Ultraviolet radiation
Light energy from the Sun, which is at the invisible part of the electromagnetic spectrum. Rays of ultraviolet light have wavelengths shorter than the blue end of the visible spectrum.

See United Nations Conference on Environment and Development.

Unconfined acquifer
An aquifer which the water table as its upper boundary. Because the aquifer is not under pressure the water level in a well is the same as the water table outside the well. An unconfined aquifer is near to the earth’s surface causing it to be easily recharged as well as contaminated.

The United Nations Environment Programme (UNEP), established in 1972, works to encourage sustainable development through sound environmental practices everywhere. Its activities cover a wide range of issues, from atmosphere and terrestrial ecosystems, the promotion of environmental science and information, to an early warning and emergency response capacity to deal with environmental disasters and emergencies.

UNICED (United Nations Conference on Environment and Development)
The United Nations Conference on Environment and Development (U.N.C.E.D.) was held from 3 to 14 June 1992 and focused on the compatibility between development, the tool with which to combat poverty, and environmental protection. It was this conference, more commonly known as the original Earth Summit, that led to the concepts of sustainable development, Agenda 21 (see) and biodiversity (see) becoming widely known. The 1997 Kyoto summit resulted in a joint protocol on the reduction of greenhouse gases.

UNIPEDE (International Union Of Producers And Distributors Of Electrical Energy)
UNIPEDE, headquartered in Bruxells, is a professional organisation which deals with the generation, transmission and distribution of electricity. Founded in 1925, it has among its objectives: – promote the image of the electricity supply industry ; – help its members ( almost all the European countries) to provide electricity to customers under the best possible conditions through the constant improvement of quality of service; – promote improvement of the means of electricity generation, transmission, distribution and utilization ; – work in the common interest of its members on an international level ; – establish and maintain contacts for co-operation with other regional organizations representing the electricity supply industry.

The process of converting heavy oil or bitumen into synthetic crude oil.

The exploration and production sector of the petroleum industry. (see Downstream)

A heavy, naturally radioactive, metallic element (atomic number 92). Its two principally occurring isotopes are 235U and 238U. The isotope 235U is indispensable to the nuclear industry because it is the only isotope existing in nature to any appreciable extent that is fissionable by thermal neutrons. The isotope 238U is also important because it absorbs neutrons to produce a radioactive isotope that subsequently decays to the isotope 239Pu, which also is fissionable by thermal neutrons.

Uranium resources
Uranium is not found in concentrated form; many tonnes of ore have to be processed to obtain even one gram of the element. The biggest deposits of uranium ore are at Blind River, Canada, in South Africa, Australia, France, and in Colorado and Utah in the United States. The most important compound of uranium is uranium hexafluoride gas, which can be used to separate uranium-238 from uranium-235, the main ingredient of the atomic bomb. Uranium ore is extracted from the earth through a variety of mining techniques. Traditionally, uranium was extracted from open pits and deep shaft mines. In the past decade, alternative methods, such as solution extraction in which solutions are injected into underground uranium deposits to dissolve uranium, have become more widely used. Newly mined ore is processed at mills to concentrate uranium.

Urban heat island
The increased temperatures in urban areas compared with surrounding rural areas. This is due to the significant amount of brick, concrete, asphalt, etc, in a city which absorbs significant amounts of heat during the day and releases it gradually at night, keeping the urban areas warmer than the surrounding rural areas.

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