NRC Glossary Flashcards
access hatch
An airtight door system that preserves the pressure integrity of the containment structure of a nuclear reactor, while allowing access to personnel and equipment.
activation
The process of making a radioisotope by bombarding a stable element with neutrons or protons.
active fuel length
The end-to-end dimension of fuel material within a fuel assembly (also known as a “fuel bundle” or “fuel element”).
activity
The rate of disintegration (transformation) or decay of radioactive material per unit time. The units of activity (also known as radioactivity) are the curie (Ci) and the becquerel (Bq). For related information, see Measuring Radiation.
Agreement State
A State that has signed an agreement with the NRC authorizing the State to regulate certain uses of radioactive materials within the State.
Air Sampling
The collection of samples of air to measure the radioactivity or to detect the presence of radioactive material, particulate matter, or chemical pollutants in the air.
Alkali silica reaction (ASR)
ASR is a chemical combining of reactive silica from the concrete aggregate with the alkali from the cement paste in the presence of moisture. The result of the reaction is a gel, which can expand and may cause micro-cracks in the concrete.
Allegation
A declaration, statement, or assertion of impropriety or inadequacy associated with NRC-regulated activities, the validity of which has not been established.
Anion
A negatively charged ion.
Anticipated transient without scram (ATWS)
An ATWS is one of the “worst case” accidents, consideration of which frequently motivates the NRC to take regulatory action. Such an accident could happen if the scram system (which provides a highly reliable means of shutting down the reactor) fails to work during a reactor event (anticipated transient). The types of events considered are those used for designing the plant.
Assumptions (for IPEs, IPEEs, and PRAs)
An ATWS is one of the “worst case” accidents, consideration of which frequently motivates the NRC to take regulatory action. Such an accident could happen if the scram system (which provides a highly reliable means of shutting down the reactor) fails to work during a reactor event (anticipated transient). The types of events considered are those used for designing the plant.
Atom
The smallest particle of an element that cannot be divided or broken up by chemical means. It consists of a central core (or nucleus), containing protons and neutrons, with electrons revolving in orbits in the region surrounding the nucleus.
Atomic energy
The energy that is released through a nuclear reaction or radioactive decay process. Of particular interest is the process known as fission, which occurs in a nuclear reactor and produces energy usually in the form of heat. In a nuclear power plant, this heat is used to boil water in order to produce steam that can be used to drive large turbines. This, in turn, activates generators to produce electrical power. Atomic energy is more correctly called nuclear energy.
Atomic Energy Commission
The Federal agency (known as the AEC), which was created in 1946 to manage the development, use, and control of atomic (nuclear) energy for military and civilian applications. The AEC was subsequently abolished by the Energy Reorganization Act of 1974 and succeeded by the Energy Research and Development Administration (now part of the U.S. Department of Energy) and the U.S. Nuclear Regulatory Commission. Atomic Energy Commission
Atomic number
The number of positively charged protons in the nucleus of an atom.
Attenuation
The process by which the number of particles or photons entering a body of matter is reduced by absorption and scattered radiation.
Auxiliary building
A building at a nuclear power plant, which is frequently located adjacent to the reactor containment structure, and houses most of the auxiliary and safety systems associated with the reactor, such as radioactive waste systems, chemical and volume control systems, and emergency cooling water systems.
Auxiliary feedwater
Backup water supply used during nuclear plant startup and shutdown to supply water to the steam generators during accident conditions for removing decay heat from the reactor.
Average planar linear heat generation rate (APLGHR)
The average value of the linear heat generation rate of all the fuel rods at any given horizontal plane along a fuel assembly (also known as a “fuel bundle” or “fuel element”).
Background radiation
The natural radiation that is always present in the environment. It includes cosmic radiation which comes from the sun and stars, terrestrial radiation which comes from the Earth, and internal radiation which exists in all living things. The typical average individual exposure in the United States from natural background sources is about 300 millirems per year.
Bayesian estimation
A mathematical formulation, using Bayes’ theorem, by which the likelihood of an event can be estimated taking explicit consideration of certain contextual features (such as amount of data, nature of decision, etc.).
Bayesian prior
Bayesian estimation
Binding energy
The minimum energy required to separate the nucleus of an atom into its component neutrons and protons.
Bioassay
The determination of kinds, quantities, or concentrations and, in some cases, locations of radioactive material in the human body, whether by direct measurement (in vivo counting) or by analysis and evaluation of materials excreted or removed (in vitro) from the human body.
Biological half-life
The time required for a biological system, such as that of a human, to eliminate, by natural processes, half of the amount of a substance (such as a radioactive material) that has entered it.
Biological shield
A mass of absorbing material placed around a reactor or radioactive source to reduce the radiation to a level safe for humans.
Boiling-water reactor (BWR)
A common nuclear power reactor design in which water flows upward through the core, where it is heated by fission and allowed to boil in the reactor vessel. The resulting steam then drives turbines, which activate generators to produce electrical power. BWRs operate similarly to electrical plants using fossil fuel, except that the BWRs are powered by 370–800 nuclear fuel assemblies in the reactor core.
