THE URANIUM ROUTE
ARMS CONTROL ASSOCIATION
Along with plutonium, highly enriched uranium (HEU) is one of two
key materials that can be used as the explosive material in nuclear
weapons. For two years, the International Atomic Energy Agency (IAEA)
has been probing Iran's covert use of uranium enrichment technologies
to determine whether Tehran has a secret program to build nuclear weapons
in violation of the nuclear Nonproliferation Treaty (NPT).
Enrichment is the process of increasing the concentration of the uranium-235
isotope, which fissions far more readily than the more common uranium-238
isotope. Natural uranium is only 0.7 percent uranium-235. Uranium that
contains uranium-235 (low-enriched uranium) is used as fuel in power
reactors.
But the same technologies that produce weapons-grade uranium, also can
produce low-enriched uranium for civilian nuclear power plants, complicating
the IAEA's task.
In July, new information emerged suggesting that Iran is attempting to
develop nuclear weapons. Western diplomatic sources, as well as a U.S.
official, confirmed press accounts of intelligence describing Iranian
attempts to purchase deuterium (or heavy water) and high-speed electronic
switches. Both are dual-use materials, which can be used to produce a
more advanced nuclear weapon. Undersecretary of State John Bolton stated
Aug. 17 that the United States wants the IAEA to investigate these procurement
attempts.
Step 1: Mine and process
uranium
WIDE CIVILIAN USE
-Iranian President Mohammad Khatami announced Feb. 9, 2003 that Iran had started mining uranium near the city of Yazd.
Step 2: Convert uranium
oxide into uranium hexafluoride for enrichment
WIDE CIVILIAN USE
-On March 3, 2003 Secretary of the Supreme National Security Council Rowhani declared Iran's uranium conversion facility operational.
-A June 6, 2003 report from IAEA Director-General Mohamed ElBaradei revealed that Iran had imported uranium compounds such as uranium hexafluoride, uranium tetrafluoride, and uranium dioxide in 1991.
-ElBaradei presented a report Aug. 26, 2003, which included Iran's admission that it had conducted uranium conversion experiments in the early 1990's.
-Iran informed the IAEA April 29 that it would begin hot testsof the facility's uranium hexafluoride production line beginning May 6, but there is no public indication that it has done so.
Step 3: Enrich Uranium
WIDE CIVILIAN USE
Gas Centrifuges: Precision rotors containing uranium hexafluoride gas spin at very high speeds. Heavier isotopes concentrate toward the wall of the rotor, where they can be removed.
-During a Feb. 21-22, 2003 visit, ElBaradei reportedly expressed surprise at the progress of the Iranian gas centrifuge facility. Iran was operating a small pilot facility with more than 160 centrifuges and planning to install up to 50,000 centrifuges at a commercial facility located at the same site. Iran suspended work at the site last December after agreeing to do so in October 2003.
-The subsequent IAEA investigation revealed that Iran had covertly tested centrifuges with nuclear material. Under
the NPT, states are permitted to possess enrichment facilities, but they must allow the IAEA to monitor their operation. Iran publicly tested a single centrifuge June 25, 2003 and began to test 10 more centrifuges two months later. On Feb. 24, 2004 ElBaradei stated that Iran had continued to manufacture centrifuge parts and assemble entire centrifuges. Iran agreed in February to suspend this activity, but it never entirely stopped manufacturing components. Tehran then announced June 24, 2004 that it would resume making components and assembling centrifuges.
-ElBaradei also revealed in February that Iran had conducted research and development on a centrifuge more advanced than the type it had disclosed to the IAEA. He further reported June 1 that a private Iranian company had made inquiries about procuring components for thousands of centrifuges.
Laser Enrichment: Laser-based enrichment technologies utilize small differences in light frequencies to ionize lighter uranium-235 from heavier uranium-238. The weapons-grade atoms are then collected on a negatively charged plate.
-In late October 2003, Iranian officials admitted to pursuing and making significant progress on laser technology but said it no longer has operating laser enrichment facilities.
Step 4: Bomb design and
development, computer simulation, and non-nuclear high-explosive
testing
* LIMITED CIVILIAN USE
-Intelligence reports described in July press accounts indicate that Iran has attempted to obtain high-speed electronic switches, although it is unclear when these attempts took place or whether Tehran is still attempting to do so. Such switches are used to ensure that conventional high explosives in implosion weapons detonate simultaneously.
-The February 2004 report from ElBaradei stated that Iran had conducted experiments with polonium, which can be used as a neutron initiator to trigger a nuclear chain reaction.
-Intelligence reports also indicate that Iran is attempting to acquire deuterium from Russia. Deuterium, along with tritium, is used as the boost gasin a certain type of nuclear weapon. Additionally, deuterium and tritium are used as neutron initiators in modern nuclear weapons. The boost gas greatly increases the yield of a given amount of fissile material. Deuterium also can be used as a moderator in heavy-water nuclear reactors (heavy water is another name for deuterium). Iran has said it is constructing such a reactor, along with a heavy-water plant.
Step 5: Fabricate highly
enriched uranium into a bomb core or pit, and assemble the weapon
NO CIVILIAN USE
-No evidence.
Possible Step Nuclear testing.*
NO CIVILIAN USE
-No evidence.
* HEU can be used to make two fundamentally different types of weapons:
gun-type weapons and implosion weapons. Gun-type weapons (such as the Little
Boybomb used in the 1945 attack on Hiroshima, Japan ) require
more HEU, but are far simpler to design and build. Such weapons require
neither a neutron trigger, nor high-explosive testing or assemblies.
These weapons also allow manufacturers very high confidence that the
devices will explode, even without testing. Implosion weapons use one-third
as much HEU (or less), but are much more difficult to design and build.