ML18226A116

NUREG-1350, Vol. 30, Information Digest 2018-2019, Glossary

ML18226A116
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NRC Source Surface Gauge Detectors Radiation Depth Bioshield Figure 31. Moisture Density Guage 156Reactors that differ from today's reactors primarily by their use of inert gases, molten salt mixtures, or liquid metals to cool the reactor core. Advanced reactors can also consider fuel materials and designs that differ radically from today's enriched-uranium dioxide pellets within zirconium cladding.Agreement State A U.S. State that has signed an agreement with the U.S. Nuclear Regulatory Commission (NRC) authorizing the State to regulate certain uses of radioactive materials within the State.The energy that is released through a nuclear reaction or radioactive decay process. One kind of nuclear reaction is ~ssion, which occurs in a nuclear reactor and releases energy, usually in the form of heat and radiation. In a nuclear power plant, this heat is used to boil water to produce steam that can be used to drive large turbines. The turbines drive generators to produce electrical power.The natural radiation that is always present in the environment. It includes cosmic radiation that comes from the sun and stars, terrestrial radiation that comes from the Earth, and internal radiation that exists in all living things and enters organisms by ingestion or inhalation. The typical average individual exposure in the United States from natural background sources is about 310 millirem (3.1 millisievert) per year.

NEUTRON NUCLEUS FRAGMENT NEW NEUTRON NUCLEUS Nuclear Reaction 157How Nuclear Reactors WorkIn a typical design concept of a commercial BWR, the following proce ss occurs:

1. The nuclear fuel core inside the reactor vessel creates heat from nuclea r fission.

2. A steam-water mixture is produced when very pure water (reactor coolant) moves upward through the core, absor bing heat.

3. The steam-water mixture leaves the top of the core and enters the two stages of moisture separation where water droplets are removed before the steam is allowed to enter the steamline.

4. The steam is piped to the main turbine, causing it to turn the turbine generator, which produces electricity.

5. The steam is exhausted to the condenser, where it is condensed into water. The resulting water is pumped out of the condenser with a series of pumps and pumped back to the reactor vessel. The reactor's core contains fuel assemblies that are cooled by water circulated using electrically powered pumps. These pumps and other operating systems in the plant receive their power from the electrical grid. If offsite power is lost, cooling water is supplied by other pumps, which can be powered by onsite diesel generators or steam generated by the core. Other safety systems, such as the containment cooling system, also need electric power. BWRs contain between 370-800 fuel a ssemblies.

Control RodsTurbineGenerator SteamlineReactor VesselCoreSeparators& DryersFeedwater Condenser Heater Condensate PumpsDemineralizerEmergency Water Supply SystemsRecirculation Pumps Feed Pumps Containment Cooling System 4 5 3 1, 2 ContainmentStructure Typical Boiling-Water Reactor Source: U.S. Nuclear Regulatory CommissionWalls made of concrete and steel 3-5 feet thick (1-1.5 meters)A nuclear reactor in which water is boiled using heat released from ~ssion. The steam released by boiling then drives turbines and generators to produce electrical power. BWRs operate similarly to electrical plants using fossil fuel, except that the BWRs are heated by nuclear ~ssion in the reactor core.

158A medical procedure during which a sealed radioactive source (or sources) 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 kills cells in the tumor as long as the device remains in place and emits radiation. Brachytherapy uses radioisotopes, such as iridiu m-1 92 or iodin e-125, which are regulated by the NRC and Agreeme nt States.As de~ned by NRC regulations, byproduct material includes any radioactive material (except enriched uranium or plutonium) produced by a nuclear reactor or through the use of a particle accelerator, or any discrete source of radiu m-226 used for a commercial, medical, or research activity. 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. In addition, the NRC, in consultation with the U.S. Environmental Protection Agency (EPA), U.S. D epartment of Energy (DOE), U.S. Department of Homeland Security (DHS), and others, can designate as byproduct material any source of naturally occurring radioactive material, other than source material, that it determines would pose a threat to public health and safety or the common defense and security of the Unit ed States.CanisterSee Dry cas k storage.

The maximum load that a generating unit, generating station, or other electrical apparatus can carry under speci~ed conditions for a given period of time without exceeding approved limits of temperature and stress.The amount of electric power that a generator, turbine transformer, transmission, circuit, or system is able to produce, as rated by the manufacturer.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 ti me period.A percentage that a generating unit ful~lled its capacity in generating electric power over a given time period. This percentage is de~ned 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. Capacity utilization is computed by dividing the amount of power actually produced by the theoretical capacity and multiplyi ng by 100.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 (HLW). Casks are often made from lead, concrete, and/or steel. Casks must meet regulatory requirements.

159The International Atomic Energy Agency's Code of Conduct on the Safety and Security of Radioactive Sources de~nes the ~ve categories for radiation sources to help ensure that suf~cient controls are being used to achieve safety and security:

• Category 1 sources, if not safely or securely managed, 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. These sources are typically used in radiothermal generators, irradiators, and radiation teletherapy.