Bone seeker
A radioisotope that tends to accumulate in the bones when it is introduced into the body. An example is strontium-90, which behaves chemically like calcium.
Breeder
A reactor that produces more nuclear fuel than it consumes. A fertile material, such as uranium-238, when bombarded by neutrons, is transformed into a fissile material, such as plutonium-239, which can be used as fuel.
The amount of heat required to change the temperature of one pound of water one degree Fahrenheit at sea level.
The amount of heat required to change the temperature of one pound of water one degree Fahrenheit at sea level.
Calibration
The adjustment, as necessary, of a measuring device such that it responds within the required range and accuracy to known values of input.
Capability
The maximum load that a generating unit, generating station, or other electrical apparatus can carry under specified conditions for a given period of time without exceeding approved limits of temperature and stress.
Cation
A positively charged ion.
Chain reaction
A reaction that initiates its own repetition. In a fission chain reaction, a fissionable nucleus absorbs a neutron and fissions spontaneously, releasing additional neutrons. These, in turn, can be absorbed by other fissionable nuclei, releasing still more neutrons. A fission chain reaction is self-sustaining when the number of neutrons released in a given time equals or exceeds the number of neutrons lost by absorption in nonfissionable material or by escape from the system.
Charged particle
An ion. An elementary particle (part of an element) carrying a positive or negative electric charge.
Chemical recombination
Following an ionization event, the positively and negatively charged ion pairs may or may not realign themselves to form the same chemical substance they formed before ionization. Thus, chemical recombination could change the chemical composition of the material bombarded by ionizing radiation.
Cladding
The thin-walled metal tube that forms the outer jacket of a nuclear fuel rod. It prevents corrosion of the fuel by the coolant and the release of fission products into the coolant. Aluminum, stainless steel, and zirconium alloys are common cladding materials.
Cleanup system
A system used for continuously filtering and demineralizing a reactor coolant system to reduce contamination levels and to minimize corrosion.
Coastdown
An action that permits the reactor power level to decrease gradually as the fuel in the core is depleted.
Cold shutdown
The term used to define a reactor coolant system at atmospheric pressure and at a temperature below 200 degrees Fahrenheit following a reactor cooldown.
Collective dose
As defined in Title 10, Section 20.1003, of the Code of Federal Regulations (10 CFR 20.1003), this is the sum of the individual doses received in a given period by a specified population from exposure to a specified source of radiation.
Combined license (COL)
An NRC-issued license that authorizes a licensee to construct and (with certain specified conditions) operate a nuclear power plant at a specific site, in accordance with established laws and regulations. A COL is valid for 40 years (with the possibility of a 20-year renewal).
Commercial sector (energy users)
Generally, nonmanufacturing business establishments, including hotels, motels, and restaurants; wholesalers and retail stores; and health, social, and educational institutions. However, utilities may categorize commercial service as all consumers whose demand or annual usage exceeds some specified limit that is categorized as residential service.
Committed dose equivalent (CDE)
As defined in Title 10, Section 20.1003, of the Code of Federal Regulations (10 CFR 20.1003), the CDE (HT,50) is the dose to some specific organ or tissue of reference (T) that will be received from an intake of radioactive material by an individual during the 50-year period following the intake.
Committed effective dose equivalent (CEDE)
As defined in Title 10, Section 20.1003, of the Code of Federal Regulations (10 CFR 20.1003), the CEDE (HE,50) is the sum of the products of the committed dose equivalents for each of the body organs or tissues that are irradiated multiplied by the weighting factors (WT) applicable to each of those organs or tissues (HE,50 = ΣWTHT.50).
Compact
A group of two or more States that have formed business alliances to dispose of low-level radioactive waste on a regional basis.
Compound
A chemical combination of two or more elements combined in a fixed and definite proportion by weight.
Condensate
A chemical combination of two or more elements combined in a fixed and definite proportion by weight.
Containment building
The air-tight building, which houses a nuclear reactor and its pressurizer, reactor coolant pumps, steam generator, and other equipment or piping that might otherwise release fission products to the atmosphere in the event of an accident. Such buildings are usually made of steel-reinforced concrete.
Contamination
Undesirable radiological, chemical, or biological material (with a potentially harmful effect) that is either airborne, or deposited in (or on the surface of) structures, objects, soil, water, or living organisms in a concentration that makes the medium unfit for its next intended use.
Control rod
A rod, plate, or tube containing a material such as hafnium, boron, etc., used to control the power of a nuclear reactor. By absorbing neutrons, a control rod prevents the neutrons from causing further fissions.
Control room
The area in a nuclear power plant from which most of the plant’s power production and emergency safety equipment can be operated by remote control.
Controlled area
At a nuclear facility, an area outside a restricted area but within the site boundary, to which the licensee can limit access for any reason.
Coolant
A substance circulated through a nuclear reactor to remove or transfer heat. The most commonly used coolant in the United States is water. Other coolants include heavy water, air, carbon dioxide, helium, liquid sodium, and a sodium-potassium alloy.
Cooldown
The gradual decrease in reactor fuel rod temperature caused by the removal of heat from the reactor coolant system after the reactor has been shutdown.
