[1]

[2]Nuclear Strikes on Iran:

[3]What We Don't Know

June 24, 2025

On [4]June 21, the United States struck three nuclear sites in Iran in an
operation designed to “severely degrade Iran’s nuclear weapons
infrastructure,” according to General Dan Cain, the Chairman of the Joint
Chiefs of Staff. Secretary of Defense Pete Hegseth went further, claiming
that “Iran’s nuclear ambitions have been obliterated.”

A number of officials, however, have [5]warned that it is still too early
to know how much damage was actually inflicted and to know how much
material and equipment may have been removed from the nuclear sites before
they were attacked. This uncertainty poses an important question: has the
military campaign pushed the threat of an Iranian bomb far into the future,
or has the campaign left enough potential behind to trigger a race to the
bomb within the next year or so. The answer will determine whether the
strikes are judged a success.

Graphic released by the U.S. Department of Defense depicting Operation
Midnight Hammer.

1. What happened to Iran’s stockpile of enriched uranium?

Iran had 408.6 kg of uranium enriched to 60% of the fissionable U-235
isotope as of [6]late May, according to the International Atomic Energy
Agency (IAEA). Agency inspectors last saw the stockpile on [7]June 10. This
level of enrichment has no plausible civilian application. It is nearly
weapons-grade and Iran’s stockpile would be sufficient to fuel up to ten
nuclear weapons, with further enrichment. The IAEA [8]warned that Iran is
“the only non-nuclear-weapon State in the world that is producing and
accumulating uranium enriched to 60%” and that this production is “a matter
of serious concern.”

The location of this 60% material is now uncertain. Iran had principally
been producing it at the Fordow enrichment plant, which was struck by the
United States on June 21. A smaller amount of 60% material had been
produced at the above-ground enrichment plant at Natanz, which was
[9]destroyed by Israel on June 13. Some of this accumulated material may
have been at these production locations. Much of the stockpile was believed
to be stored in tunnels at Esfahan, a large nuclear research and
development complex. Entrances to these tunnels appear to have been
[10]struck by the United States.

U.S. officials have [11]claimed that the 60% material had not been moved
and that U.S. strikes targeted locations where the material was still being
stored. Vice President J.D. Vance said on June 23 that the uranium was
[12]buried as a result of the U.S. strikes. However, Iran [13]informed the
IAEA on June 13, on the first day of Israel’s bombing campaign, that it
would “adopt special measures to protect our nuclear equipment and
materials”. IAEA Director General Rafael Grossi subsequently [14]said he
took this to mean that Iran planned to move the material in order to
protect it.

This [15]material could be enriched to weapons grade in a matter of weeks
and processed further in a few more weeks to fuel an implosion weapon that
would fit on a missile. Such a weapon would have to be tested.
Alternatively, Iran could further process its 60% material and use it in a
less sophisticated “gun type” nuclear weapon such as the one dropped on
Hiroshima, which would not have to be tested. Iran has enough material for
one or more such devices, but they would be heavier and larger than an
implosion device.

In addition to the fate of the 60% material, which has garnered much
attention, Iran also had 275 kg of 20% enriched uranium and 5,509 kg of 5%
enriched uranium as of late May. The availability of [16]this material has
nuclear weapon implications. Twenty percent enriched uranium is
approximately 90% of the way to weapon-grade and Iran’s stockpile would be
sufficient to fuel at least two implosion weapons. The 5% stockpile would
be sufficient to fuel at least 10 implosion weapons but would require more
enrichment work to reach this level. The location and status of these
stockpiles has not been addressed publicly.

2. Can Iran still enrich uranium?

Iran has three known gas centrifuge [17]uranium enrichment facilities: a
deeply buried plant at Fordow (located beneath a mountain) that houses
approximately 2,700 centrifuges, an underground plant at Natanz that houses
some 17,000 centrifuges, and a pilot plant at Natanz, portions of which are
located above and below ground, that houses about 1,700 centrifuges. All
three appear to have been damaged or destroyed.

