Glossary of Technical Terms
ACCELERATOR (particle accelerator): A device for imparting large kinetic energy to electrically charged elementary particles such as electrons, protons, deuterons, and helium ions through the application of electrical and/or magnetic forces. Common types of particle accelerators are direct voltage accelerators, cyclotrons, betatrons, and linear accelerators.
ACTINIDES: A group name for the series of radioactive elements from element 89 (actinium) through element 103 (lawrencium). The series includes uranium and all the man-made transuranic elements.
BINARY CYCLE: An energy recovery system based on the transfer of heat from one fluid (e.g., hot brine from a geothermal well) to a second fluid (e.g., pure water or an organic liquid) from which the heat is ultimately extracted for use.
BIOCONVERSION: The conversion of organic wastes into methane (equivalent to natural gas) through the action of microorganisms.
BLANKET: A layer of fertile material such as uranium-238 or thorium-232 that is placed around the core of a fission or fusion reactor. Its major function is to produce fissile isotopes from fertile blanket material.
BOILING-WATER REACTOR (BWR): A light water reactor that employs a direct cycle; the water coolant that passes through the reactor is converted to high-pressure steam that flows directly through the turbines.
BREEDER REACTOR: A nuclear reactor that produces more fissile material than it consumes. In fast breeder reactors, high-energy (fast) neutrons produce most of the fissions, while in thermal breeder reactors, fissions are principally caused by low-energy (thermal) neutrons.
BREEDING RATIO: The ratio of the number of fissionable atoms produced in a breeder reactor to the number of fissionable atoms consumed in the reactor. The “breeding gain” is the breeding ratio minus 1.
Btu (British thermal unit): The amount of energy necessary to raise the temperature of one pound of water by one degree Fahrenheit, from 39.2 to 40.2 degrees Fahrenheit.
CAPACITY FACTOR: The ratio of the amount of product (e.g., electrical energy or geothermal brine) actually produced by a given unit per unit of time to its maximum production rate over that period. Also called “load factor.”
COGENERATION: The generation of electricity with direct use of the residual heat for industrial process heat or for space heating.
COMBINED CYCLE: A combination of a steam turbine and a gas turbine in an electrical generating plant, with the gas-turbine exhaust heat used in raising steam for the steam turbine.
CONVERSION RATIO: The ratio of the number of atoms of new fissionable material produced in a converter reactor to the number of atoms of fissionable fuel consumed. See “breeding ratio.”
CONVERTER REACTOR: A reactor that produces some fissionable material, but less than it consumes. In some usages, a reactor that produces a fissionable material different from the fuel burned, regardless of the ratio. In both usages the process is known as conversion.
CURIE: A measure of intensity of the radioactivity of a substance; i.e., the number of unstable nuclei that are undergoing transformation in the process of radioactive decay. One curie equals the disintegration of 3.7×1010 nuclei per second, which is approximately the rate of decay of one gram of radium.
DEPLETION ALLOWANCE: A tax credit based on the permanent reduction in value of a depletable resource that results from removing or using some part of it.
DRY HOT ROCK (geothermal): See “hot dry rock.”
ELASTICITIES OF DEMAND: The arithmetic relations used by economists in quantifying the change in demand for a commodity in response to a change in another economic quantity. In this report, elasticities of demand in terms of price and income are especially important. These elasticities are calculated as the ratio of the percentage change in demand to the percentage change in price or income that evokes it.
FERTILE MATERIAL: A material, not itself fissionable by thermal neutrons, that can be converted into a fissile material by irradiation in a reactor. There are two basic fertile materials, uranium-238 and thorium-232. When these materials capture neutrons, they are partially converted into plutonium-239 and uranium-233, respectively.
FLASHING: The rapid change in state from a liquid to a vapor without visible boiling, resulting usually from a sudden reduction in the pressure maintained on a hot liquid.
FLUIDIZED BED: A body of finely divided particles kept separated and partially supported by gases blown through or evolved within the mass, so that the mixture flows much like a liquid.
FLY ASH: Fine solid particles of noncombustible ash entrained in the flue gases arising from the combustion of carbonaceous fuels. The particles of ash may be accompanied by combustible unburned fuel particles.
FUEL CELL: A device that produces electrical energy directly from the controlled electrochemical oxidation of fuel. It does not contain an intermediate heat cycle, as do most other electrical generation techniques.
FUEL CYCLE: The various processing, manufacturing, and transportation steps involved in producing fuel for a nuclear reactor, and in processing fuel discharged from the reactor. The uranium fuel cycle includes uranium mining and milling, conversion to uranium hexafluoride (UF6), isotopic enrichment, fuel fabrication, reprocessing, recycling of recovered fissile isotopes, and disposal of radioactive wastes.
GAS-CENTRIFUGE PROCESS: A method of isotopic separation in which heavy gaseous atoms or molecules are separated from light atoms or molecules by centrifugal force.