Cooling tower
A heat exchanger designed to aid in the cooling of water that was used to cool exhaust steam exiting the turbines of a power plant. Cooling towers transfer exhaust heat into the air instead of into a body of water.
Core
The central portion of a nuclear reactor, which contains the fuel assemblies, moderator, neutron poisons, control rods, and support structures. The reactor core is where fission takes place.
Capacity
The amount of electric power that a generating unit can produce. The amount of electric power that a manufacturer rates its generator, turbine transformer, transmission, circuit, or system, is able to produce.
Capacity Charge
One of two elements in a two-part pricing method used in capacity transactions (the other element is the energy charge). The capacity charge, sometimes called the demand charge, is assessed on the capacity (amount of electric power) being purchased.
Capacity factor
The ratio of the available capacity (the amount of electrical power actually produced by a generating unit) to the theoretical capacity (the amount of electrical power that could theoretically have been produced if the generating unit had operated continuously at full power) during a given time period.
Capacity factor (gross)
The ratio of the gross electricity generated, for the time considered, to the energy that could have been generated at continuous full-power operation during the same period.
Capacity factor (net)
The ratio of the net electricity generated, for the time considered, to the energy that could have been generated at continuous full-power operation during the same period.
Cask
A heavily shielded container used for the dry storage or shipment (or both) of radioactive materials such as spent nuclear fuel or other high-level radioactive waste. Casks are often made from lead, concrete, or steel. Casks must meet regulatory requirements and are not intended for long-term disposal in a repository.
Core damage frequency
An expression of the likelihood that, given the way a reactor is designed and operated, an accident could cause the fuel in the reactor to be damaged.
Core melt accident
An event or sequence of events that result in the melting of part of the fuel in the reactor core.
Counter
A general designation applied to radiation detection instruments or survey meters that detect and measure radiation. The signal that announces an ionization event is called a count.
Critical mass
The smallest mass of fissionable material that will support a self-sustaining chain reaction.
Critical organ
That part of the body that is most susceptible to radiation damage under the specific conditions under consideration.
Criticality
The normal operating condition of a reactor, in which nuclear fuel sustains a fission chain reaction. A reactor achieves criticality (and is said to be critical) when each fission event releases a sufficient number of neutrons to sustain an ongoing series of reactions.
Crud
A colloquial term for corrosion and wear products (rust particles, etc.) that become radioactive (i.e., activated) when exposed to radiation.
Cumulative dose
The total dose that an occupationally exposed worker receives as a result of repeated exposures to ionizing radiation to to the same portion of the body, or to the whole body, over time.
Daughter products
Isotopes that are formed by the radioactive decay of some other isotope. In the case of radium-226, for example, there are 10 successive daughter products, ending in the stable isotope lead-206.
Decay heat
The heat produced by the decay of radioactive fission products after a reactor has been shut down.
Declared pregnant woman
A woman who is an occupational radiation worker and has voluntarily informed her employer, in writing, of her pregnancy and the estimated date of conception (see 10 CFR 20.1003 and 20.1208).
DECON
A method of decommissioning, in which structures, systems, and components that contain radioactive contamination are removed from a site and safely disposed at a commercially operated low-level waste disposal facility, or decontaminated to a level that permits the site to be released for unrestricted use shortly after it ceases operation.
Deep-Dose Equivalent (DDE)
The external whole-body exposure dose equivalent at a tissue depth of 1 cm (1000 mg/cm2).
Departure from nuclear boiling ratio (DNBR)
The ratio of the heat flux needed to cause departure from nucleate boiling to the actual local heat flux of a fuel rod.
Departure from nucleate boiling (DNB)
The point at which the heat transfer from a fuel rod rapidly decreases due to the insulating effect of a steam blanket that forms on the rod surface when the temperature continues to increase.
Derived air concentration (DAC)
The concentration of a given radionuclide in air which, if breathed by the reference man for a working year of 2,000 hours under conditions of light work (with an inhalation rate of 1.2 cubic meters of air per hour), results in an intake of one annual limit on intake (ALI). Established DAC values are given in Table 1, Column 3, of Appendix B to Title 10, Part 20, of the Code of Federal Regulations (10 CFR Part 20), “Standards for Protection Against Radiation.”
Derived Air Concentration-Hour (DAC-hour)
The product of the concentration of radioactive material in air (expressed as a fraction or multiple of the derived air concentration for each radionuclide) and the time of exposure to that radionuclide, in hours. A licensee may take 2,000 DAC-hours to represent one annual limit on intake (ALI), equivalent to a committed effective dose equivalent of 5 rems (0.05 Sv).
Design certification
Certification and approval by the NRC of a standard nuclear power plant design independent of a specific site or an application to construct or operate a plant. A design certification is valid for 15 years from the date of issuance but can be renewed for an additional 10 to 15 years.
Design-basis accident
A postulated accident that a nuclear facility must be designed and built to withstand without loss to the systems, structures, and components necessary to ensure public health and safety.
Design-basis phenomena
Earthquakes, tornadoes, hurricanes, floods, etc., that a nuclear facility must be designed and built to withstand without loss of systems, structures, and components necessary to ensure public health and safety.
