nuclear program began during the 1950s. The United States has expressed concern
since the mid-1970s that Tehran might develop nuclear weapons. Iran’s
construction of gas centrifugebased uranium enrichment facilities is
currently the main source of proliferation concern. Gas centrifuges enrich
uranium by spinning uranium hexafluoride gas at high speeds to increase the concentration
of the uranium-235 isotope. Such centrifuges can produce both low-enriched uranium
(LEU), which can be used in nuclear power reactors, and weapons-grade highly
enriched uranium (HEU), which is one of the two types of fissile material
used in nuclear weapons.
Obtaining fissile material is widely regarded as the most difficult task in
building nuclear weapons. As of August 2012, Iran had produced an amount
of LEU containing up to 5% uranium- 235 which, if further enriched, could
theoretically produce enough HEU for several nuclear weapons. Iran has
also produced LEU containing up to 20% uranium-235, but, as of August 2012, this
amount was not sufficient to yield a sufficient amount of weapons-grade HEU for
Although Iran claims that its nuclear program is exclusively for peaceful
purposes, the program has generated considerable concern that Tehran is
pursuing a nuclear weapons program. Indeed, the U.N. Security Council has
responded to Iran’s refusal to suspend work on its uranium enrichment
program by adopting several resolutions that imposed sanctions on Tehran.
Despite evidence that sanctions and other forms of pressure have slowed
the program, Iran continues to enrich uranium, install additional
centrifuges, and conduct research on new types of centrifuges.
Tehran has also continued work on a heavy-water reactor, which is a
proliferation concern because its spent fuel will contain plutonium—the
other type of fissile material used in nuclear weapons. However, plutonium
must be separated from spent fuel—a procedure called “reprocessing.” Iran
has said that it will not engage in reprocessing.
The International Atomic Energy Agency (IAEA) monitors Iran’s nuclear
facilities and has been able to verify that Tehran’s declared nuclear
facilities and materials have not been diverted for military purposes. But
the agency still has concerns about the program, particularly evidence that Iran
may have conducted procurement activities and research directly applicable to
nuclear weapons development. The United States has assessed that Tehran
has the technical capability eventually to produce nuclear weapons, but
has not yet mastered all of the necessary technologies for building such
weapons. Whether Iran has a viable design for a nuclear weapon is unclear.
Whether Iran has a nuclear weapons program is also unclear. A National
Intelligence Estimate made public in December 2007 assessed that Tehran “halted
its nuclear weapons program” in 2003. The estimate, however, also assessed
that Tehran is “keeping open the option to develop nuclear weapons” and
that any decision to end a nuclear weapons program is “inherently reversible.”
U.S. intelligence officials have reaffirmed this judgment on several occasions.
For example, Director of National Intelligence James Clapper stated in
January 2012 that Iran “is keeping open the option to develop” nuclear
Secretary of Defense Leon Panetta stated in January 2012 that Iran would
probably need “about a year” to produce a nuclear weapon and “possibly
another one to two years” to incorporate it into a delivery vehicle.
However, Director Clapper indicated in February 2012 that it would likely take
Iran longer than a year to produce a nuclear weapon after making a decision to
do so. These estimates apparently assume that Iran would use its declared
nuclear facilities to produce fissile material for a weapon. However,
Tehran would probably use covert facilities for this purpose; Iranian
efforts to produce fissile material for nuclear weapons by using its known
nuclear facilities would almost certainly be detected by the IAEA.
Date of Report: October 17, 2012
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