Energy Glossary		Back to the Energyzone
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z absorber - Materials that readily absorb neutrons, such as cadmium and boron, are used to regulate the rate of nuclear fission within a reactor. See control rod. Top of page acid rain – Rain with a pH of less than 5. Caused by pollutants released during combustion, in particular sulphur dioxide and nitrogen oxides, dissolving in rain water. Top of page advanced gas-cooled reactor (AGR) – The advanced gas-cooled reactor was the United Kingdom’s second generation nuclear reactor. The AGR uses carbon dioxide gas as a coolant. It can operate at high temperatures than other reactors, increasing its thermal efficiency. The AGR uses enriched uranium dioxide fuel and has a graphite moderator. A heat exchanger is used to transfer heat from the carbon dioxide to water, to produce steam. Top of page air pollution - The presence of pollutants in the atmosphere which cause harm. See sulphur dioxide, nitrogen oxides, carbon monoxide, volatile organic compounds and particulates. Top of page air source heat pump – A device that transfers heat energy to or from the air to provide cooling or heating respectively. Top of page alcohol (ethanol) – Form of biofuel, usually produced from fermenting sugar cane or maize. Top of page alkanes - Hydrocarbon molecules with the general formula CnH2n+2, containing only single bonds. Top of page alkenes - Hydrocarbon molecules with the general formula CnH2n, containing one or more double bonds. Top of page alternating current (AC) - An electric current in which the direction of the flow of charge reverses with a constant frequency. Alternating current is generated using an alternator. Top of page alternator – An generator that produces an alternating current. The alternators in a power station generally have a large electromagnets rotating inside fixed coils of wire. See also dynamo. Top of page ampere (A) – The SI unit of electric current. The ampere (amp) is given the symbol A. Top of page anthracite – Hard, black coal with a high carbon content. Anthracite produces lots of heat but little smoke when it burns. Used primarily for domestic heating. Top of page articulated loading column – Device to allow tankers to load a cargo of oil at sea. The oil is piped to a loading column to prevent tankers from having to manoeuvre close to a platform. Top of page atmosphere – The gases that surround a planet. The Earth’s atmosphere is composed of nitrogen (78%), oxygen (21%), argon (1%), carbon dioxide (0.04%) and trace gases. The Earth’s atmosphere is divided into a number of layers. See ozone layer. Top of page A B C D E F G H I J K L M N O P Q R S T U V W X Y Z background radiation – The level of radiation in a location. The background radiation is due to naturally occurring cosmic rays and the radioactivity present in the Earth’s rocks and also the radioactivity released during nuclear weapons tests and by industries. Top of page barrel – A measure of volume used by the oil industry. The standard size of a barrel of oil is 159 litres (35 gallons). Top of page barrel of oil equivalent (BOE) – Unit of energy based on the energy released when a barrel of oil is burned. This is approximately 5,700,000 kilojoules. Top of page battery – A number of cells connected to provide an electric current. A battery converts chemical energy into electrical energy. Top of page biodegradable – An item that can be decomposed by living organisms. Top of page bioenergy – Energy derived from animal waste and recently living plant materials. Sustainable managed bioenergy sources are a form of renewable energy. Top of page biofuel – A fuel derived from a bioenergy source. Top of page biomass – In the energy industry, biomass the name given to recently living biological material to be used as a fuel. Top of page bitumen – A viscous, black liquid remaining after fractional distillation of crude oil. Bitumen is used to make roads. Top of page black start – The process of starting a power station after a blackout has occurred. In these circumstances a power station can not get the electricity from the grid that it requires to start operating. A small auxiliary generator can be used to start the main power station. Hydroelectric power stations generally require little electricity to be brought online; the electricity produced by a hydroelectric plant can then be used to start other power stations. Top of page boiler – A closed vessel in which a fluid, usually water, is heated under pressure. Top of page boiling water reactor (BWR) - The boiling water reactor uses water as a coolant and a moderator. The water in the reactor is allowed to boil to form steam. The steam produced in the reactor is used to drive turbines, without the need for a heat exchanger or a secondary water circuit. The BWR uses enriched uranium dioxide fuel. Top of page bubble caps - A covered hole in a tray of fractionating column through which vapour bubbles upwards through the liquid in the tray. Top of page butane – An alkane with four carbon atoms in its molecule. Butane has the chemical formula C4H10. It is a gas at standard temperature and pressure but can be liquefied by compression. Top of page A B C D E F G H I J K L M N O P Q R S T U V W X Y Z calorie – A unit of energy. The energy needed to heat one gram of water by one degree Celsius. Equivalent to 4.19 joules. Top of page Canadian-Deuterium-Uranium (CANDU) reactor - The CANDU reactor uses heavy water as a coolant and a moderator. The CANDU reactor uses un-enriched uranium dioxide fuel. A heat exchanger transfers the heat energy produced to a secondary circuit of water. The water in the secondary circuit is turned into steam to drive the turbines. Top of page capacity factor – The ratio of the amount of electricity produced by a generator(s) during a given period of time divided by the amount of electricity it/they would produce running at full capacity for the same time. The capacity factor is usually stated as a percentage. See plant factor. Top of page cap rock - An impervious layer of rock which traps oil or gas beneath it. Top of page carbon capture – Collection of the carbon dioxide gas produced from the combustion of a fuel. The carbon dioxide is then available for carbon sequestration. Top