How Close Is Iran to a Nuclear Bomb, Really?

Experts say Tehran has the capability to build a nuclear weapon within a few years but perhaps not the intent.

Iranian President Hassan Rouhani (left) and then-Swiss President Alain Berset hold a joint press conference in Bern, Switzerland, on July 3, 2018.
Iranian President Hassan Rouhani (left) and then-Swiss President Alain Berset hold a joint press conference in Bern, Switzerland, on July 3, 2018. RUBEN SPRICH/AFP/Getty Images

Iran confirmed on Monday that it has breached the limit on its stockpile of enriched uranium set by the 2015 nuclear deal, renewing concerns that Tehran could, within months, have enough weapons-grade uranium to build a nuclear bomb.

But experts say the violation is more of a symbolic move than a concrete step toward obtaining a nuclear weapon. Though most agree that Iran has the expertise and capability to eventually build such a device, it is not clear that Tehran has the intent or even sees the necessity of doing so.

“This is not a dash to a nuclear bomb,” said Kelsey Davenport, the director of nonproliferation policy at the Arms Control Association. “It is a calculated move designed to gain leverage in negotiations with the Europeans, Russia, and China on sanctions relief.”

Tehran has recently ratcheted up pressure on the remaining adherents to the nuclear deal to provide some sort of relief to U.S. President Donald Trump’s “maximum pressure” campaign. Iran has allegedly attacked oil tankers in the Gulf of Oman and most recently shot down a U.S. military surveillance drone, nearly provoking a U.S. missile attack that Trump aborted at the last minute. The regime is also threatening to suspend other commitments under the 2015 deal in just days unless European powers provide sanction relief.

The 2015 deal caps Iran’s levels of uranium enriched to 3.67 percent purity—called “low-enriched uranium” and suitable for producing fuel for nuclear power reactors—at 300 kilograms. But there are still a number of steps Iran would have to take in order to build a bomb, Davenport explained.

Tehran would need 1,050 kilograms of low-enriched uranium to make the core of one bomb, according to Joe Cirincione, the president of the Ploughshares Fund. Then, Iran would have to further enrich it, to 90 percent purity, using centrifuges until it had about 25 kilograms of what is called “highly enriched uranium.”

Experts estimate that it would take about a year for Tehran to enrich enough weapons-grade uranium for a nuclear bomb, also called the “breakout point”—potentially faster if Iran violates other parts of the 2015 accord. The fact that Iran has exceeded that 300-kilogram limit does not significantly change that timeline, Davenport said.

Prior to the 2015 agreement Iran had more than 10,000 kilograms of low-enriched uranium, but was required to ship 98 percent of it out of the country, according to Cirincione.

Once Iran has enough weapons-grade uranium for a core, it would then have to convert that uranium from gas to metal, fit it with an explosive package that could ignite the fission reaction, and mount it on a ballistic missile, Davenport said.

Going from breakout to actually having a deployable nuclear weapon could take anywhere from a few months to another year, experts estimate. Recent information about the Amad plan, Iran’s now covert nuclear weapons research program, indicates that Iran was in 2003 constructing the necessary facilities, including the Shahid Boroujerdi in Parchin, said Olli Heinonen of the Foundation for Defense of Democracies. Such an installation could still exist or be reconstructed fairly quickly, reducing the time it takes Iran to get to a full nuclear weapon, he said.

While the U.S. intelligence community assessed in 2007 that Iran had mastered the steps necessary to build a nuclear weapon, including research on mating a warhead with certain types of ballistic missiles, the regime has not actually tested that capability yet, Davenport stressed.

Experts agree that Iran has the capability to eventually build a nuclear bomb. But whether the regime will actually do so is a very different question. In what could be a signal to the White House that Tehran is open to further talks, Iranian Foreign Minister Mohammad Javad Zarif said late last month that Iran will never pursue a nuclear weapon, arguing that Islam prevents the country from doing so.

Retired Vice Adm. John Miller, who commanded the U.S. Navy’s 5th Fleet, said Iran likely realizes that obtaining a nuclear weapon would not provide much military advantage.

“Let’s just say for a hypothesis that, a year from now, Iran has a nuclear weapon—what’s going to happen next? What’s going to happen next is the Saudis are going to have a nuclear weapon,” Miller said. “Israel is a nuclear power, and now you have two Gulf states that are nuclear powers. What does that buy you in terms of actual military dominance? … It doesn’t strategically buy [Iran] anything over the long term.”

However, Tehran’s calculus could change, particularly if the United States decides to conduct a military strike targeting Iran’s nuclear facilities, Davenport warned. At that point, Iran could decide it needs a nuclear weapon to deter against future aggressive U.S. action.

The next few weeks could bring an indication of whether Tehran has actually decided to pursue a nuclear weapon. The next deadline is July 7, at which point Iran has said it would begin increasing enrichment levels to greater than 3.67 percent if it does not get sanctions relief.

“That’s a more significant proliferation risk because it starts to decrease more quickly that breakout timeline,” Davenport said.

Another step that could accelerate the timeline is installing additional centrifuges, which would violate another key piece of the 2015 deal. Before the accord, Iran had more than 19,000 centrifuges it could have used to convert the low-enriched uranium into highly enriched uranium in just a few weeks, Cirincione said. But it now has just 3,000-4,000 in operation.

Installing a few thousand additional advanced centrifuges could potentially reduce the breakout time to as little as four months, Heinonen estimated.

So far, Iran has not shown any signs that it will install additional centrifuges beyond the limits of the deal, Davenport said.

However, if that happens, the monitoring and verification mechanisms put in place by the deal would immediately alert the remaining parties to the deal.

Miller believes that the most recent violations, and Iran’s attacks on oil tankers in the Gulf, are designed to pressure the Europeans to provide sanctions relief. But at the end of the day, that effort will likely prove unsuccessful, he said.

The United States is 35 to 37 percent of the global economy, where Iran is just half a percent, Miller stressed, adding that it is very difficult to deal financially with Iran because its banks are complex and corrupt.

“[The Europeans] might have been willing to stay with Iran over the United States if a) they thought that it was morally the right thing to do and b) it was an economically feasible way ahead,” Miller said. “But they know there isn’t economically a feasible way ahead, and now there is no more moral imperative because the Iranians have broken the deal.”

Lara Seligman is a staff writer at Foreign Policy. Twitter: @laraseligman