Glossary

absorption, neutron: Any reaction in which a free neutron is absorbed by a nucleus, including capture and fission. Allowance for Funds Used During Construction (AFUDC): An account in the income statement of a utility in which interest is accumulated on the construction expenditures for construction work in progress that has not been entered into the utility's rate base and is therefore not yet earning a cash. return on investment. The accumulated interest is then added to the actual construction expenditures when the plant enters the rate base. base loaded: Keeping a power station continuously loaded at the maximum load because it is one of the lowest cost power producers on the system. boiling water reactor: A reactor cooled by water that is allowed to boil as it passes through the core. This coolant is used directly to produce the steam which generates electricity.

capacity factor: Ratio of average plant electrical energy output to rated output.

chain reaction: The continuing process of nuclear fissioning in which the neutrons released from a fission trigger at least one other nuclear fission. cladding: The term used to describe any material that encloses nuclear fuel. In a water-cooled power reactor this is the fuel rod tube.

Construction Work in Progress (CWIP): An account on the asset side of the utility's balance sheet that includes all construction expenditures for plant and equipment on plant that has not yet been placed in service.

construction leadtime: The time required to complete

construction of an electric generating plant, usually defined from either date of reactor order or construction permit to commercial operation. containment building: A thick concrete structure surrounding the pressure vessel and other reactor components. It is designed to prevent radioactive material from being released to the atmosphere in the unlikely event that it should escape from the pressure vessel.

control rods: Long thin rods that are positioned among fuel rods to regulate the nuclear chain reaction. Control rods are composed of material that absorbs neutrons readily. They interrupt or slow down a chain reaction by capturing neutrons that would otherwise trigger more fissions.

coolant: Fluid that is circulated through the core of a reactor to remove the heat generated by the fission process. In reactors that have more than one coolant system, the fluid which passes through the

core of a reactor is known as the primary coolant.

It absorbs heat in the core and then transfers it to a secondary coolant system.

core: The region of a reactor in which the nuclear chain reaction is initiated, maintained, and controlled. Coolant is constantly circulated through the core to remove heat produced by the fission process.

decay heat: The heat produced by radioactive decay of materials that are primarily the remnants of the chain reaction.

deplete: To reduce the fissile content of an isotopic mixture, particularly uranium.

elasticity: The ratio of change in demand for a product (in this case electricity) to change in a category of prices, or to change in income.

emergency core cooling system: Any engineered system for cooling the core in the event of failure of the basic cooling system, such as core sprays or injectors.

enrichment: The process of increasing the concentration of one isotope of a given element. fabrication: The final step in preparing nuclear fuel for use in a reactor.

fast breeder reactor (FBR): A reactor cooled by liquid sodium rather than waste. In this type of reactor, the transformation of uranium-238 to plutonium occurs readily. Since plutonium fissions easily, it can be recycled and used as fuel for a breeder reactor. The conversion of uranium to plutonium is so efficient in an FBR that this reactor creates more fuel than it consumes.

feedwater: Water, usually from a condenser, supplied to replenish the water inventory of components such as boilers or steam generators.

fertile: Material composed of atoms which readily absorb neutrons to produce fissionable materials. One such element is uranium-238, which becomes plutonium-239 after it absorbs a neutron. Fertile material alone cannot sustain a a chain reaction. fissile: Material composed of atoms which readily fission when struck by a neutron. Uranium-235 and plutonium-239 are examples of fissile materials. fission: The process by which a neutron strikes a nucleus and splits it into fragments. During the process of nuclear fission, several neutrons are emitted at high speed, and heat and radiation are released. fission products: The smaller atoms created when a nucleus fissions. The mass of the fission products is less than that of the original nucleus. The difference in mass is released as energy. fossil plant: A powerplant fueled by coal, oil, or gas. fuel: Basic chain-reacting material, including both fissile and fertile materials.

fuel cycle: The set of chemical and physical operations needed to prepare nuclear material for use in reactors and to dispose of or recycle the material after its removal from the reactor. Existing fuel cycles begin with uranium as the natural resource and create plutonium as a byproduct. Some future cycles may rely on thorium and produce the fissile isotope uranium-233.

fuel rod: An assembly consisting of a capped zircalloy or stainless steel tube filled with fuel pellets. half life: The period required for an unstable radioactive element to decay to one-half of its initial

mass.

heat rate: A measure of the amount of fuel used to produce electric and/or thermal energy.

total heat rate refers to the amount of fuel (in Btu) required to produce 1 kilowatt-hour of electricity with no credit given for waste heat use. incremental heat rate is calculated as the additional (or saved) Btu to produce (or not produce) the next kilowatt-hour of electricity. net heat rate (also measured in Btu/kWh) credits the thermal output and denotes the energy required to produce electricity, beyond what would be needed to produce a given quantity of thermal energy in a separate facility (e.g., a boiler).

interest coverage ratio: The ratio of a firm's earnings to its current interest obligations. isotopes: Atoms having the same number of protons,

but a different number of neutrons. Two isotopes of the same atom are very similar and difficult to separate by ordinary chemical means. Isotopes can have very different nuclear properties, however. For example, one isotope may fission readily, while another isotope of the same atom may not fission at all.

light water reactor: A general term that refers to all nuclear reactors which use ordinary water as a coolant. This includes pressurized water reactors and boiling water reactors, which are the predominant reactors in the United States.

load: The demand for electric or thermal energy at any particular time.

base load is the normal, relatively constant demand for energy on a given system. peakload is the highest demand for energy from

a supplying system, measured either daily, seasonally, or annually.

intermediate load falls between the base and peak.

load factor is the ratio of the average load over a designated time period to the peak load oc

curring during that period. Also used as a synonym for capacity factor.

load cycle pattern is the variation in demand over a specified period of time.

loss-of-coolant accident (LOCA): A reactor accident in which coolant is lost from the primary system. market potential: The number of instances in which a technology will be sufficiently attractive-all things considered-that the investment is likely to be

made.

market-to-book ratio: The ratio of the market price of a firm's stock to its book value. MWe: Megawatts of electrical energy. MWt: Megawatts of thermal energy. moderator: A component (usually water, heavy water, or graphite) of some nuclear reactors that slows neutrons, thereby increasing their chances of being absorbed by a fissile nucleus.

neutron: A basic atomic particle that has no electrical charge. Neutrons and protons, which are positively charged particles, form the central portion of the atom known as the nucleus. Negatively charged electrons orbit the nucleus at various distances. The chemical and nuclear properties of an atom are determined by the number of its neutrons, protons, and electrons.

neutron poison: The general name given to materials that absorb neutrons. These materials either interfere with the fissioning process or are used to control it.

nuclear island: The buildings and equipment that comprise the reactor and all its emergency and auxiliary systems.

nuclear steam supply system (NSSS): The basic reactor and support equipment, plus any associated equipment necessary to produce the steam that drives the turbines. once-through fuel cycle: A nuclear system wherein nuclear materials are introduced into a reactor only once; they are not recycled. plutonium: An element that is not found in nature, but can be produced from uranium in a nuclear reactor. Plutonium fissions easily, and can be used as a nuclear fuel.

power density: The power generated per unit volume of the core.

pressure vessel: A heavy steel enclosure around the core of a reactor. It is designed to withstand high pressures and temperatures to prevent radioactive material from escaping from the core. pressurized water reactor: A reactor cooled by water that is kept at high pressure to prevent it from boiling. Primary coolant passes through the core of a