Detector
A material or device that is sensitive to ionizing radiation and can display its characteristics and/or produce a signal suitable for measurement or analysis.
Deterministic effect
The health effects of radiation, the severity of which varies with the dose and for which a threshold is believed to exist. Radiation-induced cataract formation is an example of a deterministic effect (also called a non-stochastic effect) (see 10 CFR 20.1003).
Deuterium
An isotope of hydrogen with one proton and one neutron in the nucleus.
Deuteron
The nucleus of deuterium. It contains one proton and one neutron.
Differential pressure (dp or dP)
The difference in pressure between two points of a system, such as between the inlet and outlet of a pump.
Doppler coefficient
Another name used for the “fuel temperature coefficient of reactivity,” or the change in reactivity per degree of change in the temperature of nuclear fuel. The physical property of fuel pellet material (uranium-238) that causes the uranium to absorb more neutrons away from the fission process as fuel pellet temperature increases. This acts to stabilize power reactor operations.
Dose rate
The dose of ionizing radiation delivered per unit time. For example, rems or sieverts (Sv) per hour.
Dose, absorbed
The amount of energy absorbed by an object or person per unit mass. Known as the “absorbed dose,” this reflects the amount of energy that ionizing radiation sources deposit in materials through which they pass, and is measured in units of radiation-absorbed dose (rad). The related international system unit is the gray (Gy), where 1 Gy is equivalent to 100 rad.
Dosimeter
A small portable instrument (such as a film badge, thermoluminescent dosimeter, or pocket dosimeter) used to measure and record the total accumulated personal dose of ionizing radiation.
Dosimetry
The theory and application of the principles and techniques involved in measuring and recording doses of ionizing radiation.
Drywell
The containment structure enclosing the vessel and recirculation system of a boiling-water reactor. The drywell provides both a pressure suppression system and a fission product barrier under accident conditions.
Early site permit (ESP)
A permit through which the NRC resolves site safety, environmental protection, and emergency preparedness issues, in order to approve one or more proposed sites for a nuclear power facility, independent of a specific nuclear plant design or an application for a construction permit or combined license. An ESP is valid for 10 to 20 years, but can be renewed for an additional 10 to 20 years.
Earthquake, operating basis
An earthquake that could be expected to affect the site of a nuclear reactor, but for which the plant’s power production equipment is designed to remain functional without undue risk to public health and safety.
Economic Simplified Boiling-Water Reactor (ESBWR)
A 4,500-MWt nuclear reactor design, which has passive safety features and uses natural circulation (with no recirculation pumps or associated piping) for normal operation. GE-Hitachi Nuclear Energy (GEH) submitted an application for final design approval and standard design certification for the ESBWR on August 24, 2005.
Effective Dose Equivalent
The sum of the products of the dose equivalent to the organ or tissue (HT) and the weighting factors (WT) applicable to each of the body organs or tissues that are irradiated (HE = ΣWTHT).
Effective half-life
The time required for the activity of a particular radioisotope deposited in a living organism, such as a human or an animal, to be reduced by 50 percent as a result of the combined action of radioactive decay and biological elimination. Effective half-life is related to, but different from, the radiological half-life and the biological half-life.
Efficiency, plant
The percentage of the total energy content of a power plant’s fuel that is converted into electricity. The remaining energy is lost to the environment as heat.
Electric power grid
A system of synchronized power providers and consumers, connected by transmission and distribution lines and operated by one or more control centers. In the continental United States, the electric power grid consists of three systems–the Eastern Interconnect, the Western Interconnect, and the Texas Interconnect. In Alaska and Hawaii, several systems encompass areas smaller than the State.
Electric utility
A corporation, agency, authority, person, or other legal entity that owns and/or operates facilities within the United States, its territories, or Puerto Rico for the generation, transmission, distribution, or sale of electric power (primarily for use by the public). Facilities that qualify as cogenerators or small power producers under the Public Utility Regulatory Policies Act (PURPA) are not considered electric utilities.
Electrical generator
An electromagnetic device that converts mechanical (rotational) energy into electrical energy. Most large electrical generators are driven by steam or water turbine systems.
Electromagnetic radiation
A traveling wave motion resulting from changing electric or magnetic fields. Familiar electromagnetic radiation range from x-rays (and gamma rays) of short wavelength, through the ultraviolet, visible, and infrared regions, to radar and radio waves of relatively long wavelength.
Electron
An elementary particle with a negative charge and a mass 1/1837 that of a proton. Electrons surround the positively charged nucleus of an atom, and determine its chemical properties.
Element
One of the 103 known chemical substances that cannot be broken down further without changing its chemical properties. Some examples include hydrogen, nitrogen, gold, lead, and uranium.
Emergency core cooling systems (ECCS)
Reactor system components (pumps, valves, heat exchangers, tanks, and piping) that are specifically designed to remove residual heat from the reactor fuel rods in the event of a failure of the normal core cooling system (reactor coolant system).
Emergency feedwater
Another name for auxiliary feedwater.
Energy Information Administration (EIA)
The agency, within the U.S. Department of Energy, that provides policy-neutral statistical data, forecasts, and analyses to promote sound policymaking, efficient markets, and public understanding regarding energy and its interaction with the economy and the environment.
