Glossary

UK-US Mutual Defense Agreement

This 1958 bilateral treaty between the United States and the United Kingdom provides for nuclear weapons cooperation between the two countries. It was signed after the United Kingdom successfully tested its first hydrogen bomb during Operation Grapple, a series of nuclear tests conducted from 1956 to 1958 at Malden Island and Christmas Island (now Kiribati) that resulted in Britain’s becoming a thermonuclear power.

By far the most comprehensive agreement the United States has in this area, it enables the two countries to exchange classified information to enhance each party's "atomic weapon design, development and fabrication capability". It also provides for the transfer of special nuclear material (e.g. plutonium, highly enriched uranium), components and equipment, and the transfer of "non-nuclear parts of atomic weapons" to the United Kingdom.
Under this agreement the United Kingdom was able to carry out underground nuclear tests at the United States’ Nevada Test Site, the first of which took place on 1 March 1962.

Ulam

Stanislaw Ulam (1909-1984) was a Polish mathematician who participated in the Manhattan Project. He found flaws with Edward Teller’s original hydrogen bomb model and proposed putting the primary and secondary in the same casing. Teller seized this idea and with a few more modifications, created the workable design still used today.

UN General Assembly

It is the full body of the United Nations including all member states, as of March 2008 192 countries. It is responsible for much of the work of the United Nations, controlling finance, passing resolutions and electing non-permanent members of the Security Council. (See United Nations Security Council)

UN Security Council

Same as United Nations Security Council

Unauthorized launch

The accidental or unintended launch of nuclear missiles because of faulty intelligence, systematic or mechanical failures, or mistaken action of military personnel.

United Nations Convention on the Law of the Sea (The Law of the Sea)

Establishes a comprehensive legal framework to regulate all ocean space, its uses and resources. It contains, among other things, provisions relating to the territorial sea, the contiguous zone, the continental shelf, the exclusive economic zone and the high seas. It also provides for the protection and preservation of the marine environment, for marine scientific research and the development and transfer of marine technology. For purpose of nuclear-weapon-free zones, the most important provision of UNCLOS is the right of innocent passage and freedom of the high seas. It opened for signature at Montego Bay, Jamaica, on 10 December 1982. It entered into force 12 years later on 16 November 1994 and has 155 States Parties. 

United Nations General Assembly

It is the full body of the United Nations including all member states, as of March 2008 192 countries. It is responsible for much of the work of the United Nations, controlling finance, passing resolutions and electing non-permanent members of the Security Council. (See United Nations Security Council)

United Nations Security Council

Under the United Nations Charter, the Security Council has primary responsibility for maintaining international peace and security. The Council consists of fifteen members, five of which are permanent-China, France, the Russian Federation, the United Kingdom, and the United States. The other ten members are elected by the General Assembly for two-year terms. The five permanent members have veto power.

Uppsala Declaration on NWFZs

The Uppsala Declaration on NWFZs was adopted on 4 September 2000 at an international seminar in Uppsala, Sweden attended by more than 50 experts, activists and diplomats from six continents. They discussed the feasibility of establishing new nuclear-weapon-free zones across the world. In the declaration, participants adopted a programme of future activities including campaigns on both regional and global levels for public education on the value of NWFZs, with a view to creating new NWFZs and strengthening existing ones.

UPS units

An uninterruptible power supply (UPS), also known as a battery backup, is a device that maintains a continuous supply of electric power to connected equipment by supplying power from a separate source when utility power is not available.

Uranium

Uranium occurs naturally as a radioactive element and is the basic fuel of nuclear energy. “Little Boy”, the atomic bomb dropped on Hiroshima, Japan, on August 6 1945, was the first ever uranium-based detonation. Uranium is very dense, heavy and silvery-white and is found in most rocks in concentrations of 2 to 4 parts per million and is common in the Earth's crust. It also occurs in seawater, and can be recovered from the oceans.

Uranium enrichment

Uranium with an increased concentration of the isotope U-235. Natural uranium contains 0.7 percent U-235, whereas nuclear weapons typically require uranium enriched to 90 percent or more U-235. Nuclear power plant fuel typically uses uranium enriched to 3-5 percent U-235, material that is not sufficiently enriched to be used for nuclear weapons.

Uranium enrichment

Uranium enrichment is fundamental for both the generation of nuclear power for civil uses and the production of nuclear weapons. Uranium is naturally 99.284% U-238 isotope, with U-235 constituting less than 1% of its weight. The fuel for nuclear reactors has to have a higher concentration of U-235 than exists in natural uranium ore. U-235 is important because under certain conditions it can readily be split, yielding a lot of energy. It is therefore said to be 'fissile'. Enriched uranium has been processed to increase the proportion of the U-235 isotope to over 20%. This percentage is required for the construction of a gun-type nuclear device, the simplest type of nuclear weapon. The greater the proportion of U-235 (i.e. the higher the enrichment level), the less material required to cause a nuclear detonation. “Little Boy”, the codename of the atomic bomb dropped on Hiroshima, Japan, on August 6 1945, derived its explosive power from the nuclear fission of uranium 235.