing reactor will be reengineered and downsized. And enough enriched uranium to make several atomic bombs will be removed or diluted. These and other technical elements of the action plan on Iran’s nuclear program announced yesterday seek a delicate balance: preventing Iran from building an atomic arsenal while allowing it to retain significant nuclear R&D.

A final agreement, in which Iran will dismantle parts of its nuclear program and accept international inspections in return for the lifting of international sanctions, isn’t due until the end of June. But the technical fixes announced yesterday have raised hopes that negotiators will be able to reach a final agreement. “It’s great that they persevered, with all the opposition,” says Frank von Hippel, a physicist and arms control expert at Princeton University.

The goal of the United States and its negotiating partners is to slow Iran’s “breakout time”—the timescale of a crash effort to porduce enough weapons-grade fissle material for one bomb—from an estimated 2 to 3 months to at least a year. One major bone of contention has been the Arak heavy water reactor. Iranian officials say the chief aim of the 40-megawatt fission reactor, under construction in the central province of Markazi, is to make radioisotopes for medicine. But simply running the reactor on its natural uranium fuel would yield about 10 kilograms of plutonium a year, enough for one or two atomic bombs. To greatly reduce the amount of plutonium generated in Arak’s spent fuel, von Hippel and others had proposed changing the fuel to low-enriched uranium (LEU), which would greatly curtail plutonium production.

But to von Hippel’s surprise, Iran has, in principle, agreed to an even more stringent alteration. LEU fuel is more compact than natural uranium fuel and would thus take up less space in the core. Iran has said it will downsize the calandria—the vessel in which a core resides—making it harder to later reconfigure the reactor to switch back to natural uranium fuel and produce more plutonium. Von Hippel says the fuel swap alone would lengthen the breakout time Iran would need to build a plutonium bomb to more than 1 year. Iran’s commitment to a smaller calandria would “go well beyond that,” von Hippel says.

Several other facets of the Joint Comprehensive Plan of Action (JCPOA) are aimed at extending Iran’s breakout time for a uranium-based bomb. For starters, Iran has agreed to reduce the number of installed centrifuges for enriching uranium from about 19,000 to 6104—all of which would be Iran’s first-generation IR-1 centrifuge rather than a more advanced model. It will also reduce its LEU stockpile from 10,000 kilograms down to 300 kilograms. Iran would have two basic options for achieving that reduction: exporting the excess LEU or blending it with depleted uranium, which, compared with natural uranium, has less of the fissile isotope uranium-235. The most logical solution, experts say, would be to send the 9700 kilograms of LEU to Russia for conversion into fuel rods for Iran’s Russian-built Bushehr nuclear reactor, in operation since 2011.

One intriguing wrinkle of JCPOA is a plan to create what U.S. Energy Secretary Ernest Moniz calls an “international physics center” at the Fordow nuclear site. This secret facility for uranium enrichment came to light in 2009, 2 years after Iran started building it. The plan calls for largely gutting Fordow: removing about two-thirds of its centrifuges and other infrastructure. The remaining centrifuges will not be used to enrich uranium. Both the centrifuges and the remaining space would be open to foreign researchers. The proposal “is a great idea to get [Iran] into the international research community,” says Siegfried Hecker, a plutonium specialist at Stanford University in Palo Alto, California, and former director of Los Alamos National Laboratory.

Iran had insisted from the outset that it would close none of its nuclear facilities. Converting one of its most controversial sites to a civilian R&D center “is clearly a face-saving gesture,” says physicist James Acton, a nonproliferation expert at the Carnegie Endowment for International Peace in Washington, D.C. “It’s not clear what sort of research will be done at Fordow,” says Pierce Corden, a disarmament expert and visiting scholar at AAAS (publisher of ScienceInsider). Von Hippel speculates that the remaining centrifuges there could be used to make purer preparations of mercury isotopes for fluorescent lighting, for example, or for enriching molybdenum-98, which could then be irradiated with neurtons to produce molybdenum-99, a radioisotope used in medicine. “It is likely not going to do much for basic physics,” Hecker says. “But isotope work would be great.”

Others are skeptical. “It is very speculative at this stage,” says Yousaf Butt, senior scientific adviser to the British American Security Information Council in Washington, D.C. “I sincerely doubt American and Iranian nuclear scientists will be working together anywhere anytime soon.”

Nuclear negotiators have set a 30 June deadline to hammer out a final agreement. Until then, Acton says, it’s worth bearing in mind that “we don’t have a deal yet.”

Corrections and clarifications, 4/6/2015, 10:30am: Errors regarding the amount of enriched urnaium affected by the agreement, and the role of molybdenum-99,  have been corrected. Details regarding operations of the Arak reactor have been clarified.