The U.S. War on Iran: New and Lingering Nuclear Risks

 

The U.S. War on Iran: New and Lingering Nuclear Risks

Issue Briefs

Volume 18, Issue 4, March 10, 2026

https://www.armscontrol.org/issue-briefs/2026-03/us-war-iran-new-and-lingering-nuclear-risks#:~:text=An%20operation%20to%20recover%20Iran's,%E2%80%9Cless%20than%20secure%20state.%E2%80%9D

 

U.S. President Donald Trump continues to allege, without evidence, that Iran’s nuclear program posed an imminent threat to the United States, justifying his decision to join Israel in striking Iran on Feb. 28. Although strikes can set back Iran’s nuclear program and destroy key infrastructure, as the United States and Israel did in June 2025, military force cannot eliminate Tehran’s proliferation risk. At the end of the conflict, Iran will retain the nuclear expertise and likely key materials necessary for building a nuclear bomb.

 

But not only are strikes ineffective in addressing proliferation risks in the long-term, the ongoing miltiary action—and Trump’s threats to deploy U.S. troops to seize Iran’s enriched uranium—is creating a new set of nuclear risks and safety hazards.

 

The following are answers to frequently asked questions about Iran’s proliferation risk and nuclear security issues that have emerged or remained a concern since the United States and Israel attacked Iran on Feb. 28.

 

What is the status of Iran's uranium enriched to 60 percent uranium-235?

Prior to the Israeli and U.S. strikes on Iran in June 2025, Iran had produced approximately 440 kilograms of uranium enriched to 60 percent U-235, a level that can be quickly enriched to weapons-grade, or 90 percent. Nearly all of the 60 percent material was in gas form (UF6) and stored in small canisters, roughly the size of a scuba tank.

 

Comments from some U.S. officials initially suggested that, after the U.S. struck on June 21, the majority of the 60 percent material was intact at Esfahan, but inaccessible. The United States did not attempt to destroy the underground storage site at Esfahan, where at least a portion of the material was stored. Chairman of the Joint Chiefs General Dan Caine reportedly told Congress that the storage area is so deeply buried that even the massive ordinance penetrator (the largest U.S. conventional munition) would not be able to destroy it. Instead, the United States targeted the tunnel entrances to prevent access.  (A massive strike on a storage area housing 60 percent enriched uranium could also have been deemed too risky. Although it is unlikely, strikes that blow up enough 60 percent enriched uranium material could produce a fission reaction.)

 

Although the International Atomic Energy Agency (IAEA) has not been given access to Iran’s bombed sites to confirm what portion of the 60 percent stockpile survived the June 2025 strikes or where all the material is located, Director General Rafael Mariano Grossi said on March 9 that the agency assesses that little over 200 kilograms of 60 percent enriched uranium is underground at Esfahan. Around 200 kilograms of 60 percent would be enough material for around five nuclear warheads, if enriched to weapons-grade levels (90 percent).

 

According to a March 7 report in The New York Times, the U.S. intelligence community assesses that Iran can access the 60 percent material stored at Esfahan via a small opening. The story quoted an intelligence official as suggesting that the United States and Israel are monitoring the site and have a high degree of confidence that they would detect any attempt to move the material.

 

Grossi was less specific about the location of the remaining 60 percent enriched uranium. Presumably, some of the remaining ~200 kilograms of 60 percent enriched uranium may have been destroyed or compromised in the strikes on Natanz and Fordow in June 2025 or is still stored at those sites. Iran enriched to 60 percent at the above-ground Pilot Fuel Enrichment Plant at Natanz, which was targeted by Israel on the opening day of the strikes, suggesting Tehran would not have had time to move the material. Grossi suggested on March 9 that some 60 percent enriched uranium might still be at Natanz.

 

Before the June 2025 attacks, Iran produced the majority of 60 percent enriched uranium at Fordow. There were 8 days between Israel’s first strikes and the U.S. strike on Fordow (Israel did not attack Fordow), which could have allowed Iran to move 60 percent enriched uranium from that site, but it is unclear if Tehran did so. The IAEA and U.S. intelligence assessed that Fordow is inoperable after the June 21 U.S. attack, but it is not clear if the damage would have destroyed any enriched uranium cannisters at the facility.

 

Iran did make clear to the IAEA its intention to invoke “special measures” and move its nuclear materials in the event of a miltiary attack before the June strikes, suggesting Iran had plans in place for dispersion. On June 16, Iran notified the IAEA it took those steps. These plans, combined with the mobility of the 60 percent material, suggest that diversion to an undeclared site was possible.