of page carbon dioxide (CO2) – A colourless, odourless gas at standard temperature and pressure. Carbon dioxide is naturally present in the Earth’s atmosphere. The gas is absorbed by plants during photosynthesis; however, the gas is released during respiration and combustion. Since the Industrial Revolution the amount of carbon dioxide in the Earth’s atmosphere has been increasing. Carbon dioxide is a greenhouse gas. Reducing carbon dioxide emissions is the focus of actions to combat global warming. Top of page carbon intensity – A ratio of the amount of carbon emitted for each unit of economic activity (gross domestic product). Top of page carbon monoxide (CO) - A colourless, odourless gas at standard temperature and pressure. Carbon monoxide is formed by the incomplete combustion of carbon. Carbon monoxide is a toxic air pollutant. Top of page carbon sequestration – The storage of carbon dioxide collected during carbon capture. There are a number of options for the long-term storage of the gas: saline aquifers; the Earth’s ocean at depth; oil wells, allowing enhanced oil recovery; and coal mines, allowing enhanced recovery of coal bed methane. Top of page catalyst – A substance that increases the rate of a chemical reaction with undergoing permanent changed. Top of page catalytic converter – A device fitted to the exhaust systems of motor vehicles to reduce the amount of carbon monoxide, unburned hydrocarbons, and nitrogen oxides (NOx) produced. Top of page catalytic cracking – The use of catalysts to reduce the temperatures required during the cracking of hydrocarbons. Top of page Celsius (C) – A centigrade scale of temperature defined by the melting point (0°C) and boiling point (100°C) of water. Top of page chain reaction - During nuclear fission, two or three free neutrons are released and these neutrons may fission other nuclei. In a nuclear reactor the excess neutrons can be prevented from causing fissions so that on average only one neutron from each fission is allowed to fission a further nucleus allowing the process to proceed at a steady rate. This is a critical chain reaction. If, on average, more than one of the free neutrons fissions another nucleus then a runaway, supercritical chain reaction can occur, resulting in a large explosion. Top of page chemical energy – The energy released during a chemical reaction. Top of page chlorofluorocarbons (CFCs) – A groups of chemical compounds in which the hydrogen atoms in a hydrocarbon have been replace with chlorine or fluorine atoms. CFCs were widely used as refrigerants and aerosol propellants until the environmental damage they cause was realised. Chlorofluorocarbons break apart ozone molecules at high altitude, this caused a hole in the ozone layer. CFCs are also potent greenhouse gas. Top of page clean coal technology – A term used to describe technological developments designed to reduce the environmental impacts of burning coal. Top of page climate change – Variation in the Earth’s climate. The Earth’s climate undergoes natural variation; however, a majority of scientists agree that human activities are now changing the Earth’s climate. Human activities are believed to be causing global warming as a result of the greenhouse effect. Top of page coal – Fossil fuel formed from the compression and heating of vegetation. There are a number of ranks of coal, ranging from lignite to anthracite, which are classified by the amount of volatile substances and water they contain. Top of page coal conversion – The processing of coal to produce liquid fuels or gas. See coal gas. Top of page coal gas – Gas produced from the heating of coal in the absence of air. Coal gas, sometimes called town gas, is a mixture of hydrogen, methane and carbon monoxide. Top of page cogeneration - See combined heat and power (CHP). Top of page combined cycle gas turbine (CCGT) – A combined cycle gas turbine uses the hot exhaust gases from a gas turbine to raise steam. The steam produced is used to power a steam turbine. The gas turbine and steam turbine are both connected to a generator to produce electricity. Top of page combined heat and power (CHP) – Combined heat and power is the cogeneration of electricity and useful heat. The heat produced can be used for industrial processes or to meet a heating demand. See district heating. Top of page combustion – A chemical reaction in which a substance combines with oxygen, releasing heat and light. The combustion of fuels containing carbon releases carbon dioxide and water vapour. Top of page community heating - See district heating. Top of page conservation of energy – 1. The physical principle that states the total energy of an isolated system will remain constant. Simply stated, energy cannot be created or destroyed, only transformed from one form to another. In a nuclear reaction the ‘creation’ of energy is due to a decrease in mass of the particles involved. 2. The practice of attempting to reduce the amount of energy used. Often this is called energy conservation. Top of page containment - To prevent the escape of radiation into the environment nuclear reactors are enclosed in a pressure vessel, which is surrounded by a thick concrete shield. Top of page control rod - Control rods made from materials that absorb neutrons. The control rods can be moved in, or out, of a nuclear reactor to reduce, or increase, the reaction rate respectively. See absorber. Top of page coolant - The coolant transfers the heat produced by nuclear fission from the reactor. Water, heavy water and carbon dioxide are commonly used coolants. Most nuclear power stations have a separate circuit of water, which is used to drive the plant’s turbines. Top of page cooling tower – Cooling towers help to condense the steam produced during electricity production and other industrial processes. This is important as decreasing the output temperature of a heat engine raises it’s efficiency. The characteristic shape of hyperbolic cooling towers is chosen as it provides the necessary structural strength while using the minimum of materials; they make use of the natural draft produced as the hot, moist air rises and do not require fans. Other cooling tower designs require fans to operate. Top of page cracking – The process of breaking down large hydrocarbon