Glossary of Nuclear Terms

Atomic bomb: An explosive device whose energy typically comes from the fissioning of uranium or plutonium.

Crowd looking at model of Shaheen missile (AP Images)
Crowd looking at model of Shaheen missile (AP Images)

Comprehensive Nuclear Test Ban Treaty (CTBT): Bans nuclear explosions in all environments for military or civilian purposes. It was adopted by the United Nations General Assembly in 1996 but cannot enter into force until ratified by 44 designated countries. Of these 44, India, Pakistan, and North Korea have not signed, and China, the United States, Israel, Egypt, Iran and Indonesia have not ratified it. For more than a decade, the United States has reaffirmed its unilateral moratorium against testing. Although the United States signed the accord, the U.S. Senate voted 48 for and 51 against consent to ratification. President Obama has pledged to aggressively pursue the Senate’s consent to ratify the treaty. See also

The Cooperative Threat Reduction Program, also known as the Nunn-Lugar Program: Provides U.S. financial assistance and expertise to help countries of the former Soviet Union safeguard and dismantle stockpiles of nuclear and other weapons of mass destruction and related material and delivery systems. See also

Dismantlement: Disassembling a weapons system to its component parts.

Downloading: The removal of some warheads from a multiple independently targetable re-entry vehicle (MIRV).

First Use: The first use of a nuclear weapons in a conflict. (“No first use” is a phrase that means a nation pledges not to be the first one to employ such weapons in a conflict.)

Fissile Material: Nuclear material such as enriched U-235 and Pu-239, used to make nuclear weapons.

Fissile Material Cut-Off Treaty (FMCT): A treaty that would prohibit the production of fissile material for use in nuclear weapons. Such a treaty is seen as a necessary step toward the goal of the total elimination of nuclear weapons. Negotiations for an FMCT have been deadlocked in the Conference on Disarmament since 1999. President Obama has called for prompt negotiation of a verifiable FMCT as part of his Prague Vision.

Fuel Cycle: The sequence of operations involved in producing fuel for nuclear reactors, irradiating the fuel in a nuclear reactor and treating the fuel elements following discharge from the reactor. (related info at

Fuel Rod: The tubes, up to four or five meters long and usually made of clad with Zircaloy, containing the fuel for a nuclear reactor.

Full-Scope Safeguards: Placed by the International Atomic Energy Agency on nuclear facilities, these specific procedures, such as the use of sensors, inspections and accounting methods, ensure that nuclear materials are used only for peaceful purposes. See

Highly Enriched Uranium (HEU): Uranium that is enriched from its naturally occurring 0.7 percent to above 20 percent of the U-235 isotope. Weapons-grade material is usually enriched to 90 percent U-235 or greater.

Intercontinental Ballistic Missile (ICBM): A long-range, land-based ballistic missile with a range in excess of 5,500 kilometers.

Yoriko Kawaguwi, right, and Gareth Evans co-chair the International Commission on Nuclear Nonproliferation and Disarmament.
Yoriko Kawaguwi, right, and Gareth Evans co-chair the International Commission on Nuclear Nonproliferation and Disarmament.

Intermediate-range Nuclear Forces Treaty (INF): A 1987 bilateral treaty between the United States and the Soviet Union (PDF, 134KB) that required destruction of ground-launched ballistic and cruise missiles with ranges of between 500 and 5,500 kilometers, their launchers and associated support structures and equipment. When the Soviet Union was dissolved in 1991, the United States secured continuation of the agreement with the 12 former Soviet republics.

International Atomic Energy Agency (IAEA): An independent international organization affiliated with the United Nations that works for the safe, secure and peaceful uses of nuclear science and technology. It was established as an autonomous organization in 1957 and has become the primary tool for verifying compliance and detecting noncompliance with the safeguards obligations required by Article III of the Nuclear Non-Proliferation Treaty.  Website

Lisbon Protocol (also known as the START Protocol): The protocol signed in 1992 by the United States, Russia, Belarus, Kazakhstan and Ukraine as a mechanism to formalize the accession of all five parties to the Strategic Arms Reduction Treaty and commit the three non-Russian, former Soviet republics to join the Nuclear Non-Proliferation Treaty as non-nuclear weapon states.

Multiple Independently Targetable Re-entry Vehicle (MIRV): Refers to the ability of a missile with a front section that can deliver two or more nuclear warheads to distinct, separate targets.

Negative Security Assurance (NSA): A promise by a state not to use or threaten to use nuclear weapons against another state.

Non-Aligned Movement (NAM): A group of 115 nations representing the priorities and interests of developing countries.

Nonproliferation (NP): Actions taken — by way of diplomacy, arms control measures, multilateral treaties, financial assistance or export controls — to prevent the spread of weapons of mass destruction and related technology and expertise.