The Fordow plant was first [18]struck by the United States on June 21,
using 12 bunker-busting bombs. Israel subsequently [19]struck roads leading
to Fordow in order to disrupt access to the site. It is impossible to fully
assess the damage at Fordow, but the IAEA Director General has [20]stated
that “Given the explosive payload utilized, and the extreme
vibration-sensitive nature of centrifuges, very significant damage is
expected to have occurred.”

Israel [21]destroyed the above ground Natanz plant in its initial strikes
on June 13, along with electricity infrastructure that may have caused
broader damage to centrifuges operating in underground locations, according
to the IAEA. The United States also used ground-penetrating munitions to
[22]strike the underground centrifuge halls at Natanz on June 21, causing
further damage to this facility.

It is unclear whether Iran was able to remove centrifuges or other
equipment from these facilities before they were struck. Installed or
operating centrifuges are connected together and secured to the floor and
would not be quick to remove.

Iran is known to make and store centrifuge components at other locations,
which have not been monitored by the IAEA since [23]February 2021. Some of
these sites have been [24]struck by Israel since June 13 (at Esfahan, the
Tehran Nuclear Research Center, and Karaj) but Iran may have removed its
equipment beforehand. The remaining centrifuges might be sufficient to set
up a small enrichment plant. Or Iran may be manufacturing centrifuge
components (or storing them) at additional locations, unknown to the IAEA
and not struck by Israel.

Iran also [25]announced on June 12, the day before Israeli strikes began,
that it was building a fourth uranium enrichment plant, reportedly deeply
buried. The [26]IAEA said the plant was located within the Esfahan complex.

3. Does Iran have secret facilities for uranium work?

The nuclear complex at Esfahan houses a number of plants critical to
producing nuclear weapons fuel, notably a plant to convert enriched uranium
gas to metal, which would allow for the production of weapon components.
Israeli strikes on June 13 [27]damaged this plant. Without an alternative
plant to conduct this work, Iran would be unable to produce nuclear weapons
components.

However, Iran could already have such a plant, or if not, could construct
one. Only dual-use industrial equipment is needed to convert the uranium in
the gas to metallic form, and then to cast and machine the metal into
weapon components. The process could be done on a laboratory scale and
would be difficult to detect.

If Iran’s stockpile of enriched uranium is not available, Iran would need a
plant to convert natural uranium ore to the gas that is enriched in
centrifuges. Israel [28]damaged the primary chemical laboratory and uranium
conversion plant at Esfahan on June 13 and U.S. strikes [29]hit buildings
“related to the uranium conversion process” on June 21, according to the
IAEA.

4. What are the long-term risks of military strikes?

Israeli and U.S. air strikes may push Iran to pursue a crash program to
develop nuclear weapons, since the threshold nuclear program Iran had
achieved was not sufficient to deter the strikes. In addition, Iran’s other
deterrent, which consisted of missile attacks by itself or its proxies, has
been virtually eliminated. These developments may convince Iran that it
needs nuclear weapons as a more reliable deterrent.

A second risk is loss of public knowledge of Iran’s nuclear program. Before
the strikes, Agency inspectors had continued to verify Iran’s enriched
uranium and the locations where it was being produced. Such access has been
suspended as a result of the military strikes. In the aftermath of the
strikes, Iran may reduce or terminate its cooperation with the IAEA. Iran
may also decide to withdraw from the Nuclear Nonproliferation Treaty, which
provides the legal basis for the IAEA’s access to nuclear sites in Iran.

Iran has been building its nuclear program for decades. The program has
advanced despite a decades-long effort to stop it diplomatically and an
equally lengthy campaign of sanctions and sabotage. Have Israeli and U.S.
air strikes now succeeded in seriously setting back Iran’s nuclear weapons
bid or rather accelerated Iran’s race to the bomb?

[30]READ THE REPORT ON IRAN WATCH

Iran Watch is a website published by the Wisconsin Project on Nuclear Arms
Control. The Wisconsin Project is a non-profit, non-partisan organization
that conducts research, advocacy, and public education aimed at inhibiting
strategic trade from contributing to the proliferation of weapons of mass
destruction.

Copyright © 2025 - Wisconsin Project on Nuclear Arms Control

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