molecules into smaller ones. Cracking increases the proportion of small hydrocarbons from a given quantity of crude oil. Cracking is carried out by heating the heavy fractions, produced by fractional distillation of crude oil, in the presence of catalysts. Top of page crude oil - Crude oil is a mixture of hydrocarbons with small quantities of other chemicals such as sulphur, nitrogen and oxygen. Crude oil is a fossil fuel formed from the compression and heating of organic matter, generally in marine conditions. In a refinery, fractional distillation of crude oil is used to produce a range of fuels and products. Top of page current - See electric current. Top of page A B C D E F G H I J K L M N O P Q R S T U V W X Y Z decentralised energy – See distributed energy. Top of page decommissioning – The process of withdrawing a facility from service and then dismantling it. This is a complex process when decommissioning nuclear facilities because of the dangers associated with radioactive waste. Top of page delivered energy – The amount of energy received by a customer and paid for. Top of page demand side management – Actions to alter the patterns of energy use by energy users. This may be through decreasing the amount of energy used or changing the time at which the energy is used. Top of page deuterium - Deuterium is an isotope of hydrogen that contains an additional neutron. Top of page deviation drilling – See directional drilling. Top of page diesel – A fuel produced from the middle distillate of crude oil during fractional distillation. The fuel is used in diesel engines. Top of page diesel engine – An internal combustion engine in which a fuel and air mixture is ignited by compression. Top of page direct current (DC) - An electric current in which the direction of the flow of charge is in one direction. Direct current is produced by batteries, dynamos and fuel cells. Top of page directional drilling – Instead of simply drilling straight down, wells are drilled in different directions from a platform. This enables many parts of a reservoir to be reached from a single platform, thereby maximising the recovery possible. Directional drilling, otherwise known as deviation drilling, allows a number of wells to be drilled from a single platform. Top of page distillation - See fractional distillation. Top of page distributed energy – The generation of electricity from many small energy sources. These may be connected to the distribution network to export electricity when the amount generated exceeds that used on-site. Distributed energy is also known as decentralised energy and embedded energy. Top of page distribution – The delivery of electricity from sub-stations to end users. Top of page district heating – The supply of heat to a number of buildings or residences from a centralised heating system. The use of district heating allows greater efficiencies to be achieved. The heating system may also be used to produce electricity in a combined heat and power system. Top of page drill bit – To access oil and gas reservoirs below ground or below the seabed a drill bit that can cut through rock is used. This is made of hardened steel, can have several toothed cones and may be coated with diamonds. Depending on the source rock to be drilled, different types and sizes of drill bit can be used. Top of page drilling platform - An offshore structure used to drill for oil and gas. There are a number of designs, depending on the conditions and objectives. Platforms may be fixed to the sea floor, by their weight or steel piles; these are known as fixed installations. Other structures have retractable legs; these are known as jack-ups, and this allows them to be floated between locations. There are also floating structures to support a drilling rig, those having pontoon hulls are known as semi-submersibles and those having a mono-hull are known as drill ships. Top of page drilling rig – The machinery and equipment used to drill a well to reach oil and gas. Top of page dynamo – A generator of electricity. A dynamo is generally the name given to a generator producing a direct current. See also alternator. Top of page A B C D E F G H I J K L M N O P Q R S T U V W X Y Z efficiency – A ratio of the useful energy output of system compared to the total energy input. Efficiency is usually expressed as a percentage. See also energy efficiency. Top of page electric current – A flow of electric charge. Electric current is measure in amperes. See alternating current and direct current. Top of page electric motor – A device which transforms electrical energy into movement (kinetic energy). Top of page electrical energy – The quantity of energy transferred by electricity. This is measured in joules or kilowatt-hours. Top of page electricity – The name given to the effects that result from the presence and movement of charged particles. Top of page electromagnetic waves – Waves that travel at the speed of light due to the oscillation of electric and magnetic fields. The characteristics of electromagnetic waves are determined by their wavelength. See electromagnetic spectrum. Top of page electromagnetic spectrum – The range of wavelengths of electromagnetic waves. The regions of the electromagnetic spectrum in order of decreasing wavelength are radio waves, microwaves, infra-red, visible light, ultraviolet, X-rays and gamma rays. Top of page element – A substance that contains only one type of atom. An element cannot be split into simpler substances by a chemical reaction. Top of page embedded generation – See distributed energy. Top of page embodied energy – The amount of energy required to produce a good or service. Top of page energy – A measure of a system’s ability to do work. Energy is usually measured in joules or kilowatt-hours. Top of page energy carrier – A substance used to store and/or transport energy. Top of page energy conservation – See conservation of energy. Top of page energy content – See energy density. Top of page energy density - The amount of energy released when a given quantity of a fuel is used. Energy density is usually expressed in units of megajoules per kilogram. Top of page energy efficiency – Actions to reduce the amount of energy that is used to provide an energy service. This can be achieved through