How Close Is Iran to Getting a Nuclear Weapon?

Why Tehran’s breakout time has shrunk—and the technological hurdles that remain.

Iran's chief nuclear negotiator Ali Bagheri Kani arrives in Vienna.
Iran's chief nuclear negotiator Ali Bagheri Kani arrives in Vienna.
Iran's chief nuclear negotiator Ali Bagheri Kani arrives for nuclear talks in Vienna on Dec. 27, 2021. ALEX HALADA/AFP via Getty Images

The Biden administration has warned that Iran is on the brink of producing enough fuel for a nuclear bomb. But how close is Iran to actually having the ability to launch a nuclear weapon?

The Biden administration has warned that Iran is on the brink of producing enough fuel for a nuclear bomb. But how close is Iran to actually having the ability to launch a nuclear weapon?

There are a number of critical technological hurdles Tehran must surmount first to acquire a fully functioning nuclear weapons program. Iran must develop enough highly enriched, weapons-grade uranium to fuel one or more nuclear bomb; construct a nuclear warhead capable of housing the fissile nuclear fuel; and develop a ballistic missile system capable of delivering a nuclear explosive to its target. Finally, it needs to conduct a test to see if the explosive actually works.

How long it will take Iran to master those challenges has taken on greater urgency as the United States, Iran, and several other key powers meet this month in Vienna in a last-chance bid to revive the landmark 2015 nuclear deal known as the Joint Comprehensive Plan of Action, or JCPOA. The nuclear pact—which was endorsed by the five permanent members of the United Nations Security Council (the United Kingdom, China, France, Russia, and the United States) as well as Germany and the European Union—promised Iran sanctions relief in exchange for verifiable assurances that its nuclear program is peaceful.

The Vienna talks have made “some progress” in recent weeks, a senior U.S. official told Foreign Policy in a telephone interview Sunday, but not enough to justify open-ended negotiations. “The pace at which talks are progressing is not catching up with the pace of Iran’s nuclear advances,” the official added, speaking on condition of anonymity because of the confidential nature of the nuclear negotiations. If the talks continue over the coming weeks at the current plodding pace, the official added, Washington may have to reconsider the relevance of the nuclear pact altogether and “decide on a course correction.”

Under the terms of the 2015 nuclear pact, Iran was permitted to produce low-enriched uranium for a peaceful nuclear energy program, subject to monitoring by the International Atomic Energy Agency (IAEA). Iran largely abided by the pact until 2018, when then-U.S. President Donald Trump withdrew from the agreement. That prompted Iran the following year to begin a gradual process of halting compliance with the nuclear deal, raising concerns among Western powers and Israel that it will achieve technological breakthroughs that render the JCPOA meaningless. 

Israel and the United States have sought to slow down Iran’s nuclear progress by sabotaging its nuclear infrastructure, including by infecting the computers that run Iran’s enrichment centrifuges. Israel is also suspected of having assassinated a key Iranian nuclear scientist, Mohsen Fakhrizadeh, in November 2020. But those efforts have failed to prevent Iran from making significant strides in its nuclear program.

U.S. President Joe Biden vowed to recommit to the JCPOA and lift nuclear-related sanctions on Iran if it agreed to return to full compliance with the deal. Iran wants to see the sanctions lifted first and to receive ironclad assurances that a future U.S. administration cannot renege on the deal again.

Here’s what we know about Iran’s timeline for enriching weapons-grade fuel, designing a workable warhead, and loading it onto a ballistic missile capable of striking targets in the Middle East. 

Iran’s breakout time has shrunk considerably.

In assessing Iran’s potential nuclear weapons capability, the United States has largely focused on Tehran’s estimated “breakout time”: the amount of time it would take Iran to produce a single nuclear bomb if it were to launch an all-out race to do so.

With JCPOA restrictions in place, the United States estimated in 2015 that it would take Iran 12 months to produce enough nuclear fuel for a bomb should it decide to abandon the deal and seek a workable weapon. Today, that estimate has shrunk to about one month as Tehran has installed more advanced centrifuges in its nuclear centers, enriched uranium of a far higher quality than allowed under the original nuclear pact, and restricted international inspectors’ access to Iranian nuclear facilities.

