As the U.S. intelligence community has consistently noted since 2007, Iran has the scientific, technical, and industrial capacity to produce nuclear weapons if it chooses to do so. The U.S. intelligence community has also assessed that if Iran were to make a decision to build nuclear weapons, it is more likely that it would seek to do so by means of undeclared, secret facilities, a scenario sometimes called a “sneak-out.”
Thus, the realistic goal of the P5+1 for the final deal was not to make breakout impossible but to make it a more difficult and unattractive policy option for Iran.
The JCPOA accomplishes this core goal by putting in place restrictions on its uranium-enrichment capacity, the level of uranium enrichment, its uranium stockpile, and research and development in a way that lengthens the time it would take for Iran to amass enough bomb-grade nuclear material to no less then 12 months for more than a decade, by eliminating its ability to produce and separate plutonium for at least 15 years, and by putting in place stringent monitoring and verification mechanisms to quickly detect and deter any attempt to pursue a covert program.
The JCPOA will limit Iran’s installed centrifuges to 6,104 IR-1 centrifuges, of which 5,060 will be used to enrich uranium for 10 years. This, combined with the 300-kilogram limit on Iran’s stockpile of 3.5 percent enriched uranium gas, increases the time it would take Iran to accumulate enough material for one bomb to more than a year, if such an effort were not detected.
Other restrictions limit Iran’s breakout potential through the uranium route. For 15 years, Iran’s low-enriched uranium stockpile cannot exceed 300 kg. Agreed limits on Iran’s deployment of advanced centrifuge machines in years 11-13 of the JCPOA will ensure that its overall enrichment capacity remains the same. Given other reporting requirements and monitoring of Iran’s centrifuge program through year 20 of the agreement, Tehran will not have the ability to quickly ramp up its enrichment capacity without prompt detection.
It is important to remember that the milestone being measured in this definition of “breakout” is the accumulation of enough uranium hexafluoride gas for one bomb, not the bomb’s actual construction or initial operating capability. Although the production of fissile material is arguably the most resource intensive and difficult step toward building nuclear weapons, there are several additional technical hurdles, including designing and constructing an explosive device and integrating it into a delivery system (most likely a ballistic missile) so it would reliably detonate.
Iran would need to convert the material into powder form, fabricate the metallic core of the weapon from the powder, assemble other weapons components that had been previously developed or acquired on an independent track, and integrate the weapons package into a delivery vehicle.
This process could be more easily hidden, but it would require several months or longer.
States developing nuclear weapons typically conduct multiple, large-scale nuclear test explosions to perfect their warhead designs, particularly the smaller, lighter, and more efficient designs needed for missiles.
With existing U.S. national means of intelligence and the International Monitoring System established to verify compliance with the Comprehensive Test Ban Treaty, any Iranian test would very likely be detected. If Iran were to try to “sneak out” to build nuclear weapons, Tehran would have to accept a lower confidence level concerning its warhead design or risk detection.
Iran is very unlikely to break out of the nuclear Nonproliferation Treaty to acquire only one nuclear weapon.
Even if Iran were willing to tolerate the large uncertainties deriving from an untested nuclear weapons design, a single weapon would add additional uncertainties regarding missile performance and the ability of the warhead to penetrate the sophisticated missile defenses deployed in the region. Tehran would be staking everything on the perfect performance of one untested system. It is highly improbable that Iran would plan to break out of the NPT by building only one nuclear weapon. Calculating timelines based on a one-device scenario therefore compounds the misimpression already left by using a breakout definition that falls short of actually building a weapon.
However, if Tehran were to choose to increase the odds of success by planning to build multiple weapons, it would increase the need for fissile material, thus lengthening the breakout timelines and increasing the chances of international detection and blocking actions.
The robust inspection regime in the JCPOA would include increased reporting requirements for Iran on its nuclear activities and grant the right of timely, on-site inspections at undeclared sites to the International Atomic Energy Agency. While designed to detect clandestine enrichment activities, such a regime will also significantly enhance the collection of information relevant to the identification of post-enrichment activities that could be targeted to disrupt a weapons program.