Nuclear-Free Zones (NFZs): Areas in which the development, testing, production or deployment of nuclear weapons is prohibited by mutual agreement. Treaties establishing nuclear-free zones include the Antarctic Treaty (1959), the Outer Space Treaty (1967), the Treaty of Tlatelolco (Latin America, 1968), the Seabed Treaty (1971), the Rarotonga Treaty (South Pacific, 1995), and the Pelindaba Treaty (Africa, 1996). See also

Nuclear Non-Proliferation Treaty (NPT): A 1968 multilateral treaty designed to limit the proliferation of nuclear weapons. The NPT entered into force in 1970 and was extended indefinitely in 1995. The treaty is reviewed every five years. In the May 2010 Review Conference, the United States is seeking commitments to strengthen the treaty and to encourage universal membership.

Nuclear Proliferation: The spread of nuclear weapons-related components, technology or expertise to nations or groups without an existing capability.

Nuclear Posture Review (NPR): A period Defense Department review of U.S. nuclear deterrence policy, strategy and force posture that looks five to ten years into the future. The 2010 review is, for the first time, an unclassified document.

Nuclear Risk Reduction Center (NRRC): Permanent offices with direct communication links established in 1987 among Washington, Moscow, Minsk, Kyiv and Alamaty as a way to exchange data and carry out notifications required by arms-control and confidence-building agreements. See also our NRCC FActsheet and the NRCC website.

Nuclear Suppliers Group (NSG), also known as the London Group: Established in response to the 1974 Indian nuclear test. Intended to go beyond the measures adopted by the Zangger Committee and the NPT, the NSG maintains nuclear guidelines and a “trigger list” for control of the transfer of nuclear facilities, equipment and materials. Website

Nuclear Umbrella: A guarantee by a nuclear-weapon state to extend assurance of nuclear deterrence to non-nuclear allies and friends.

Nuclear Weapon: A device that releases nuclear energy in an explosive manner as the result of nuclear chain reactions involving the fission or fusion, or both, of atomic nuclei.

Nuclear Yield: The amount of energy released by a nuclear explosion, generally measures in equivalent tons of the chemical compound TNT. A kiloton is equivalent to 1,000 tons of TNT; a megaton is equivalent to 1 million tons of TNT.

On-Site Inspections: Visits by teams of specialists to allow parties to a treaty to verify each other’s compliance with the treaty provisions. Inspections generally take place throughout the implementation of a treaty and may include review of force deployments or inspection of treaty-specific equipment and support structures.

Positive Security Assurances (PSAs): A promise to aid a non-nuclear-weapon state that has been threatened with or attacked by nuclear weapons.

Stockpile Stewardship Program (SSP): A Department of Energy program to maintain the safety and reliability of U.S. nuclear weapons without testing. Website at

Strategic Nuclear Forces: Land-based ballistic missiles with ranges of more than 5,500 kilometers, modern submarine-launched ballistic missiles, and heavy bombers.

Strategic Offensive Reductions Treaty (SORT), also known as the Moscow Treaty (PDF, 111KB): A 2002 treaty in which the United States and Russia agreed to limit their nuclear arsenals to a range of 1,700 to 2,200 strategic nuclear warheads.

Strategic Arms Reduction Treaty (START): The United States and the Soviet Union agreed in 1991 to reduce the number of strategic warheads on each side from 10,000 to 6,000 and to allow each side to have no more than 1,600 delivery vehicles. In the New START Treaty signed April 8, 2010, Presidents Obama and Medvedev committed their countries to: reduce warheads to 1,550; limit deployed and non-deployed intercontinental ballistic missile (ICBM) and submarine launched ballistic missile (SLBM) launchers and heavy bombers to 800; and reduce deployed strategic ballistic missiles and heavy bombers to 700.

START II: Addressed further strategic reductions for the United States and Russia. The United States ratified the START II agreement in 1996, and Russia followed suit in 2000, contingent on U.S. observance of the ABM Treaty. Following U.S. withdrawal from the ABM Treaty in 2002, Russia declared itself no longer bound by the START II provisions and the treaty never entered into force.

Tactical Nuclear Weapons: Nuclear weapons, such as artillery shells, bombs and short-range missiles, for use in localized, battlefield operations.

Telemetry: In the context of verification, electronic data transmitted from a weapon system being tested that communicates the system’s function and performance parameters.

Theater Nuclear Forces: Nuclear forces designed for localized, regional military missions.

Weapons-Grade Material: Nuclear material considered most suitable for a nuclear weapon. It usually connotes uranium enriched to above 90 percent U-235 or plutonium with greater than 90 percent Pu-239. (Crude weapons can be fabricated from lower-grade material.)

Weapons of Mass Destruction (WMD): nuclear, chemical, biological and radiological weapons.

Zangger Committee, also known as the Nuclear Non-Proliferation Treaty Exporters Committee: It developed the Zangger List, which identifies items whose export would “trigger” the application of IAEA safeguards to the facility for which the items are being provided. Website:

Source: “Arms Control and Disarmament: The U.S. Commitment” published by the U.S. Information Agency, 1997.