changes to technology or behaviour. Top of page energy intensity – A ratio of the amount of energy used to produce each unit of economic activity (gross domestic product). Top of page energy service – A service that end-users want: warmth, illumination, motive power, etc. Top of page enhanced oil recovery (EOR) – The pumping of steam or carbon dioxide into an reservoir, raising the pressure, to increase the amount of oil that can be extracted. Otherwise known as tertiary recovery. Top of page enriched uranium - Enriched uranium has a higher proportion of the isotope U235 compared to the composition of natural uranium. A composition of between 2-3% U235 is usual for thermal reactors. Fast breeder reactors require highly enriched uranium, up to 20% U235 to compensate for the increased neutron absorption by U238. Top of page ethane - Ethane is the alkane with two carbon atoms in its molecule. It has the chemical formula C2H6. Ethane is a gas at standard temperature and pressure. Top of page exhaust – A system for removing the waste (exhaust) gases produced during combustion. Top of page exploration - The search for fossil fuels. Geological and geophysical surveys are followed by exploratory drilling in the most promising locations. Top of page extraction – See mining. Top of page A B C D E F G H I J K L M N O P Q R S T U V W X Y Z fast breeder reactor (FBR) – Fast breed reactors Do not have a moderator. They use fast neutrons to fission highly enriched uranium fuel (around 20% U235). Fast neutrons can interact with U238 to produce plutonium, which can be used a nuclear fuel. Top of page fast neutrons – Neutrons travelling at high speed that are ejected from a nucleus undergoing nuclear fission. Fast neutrons are absorbed by U238 to produce plutonium. Top of page fault - A fracture in rocks caused by movement in the Earth's crust. Top of page fault trap – A formation of a reservoir beneath an impermeable layer of rock due to a fault in the Earth’s crust. Top of page feedstock - A raw material used in an industrial process. Top of page field - An area containing an oil or gas reservoir, or the location of a group of oil and gas wells. Top of page fission - See nuclear fission. Top of page flue gas desulphurisation (FGD) – The removal of sulphur dioxide from the flue gases of power stations that burn coal or oil. The sulphur dioxide is usually removed by reacting it with limestone to produce calcium sulphate. Top of page flue gases – The gases released from the combustion of fuels, for example carbon dioxide, water vapour, nitrogen oxides, sulphur dioxide and volatile organic compounds. Top of page fluidized bed combustion (FBC) – An efficient boiler design that can be used to burn coal and other fuels efficiently. Jets of air are blown through a layer of sand or gravel to which the fuel is added. This allows rapid combustion and good heat transfer, which reducing emissions and increases plant efficiency. Top of page fossil fuel – A fuel derived from the remains of organisms that have been altered by temperature and pressure during geological time. The fossil fuels are coal, oil and natural gas. Fossil fuels contain carbon which is released in the form of carbon dioxide during combustion. Top of page fractional distillation – The process of separating a mixture of liquids with different boiling points using distillation. The liquid is heated in a fractionating column. Fractional distillation of crude oil produces fractions with different boiling points: volatile gases; light distillate, with boiling points from 70-200°C including gasoline and kerosene; middle distillate, with boiling points from 200-350°C including diesel; heavy distillate, with boiling points in excess of 350°C including fuel oil; and residuals including bitumen and lubricants. Top of page fuel – A substance that can be combusted or undergo nuclear fission or nuclear fusion to release useful heat energy. Top of page fuel cell – A device in which the chemical energy in a fuel is converted directly into electrical energy. There is wide range of fuel cell designs. In general, the chemical reactions take place at two electrodes, which act as catalysts. An electrolyte in contact with the electrodes carries the electric current produced. Fuel cells are efficient devices for producing electricity. Top of page fuel economy – The amount of a fuel required to move a vehicle a given distance. Usually express in units of miles per gallons or alternatively litres per one hundred kilometres. Top of page fuel oil – A heavy fuel separated from crude oil using the process of fractional distillation. Used in power stations and large industrial boilers. Top of page fuel poverty - A household is said to be in fuel poverty if it needs to spend more than ten per cent of its income on fuel to maintain health and comfort. Top of page fuel rod – Tube inserted into a reactor that contains the nuclear fuel. Top of page fusion - See nuclear fusion. Top of page A B C D E F G H I J K L M N O P Q R S T U V W X Y Z gas - See natural gas. Top of page gas turbine – A gas turbine uses the hot gases from the combustion of a fuel to produce rotary motion. Top of page gasification – The production of a gaseous fuel from solid or liquid fuels. The resulting gas has a higher energy density. Top of page gasoline – A liquid fuel produced from the fractional distillation of crude oil. Gasoline, otherwise known as petrol, is a mixture of hydrocarbons containing five to eight carbon atoms. It is used as a fuel for motor vehicles and a chemical feedstock. Top of page generator – A machine that converts movement (kinetic energy) into electrical energy. A generator consists of magnets moving relative to a coil of wire. Top of page geothermal energy – Heat energy from inside the Earth. Geothermal energy was produced during the formation of the Earth and continues to be produced by the natural radioactivity of the Earth constituents. Geothermal energy is a form of renewable energy. Top of page global warming – The observed increase in the Earth’s average surface temperature. Although there is natural variation in the Earth’s temperature, the majority of scientists agree that the emission of greenhouse gases by human activities is increasing the Earth’s temperature, as a result of the