Under the terms of the 2015 agreement, Iran was permitted to stockpile up 300 kilograms of low-enriched uranium and operate just over 5,000 1st-generation centrifuges at the Natanz Fuel Enrichment Plant. Tehran is prohibited from enriching uranium with greater than a 3.67 percent concentration of uranium-235, the fissile material that can generate electrical power at low levels but can fuel a nuclear device if it reaches a 90 percent concentration.

Since the U.S. withdrawal from the nuclear pact, Iran has been steadily enriching uranium at higher levels. In July 2019, Iran began enriching up to 5 percent; to 20 percent in January 2021; and to 60 percent in April 2021. From there it is a relatively short step to producing weapons-grade nuclear fuel.

Producing weapons-grade fuel requires extracting the fissile material that can trigger a nuclear reaction (uranium-235) from mined uranium. Refining uranium to 3.67 percent purity removes the vast majority of excess atoms, making the process of refining to 5, 20, and 90 percent purity less time consuming and increasingly easy.

In order to accelerate the pace of enrichment, Iran has installed thousands more advanced centrifuges capable of enriching uranium at a higher quality at both Natanz and its Fordow Fuel Enrichment Plant. (The JCPOA barred Iran from enriching uranium at Fordow.) As of November 2021, Iran had built up a stockpile of some 2,313.4 kilograms of enriched uranium, including 1,622.3 kilograms of uranium enriched to 5 percent, 113.8 kilograms enriched to 20 percent, and 17.7 kilograms enriched to 60 percent, according to the IAEA.

David Albright, the founder of the Institute for Science and International Security, said that Iran has already acquired enough 20 and 60 percent uranium to produce at least 45 kilograms of highly enriched uranium at 90 percent—enough weapons-grade fuel to produce a nuclear bomb in short order. In several months, he added, it could produce enough fuel for two more bombs. In six months, he estimates, Iran may be in a position to test a nuclear explosive.

Albright said that is cause for alarm because the production of nuclear-weapons-grade fuel is among the most difficult technical achievements on the road to the bomb.

Some nonproliferation experts say that may be so, but nuclear fuel alone does not make a nuclear weapons arsenal.

“Breakout time has been the name of the game when it comes to metrics related to Iran’s nuclear program, but it is quite limited in utility as it doesn’t include the time it would take to design, manufacture, or put together bomb components or the weapon itself,” said Sahil Shah, a policy fellow at the European Leadership Network. “The proclivity for some countries, namely the U.S. and its transatlantic partners, to place a large emphasis on breakout time deliberately ignores the amount of time it would take Iran to move from having a meaningful stockpile of highly enriched uranium to a usable nuclear weapon.”

In a recent interview, Russia’s nuclear negotiator, Mikhail Ulyanov, put it more bluntly, telling Foreign Policy the “so-called breakout time, it’s an American concept. We don’t share it at all.”

“Even if they produce a significant amount of nuclear material, so what?” he added. “It cannot be used without warheads, and the Iranians do not have warheads and will not get the relevant technologies for a long time.”

Iran is not believed to have a workable nuclear warhead. But it could make one.

There remains considerable mystery over the amount of time it would take Iran to develop a working nuclear warhead. Iran has long denied it has ever had any intention of pursuing a nuclear weapon, noting that the country’s Supreme Leader Ali Khamenei issued a fatwa, or religious edict, in 2003 prohibiting the use of nuclear weapons. But the IAEA confirmed reports that Iran was developing a nuclear weapons program up until 2003.

“The organizing question is how long would it take for Iran to be able to deliver nuclear weapons, after having acquired enough fissile material for one bomb?” said Daryl Kimball, director of the Arms Control Association. “It would be a period of years.”

The Israeli government estimates that Iran would require about one to two years to be able to produce a nuclear weapon. The Biden administration “wouldn’t dispute there is a longer timeline for weaponization,” the senior U.S. official told me. But, the official added, “we have more confidence in our ability to measure, track, and to know what’s going on when it comes to enrichment.”