• Category 2 sources, if not safely or securely managed, 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. These sources are typically used in industrial gamma radiography, high- and medium-dose rate brachytherapy, and radiography.

• Category 3 sources, if not safely or securely managed, could cause permanent injury to a person who handled them or was otherwise in contact with them for hours. It could possibly-although it is unlikely to-be fatal to be close to this amount of unshielded radioactive material for a period of days to weeks. These sources are typically used in ~xed industrial gauges such as level gauges, dredger gauges, conveyor gauges, spinning pipe gauges, and well-loggi ng gauges.

• Category 4 sources, if not safely managed or securely protected, could possibly cause temporary injury to someone who handled them or was otherwise in contact with or close to them for a period of many weeks, though this is unlikely. It is very unlikely anyone would be permanently injured by this amount of radioactive material. These sources are typically used in ~xed or portable gauges, static eliminators, or low-dose brachytherapy.

• Category 5 sources cannot cause permanent injury. They are used in x-ray uorescence devices and electron captur e devices.Only Categories 1 and 2 for radiation sources are de~ned by NRC requirements.The NRC categorizes special nuclear materials and the facilities that possess them into three categories based upon the materials' potential for use in nuclear weapons or their "strategic significance":

• Category I, high strategic si gnificance

• Category II, moderate strategic s igni~cance* Category III, low strategic si gnificanceThe NRC's physical security and safeguards requirements differ by category, with Category I facilities subject to more stringent requirements because they pose greater security and safeguards risks.

160Information that has been determined pursuant to an Executive order to require protection against unauthorized disclosure and is marked to indicate its classi~ed status when in documentary form. The NRC has two types of classi~ed information. The ~rst type, known as national security information, is information that is classi~ed by an Executive order. Its release would damage national security. The second type, known as restricted data, would assist individuals or organizations in designing, manufacturing, or using nuclear weapons. Access to both types of information is restricted to authorized persons who have been properly cleared and have a "need to know" the information to accomplish their of~ci al duties.An NRC-issued license that authorizes a licensee to construct and (with certain speci~ed conditions) operate a nuclear power facility, such as a nuclear plant at a spec ific site.A facility that uses high doses of radiation to sterilize or treat products, such as food and spices, medical supplies, and wood ooring. Irradiation can be used to eliminate harmful bacteria, germs, and insects or for hardening or other purposes. The radiation does not leave radioactive residue or make the treated products radioactive. Radiation sources include radioactive materials (e.g., cobal t-60), an x-ray machine, or an electron beam.A group of two or more U.S. States that have formed alliances to dispose of low-level radioactive waste (LLW).The maximum number of years that could be added to a nuclear power plant's license expiration date to recapture the period between the date the NRC issued the plant's construction permit and the date it granted an operating license. A licensee must submit an application to request this extension.

Figure 34.

Commercial IrradiatorSource: U.S. Nuclear Regulatory Commission Radiation Shield Control Console Storage Pool RadiationSource Irradiation Room Loading Conveyor System UnloadingProcessedProductPhoto courtesy: Nordion 161A resilient gas-tight shell or other enclosure around a nuclear reactor to con~ne ~ssion products that otherwise might be released to the atmosphere in the event of a severe reactor accident. Such enclosures are usually dome-shaped and made of steel-reinforced concrete.ContaminationUndesirable radiological or chemical 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.The condition involving ~ssion of nuclear materials when the number of neutrons produced equals or exceeds the nuclear containment. During normal reactor operations, nuclear fuel sustains a ~ssion chain reaction or criticality. A reactor achieves criticality (and is said to be critical) when each ~ssion event releases a suf~cient number of neutrons to sustain an ongoing series of reactions.The process of safely closing a nuclear power plant (or other facility where nuclear materials are handled) to retire it from service after its useful life has ended. This process primarily involves decontaminating the facility to reduce residual radioactivity and then releasing the property for unrestricted or (under certain conditions) restricted use. This often includes dismantling the facility or dedicating it to other purposes.

Se e SAFSTOR.A phase of reactor decommissioning in which structures, systems, and components that contain radioactive contamination are removed from a site and safely disposed of at a commercially operated low-level waste disposal facility or decontaminated to a level that permits the site to be released for unrestr icted use.A process used to reduce, remove, or neutralize radiological or chemical contamination to reduce the risk of exposure. Decontamination may be accomplished by cleaning or treating surfaces to reduce or remove the contamination, ~ltering contaminated air or water, or subjecting contamination to evaporation and precipitation. The process can also simply allow adequate time for radioactive decay to decrease the radioactivity.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 controls or design features to compensate for potential human and mechanical failures so that no single control, no matter how robust, is exclusively relied upon to achieve safety or security. Defense in depth includes the use of access controls, physical barriers, redundant and diverse key safety functions, and emergency response measures.

