Glossary of Terms

*Unless otherwise noted, the following definitions are from Olli Heinonen and Simon Henderson’s “Nuclear Iran: A Glossary of Terms,” Policy Focus 121, Washington Institute for Near East Policy and Belfer Center for Science and International Affairs, May 2013. 

  • Additional Protocol: Agreement with IAEA that “provides additional measures for improving the effectiveness and efficiency of agency safeguards. Specifically, it gives the IAEA an expanded declaration containing information on all aspects of a country’s nuclear fuel cycle activities and granting broader access to all relevant sites, including those where nuclear material is not customarily used.” Iran signed in 2003, but withdrew in 2006 after censure from the IAEA for non-compliance. 
  • Breakout: “The ability of the Iranians to suddenly abandon constraints, kick out inspectors, disable monitoring equipment, and use existing enrichment facilities to produce enough weapons-grade uranium for one or more nuclear weapons – and to do these things before the international community can take effective action to stop them.” (Robert Einhorn, remarks, 10/24/13
  • Cascade: “Arrangement of groups of centrifuges to produce successively higher concentrations of U-235. . . . To produce 90 percent enriched uranium more than 65 stages are required.” In A.Q. Khan’s scheme, “a 164-centrifuge cascade enriches uranium from 0.7 percent to 3.5 percent. Then another 164-machine cascade enriches the material from 3.5 to 20 percent, a 114-machine cascade enriches from 20 to 60 percent, and a final 64-machine cascade enriches from 60 to 90 percent.” 
  • Centrifuge: “Machine used to enrich uranium by sepa­rating the isotope U-235 (which occurs naturally as only 0.7 percent of the metal) from U-238 (most of the other 99.3 percent). Separation is achieved by spinning at high speed.” 
  • Diversion of nuclear material: “A case of noncompliance that involves one or more of the following: undeclared removal of declared nuclear material from a safeguarded facility; use of a safeguarded facility for the introduction, production, or processing of undeclared nuclear material (e.g., undeclared production of high-enriched uranium in an enrichment plant); or undeclared production of plutonium in a reactor through irradiation and subsequent removal of undeclared uranium targets.” 
  • Enrichment: “The process of increasing the amount of the fissile isotope U-235 within nuclear material. Natural uranium contains only 0.7 percent U-235, but enrichment can increase it to 3–5 percent (the level used for nuclear reactors) or over 90 percent (used in atomic bombs). Enriching is a progressively easier process—for example, if the aim is to produce 90 percent enriched uranium, reaching the 3.5 percent level requires some 75 percent of the work. And by the time 20 percent enrichment is reached—a level Iran currently achieves—90 percent of the work has been completed.” 
  • Heavy-water reactor: “A reactor using heavy water (deuterium) as the moderator. . . .  Spent fuel rods from such facilities contain significant quantities of plutonium, a nuclear explosive. Iran decided in the mid-1990s to build its IR-40 heavy-water reactor, the ‘40’ denoting its power output in megawatts. . . . Such a reactor produces weapons-grade plutonium sufficient for at least one nuclear device annually.” 
  • High-enriched uranium (HEU): “Uranium contain­ing 20 percent or more of the fissile isotope U-235. Weapons-grade uranium is usually enriched to 90 per­cent or higher levels of U-235.” 
  • Inspections: “Most IAEA onsite inspections are carried out according to a defined schedule, though some are unannounced or short-notice. Inspections are limited to locations within a declared nuclear facility or other loca­tions containing nuclear material. During onsite visits, inspectors audit the facility’s accounting and operating records, verify the nuclear material inventory, take envi­ronmental samples, and apply containment and surveil­lance measures such as seals and cameras. The frequency of inspections depends on the type of facility and its inventory of nuclear material. A light-water reactor (e.g., Bushehr) is typically inspected quarterly, while an enrichment plant (e.g., Natanz) has monthly announced inspections as well as additional unannounced visits at least once a month. The IAEA’s annual inspection effort in Iran totals about 500 person-days.” 
  • International Atomic Energy Agency (IAEA): Considered the world’s nuclear “watchdog,” the IAEA “independently verifies the correctness and completeness of the declarations made by States about their nuclear material and activities.” (IAEA website, 2013
  • IR-1 centrifuge: “This Iranian model is based on the early Dutch SNOR design acquired by Pakistani sci­entist Abdul Qadeer Khan, who developed it further and called it ‘P1.’ The design was subsequently given to Iran, Libya, and North Korea.” 
  • IR-2 centrifuge: “Iran’s original IR-2 was made of car­bon fiber, without bellows. A more advanced model, the IR-2m, uses two carbon fiber rotors and a maraging steel bellows. Both models are based on the Pakistani P2 cen­trifuge, a German design acquired by A.Q. Khan, which uses a maraging steel rotor.” 
