Nuclear Weapons Proliferation

I

Introduction

Nuclear Weapons Proliferation, the spread of nuclear weapons to countries or terrorist organizations that formerly did not possess them. Many observers believe that the problem of nuclear weapons proliferation is likely to be one of the most important issues facing the United States and the world for many years to come. The 1968 Treaty on the Non-Proliferation of Nuclear Weapons (NPT) attempted to address the problem, but the number of countries possessing nuclear weapons has grown since the treaty went into effect.

II

Who Possesses Nuclear Weapons?

Nuclear weapons were first developed by the United States during World War II (1939-1945) as a result of a massive, secret program known as the Manhattan Project. The United States tested the first nuclear weapon in July 1945 at Alamogordo in the New Mexico desert, and then used two nuclear weapons against the Japanese cities of Hiroshima (August 6, 1945) and Nagasaki (August 9, 1945). These are the only times nuclear explosives have been used as a weapon, although there have been more than 2,000 nuclear weapon tests and more than 100 experiments using nuclear explosives for peaceful purposes, such as excavation.

Today, the United States and seven other countries have openly declared that they possess nuclear weapons and have conducted one or more nuclear test explosions to demonstrate this capability. The countries and the dates of their first nuclear test are: Russia (first test conducted by the former Union of Soviet Socialist Republics, 1949); Britain (1952); France (1960); China (1964); India (peaceful nuclear explosion, 1974; nuclear weapons test, 1998); Pakistan (1998); and North Korea (2006).

Israel is generally believed to possess nuclear weapons, although it has not acknowledged this and is not known to have conducted a nuclear test. Including Israel, the total number of countries generally recognized as possessing nuclear weapons is nine.

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A tenth country, South Africa, has also admitted that it developed a small arsenal of nuclear weapons (first weapon completed, 1977), but it dismantled this arsenal in the early 1990s. When the Soviet Union broke apart in 1991, 3 of the 15 newly independent countries, in addition to Russia, had nuclear weapons on their territory. By the mid-1990s, the three countries—Belarus, Kazakhstan, and Ukraine—had transferred all of these nuclear weapons to Russia.

Virtually all countries of the world—other than the nine nations believed to possess nuclear weapons today—have formally pledged not to manufacture them. This pledge was made under the 1968 Treaty on the Non-Proliferation of Nuclear Weapons (NPT), which entered into force in 1970. The treaty has been ratified by 187 non-nuclear weapon states. Many nations have expressed concern, however, that one such party to the treaty, Iran, may be actively seeking to develop such weapons. See also Arms Control.

No terrorist organizations possess nuclear weapons. Al-Qaeda is known to desire them, however, and a Japanese cult, the Aum Shinrikyo, began an effort to develop them in the late 1980s, but was unsuccessful.

III

How Are Nuclear Weapons Made?

The nuclear weapons that the United States developed through the Manhattan Project are known as “atomic” or “fission” weapons because they obtain their energy from the splitting (or fissioning) of certain highly unstable atoms. Two materials have been used as the core of fission weapons: highly enriched uranium and plutonium.

Highly enriched uranium is uranium in which one type of unstable uranium atom, an isotope known as uranium 235 or U-235, has been artificially concentrated. In naturally occurring uranium, U-235 makes up only 0.7 percent of a typical uranium sample, but in fission weapons U-235 is concentrated to much higher levels. Concentrations of more than 90 percent U-235 are considered best for fission weapons, but lower concentrations can also be used. The IAEA and virtually all countries, including the United States, treat uranium enriched to more than 20 percent U-235 as potentially usable for weapons. Material enriched above this level is known as “highly enriched uranium” and is protected by special security measures. The process of increasing the concentration of U-235 is performed in a facility known as a uranium enrichment plant.

Plutonium is produced by irradiating uranium fuel in a nuclear reactor. During the reactor’s operation some uranium atoms absorb an atomic particle known as a neutron, ultimately creating a new element, plutonium. Roughly 1 percent of uranium atoms are transformed into plutonium by this means. The irradiated uranium material is then removed from the reactor in the form of “spent fuel” rods, and the plutonium is extracted from them by chemical processes in a facility known as a reprocessing plant.

To cause a nuclear explosion, the highly enriched uranium or plutonium must be compressed by means of conventional high explosives. The compression causes the nuclear materials to become more dense so as to achieve a supercritical mass that leads to an uncontrolled chain reaction. A nuclear explosion is an uncontrolled chain reaction, whereas the energy generated by a nuclear power plant is a controlled chain reaction.

Highly enriched uranium can be detonated by means of a relatively simple, “gun-type” device, in which one quantity of highly enriched uranium is fired into another within a gun-barrel-like cylinder, thereby achieving the necessary supercritical mass. Plutonium must be compressed much more rapidly than highly enriched uranium, however, because plutonium spontaneously emits neutrons that can interfere with the chain reaction that produces the explosion. To detonate plutonium, a much more complicated implosion-type design is required, in which a hollow plutonium sphere is crushed inward with great precision by a series of shaped, high-explosive charges, known as lenses, that surround the plutonium and are detonated at exactly the same moment.

During the Manhattan Project, the United States simultaneously pursued several means for enriching uranium and also produced plutonium. The Manhattan Project scientists had such confidence in the gun-type design that the highly enriched uranium bomb was not tested before it was used against Hiroshima. The scientists were less sure about the more complex implosion design for the Nagasaki bomb, however, and this was the design tested at Alamogordo.

Today, nuclear weapons inspectors with the IAEA assume that 25 kg (55 lb) of highly enriched uranium or 8 kg (18 lb) of plutonium would be sufficient to manufacture a nuclear weapon. However, depending on the design of the weapon, considerably less could be used. According to some estimates, it is theoretically possible to develop a nuclear weapon with less than 8 kg of plutonium.

In the late 1940s the United States began to develop a far more potent type of nuclear armament, known as thermonuclear weapons, or the “hydrogen bomb.” These bombs use small fission weapons to create extreme conditions that cause certain types of hydrogen atoms (deuterium and tritium) to fuse together, releasing vast quantities of explosive energy. Some thermonuclear weapons release the equivalent of millions of tons of TNT.

Only five of the states possessing nuclear weapons are known to have developed thermonuclear arms: the United States (first test 1952), Russia (1953), Britain (1957), China (1967), and France (1968). Developing these weapons requires extensive nuclear test detonations. The other, more recent nuclear states have conducted very few (and in some cases no) nuclear tests to avoid calling attention to their nuclear weapon programs, which are often the subject of international criticism. This has slowed their development of thermonuclear weapons.

IV

How Easy Is It to Make the Bomb?

The most difficult challenge for a country that seeks to build nuclear weapons is obtaining the necessary highly enriched uranium or plutonium. In addition to access to uranium supplies, this requires considerable industrial and scientific capabilities. Even less developed countries, however, such as China, India, North Korea, and Pakistan, have succeeded by concentrating their resources on this effort and, in most cases, by obtaining help from governments or individuals in more advanced countries. For example, China’s nuclear weapon program benefited from early assistance provided by the Soviet Union. India’s program took advantage of Canadian and U.S. assistance provided for peaceful nuclear research, and Pakistan’s program relied on assistance from China, along with technology and equipment secretly obtained from Western European supplier companies. Without such assistance, nuclear weapon programs in these states would have been greatly delayed and might not have succeeded.

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