Updated July 25, 2022
Iran and Nuclear Weapons Production
Background
Assessment observes that “Iran is not currently undertaking
Iran’s nuclear program has generated widespread concern
the key nuclear weapons-development activities ...
that Tehran is pursuing nuclear weapons. According to U.S.
necessary to produce a nuclear device.” An April 2022
intelligence assessments, Tehran has the capacity to
State Department report contains a similar conclusion.
produce nuclear weapons at some point, but has halted its
The JCPOA-mandated restrictions on Iran’s nuclear
nuclear weapons program and has not mastered all of the
program and Iran-specific monitoring and reporting
necessary technologies for building such weapons. (For
requirements both supplement Tehran’s obligations
additional information, see CRS Report RL34544, Iran’s
pursuant to the government’s comprehensive IAEA
Nuclear Program: Status, by Paul K. Kerr.)
safeguards agreement. Such agreements empower the
Since the early 2000s, Tehran’s construction of gas
agency to detect the diversion of nuclear material from
centrifuge uranium enrichment facilities has been the main
peaceful purposes, as well as to detect undeclared nuclear
source of proliferation concern. Gas centrifuges enrich
activities and material. These agreements also require
uranium by spinning uranium hexafluoride (UF6) gas at
governments to declare their entire inventory of certain
high speeds to increase the concentration of the uranium-
nuclear materials, as well as related facilities. Safeguards
235 (u-235) isotope. Such centrifuges can produce both
include agency inspections and monitoring of declared
low-enriched uranium (LEU), which can be used in nuclear
nuclear facilities. (For more information, see CRS Report
power reactors, and highly enriched uranium (HEU), which
R40094, Iran’s Nuclear Program: Tehran’s Compliance
is one of the two types of fissile material used in nuclear
with International Obligations, by Paul K. Kerr.)
weapons. Tehran asserts that its enrichment program is
Prior and subsequent to the JCPOA’s January 2016
meant to produce fuel for peaceful nuclear reactors.
implementation, IAEA and U.S. officials expressed
The 2015 Joint Comprehensive Plan of Action (JCPOA)
confidence in the ability of both the IAEA and the U.S.
requires Iran to implement various restrictions on its
intelligence community to detect an Iranian breakout
nuclear program, as well as to accept specific monitoring
attempt using either Tehran’s IAEA-monitored facilities or
and reporting requirements. (For additional information, see
clandestine facilities. (See CRS Report R43333.)
CRS Report R43333, Iran Nuclear Agreement and U.S.
Estimated Nuclear Weapons
Exit, by Paul K. Kerr and Kenneth Katzman.)
Development Timelines
Then-President Donald Trump announced in May 2018 that
U.S. estimates concerning Iranian nuclear weapon
the United States was ending U.S. participation in the
development account for the time necessary to produce a
JCPOA. Following this decision, Iran stopped
sufficient amount of weapons-grade HEU and also
implementing much of this agreement, as well as JCPOA-
complete the remaining steps necessary for an implosion-
required International Atomic Energy Agency (IAEA)
style nuclear device suitable for explosive testing.
monitoring. Beginning in July 2019, the IAEA verified that
some of Iran’s nuclear activities were
Fissile Material Production
exceeding JCPOA-
The time needed to produce enough weapons-grade HEU
mandated limits. Tehran’s subsequent expansion of the
country’s
for a nuclear weapon is a function of a nuclear program’s
enrichment program has decreased the amount of
enrichment capacity, as well as the mass and u-235 content
time needed for Iran to produce enough weapons-grade
of the UF6 stockpile fed into the enrichment process. LEU
HEU for a nuclear weapon—an action frequently termed
“breakout.”
used in nuclear power reactors typically contains less than

5% u-235; research reactor fuel can be made using enriched
According to official U.S. assessments, Iran halted its
uranium containing 20% u-235; HEU used in nuclear
nuclear weapons program in late 2003 and has not resumed
weapons typically contains about 90% u-235.
it. For example, the CIA has no evidence that Iranian
The JCPOA mandates restrictions on Iran’s declared
Supreme Leader Ayatollah Ali Khamene’i “has made a
decision to move to weaponize,”
enrichment capacity and requires that Iran’s enriched
CIA Director William
uranium stockpile must not exceed 300 kilograms of UF6
Burns said stated during a December 2021 Wall Street
containing 3.67% u-235 “or the equivalent in other
Journal interview. This program’s goal, according to U.S.
chemical forms.” This quantity of uranium hexafluoride
officials, was to develop an implosion-style nuclear weapon
for Iran’s Shahab
“corresponds to 202.8 kg of uranium,” according to the
-3 ballistic missile.
IAEA.
The U.S. government assessed prior to the JCPOA that
The aforementioned JCPOA restrictions constrained Iran’s
Tehran had not mastered all of the necessary technologies
nuclear program so that Tehran, using its declared
for building a nuclear weapon. Apparently confirming
persisting gaps in Iran’s nuclear weapons knowledge, the
enrichment facilities, would, for at least 10 years, have
needed a minimum of one year to produce enough
2022 U.S. Intelligence Community Annual Threat
https://crsreports.congress.gov