 

How is the Trump administration considering addressing the proliferation risk posed by the 60 percent enriched uranium? Is a special operation to extract the material a viable option?

 

U.S. President Donald Trump has said one of the U.S. goals for the military strikes on Iran is to prevent Tehran from developing nuclear weapons. This suggests the United States, or Israel, may be unwilling to end the conflict while Iran retains near-weapons-grade uranium.

 

Trump has suggested that the United States might attempt to seize Iran’s stockpile of 60 percent enriched uranium by force, inserting special forces into Iran to recover it. Any such operation would come after further strikes against Iran, Trump said, presumably to try to mitigate any Iranian response to a ground operation.

 

An operation to recover Iran’s 60 percent material would put U.S. troops directly on the ground, a move that some Republican members of Congress have already stated their opposition to, and would involve significant safety and security risks. Beyond the risk that Iranian forces would attack U.S. troops—a risk that increases if troops need to excavate facilities to remove the materials and neutralize it onsite—UF6 gas is toxic. Furthermore, uranium enriched to 60 percent, even in gas form, can sustain a fission reaction, making it more dangerous to transport. Troops will need special safety gear to handle the material, particularly if any of the canisters are compromised, and adequate protection if any highly-enriched uranium is transited out of the country. The military does have units that train for responding to WMD threats, but any operation would still be risky.

 

The United States has developed equipment and procedures to secure highly enriched uranium on-site in a foreign country. The Mobile Uranium Facility was designed to package and remove highly-enriched uranium from a “less than secure state.” But deploying it would require a large ground operation, likely including cargo planes and complex logistical support that could put a greater number of U.S. personnel at risk for a longer period.

 

Furthermore, as discussed above, the United States may need to conduct ground operations at multiple sites to neutralize the entirety of the 60 percent stockpile, increasing the risks to U.S. troops.

 

Would removing the 60 percent enriched uranium reduce Iran’s proliferation risk?

If the United States were to remove Iran’s stockpile of 60 percent material or neutralize it onsite, it could impact how quickly Iran could build a nuclear weapon—enriching 60 percent to the 90 percent considered weapons-grade is the most straightforward option for producing fissile material for a bomb.

 

But even if the Trump administration was confident that it could identify and safely neutralize the 60 percent enriched uranium, removing that material would not eliminate the proliferation threat. Iran would retain the materials and knowledge necessary that could allow it to eventually produce nuclear weapons, if the political decision were made to do so.

 

Furthermore, it is very likely that Iran has uranium enriched up to five percent and up to 20 percent stored at several locations, possibly in addition to sites where 60 percent material is. Any attempt to retrieve that material would increase risks to U.S. troops during a recovery operation but leaving it would allow Iran to jumpstart any future nuclear weapons development effort.

 

Using 20 percent or less than 5 percent enriched uranium as feed would take longer to enrich to weapons-grade levels than if Iran started with 60 percent. But since Iran has likely retained centrifuges, the machines necessary to enrich (or could produce more), and the knowledge to convert the material and build the explosives package, the proliferation risk will remain.

 

Given the attacks on Iran’s nuclear infrastructure and the unknowns about the status of certain sites and materials, it is challenging to say definitively how long it would take Iran to build a bomb if it started from low-enriched or natural uranium. A number of other variables would also influence that timeline, including if Iran prioritized secrecy or speed.

 

Could the United States seize all of Iran’s centrifuges?

No. The IAEA lost continuity of knowledge regarding Iran’s centrifuge production in 2021. From 2021-June 2025 (the known operating centrifuge production facilities were destroyed in June 2025), Iran had the capacity to produce more centrifuges than the IAEA reported installed at Natanz and Fordow. Some of those machines may be at a third enrichment facility at Esfahan, which Iran declared to the IAEA, but the agency never visited (it was set to do so on June 13 when Israel struck Iran).

 

Given these uncertainties, is extremely unlikely that the United States and Israel have been able to keep track of all of Iran’s centrifuges. Furthermore, Iran retains the knowledge to produce more.

 

Are there longer-term implications of a U.S. seizure option?

In the long-term, the U.S. seizure of Iran’s stockpile could have negative implications for future efforts to account for Iran’s nuclear material, including by the IAEA. At some point, the IAEA will need to return to Iran and begin to determine if all nuclear materials are accounted for and are only being used for peaceful purposes. If the United States removes material or neutralizes it onsite, that could complicate the agency’s efforts to verify accountancy and provide assurance that nuclear materials have not been diverted. Documentation and consultation with the IAEA on accountancy measures before an operation could mitigate those risks, but a hostile environment could pose unanticipated challenges.