Environmental qualification
A process for ensuring that equipment will be capable of withstanding the ambient conditions that could exist when the specific function to be performed by the equipment is actually called upon to be performed under accident conditions.
Event Notification System
An automated event tracking system used internally by the NRC’s Headquarters Operations Center to track incoming notifications of significant nuclear events with an actual or potential effect on the health and safety of the public and the environment. Significant events are reported to the Operations Center by the NRC’s licensees, Agreement States, other Federal agencies, the public, and other stakeholders.
Exclusion area
The area surrounding the reactor where the reactor licensee has the authority to determine all activities, including exclusion or removal of personnel and property.
Excursion
A sudden, very rapid rise in the power level of a reactor caused by supercriticality. Excursions are usually quickly suppressed by the moderator temperature coefficient, the fuel temperature coefficient, or the void coefficient of reactivity (depending upon reactor design), or by rapid insertion of control rods.
External radiation
Exposure to ionizing radiation when the radiation source is located outside the body.
Extremities
The hands, forearms, elbows, feet, knees, leg below the knees, and ankles. Permissible radiation exposures in these regions are generally greater than those for whole body exposure because the extremities contain fewer blood-forming organs and have smaller volumes for energy absorption. (See 10 CFR 20.1003.)
Fast fission
Fission of a “heavy” atom (such as uranium-238) when it absorbs a fast (high energy) neutron. All fissionable materials can fission with fast neutrons. However, some (such as uranium-235 and Plutonium-239) fission more readily with slow (thermal) neutrons.
Fast neutron
A neutron with kinetic energy greater than its surroundings when released during fission.
Federal Emergency Management Agency (FEMA)
A component of U.S. Department of Homeland Security responsible for protecting the nation and reducing the loss of life and property from all hazards, such as natural disasters and acts of terrorism. FEMA leads and supports a risk-based, comprehensive emergency management system of preparedness, protection, response, recovery, and mitigation. FEMA also administers the National Flood Insurance Program.
Federal Energy Regulatory Commission (FERC)
An independent agency that regulates the interstate transmission of electricity, natural gas, and oil. FERC also regulates and oversees hydropower projects, and the construction of liquefied natural gas terminals and interstate natural gas pipelines. FERC protects the economic, environmental, and safety interests of the American public, while working abundant, reliable energy in a fair, competitive market.
Feedwater
Water supplied to the reactor pressure vessel in a boiling-water reactor (BWR) or the steam generator in a pressurized-water reactor (PWR) that removes heat from the reactor fuel rods by boiling and becoming steam. The steam becomes the driving force for the plant’s turbine generator.
Fertile material
A material, which is not itself fissile (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 fertile materials capture neutrons, they are converted into fissile plutonium-239 and uranium-233, respectively.
Film badge
Photographic film used to measure exposure to ionizing radiation for purposes of personnel monitoring. The film badge may contain two or three films of differing sensitivities, and it may also contain a filter that shields part of the film from certain types of radiation.
Fiscal year (FY)
The 12-month period from October 1 through September 30 used by the Federal Government for budget formulation and execution. The fiscal year is designated by the calendar year in which it ends; for example, FY 2009 runs from October 1, 2008, through September 30, 2009.
Fission gases
Those fission products that exist in the gaseous state. In nuclear power reactors, this includes primarily the noble gases, such as krypton and xenon.
Fission products
The nuclei (fission fragments) formed by the fission of heavy elements, plus the nuclide formed by the fission fragments’ radioactive decay.
Flux
A term applied to the amount of some type of particle (neutrons, alpha particles, etc.) or energy (photons, heat, etc.) crossing a unit area per unit time. The unit of flux is the number of particles, energy, etc., per square centimeter per second.
Foreign Assignee Program
An on-the-job training program, sponsored by the NRC for assignees from other countries, usually under bilateral information exchange arrangements with their respective regulatory organizations.
Formula quantity
Special nuclear material, in any combination, in a quantity of 5000 grams or more computed by the formula, grams = (grams contained U-235) + 2.5 (grams U-233 + grams plutonium). This class of material is sometimes referred to as a Category I quantity of material (see 10 CFR 70.4).
Freedom of Information Act (FOIA)
A Federal law that requires Federal agencies to provide, upon written request, access to records or information. Some material is exempt from FOIA, and FOIA does not apply to records that are maintained by State and local governments, or Federal contractors, grantees or private organizations or businesses.
Fuel assembly (fuel bundle, fuel element)
A structured group of fuel rods (long, slender, metal tubes containing pellets of fissionable material, which provide fuel for nuclear reactors). Depending on the design, each reactor vessel may have dozens of fuel assemblies (also known as fuel bundles), each of which may contain 200 or more fuel rods.
Fuel rod
A long, slender, zirconium metal tube containing pellets of fissionable material, which provide fuel for nuclear reactors. Fuel rods are assembled into bundles called fuel assemblies, which are loaded individually into the reactor core.
Fuel temperature coefficient of reactivity
The change in reactivity per degree of change in the temperature of nuclear fuel. The physical property of fuel pellet material (uranium-238) that causes the uranium to absorb more neutrons away from the fission process as fuel pellet temperature increases. This acts to stabilize power reactor operations. This coefficient is also known as the Doppler coefficient.