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Iran and Nuclear Weapons Production
weapons-grade HEU for one nuclear weapon. The JCPOA
An implosion-style nuclear explosive device, according to
does not explicitly mandate such a timeline.
the Office of Technology Assessment, uses “a shell of
chemical high-explosive surrounding the nuclear material ...
Iran’s number of installed centrifuges, the mass and u-235
designed (for example, by being detonated nearly
concentration of Tehran’s enriched uranium stockpile, and
simultaneously at multiple points) to rapidly and uniformly
number of enrichment locations currently exceed JCPOA-
compress the nuclear material to form a supercritical mass”
mandated limits. Tehran is also conducting JCPOA-
necessary for a sustained nuclear chain reaction.
prohibited research and development, illicit uranium metal
production, and centrifuge manufacturing and installation.
IAEA reports suggest that Iran does not yet have a viable
nuclear weapon design or a suitable explosive detonation
A May 2022 IAEA report estimates Tehran’s total enriched
system. Tehran may also need additional experience in
uranium stockpile to be 3809.3 kilograms of uranium. This
producing uranium metal; weapons-grade HEU metal for
amount includes batches of enriched uranium containing up
use in a nuclear weapon is first “cast and machined into
to to 2% u-235, up to 5% u-235, up to 20% u-235, and up to
suitable components for a nuclear core.”
60% u-235, respectively. Iran has enough fissile material
that, if further enriched, would be sufficient for several
Discussion
nuclear weapons, according to U.S. officials.
The aforementioned one-year fissile-material breakout
estimate assumes that Iran would use its declared nuclear
According to an April 2021 State Department report,
“Iran’s expansion of uranium enrichment activities
facilities to produce fissile material for a weapon. But the
... allow
breakout concept does not accurately measure Tehran’s
[sic] Iran to enrich more uranium more quickly and to
higher levels.”
nuclear weapons capability.
The U.S. government estimates that Iran
would currently need as little as one week to produce
The U.S. government continues to assess that Iran is more
enough weapons-grade HEU for one nuclear weapon,
likely to use covert, rather than declared, facilities to
according to a State Department official in March 2022.
produce the requisite fissile material. Neither the U.S.
government nor the IAEA have publicly described any
If Tehran were to resume implementing its current JCPOA
evidence that Iran is conducting such activities. Former
obligations, this fissile material production timeline would
National Nuclear Security Administration official Corey
increase, but would be less than one year, according to State
Hinderstein, who was involved in JCPOA implementation,
Department officials. This estimate reflects Iran’s recent
wrote in a January 2020 Defense One article that producing
accumulation of knowledge gained by operating centrifuges
fissile material in such a manner would require more time
that are more sophisticated. Former National Intelligence
than executing a breakout scenario. As noted, IAEA and
Council official Eric Brewer noted in an October 2021
U.S. officials have expressed confidence in the ability of
Center for Strategic and International Studies publication
both the IAEA and the U.S. intelligence community to
that, absent this experience, Iran would probably have used
detect an Iranian covert breakout effort.
less efficient, first-generation centrifuges for a breakout
attempt.
The breakout timeline was an unclassified proxy measure of
Iranian nuclear weapons capabilities. A State Department
Even with a breakout timeline of less than one year, Iran
official described the breakout “concept” in a September
would be “unlikely” to make such an attempt, Brewer
2021 email as “a useful metric to help quantify” U.S.
wrote, arguing that the JCPOA monitoring provisions
“would almost certainly” enable the United States to
negotiating goals and as “a useful analytic framework to
detect
structure the negotiation of technical measures related to
such a move.
enrichment.” The timeline was also “helpful in explaining
JCPOA restrictions on Iran’s enrichment capacity, as well
the deal and selling it politically,” the official noted, adding
as the mass and u-235 content of the UF6 stockpile, begin
that the timeline has “become an important political
to expire in January 2026. At that point, the breakout
yardstick” for evaluating the agreement’s merits.
timeline would begin to decrease.
In a February 2022 Bulletin of the Atomic Scientists article,
Weaponization
Jon Wolfsthal, a National Security Council official during
At the time when the JCPOA negotiations concluded, the
the Obama Administration, explained that the “one-year
U.S. intelligence community assessed that Iran would have
breakout timeline” was “based on how much time that
needed one year to complete the necessary steps for
JCPOA members believed it would take to generate an
producing a nuclear weapon that do not involve fissile
international response to any Iranian move to build
material production. This estimate assumed that Iran could
weapons.”
complete fissile material production and weaponization in
Former State Department official Robert Einhorn discussed
parallel, which meant that Iran would have needed about
this point in a 2021 United Nations Institute for
one year to produce a nuclear weapon.
Disarmament Research report. The Obama Administration,
The U.S. intelligence community assesses that Iran has not
according to Einhorn, argued that stopping Iran from
resumed work on its weaponization research. A State
developing nuclear weapons required preventing Tehran
Department official told CRS in a March 2022 email that
“from having the fissile material production infrastructure”
Iran would need approximately one year to complete the
to break out “in less time than it would take the
necessary weaponization steps. This timeline “takes into
international community to intervene to block it.”
consideration assessed knowledge gaps and reflects” the
intelligence community’s “view of Iran’s fastest reasonable
Paul K. Kerr, Specialist in Nonproliferation
path to overcome them,” the official added.
IF12106
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Iran and Nuclear Weapons Production


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https://crsreports.congress.gov | IF12106 · VERSION 3 · UPDATED

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