greenhouse effect. See climate change. Top of page gravitational potential energy – Sometimes called gravitational energy. This is energy an object has due to its position in a gravitational field. An object that has been raised above the Earth’s surface will lose gravitational energy as its height is decreased. As an object falls its gravitational potential energy is transformed into kinetic energy. Top of page greenhouse effect – The increase in the Earth’s temperature caused by the absorption of infra-red radiation by molecules in the Earth’s atmosphere. Some of the heat energy the Earth receives from the Sun is re-emitted by the Earth as infra-red radiation. Some chemicals, referred to as greenhouse gases, in the Earth’s atmosphere absorb the infra-red radiation, prevented the heat energy it carries from escaping into space. The Earth has a natural greenhouse effect that increases the Earth’s average temperature by over 30°C, to around 15°C. The release of greenhouse gases by human activities is believed to be causing the anthropogenic greenhouse effect, the cause of global warming. Top of page greenhouse gas (GHG) – A gas in the atmosphere that absorbs infra-red radiation, reducing the heat energy the Earth loses into space. The action of greenhouse gases causes the Earth’s average temperature to increase, producing the greenhouse effect. The most important greenhouse gases are water vapour, carbon dioxide, methane, nitrogen oxides, ozone and chlorofluorocarbons. Top of page ground source heat pump – A device that transfers heat energy to or from the ground to provide cooling or heating respectively. Ground source heat pumps can operate with a very high efficiency. Top of page A B C D E F G H I J K L M N O P Q R S T U V W X Y Z half-life – The time taken for half of the radioactive atoms in a sample to decay. Each isotope has its own half-life Top of page heat energy – The internal energy of a substance due to the movement of its constituent particles. Heat energy is measured in joules. Top of page heat engine – A device for converting heat energy into kinetic energy. Top of page heat exchanger – A device for transferring heat between two fluids without them coming into contact. Top of page heavy water – Heavy water (deuterium oxide) is water in which the hydrogen atoms have been replaced by atoms of deuterium. Top of page heavy water reactor – A nuclear reactor that uses heavy water (deuterium oxide) as a coolant and as a moderator. Top of page horizontal axis wind turbine (HAWT) – A wind turbine in which the blades rotate around a horizontal axis. Top of page horsepower – An early unit used to measure power. 1 horsepower is equal to 745.7 watts. Top of page hydrocarbon – Chemical compounds containing only hydrogen and carbon atoms. There are many different types of hydrocarbon, for example the alkanes and alkenes. They may exist as solids, liquids or gases. Top of page hydroelectricity – Generating electricity from the movement of water. Most hydroelectric scheme use dams to control the flow of water through its turbines. Hydroelectricity is a form of renewable energy. Top of page hydrogen (H) – A colourless, odourless gas at standard temperature and pressure. Hydrogen is the lightest element. Solar energy is produced by the nuclear fusion of hydrogen in the Sun. The combustion of hydrogen produces water vapour. Hydrogen can also be used to power fuel cells. Top of page hydrogen economy – An economy based on the use of hydrogen as an energy carrier. Top of page A B C D E F G H I J K L M N O P Q R S T U V W X Y Z infra-red radiation - See electromagnetic spectrum. Top of page insulation – Material used to reduce the transfer of heat energy. Top of page isotope – Isotopes are atoms of the same element that contain different numbers of neutrons. The isotopes of an element have the same chemical properties. Top of page A B C D E F G H I J K L M N O P Q R S T U V W X Y Z joule (J) - The SI unit of energy. The joule is given the symbol J. Top of page A B C D E F G H I J K L M N O P Q R S T U V W X Y Z kerosene – Kerosene is a mixture of hydrocarbons with eleven to twelve carbon atoms. Kerosene is separated from crude oil using the process of fractional distillation. Kerosene is used for lighting, heating and aircraft fuel. Top of page kilogram (kg) – The SI unit of mass. There are one-thousand grams in a kilogram. Top of page kilojoule (kJ) – One thousand joules of energy. Top of page kilowatt (kW) – A kilowatt is a unit of power equal to one-thousand watts. Top of page kilowatt-hour (kWh) – A unit of electrical energy used by the energy industry. One kilowatt-hour is equivalent to a power consumption of one-thousand watts for one hour, which is equivalent to 3.6 megajoules. Top of page kinetic energy – The energy possessed by an object in that is moving. Top of page A B C D E F G H I J K L M N O P Q R S T U V W X Y Z landfill gas – The gas produced by the anaerobic digestion of municipal solid waste produced by bacteria. Landfill gas is a mixture of methane and carbon dioxide. Top of page light water reactor (LWR) – A nuclear reactor that uses water as a coolant and/or as a moderator. Top of page lignite – Also known as brown coal. It contains a significant amount of volatile matter. Mainly used for electricity generation. Top of page liquefied natural gas (LNG) – See natural gas. Top of page load factor - The ratio of the average electricity demand during a given period of time to the peak of electricity demand. The load factor is usually stated as a percentage. Top of page load-shedding – Demand side management of energy use to limit peak energy demand by temporarily switching off non-essential systems. Top of page lubricant – A viscous liquid hydrocarbon used to reduce friction in a machine. Top of page A B C D E F G H I J K L M N O P Q R S T U V W X Y Z Magnox reactor - Nuclear reactor design, named after the non-oxidising magnesium alloy (Magnox) cladding used to contain the natural uranium fuel. Magnox reactors use carbon dioxide gas as a coolant. They use a heat exchanger to transfer heat to a secondary circuit of water, to produce steam. Top of page mass – The amount of matter an object contains. Mass is measured in kilograms. Top of page megajoule (MJ) – One million joules of energy. Top of