 

Furthermore, if the Iranian regime remains intact, it will likely view a U.S. ground incursion as a further violation of its territorial integrity, which could provide further justification for factions calling for the development of nuclear weapons to deter future attacks.

 

What nuclear facilities are being targeted in Operation Epic Fury?

Iran’s nuclear facilities were not targeted in the initial round of U.S. and Israeli strikes on Feb. 28.

 

On March 2, Iran’s Ambassador to the IAEA, Reza Najafi, stated that Natanz was struck. The IAEA later confirmed that attack. The strike appeared to have been focused on preventing access to the facility. Israel also claims to have targeted a site northeast of Tehran, referred to as Min Zadei, which the IDF claimed would be relevant to producing a component necessary for nuclear weaponization. (The IAEA has reiterated that it did not see evidence of a structured nuclear weapons program).

 

U.S. and/or Israeli strikes occurred near the Atomic Energy Organization of Iran and facilities associated with the Organization of Defense Innovation and Research or SPND. (When Iran abandoned its illicit nuclear weapons development efforts in 2003, officials that effort, known as the Amad Plan, moved to work for the SPND).

 

It does not appear that the site under construction near the Natanz complex, known as Pickaxe, has been struck. Iran claims Pickaxe will be a centrifuge assembly facility. The IAEA has not had access to the site, which may be more deeply buried than Fordow, suggesting it would be challenging to destroy with conventional strikes.

 

(For more information about Iran’s nuclear program not posing an imminent threat at the time of the Feb. 28 strikes, see here.)

 

Are there nuclear security risks around Iran’s reactors?

Yes. Iran has an operational light-water power reactor at the Bushehr site, which is operated by Rosatom, the Russian state-owned nuclear energy company. The reactor is located outside of the coastal city of Bushehr. Although Rosatom evacuated some personnel from Bushehr, the head of the organization, Alexey Likhachev, said on March 3 that the operating reactor unit is at full capacity. He said a strike on the facility “would certainly be a regional-scale disaster.”

 

Iran also runs a research reactor, the Tehran Research Reactor, located Tehran, and has an MNSR research reactor at Esfahan.

 

A strike on any of the nuclear reactors or systems that help moderate reactor temperatures could cause a meltdown and radioactive release, and any such attack would be a clear violation of international law.

 

Strikes on infrastructure necessary for the safe operation of a reactor could also create safety risks. Knocking out the electrical grid supporting the Bushehr reactor, for instance, could have negative implications. Given that Iran is not a member of the Convention of Nuclear Safety, it is unclear if the country has best practices and protocols in place to prevent such accidents.

 

Given the devastating environment and humanitarian consequences posed by striking a nuclear reactor, it is unlikely that the United States or Israel would deliberately target one of those facilities. However, there is a risk that a reactor is struck accidentally, particularly because some of these facilities are in the vicinity of military targets. The Bushehr reactor, for instance, is in proximity to IRGC military installations.

 

Are there nuclear security risks in the region?

An Iranian official reportedly threatened to target Israel’s Dimona reactor complex, where the country produces fissile material for its unacknowledged nuclear weapons program, if the United States and Israel push for regime change. It is unlikely that Iran could hit the facility, but any such strike could compromise the safety of the complex and have a devastating impact. Past studies on a potential strike on Israel's Dimona nuclear weapons facility suggest significant radiological risks to surrounding populations.

 

Additionally, the United Arab Emirates (UAE) operates four large reactors at the Barakah nuclear power plant.  Again, it is highly unlikely this facility would be deliberately targeted by Iran; however, the reactor units or spent fuel could be hit by accidental strikes or damage to supporting infrastructure could compromise safe operations. Any serious accident at Barakah could have significant regional implications.

 

Is there a risk of nuclear terrorism? Or non-state actors gaining access to Iranian nuclear materials?

Currently, the risk of nuclear terrorism or nuclear material moving to the black market remains low. Non-state actors would face challenges in accessing enriched uranium and it is unlikely they would have the infrastructure to enrich it to weapons-grade and covert it to the metallic form necessary for a warhead core.

 

However, if the current Iranian government implodes or the conflict causes significant internal instability, there is an increased risk that nuclear materials will be stolen or diverted to undeclared sites. There is also a risk that Iranian nuclear scientists may be willing to sell their expertise to state, or non-state, nuclear weapons aspirants.—KELSEY DAVENPORT