GASEOUS DIFFUSION: A process used to enrich uranium in the isotope uranium-235. Uranium in the form of a gas, uranium hexafluoride (UF6), is forced through a thin porous barrier. Since the lighter gas molecules containing uranium-235 move at a higher velocity than the heavy molecules containing uranium-238, the lighter molecules pass through the barrier more frequently than do the heavy ones, producing a slight enrichment in the lighter isotope. Many stages in series are required to produce material enriched sufficiently for use in a light water reactor.
GEOPRESSURED RESERVOIR (geothermal): A hydrothermal reservoir in which the pore fluid is confined under pressure significantly greater than normal hydrostatic pressure, developed principally by the weight of overlying rocks and sediments. Also called “overpressured” and “geopressurized” reservoirs.
GEOTHERMAL GRADIENT: The rate at which the temperature of the earth increases with depth below its surface. This varies widely from place to place, but the average or “normal” geothermal gradient is about 30 degrees Celsius per kilometer of depth (16.5 degrees Fahrenheit per thousand feet).
GROSS DOMESTIC PRODUCT (GDP): Gross national product minus net factor payments abroad (such as income from foreign investments and wages paid to foreign workers). GDP is preferable to gross national product (q.v.) as a measure for international comparisons.
GROSS NATIONAL PRODUCT (GNP): The total market value of the goods and services produced in a national economy, during a given year, for final consumption, capital investment, and governmental use. (Note that GNP does not include the value of intermediate goods and services sold to producers and used in the production process itself.) See “gross domestic product.”
HEAVY WATER: Water containing significantly more than the natural proportion (1 in 6500) of heavy hydrogen (deuterium) atoms to ordinary hydrogen atoms. Heavy water is used as a moderator in certain reactors because it slows down neutrons effectively and also has a low cross section for absorption of neutrons.
HIGH-LEVEL WASTE: A by-product of the operation of nuclear reactors that includes a variety of aqueous wastes from fuel reprocessing and their solidified derivatives, such as alkaline aqueous waste, calcine, crystallized salts, insoluble precipitates, salts of cesium and strontium extracts, and coating wastes from chemical decladding of fuel elements.
HIGH-TEMPERATURE GAS-COOLED REACTOR (HTGR): A graphite-moderated, helium-cooled advanced reactor that utilizes the thorium fuel cycle. The initial core is fueled with a mixture of fully enriched uranium-235 and thorium. When operated in the recycle mode, the reactor is refueled with a mixture of uranium-233 (produced from thorium) with the balance of the fissile material provided from an external source of fully enriched uranium-235.
HOT DRY ROCK (geothermal): Naturally heated but unmelted rock sufficiently low in either permeability or pore-fluid content that wells drilled into it do not yield either hot water or steam at commercially useful rates. To be compared with “hydrothermal reservoir.”
HYDROTHERMAL RESERVOIR: A body of porous, permeable rock, gravel, or soil containing natural steam or naturally heated water at a temperature significantly above the average temperature at the earth’s surface.
ISOTOPE: One of two or more atoms with the same atomic number (i.e., the same chemical element) but with different atomic weights. Isotopes usually have very nearly the same chemical properties but somewhat different physical properties.
KEROGEN: A solid, largely insoluble organic material, occurring in oil shale, which yields oil when it is heated in the absence of oxygen.
LIGHT WATER REACTOR (LWR): A nuclear reactor that uses ordinary water as both a moderator and a coolant and utilizes slightly enriched uranium-235 fuel. There are two commercial light water reactor types—the boiling-water reactor (BWR) and the pressurized-water reactor (PWR).
LIQUEFIED NATURAL GAS (LNG): Natural gas cooled to −259 degrees Fahrenheit so that it forms a liquid at approximately atmospheric pressure. As natural gas becomes liquid, it reduces in volume nearly 600-fold, thus allowing economical storage and making long-distance transportation economically feasible. Natural gas in its liquid state must be regasified and introduced to the consumer at the same pressure as other natural gas. The cooling process does not alter the gas chemically, and the regasified LNG is indistinguishable from other natural gases of the same composition.
LIQUEFIED PETROLEUM GAS (LPG): A gas containing certain specific hydrocarbons that are gaseous under normal atmospheric conditions but that can be liquefied under moderate pressure at normal temperatures. Propane and butane are the principal examples.
LOAD FACTOR: Capacity factor (q.v.).
LOW-LEVEL WASTE: Generally a solid by-product of special nuclear materials production, utilization, and research and development. Examples of solid low-level waste are discarded equipment and materials, filters from gaseous waste cleanup, ion-exchange resins from liquid waste cleanup, liquid wastes that have been converted to solid form by techniques such as mixing with cement, and miscellaneous trash. Low-level liquid waste is generally decontaminated and released under controlled conditions.
MILLING (uranium processing): A process in the uranium fuel cycle in which ore that contains only about 0.2 percent uranium oxide (U3O8) is concentrated into a compound called yellowcake, which contains 80–90 percent uranium oxide.
MODERATOR: A material, such as ordinary water, heavy water, or graphite, used in a reactor to slow down high-velocity neutrons, thus increasing the likelihood of further fission.