page methane - An alkane with one carbon atoms in its molecule. Methane has the chemical formula CH4. Methane is the main constituent of natural gas. It is a gas at standard temperature and pressure. Top of page metric ton - See tonne. Top of page millions of tonnes of oil equivalent (Mtoe) – The heat energy released by the combustion of one million tonnes of oil. See tonne of oil equivalent. Top of page mining – The extraction of resources, such as coal and uranium, from the Earth. This may be from opencast mines at the surface or from tunnels dug into the Earth. Top of page moderator – The moderator is part of nuclear reactors. The moderator is made from a substance that will interact with the free neutrons slowing them down. Water is the most common moderator, although graphite and heavy water (deuterium oxide) are also used. The slowed neutrons are known as thermal neutrons and are more effective at causing the nuclei of U235 atoms to fission. In addition, slowing the neutrons reduces the formation of plutonium (P239), as fewer neutrons are captured by U238. Reactors with moderators are known as thermal reactors, as the free neutrons are slowed to ‘thermal’ speeds. Reactors without moderators are known as fast breeder reactors, as their fast neutrons produce (breed) a significant amount of plutonium. Top of page A B C D E F G H I J K L M N O P Q R S T U V W X Y Z naphtha – The very light fractions separated from crude oil by fractional distillation. Naphtha is used as feedstock to produce gasoline and other petrochemicals. Top of page natural gas – Fossil fuel formed from the compression and heating of organic matter, generally in marine conditions. Natural gas is a mixture of gaseous hydrocarbons, predominately methane with some ethane, propane and butane. It is found in porous sedimentary rock, it is often found in the same locations as crude oil. Natural gas can be cooled to form liquefied natural gas for storage and transportation. Top of page natural uranium - See uranium. Top of page neutron – The uncharged particle found in the nucleus of atoms. Top of page nitrogen dioxide (NO2) - A colourless gas, formed during combustion. Nitrogen dioxide is a greenhouse gas. Top of page nitrogen monoxide (NO) – A colourless gas, otherwise know as nitric oxide, formed during combustion. Nitrogen monoxide readily reacts with oxygen to form nitrogen dioxide. Top of page non-renewable energy – Energy derived from fossil fuels (and uranium). Human use of fossil fuels is significantly depleting the Earth available fossil fuel resources because they take a millions of years to form. Top of page nitrogen oxides (NOx) – The name given to nitrogen oxide and nitrogen dioxide. These compounds dissolve in rain water, contributing to acid rain. Top of page nuclear energy – energy released when large atomic nucleus splits (nuclear fission) or when small atomic nuclei join together (nuclear fusion). The heat energy released can be used to produce electricity in a nuclear power station. Top of page nuclear fission – Heavy elements with large nuclei can undergo fission. During a nuclear fission, the large parent nucleus splits into two smaller daughter nuclei and a small number of free neutrons. Although nuclear fission can occur spontaneously, nuclear reactors use neutrons to induce large nuclei to fission. Free neutrons are able to pass through an atom’s electron ‘cloud’ because they are uncharged. This allows them to get close enough to interact with the nucleus, causing it to fission. Top of page nuclear fuel – The fuel used in a nuclear reactor. Most nuclear reactors use enriched uranium dioxide as their fuel. The fuel is generally in the form of pellets, housed in fuel rods. The fuel rods can then be replaced when necessary to refuel the reactor, typically every three years. Top of page nuclear fuel cycle – The processing that occurs during the production, use and disposal of nuclear fuel. Uranium ore is extracted from uranium mines. It is processed to separate the uranium oxide from the ore. For most nuclear reactors the natural uranium must be enriched, to increase the concentration of the isotope U235. The enriched uranium oxide is formed into small pellets. The pellets are then put inside fuel rods during fuel fabrication. The fuel is then ready for use in a nuclear reactor. After it has been removed from a nuclear reactor the spent fuel must be dealt with. In an open fuel cycle the spent fuel is put in storage prior to disposal. In a closed fuel cycle spent fuel is reprocessed. Reprocessing extracts remaining uranium and the plutonium produced. These can then be used to produce more nuclear fuel. The remaining highly radioactive waste must then be disposed. Top of page nuclear fusion – Light elements with small nuclei can undergo fusion. During nuclear fusion, to small nuclei combine to form a larger nucleus, releasing nuclear energy. For atomic nuclei to fuse they must be heated to very high temperatures. Nuclear fusion of hydrogen to produce helium occurs in the Sun. Top of page nuclear power – The production of electricity (or heat or motion) from nuclear energy. Top of page nuclear reactor – A device in which energy is released from a nuclear fuel is controlled manner. In nuclear fission reactor this requires the maintenance of a critical chain reaction Top of page nuclear waste - See radioactive waste. Top of page nucleus - The nucleus (plural nuclei) forms the centre of an atom. It is made of uncharged neutrons and positively charged protons. At a considerable distance from the nucleus, a ‘cloud’ of negatively charged electrons form the remainder of the atom. The nucleus contains almost all of an atom’s mass. Top of page A B C D E F G H I J K L M N O P Q R S T U V W X Y Z offshore wind – The generation of electricity using wind turbines positioned at sea. Top of page oil – See crude oil. Top of page oil refinery - See refinery. Top of page opencast mining - See mining Top of page ozone (O3)– Molecules of oxygen containing three oxygen atoms. At low altitudes, ozone is a by-product of combustion and is harmful. At high altitudes ozone in the ozone layer protects life on Earth from ultraviolet radiation. Top of page ozone layer – The ozone layer is a layer of ozone gas in the stratosphere. The ozone layer