Nuclear Terrorism FAQ

Despite various terrorist claims, there is no convincing evidence that any terrorist group has yet succeeded in getting a nuclear bomb or the HEU or plutonium needed to make one.

What has been done to reduce the risk of nuclear theft and terrorism?

A wide range of programs in the United States and elsewhere are making real progress in reducing the global danger of nuclear terrorism -- but much more remains to be done. Through Nunn-Lugar cooperative threat reduction programs and related efforts, security has been dramatically improved at scores of buildings and bunkers with either nuclear weapons or the materials needed to make them in the former Soviet Union and in other countries around the world. Hundreds of kilograms of HEU have been removed from potentially vulnerable nuclear sites around the world. HEU-fueled research reactors are being converted to run on low-enriched uranium (LEU) fuel that cannot be used in a nuclear bomb, and their HEU is being removed. As a second line of defense, radiation detectors are being installed at key ports and border crossings around the world -- and at U.S. border crossings and elsewhere within the United States. Hundreds of tons of potential nuclear bomb material are actually being destroyed (for example, by blending HEU with other uranium to produce LEU reactor fuel that cannot be used in a bomb); remarkably, roughly one of every 10 light bulbs in the United States is powered with fuel from dismantled Russian nuclear weapons. These programs continue to be excellent investments in U.S. and world security.

But important gaps remain. Security upgrades have not yet been completed for scores of nuclear material buildings and warhead sites in Russia -- and for some, there is no agreement to cooperate on security upgrades. Upgrades in China are just beginning, and India has not yet agreed to cooperate on nuclear security improvements. Only a small fraction of the world's HEU-fueled research reactors have had all their HEU removed. Most of the HEU the United States itself shipped to countries around the world for use as research reactor fuel is not yet eligible for the U.S. offer to take it back. A dangerous gap remains between the urgency of the threat and the scope and pace of the U.S. and international response.

What is highly enriched uranium? What is enrichment?

Highly enriched uranium is uranium that contains 20 percent or more of the isotope uranium-235 (U-235 for short). Because it easily fissions, uranium-235 is useful in powering nuclear reactors or nuclear bombs.

Natural uranium mined from the ground contains only 0.7 percent U-235 and cannot sustain the explosive nuclear chain reaction needed for a nuclear bomb. To make HEU, the uranium has to be "enriched" ¿ that is, the concentration of U-235 has to be increased. Separating the atoms of U-235 from the atoms of U-238 (which make up more than 99 percent of natural uranium) requires complex and difficult technology, since these atoms have the same chemical properties and differ only slightly in weight. Terrorist groups would almost certainly not have the technical or financial means to enrich their own uranium. Unfortunately, the same technologies used to make LEU for peaceful reactor fuel can also be used to make HEU for nuclear weapons -- which is why Iran's pursuit of uranium enrichment technology is raising international concern.

What is plutonium and where is it found?

Plutonium is a man-made radioactive element that can be used in nuclear fuel or nuclear weapons. It is extremely heavy, with 94 protons in its nucleus. Plutonium is produced when an atom of U-238 absorbs a neutron, typically in a nuclear reactor. All current nuclear power reactors produce plutonium in their spent fuel, though this plutonium cannot be used in nuclear weapons until it has been chemically separated from the uranium and the intensely radioactive fission products in the spent fuel, a step known as reprocessing. As with uranium enrichment, it is extremely unlikely that terrorists could build and operate their own nuclear reactor and reprocessing facility to produce plutonium for a bomb. Plutonium-239, the most common isotope and the one most useful in nuclear weapons, has a half-life of 24,000 years (meaning that half of it will have decayed after that time, half of the remainder after another 24,000 years, and so on). Over geologic time, therefore, plutonium has decayed away and little of it exists in nature.

What are weapons-grade uranium and weapons-grade plutonium?

In principle, any HEU can fuel a nuclear bomb. However, the greater the concentration of U-235, the less HEU is needed for the bomb. Weapons-grade uranium consists of 90 percent or greater U-235. Despite this definition, however, nuclear bombs can be and have been made with less enriched material. The average enrichment of the HEU used in the Hiroshima bomb was roughly 80 percent.

Weapon-grade plutonium typically contains 93 percent or more plutonium-239 (Pu-239), the isotope most useful in nuclear weapons. The plutonium in the spent fuel discharged from typical power reactors is "reactor-grade," containing larger concentrations of Pu-240 and Pu-241, which are more troublesome for weapons designers. Nevertheless, government studies have concluded that any state or group that could make a bomb from weapon-grade plutonium could also make a bomb from reactor-grade plutonium.