Full-time equivalent (FTE)
A human resources measurement equal to one staff person working full-time for one year.
Fusion reaction
A reaction in which at least one heavier, more stable nucleus is produced from two lighter, less stable nuclei. Reactions of this type are responsible for enormous release of energy, such as the energy given off by stars.
Gamma radiation
High-energy, short-wavelength, electromagnetic radiation emitted from the nucleus of an atom. Gamma radiation frequently accompanies emissions of alpha particles and beta particles, and always accompanies fission. Gamma rays are similar to x-rays, but are very penetrating and are best stopped or shielded by dense materials, such as lead or depleted uranium.
Gap
The space inside a reactor fuel rod that exists between the fuel pellet and the fuel rod cladding.
Gas chromatography
A way of separating chemical substances from a mixed sample by passing the sample, carried by a moving stream of gas, through a tube packed with a finely divided solid that may be coated with a liquid film. Gas chromatography devices are used to analyze air pollutants, blood alcohol content, essential oils, and food products.
Gas-cooled reactor
A nuclear reactor in which the coolant is a gas.
Gaseous diffusion plant
A facility where uranium hexafluoride gas is filtered. Uranium-235 is separated from uranium-238, increasing the percentage of uranium-235 from 1 to about 3 percent. The process requires enormous amounts of electric power.
Gases
A substance possessing perfect molecular mobility and the property of indefinite expansion, as opposed to a solid or liquid; any such fluid or mixture of fluids other than air. Normally, these formless substances completely fill the space, and take the shape of, their container.
Generation (gross)
The total amount of electric energy produced by a generating station as measured at the generator terminals.
Generation (net)
The gross amount of electric energy produced by a generating station, minus the amount used to operate the station. Net generation is usually measured in watthours (Wh).
Generator capacity
The maximum amount of electric energy that a generator can produce (from the mechanical energy of the turbine), adjusted for ambient conditions. Generator capacity is commonly expressed in megawatts (MW).
Generator nameplate capacity
The maximum amount of electric energy that a generator can produce under specific conditions, as rated by the manufacturer. Generator nameplate capacity is usually expressed in kilovolt-amperes (kVA) and kilowatts (kW), as indicated on a nameplate that is physically attached to the generator.
Gigawatt (GW)
A unit of power equivalent to one billion watts.
Gigawatthour (GWh)
One billion watthours.
Half-life
The time in which one half of the atoms of a particular radioactive substance disintegrate into another nuclear form. Measured half-lives vary from millionths of a second to billions of years. Also called physical or radiological half-life.
Half-life (radiological)
The time required for half the atoms of a particular radioisotope to decay into another isotope. A specific half-life is a characteristic property of each radioisotope. Measured half-lives range from millionths of a second to billions of years, depending on the stability of the nucleus. Radiological half-life is related to, but different from, the biological half-life and the effective half-life.
Half-life, biological
The time required for the body to eliminate one half of the material taken in by natural biological means.
Half-life, effective
The time required for the activity of a particular radioisotope deposited in a living organism, such as a human or an animal, to be reduced by 50 percent as a result of the combined action of radioactive decay and biological elimination. Effective half-life is related to, but different from, the radiological half-life and the biological half-life.
Half-thickness
Any given absorber that will reduce the intensity of an original beam of ionizing radiation to one-half of its initial value.
Head, reactor vessel
The removable top section of a reactor pressure vessel. It is bolted in place during power operation and removed during refueling to permit access of fuel handling equipment to the core.
Health physics
The science concerned with recognizing and evaluating the effects of ionizing radiation on the health and safety of people and the environment, monitoring radiation exposure, and controlling the associated health risks and environmental hazards to permit the safe use of technologies that produce ionizing radiation.
Airborne Radioactivity Area
the airborne radioactivity area is a room, enclosure, or area in which airborne radioactive materials, composed wholly or partially of licensed material, exist in concentrations that (1) exceed the derived air concentration limits (DACs), or (2) would result in an individual present in the area without respiratory protection exceeding, during those hours, 0.6 percent of the annual limit on intake (ALI) or 12 DAC-hours.
ALARA
as low as reasonably achievable
Alpha Particle
A positively charged particle ejected spontaneously from the nuclei of some radioactive elements. It is identical to a helium nucleus that has a mass number of 4 and an electrostatic charge of +2. It has low penetrating power and a short range (a few centimeters in air). The most energetic alpha particle will generally fail to penetrate the dead layers of cells covering the skin, and can be easily stopped by a sheet of paper.
Annual Limit on Intake (ALI)
ALI is the derived limit for the amount of radioactive material taken into the body of an adult worker by inhalation or ingestion in a year. ALI is the smaller value of intake of a given radionuclide in a year by the “reference man” that would result in a committed effective dose equivalent (CEDE) of 5 rems (0.05 sievert) or a committed dose equivalent (CDE) of 50 rems (0.5 sievert) to any individual organ or tissue.
Becquerel (Bq)
1 Bq represents a rate of radioactive decay equal to 1 disintegration per second, and 37 billion (3.7 x 1010) Bq equals 1 curie (Ci).