blocks harmful ultraviolet radiation from the Sun. Chemicals called chlorofluorocarbons (CFCs) damaged the ozone layer. Top of page A B C D E F G H I J K L M N O P Q R S T U V W X Y Z particulates – Small particles of smoke and dust released during combustion. Particulates can damage the lungs. Top of page petrochemical - Chemicals obtained from the fractional distillation of crude oil or from natural gas. Petrochemicals are used to make a wide range of products including plastics and lubricants. Top of page petrol – See gasoline. Top of page petrol engine - An internal combustion engine in which a fuel and air mixture is ignited by sparks. Top of page petroleum – See crude oil. Top of page photovoltaic – A device that converts light directly into electricity. Top of page pipeline – A pipeline used to transport oil or gas over land. See also tanker. Top of page plant factor - The ratio of the amount of electricity produced by a power station during a given period of time over the amount of electricity it would produce running at full capacity for the same time. The plant factor is usually stated as a percentage. See capacity factor. Top of page pollutant – A substance that is harmful to health and or the environment Top of page pollution – The contamination of an environment with harmful substances. Top of page possible reserves - Oil and gas reserves which it may be possible to develop. Top of page potential difference – The energy transferred in moving a unit of electrical charge from one point to another. Potential difference, often called voltage is measured in volts. Top of page potential energy – Energy stored within a system. Examples include chemical energy and gravitational potential energy. Top of page power – The rate at which energy is transferred. Power is measured in watts. Top of page power plant – See power station. Top of page power station – A facility, sometimes called a power plant, for the generation of electricity. Top of page pressure vessel – The housing of a nuclear reactor designed to withstand the high pressure created. The term is also used to describe boilers and components of oil refineries and drilling platforms. Top of page pressurized water reactor (PWR) - Pressurized water reactors use water as a coolant and a moderator. The water is kept under high pressure to prevent it boiling. PWRs use enriched uranium dioxide fuel. A heat exchanger transfers the heat energy produced to a secondary circuit of water. The water in the secondary circuit is turned into steam to drive the turbines. Top of page primary energy – The total amount of energy present in the original resource. Top of page primary recovery – The crude oil produced by an reservoir under natural pressure. To increase the output from a reservoir secondary recovery and tertiary recovery techniques may be used. Top of page probable reserves - Undeveloped oil and gas reserves from tested formations, but for which there is a lack of information. Top of page production platform - An offshore structure fixed to the seabed from which wells are drilled. Top of page propane - An alkane with three carbon atoms in its molecule. Propane has the chemical formula C3H8. It is a gas at standard temperature and pressure but can be liquefied by compression. Top of page proven reserves – Reserves of oil and gas that are economically and technologically feasible to exploit. Top of page pumped storage – The use of reservoirs of water with different elevations to generate hydroelectricity. During times of low electricity demand water is pumped up to the higher reservoir. This can be released during peaks in electricity demand. Top of page A B C D E F G H I J K L M N O P Q R S T U V W X Y Z Top of page A B C D E F G H I J K L M N O P Q R S T U V W X Y Z radioactive waste – Waste material that contain radioactive substances. Radioactive waste is produced by a number of industries, including nuclear power generation and the nuclear fuel cycle. There are three main categories of radioactive waste: high-level waste, such as spent fuel rods which require cooling until their radioactivity has reduced; intermediate-level waste, such as reactor components and reprocessing plant waste, which may need to be solidified (see vitrification) before it is stored; and low-level waste, materials contaminated with some small amounts of radioactivity, which must be disposed of at special sites. Top of page radioactivity – The spontaneous release of energy, by the emission of particles or gamma rays, from the nucleus of an unstable atom. Top of page RBMK reactor – Russian reactor design with a graphite moderator. The RBMK design uses enriched uranium fuel and is water cooled. The reactors at Chernobyl are of the RBMK design. Top of page reactor - See nuclear reactor. Top of page refinery – An industrial plant that processes materials to produce useful products. An oil refinery separates crude oil using fractional distillation to produces fuels and petrochemicals. Top of page renewable energy – An energy source that does not significantly deplete the available resource as it is continually replenished. There are number of forms of renewable energy: bioenergy, geothermal energy, hydroelectricity, solar energy, wind energy, tidal energy and wave energy. Top of page reprocessing – See nuclear fuel cycle. Top of page reserves – The amount of oil and/or gas that can be extracted from a reservoir. Top of page reservoir – An accumulation of oil and/or gas in porous rock beneath the ground. Top of page A B C D E F G H I J K L M N O P Q R S T U V W X Y Z Sankey diagram – A type of diagram used to represent the flow of energy into and out of a device or system. Top of page secondary recovery – The injection of natural gas or water into a reservoir to increase its oil production. Top of page seismic survey – A survey to determine the detailed structure of rocks in a particular area. The underlying geology is determined by analysing reflected signals from acoustic shock waves Top of page sequestration - See carbon sequestration. Top of page solar energy – Light and heat energy (both in the form of electromagnetic waves) emitted by the Sun. Solar energy can be used to provide heating or used with photovoltaic technology to generate electricity. Solar energy is a form