NUCLEAR WASTE: The radioactive products formed by fission and other nuclear processes in a reactor. Most nuclear waste is initially in the form of spent fuel. If this material is reprocessed, new categories of waste result: high-level, transuranic, and low-level wastes (as well as others).
PARTICULATES: Microscopic pieces of solids that emanate from a range of sources and are the most widespread of all substances that are usually considered air pollutants. Those between 1 and 10 microns are most numerous in the atmosphere, stemming from mechanical processes and including industrial dusts, ash, etc.
PLUTONIUM: A heavy, radioactive man-made metallic element with atomic number 94, created by absorption of neutrons in uranium-238. Its most important isotope is plutonium-239, which is fissionable.
PRESSURIZED-WATER REACTOR (PWR): A light water moderated and cooled reactor that employs an indirect cycle; the cooling water that passes through the reactor is kept under high pressure to keep it from boiling, but it heats water in a secondary loop that produces steam that drives the turbine.
PRIMARY CONTAINMENT: An enclosure that surrounds a nuclear reactor and associated equipment for the purpose of minimizing the release of radioactive material in the event of a serious malfunction in the operation of the reactor.
PYROLYSIS: Decomposition of materials through the application of heat with insufficient oxygen for complete oxidation.
QUAD: A quantity of energy equal to 1015 British thermal units.
REACTOR CORE: The central portion of a nuclear reactor, containing the fuel elements and the control rods.
REPROCESSING: A generic term for the chemical and mechanical processes applied to fuel elements discharged from a nuclear reactor; the purpose is to recover fissile materials such as plutonium-239, uranium-235, and uranium-233 and to isolate the fission products.
RESERVES: Resources that are known in location, quantity, and quality and that are economically recoverable using currently available technologies.
RESOURCE (energy): That part of the resource base believed to be recoverable using only current or near-current technology, without regard to the cost of actually recovering it. To be distinguished from both “resource base” and “reserves” (q.v.).
RESOURCE BASE (energy): The total quantity of energy or of any given energy-producing or energy-related material that is estimated to exist in or on the earth or in its atmosphere, independent of quality, location, or the engineering or economic feasibility of recovering it.
SCRUBBER: An air pollution control device that uses a liquid spray for removing pollutants such as sulfur dioxide or particulate matter from a gas stream by absorption or chemical reaction.
SECONDARY RECOVERY: Methods of obtaining oil and gas by the augmentation of reservoir energy, often by the injection of air, gas, or water into a production formation. (See “tertiary recovery”)
SOLAR CONSTANT: The solar radiation falling on a unit area at the outer limits of the earth’s atmosphere.
SPECTRAL-SHIFT REACTOR: A reactor in which a mixture of light water and heavy water is used as the moderator and coolant. The ratio of light to heavy water is varied to change (shift) the energy spectrum of the neutrons in the reactor core. Since the probability of neutron capture varies with neutron velocity, a measure of reactor control is thus obtained.
SYNTHESIS GAS: A fuel gas containing primarily carbon monoxide and hydrogen; it can be used after careful removal of impurities, particularly sulfur compounds, for conversion to methane (high-Btu gas), methanol, liquid hydrocarbons, and a wide variety of other organic compounds.
TAILINGS: Waste material from a separation process. Commonly the finely divided waste from a mineral separation operation.
TAILS: Contraction of “tailings” (q.v.).
TAILS (OR TAILINGS) ASSAY: The percentage of valuable material that remains unrecovered in the tailings of a separation process.
TAR SANDS: Hydrocarbon-bearing deposits distinguished from more conventional oil and gas reservoirs by the high viscosity of the hydrocarbon, which is not recoverable in its natural state through a well by ordinary production methods.
TERTIARY RECOVERY: Use of heat and methods other than air, gas, or water injection to augment oil recovery (presumably occurring after secondary recovery).
THORIUM: A radioactive element of atomic number 90; naturally occurring thorium has one main isotope—thorium-232. The absorption of a neutron by a thorium atom can result in the creation of the fissile material uranium-233.
THROWAWAY FUEL CYCLE: A fuel cycle in which the spent fuel discharged from the reactor is not reprocessed to recover residual plutonium and uranium values.
TRANSURANIC ELEMENTS: Radioactive nuclides generated as fission products from the fissioning of nuclear fuel during reactor operation and as induced activity from the capture of neutrons in fuel cladding, reactor structures, and reactor coolant.
URANIUM: A radioactive element of atomic number 92. Naturally occurring uranium is a mixture of 99.28 percent uranium-238, 0.71 percent uranium-235, and 0.0058 percent uranium-234. Uranium-235 is a fissile material and is the primary fuel of light water reactors. When bombarded with slow or fast neutrons, it will undergo fission. Uranium-238 is a fertile material that is transmuted to plutonium-239 upon the absorption of a neutron.
URANIUM HEXAFLUORIDE (UF6): A compound of uranium, which is used in gaseous form in the enrichment of uranium isotopes.
YELLOWCAKE: A uranium concentrate that results from the milling (concentrating) of uranium ore. It typically contains 80–90 percent uranium oxide (U3O8).