Beta Particle
A charged particle (with a mass equal to 1/1837 that of a proton) that is emitted from the nucleus of a radioactive element during radioactive decay (or disintegration) of an unstable atom. A negatively charged beta particle is identical to an electron, while a positively charged beta particle is called a positron. Large amounts of beta radiation may cause skin burns, and beta emitters are harmful if they enter the body. Beta particles may be stopped by thin sheets of metal or plastic.
Beyond Design Basis Accidents
This term is used as a technical way to discuss accident sequences that are possible but were not fully considered in the design process because they were judged to be too unlikely.
Brachytherapy
A nuclear medicine procedure during which a sealed radioactive source is implanted directly into a person being treated for cancer (usually of the mouth, breast, lung, prostate, ovaries, or uterus). The radioactive implant may be temporary or permanent, and the radiation attacks the tumor as long as the device remains in place. Brachytherapy uses radioisotopes, such as iridium-192 or iodine-125
Byproduct Material
any radioactive material (except enriched uranium or plutonium) produced by a nuclear reactor. It also includes the tailings or wastes produced by the extraction or concentration of uranium or thorium or the fabrication of fuel for nuclear reactors. Additionally, it is any material that has been made radioactive through the use of a particle accelerator or any discrete source of radium-226 used for a commercial, medical, or research activity.
Dry Cask Storage
A method for storing spent nuclear fuel above ground in special containers known as casks. After fuel has been cooled in a spent fuel pool for at least 1 year, dry cask storage allows approximately one to six dozen spent fuel assemblies to be sealed in casks and surrounded by inert gas.
Category 1 Radioactive Source
Category 1 sources, if not safely managed or securely protected, would be likely to cause permanent injury to a person who handled them or was otherwise in contact with them for more than a few minutes. It would probably be fatal to be close to this amount of unshielded material for a period of a few minutes to an hour.
Category 2 Radioactive Source
Category 2 sources, if not safely managed or securely protected, could cause permanent injury to a person who handled them or was otherwise in contact with them for a short time (minutes to hours). It could possibly be fatal to be close to this amount of unshielded radioactive material for a period of hours to days.
Category 3 Radioactive Source
Category 3 sources, if not safely managed or securely protected, could cause permanent injury to a person who handled them or was otherwise in contact with them for some hours. It could possibly – although it is unlikely – be fatal to be close to this amount of unshielded radioactive material for a period of days to weeks.
Condenser
A large heat exchanger designed to cool exhaust steam from a turbine below the boiling point so that it can be returned to the heat source as water.
Construction Recapture
The maximum number of years that could be added to a facility’s license expiration date to recapture the period between the date the NRC issued the facility’s construction permit to the date it granted an operating license.
Capacity Utilization
A percentage representing the extent to which a generating unit fulfilled its capacity in generating electric power over a given time period. This percentage is defined as the margin between the unit’s available capacity (the amount of electrical power the unit actually produced) and its theoretical capacity (the amount of electrical power that could have been produced if the unit had operated continuously at full power) during a certain time period.
cask
a heavily shielded container used for the dry storage or shipment (or both) of radioactive materials such as SNF or other HLW. Casks are often made from lead, concrete, or steel. Casks must meet regulatory requirements and are not intended for long-term disposal in a repository.
cation
a positively charged ion
chain reaction
a reaction that initiates its own repetition. In a fission chain reaction, a fissionable nucleus absorbs a neutron and fissions spontaneously, releasing additional neutrons. These, in turn, can be absorbed by other fissionable nuclei, releasing still more neutrons.
charged particle
an ion. An elementary particle (part of an element) carrying a positive or negative electric charge.
chemical recombination
following an ionization event, the positively and negatively charged ion pairs may or may not realign themselves to form the same chemical substance they formed before ionization. Thus, chemical recombination could change the chemical composition of the material bombarded by ionizing radiation.
cladding
the thin-walled metal tube that forms the outer jacket of a nuclear fuel rod. It prevents corrosion of the fuel by the coolant and the release of fission products into the coolant. Aluminum, stainless steel, and zirconium alloys are common cladding materials.
cleanup system
a system used for continuously filtering and demineralizing a reactor coolant system to reduce contamination levels and to minimize corrosion.
coastdown
an action that permits the reactor power level to decrease gradually as the fuel in the core is depleted.
cold shutdown
the term used to define a reactor coolant system at atmospheric pressure and at a temperature below 200F following a reactor SD
collective dose
as defined by 10 CFR 20.1003, this is the sum of the individual doses received in a given period by a specified population fro exposure to a specified source of radiation.
combined license (COL)
an NRC-issued license that authorizes a licensee to construct and (with certain specified conditions) operate a NPP at a specific site, IAW established laws and regulations. A COL is valid for 40 years (with the possibility of a 20 year renewal).