But some experts say that is no reason to be complacent. The risk if Iran obtains a stockpile of weapons-grade fuel, they say, is that policymakers will be making assessments about Iran’s capabilities in the dark. That, they warn, could narrow Washington’s diplomatic options, raising the prospects of military conflict.

Iran has done considerable design work on a nuclear weapon. In the 1990s, an arms-trafficking network led by A.Q. Khan, the father of Pakistan’s nuclear weapons program, supplied Iran with the basic designs for nuclear weapon components. In 2009, an internal IAEA assessment concluded that before 2003, Iran had accumulated “sufficient information to be able to design and produce a workable implosion nuclear device based on HEU [highly enriched uranium] as fission fuel.”

A 2007 U.S. National Intelligence Estimate concluded that it had “high confidence” Iran had halted its nuclear weapons program in 2003 in response to mounting international pressure, and a moderate to high degree of confidence that Tehran was keeping the door open to resuming the program at some future stage.

In recent years, Iran’s research and development activities have drawn concern from nuclear nonproliferation experts. In February 2021, for instance, Iran produced a small amount of natural uranium metal at its nuclear facility in Isfahan, according to a confidential IAEA report obtained by the Wall Street Journal.

The metal was not produced with enriched uranium, which is a critical element of a nuclear weapon’s core, but the technological know-how required to convert uranium into metal can be applied to a nuclear weapons program.

“The real core truth is that simply no one, including those with access to more detailed intelligence on Iran’s nuclear program, can be certain on any of these timelines, especially as we do not have a solid idea of what research and development Iran has been able to historically and currently work on,” Shah said.

Iran has one of the most sophisticated ballistic missile programs in the Middle East.

Ballistic missiles play a critical role in any nuclear weapons program, and Iran has had years of experience developing them.

The Shahab-3, which is modeled on North Korea’s Nodong ballistic missile, has a range of about 800 miles. Iran also has several souped-up versions, including the Emad, the Sejjil, and the Ghadr-110. The Ghadr-110 has a range of around 1,200 miles, placing it within striking distance of Tel Aviv, Israel. Iran’s rocket scientists have also been producing the medium-range Khorramshahr rocket, which is based on the failed North Korean Musudan missile.

However, having ballistic missiles isn’t the same thing as having workable, nuclear-armed ballistic missiles. You still have to figure out how to fit a nuclear weapon onto the missiles and make sure the (extremely sensitive) nuke will survive long enough to make it to the target and detonate. It remains unclear how far Iran has progressed in weaponizing its missiles.

“Designing the missile wasn’t the hard part; fitting a weapons design is not an easy task. It’s not known whether Iran acquired the technology from the North Koreans,” said Mark Fitzpatrick, an associate fellow at the International Institute for Strategic Studies and a former U.S. acting deputy assistant secretary of state for nonproliferation.

A 2009 internal IAEA report suggested that Iran hadn’t surmounted critical technical obstacles. “Overall the Agency does not believe that Iran has yet achieved [as of 2003] the means of integrating a nuclear payload into the Shahab 3 missile with any confidence that it would work,” the internal document says. “Nonetheless, with further effort it is likely that Iran will overcome problems and confidence will be built up.”

With talks underway, Iran has sought to flex its missile prowess, putting three ballistic missiles—the Dezful, Qiam, and Zolfaghar—on display in central Tehran Friday. The three missiles, which have a range of over 600 miles—were purportedly used in strikes on U.S. military bases in the region. And last month, Iran launched its Simorgh satellite rocket, the latest step in an ongoing Iranian space program that has the potential to advance the country’s ability to master solid-fuel rocket technology required for longer-range rockets.

“There has to be a sense of urgency, but if a deal is not concluded by mid-February I wouldn’t conclude you have to go to option B, or military action,” Fitzpatrick said. “There may still be time for diplomacy.”

Colum Lynch was a staff writer at Foreign Policy between 2010 and 2022. Twitter: @columlynch

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