of renewable energy. Top of page spinning reserve - The additional generating capacity that is available by increasing the power output of generators that are supplying electricity. Top of page steam – Water that has been heated to become a gas. Top of page steam turbine - A steam turbine uses steam to produce rotary motion. Top of page sulphur dioxide (SO2) – Sulphur dioxide is produced when burning fuels that contain sulphur and its compounds. It dissolves in rain water producing acid rain. Top of page supply – Fuel or electricity available for use. Top of page A B C D E F G H I J K L M N O P Q R S T U V W X Y Z tailings – The materials that remain in mining after the resource has been extracted from its ore. Top of page tanker – A large ship used for the transportation of crude oil or the products of an oil refinery. Top of page temperature – A measure of the average energy of the motions of particles in a substance. Temperature is usually measured in degrees Celsius. Top of page tertiary recovery – See enhanced oil recovery. Top of page thermal cracking - See cracking. Top of page thermal energy – See heat energy. Top of page thermal neutron – Neutrons that have been slowed by a moderator are called thermal neutrons. Thermal neutrons have an average speed of 2,200 m/s. Thermal neutrons are more likely to induce nuclear fission of a U235 nucleus than fast neutrons. Top of page thermal power station – A facility that burns fuel, producing steam, to generate electricity. Top of page tidal barrage – A low dam built to exploit the tidal energy resource in an estuary. Top of page tidal energy – Energy associated with movement of water due to the gravitational attraction of the Moon and the Sun. The amount of tidal energy is a predictable source of renewable energy. Tidal energy can be used to generate electricity using a tidal barrage or a tidal stream device. Top of page tidal stream – A flow of water produces by the tides. The tidal energy in a tidal current can be converted into rotational kinetic energy using a turbine, to enable electricity to be generated. Top of page tonne – A unit of mass equal to one-thousand kilograms. It is also known as a metric ton. Top of page tonne of coal equivalent (tce) – The heat energy released by the combustion of one tonne of coal. This is approximately 2,900 MJ. Top of page tonne of oil equivalent (toe) - The heat energy released by the combustion of one tonne of oil. This is approximately 4,200 MJ. Top of page town gas – See coal gas. Top of page transformer – A device for changing the voltage (potential difference) and current when transferring electrical energy from one circuit to another. Transformers only work with an alternating current. Top of page transmission – The transfer of electricity from power stations to and sub-stations at high voltage. To reduce losses due to heating, transformers are used to increase the voltage in the cables. Top of page turbine – A turbine is a rotary engine. A turbine uses the energy from the flow of a fluid (usually steam, water or gas) to produce rotary motion. Turbines are often connected to generators to produce electricity. Top of page A B C D E F G H I J K L M N O P Q R S T U V W X Y Z ultraviolet radiation – electromagnetic waves with a shorter wavelength than visible light. See electromagnetic spectrum. Top of page uranium - Uranium (U) occurs naturally in the Earth’s crust in the form of uranium oxides. There are different types of uranium, known as isotopes, which contain different numbers of neutrons. The isotopes of have identical chemical properties but behave differently in nuclear reactions. Almost 99.3% uranium is in the form of the heavy isotope uranium-238 (U238) and most of the remaining 0.7% is in the form of uranium-235 (U235). Top of page useful energy – The energy available to provide energy services. The useful energy is the amount of energy that remains after the energy losses have been deducted from the delivered energy. Top of page A B C D E F G H I J K L M N O P Q R S T U V W X Y Z vertical axis wind turbine (VAWT) – A wind turbine in which the blades rotate about a vertical axis. Top of page vitrification – Process used to convert liquids into a glass-like solid. Vitrification is used to solidify radioactive waste. Top of page volatile organic compounds (VOCs) – A class of pollutants release during combustion. For example, hydrocarbons released due to incomplete combustion. Top of page volt (V) – The SI unit of potential difference. One volt is the potential difference between two points when an electric current of one ampere is flowing between them when the power dissipated is one watt. Top of page voltage - See potential difference. Top of page A B C D E F G H I J K L M N O P Q R S T U V W X Y Z watt (W) – The SI unit of power. One watt is equal to an energy transfer at a rate of one joule per second. Top of page wave energy – The conversion of the kinetic energy of water waves into more useful forms of energy, usually electricity, using a machine. The waves are produces by the movement of air (wind) across the surface of bodies of water. Wave energy is a form of renewable energy. Top of page well – A hole drilled into rock to extract natural resources. Top of page wind energy – The kinetic energy of a naturally moving body of air. Wind is produces by the movement of air along pressure gradients produced by geographical differences in the amount of heat energy provided by the Sun. Wind energy is a form of renewable energy. Top of page wind power – The conversion of the kinetic energy of wind into more useful forms of energy using wind turbines. Top of page wind turbine – A device that converts the kinetic energy of the wind into rotational motion. The resulting motion can be used for motive power or to generate electricity. Top of page A B C D E F G H I J K L M N O P Q R S T U V W X Y Z Top of page A B C D E F G H I J K L M N O P Q R S T U V W X Y Z yellowcake – An intermediate substance produced during the processing of uranium to produce nuclear fuel. Top of page A B C D E F G H I J K L M N O P Q R S T U V W X Y Z zero-emissions vehicle (ZEV) – A vehicle that does not produce emissions at the point of use; however, there may be emissions produced during production of the fuel used. Top of page