Committed Dose Equivalent (CDE)
as defined by 10 CFR 20.1003, the CDE is the dose to some specific organ or tissue that will be received from an intake of radioactive material by an individual during the 50 year period following the intake
Committed Effective Dose Equivalent (CEDE)
as defined by 10CFR 20.1003, the CEDE is the sum of the products of the CDEs for each of the body organs or tissues that are irradiated multiplied by the weighting factors applicable to each of those organs or tissues
Compact
a group of two or more states that have formed business alliances to dispose of LLW on a regional basis
Compound
a chemical combination of two or more elements combined in a fixed and definite proportion by weight.
condensate
water that has been produced by the cooling of steam in a condenser
condenser
a large heat exchanger designed to cool exhaust steam from a turbine below the boiling point so that it can be returned to the heat source as water. In a PWR, the water is returned to the SG. In a BWR, it returns to the reactor core. The heat removed from the steam by the condenser is transferred to a circulating water system and is exhausted to the environment.
construction recapture
the maximum number of years that could be added to a facility’s license expiration date to recapture the period between the date the NRC issued the facility’s construction permit to the date it granted an operating license.
containment building
the air-tight building, which houses a nuclear reactor and its pressurizer, RCPs, and SG, and other equipment or piping that might otherwise release fission products to the atmosphere in the event of an accident. Such buildings are usually made of steel-reinforced concrete.
containment structure
a gas-tight shell or other enclosure around a nuclear reactor to confine fission products that otherwise might be released to the atmosphere in the event of an accident. Such enclosures are usually dome-shaped and made of steel-reinforced concrete.
contamination
undesirable radiological, chemical, or biological material (with a potentially harmful effect) that is either airborne, or deposited in (or on the surface of) structures, objects, soil, water, or living organisms in a concentration that makes the medium unfit for its next intended use.
control rod
a rod, plate, or tube containing a material such as hafnium, boron, etc., used to control the power of a nuclear reactor. By absorbing neutrons, a control rod prevents the neutrons from causing further fission.s
control room
the area in a nuclear power plant from which most of the plant’s power production and emergency safety equipment can be operated by remote control.
controlled area
at a nuclear facility, an area outside a restricted area but within the site boundary, to which the licensee can limit access for any reason.
coolant
a substance circulated through a unclear reactor to remove or transfer heat. The most commonly used coolant in the US is water. Other coolants include heavy water, air, CO2, helium, liquid sodium, and a sodium-potassium alloy.
cooldown
the gradual decrease in reactor fuel rod temperature caused by the removal of heat from the RCS after the reactor has been SD.
cooling tower
a heat exchanger designed to aid in the cooling of water that was used to cool exhaust steam exiting the turbines of a power plant. Cooling towers transfer exhaust heat into the air instead of into a body of water.
core
the central portion of a nuclear reactor, which contains the fuel assemblies, moderator, neutron poisons, control rods, and support structures. The reactor core is where fission takes place.
core damage frequency (CDF)
an expression of the likelihood that, given the way a reactor is designed and operated, an accident could cause the fuel in the reactor to be damaged.
core melt accident
an event or sequence of events that result in the melting of part of the fuel in the reactor core.
cosmic radiation
a source of natural background radiation, which originates in outer space and is composed of penetrating inning radiation (both particulate and electromagnetic). Accounts for ~45-50 of the 360 mrem/year.
counter
a general designation applied to radiation detection instruments or survey meters that detect and measure radiation. The signal that announces an ionization event is called a count.
critical mass
the smallest mass of fissionable material that will support a self-sustaining chain reaction.
critical organ
that part of the body that is most susceptible to radiation damage under the specific conditions under consideration.
criticality
the normal operating condition of a reactor, in which nuclear fuel sustains a fission chain reaction.
crud
a colloquial term for corrosion and wear products that become radioactive when exposed to radiation.
cumulative dose
the total dose that an occupationally exposed worker receives as a result of repeated exposures to ionizing radiation to the same portion of the body, or to the whole body, over time.
Curie (Ci)
- 7x10^10 disintegrations per second
3. 7x10^10 Bq
Daughter Products
isotopes that are formed by eh radioactive decay of some other isotope. IN the case of radium-226, there are 10 successive daughter products, ending in the stable isotope lead-206.
decay heat
the heat produced by the decay of radioactive fission products after ar reactor has been shut down.
decay, radioactive
the spontaneous transformation of one radioisotope into one or more different isotopes (known as “decay products”), accompanied by a decrease in radioactivity.
declared pregnant woman
a woman who is an occupation radiation worker and has voluntarily informed her employer, in writing, of her pregnancy and the estimated date of conception.
decommissioning
the process of safely closing a NPP to retire it from service after its useful life has ended.
DECON
a method of decommissioning, in which structures, systems, and components that contain radioactive contamination are removed from a site and safely disposed at a commercially operated LLW disposal facility, or decontaminated to a level that permits the site to be released for unrestricted use shortly after it ceases operation.
decontamination
a process used to reduce, remove, or neutralize radiological, chemical, or biological contamination to reduce the risk of exposure.
deep-dose equivalent
the external whole-body exposure dose equivalent at a tissue depth of 1 cm.
defense-in-depth
an approach to designing and operating nuclear facilities that prevents and mitigates accidents that release radiation or hazardous materials. The key is creating multiple independent and redundant layers of defense to compensate for potential human and mechanical failures so that no single layer is exclusively relied upon.