  • Kiloton: “A measure of the explosive power of an atomic bomb, equivalent to one thousand tons of TNT. The bomb tested at Alamogordo, New Mexico, in July 1945 was 20 kilotons. The one dropped on Hiroshima was 12 to 15 kilotons; the one dropped on Nagasaki was 20 to 22 kilotons. The destructive power of the much more powerful hydrogen bomb is rated in megatons, equivalent to millions of tons of TNT.” 
  • Light-water reactor (LWR): “A power reactor that is both moderated and cooled by ordinary (light) water. LWR fuel assemblies usually consist of Zircaloy-clad fuel rods containing uranium oxide pellets of low enrich­ment (generally less than 5 percent). There are two types of LWR: boiling water reactors and pressurized water reactors. The LWR at Bushehr is the second type.” (Contrast with heavy-water reactors (above), a greater proliferation risk because of their plutonium byproduct.) 
  • Low-enriched uranium (LEU): “Uranium contain­ing between 0.7 and 20 percent of the isotope U-235 found in the natural metal. At 20 percent the material becomes known as high-enriched uranium.” 
  • Megaton: “A measure of the explosive power of a hydrogen bomb, equivalent to one million tons of TNT. Atomic bombs are much less powerful and are therefore rated in kilotons.” 
  • Nuclear Nonproliferation Treaty (NPT): “A global treaty designed to halt the spread of nuclear weap­ons, promote the spread of peaceful nuclear technol­ogy, and further the goal of disarmament. The NPT, which went into force in 1970, divides its signatories into two categories: nuclear weapons states and non-nuclear weapons states. The five official nuclear weap­ons states are the United States, Russia, Britain, France, and China. The non-nuclear weapons states—which include Iran—agree not to pursue nuclear weapons in exchange for access to peaceful nuclear technologies. The nuclear weapons states are obligated to assist in the development of nuclear energy while also working in good faith toward nuclear disarmament.” 
  • Nuclear weapons: “A complete assembly (i.e., implosion type, gun type, or thermonuclear type), in its intended ultimate configuration which, upon completion of the prescribed arming, fusing, and firing sequence, is capable of producing the intended nuclear reaction and release of energy.” (Dictionary of Military and Associated Terms, US Department of Defense, 2005) 
  • Plutonium (Pu): “A radioactive element that occurs in only trace amounts in nature. When produced by irradiating uranium fuels, plutonium contains varying percentages of the isotopes Pu-238, 239, 240, 241, and 242. Plutonium containing any Pu-239 is considered a special fissionable material. The International Atomic Energy Agency has defined 8 kg of plutonium as a ‘sig­nificant quantity,’ that is, the amount sufficient for a nuclear bomb.” 
  • Significant quantity: “The approximate minimum quantity of nuclear material required for the manufac­ture of a nuclear explosive device. . . . The IAEA has defined 25 kg of U-235 for high-enriched uranium (U-235≥20 %), 75 kg U-235 for low-enriched uranium (U-235<20%), or 8 kg of Pu-239 or U-233 as a ‘significant quantity.’ Some outside experts argue that an aspiring nuclear weapons state could construct a simple fission weapon with as little as 3 kg of weapons-grade plutonium, or between 2 and 7 kg of HEU.” 
  • “Sneakout”: In contrast with “breakout” (see above), scenario in which Iran “would create a fog of confusion beneath which it would divert LEU or MEU to a secret site for further enrichment.” This “requires a secret site to which the material would be moved and where centrifuges would produce HEU that would be shaped into uranium metal and used for a bomb.” (Graham Allison, 8/1/13
  • Stuxnet: “A computer virus reportedly developed jointly by the U.S. and Israeli governments, designed to interfere with centrifuges.” (For more on Stuxnet, see David Sanger, 6/1/12.) 
  • Uranium: “A naturally occurring radioactive element with atomic number 92. Natural uranium contains the isotopes U-234, 235, and 238; the isotopes U-232, 233, and 236 are produced by radioactive decay.” 
  • Uranium dioxide: “Processed natural or enriched ura­nium used for fuel rods, particularly in light-water and heavy-water reactors.” 
  • Uranium hexafluoride (UF6): “The gaseous feedstock used in the uranium enrichment process that produces fuel for nuclear reactors and weapons.”
  • Yellowcake: “Semi-processed ore containing a variety of oxides of uranium but principally triuranium octoxide, U3O8. The yellowcake produced by most modern ura­nium mills is actually brown or black, not yellow; the name comes from the color and texture of the concen­trates produced by early mining operations.”