162Uranium with a percentage of uraniu m-235 lower than the 0.7 percent (by mass) contained in natural uranium. Depleted uranium is the byproduct of the uranium enrichment process. Depleted uranium can be blended with highly enriched uranium, such as that from weapons, to make rea ctor fuel.A description of the type, composition, and capabilities of an adversary that a security system is designed to protect against. The NRC uses the DBT as a basis for designing safeguards systems to protect against acts of radiological sabotage and to prevent the theft of special nuclear material. Certain nuclear facility licensees are required to defend against the DBT.Certi~cation and approval by the NRC of a standard nuclear power plant design independent of a speci~c site or an application to construct or operate a plant. A design certi~cation is valid for 15 years from the date of issuance but can be renewed for an additional 10 to 15 years.The National Council on Radiation Protection and Measurements estimates that an average person in the United States receives a total annual dose of about 0.62 rem (620 millirem or 6.2 millisievert) from all radiation sources, a level that has not been shown to cause humans any harm. Of this total, natural background sources of radiation-including radon and thoron gas, natural radiation from soil and rocks, radiation from space, and radiation sources that are found naturally within the human body-account for about 50 percent. Medical procedures such as computed tomography (CT) scans and nuclear medicine account for about another 48 percent. Other small contributors of exposure to the U.S. population include consumer products and activities, industrial and research uses, and occupational tasks. The maximum permissible yearly dose for a person working with or around nuclear material is 5 rem (50 mill isievert).A method for storing spent nuclear fuel in special containers known as dry casks. After fuel has been cooled in a spent fuel pool, dry cask storage allows spent fuel assemblies to be sealed in casks and surrounded by inert gas. They are welded or bolted closed, and each cask includes steel, concrete, lead, or other material to provide leak-tight containment and radiation shielding. The casks may store fuel horizontally or vertically.

163A permit granted by the NRC to approve one or more proposed sites for a nuclear power facility, independent of a speci~c 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.A 4,500-megawatt thermal nuclear reactor design that has passive safety features and uses natural circulation (with no recirculation pumps or associated piping) for normal operation. The NRC certi~ed the ESBWR standard design submitted by General Electric-Hitachi Nuclear Energy on October 15, 2014.The percentage of the total energy content of a power plant's thermal energy that is converted into electricity. The remaining energy is lost to the environmen t as heat.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.A corporation, agency, authority, person, or other legal entity that owns 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 are not considered electric utilities.Sets of plant conditions that indicate various levels of risk to the public and that might require response by an offsite emergency response organization to protect citizens near the site.The programs, plans, training, exercises, and resources used to prepare for and rapidly identify, evaluate, and respond to emergencies, including those arising from terrorism or natural events such as hurricanes. EP strives to ensure that operators of nuclear power plants and certain fuel cycle facilities can implement measures to protect public health and safety in the event of a radiological emergency. Licensees who operate certain nuclear facilities, such as nuclear power plants, must develop and maintain EP plans that meet NRC requirements.The agency within the U.S. Department of Energy that provides policy-neutral statistical data, forecasts, and analyses to promote sound policymaking, ef~cient markets, and public understanding about energy and its interaction with the economy and the environment.

164 See Uranium e nrichment.An automated system used by the NRC to document incoming noti~cations of signi~cant nuclear events with an actual or potential effect on the health and safety of the public and the environment. Signi~cant events are reported to the NRC by licensees, Agreement States, other Federal agencies, the public, and other countries.Absorption of ionizing radiation or the amount of a hazardous substance that has been ingested, inhaled, or contacted the skin. Acute exposure occurs over a short period of time. Chronic exposure is exposure received over a long period of time, such as during a lifetime.

See Occupati onal dose.A component of the 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 m itigation.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 lique~ed natural gas terminals and interstate natural gas pipelines. FERC protects the economic, environmental, and safety interests of the American public, while working to ensure abundant, reliable energy in a fair, competiti ve market.The 12-month period from October 1 through September 30 used by the Federal Government for budget formulation and execution. The FY is designated by the calendar year in which it ends; for example, FY 2017 runs from October 1, 2016, through September 30, 2017.Fissile materialA nuclide that is capable of undergoing ~ssion after capturing neutrons. Although sometimes used as a synonym for ~ssionable material, this term has acquired its more restrictive interpretation with the limitation that the nuclide must be ~ssionable by thermal neutrons. With that interpretation, the three primary ~ssile materials are uraniu m-2 33, uraniu m-2 35, and plutoniu m-239. This de~nition excludes natural uranium and depleted uranium that have not been irradiated or have only been irradiated in thermal reactors.

165FissionThe splitting of an atom, which releases a considerable amount of energy (usually in the form of heat). Fission may be spontaneous but is usually caused by the nucleus of an atom becoming unstable (or "heavy") after capturing or absorbing a neutron. During ~ssion, the nucleus splits into roughly equal parts, producing the nuclei of at least two lighter elements. In addition to energy, this reaction usually releases gamma radiation and two or more daughter neutrons.A type of security exercise designed to evaluate and improve the effectiveness of a security system. For the NRC, force-on-force exercises are used to assess the ability of the licensee to defend a nuclear power plant and other nuclear facilities against a design-basis threat.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. The assignees' regulatory authorities generally identify the individuals participating and pay their salaries.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, Federal contractors, grantees, or private organizations or b usinesses.A structured group of fuel rods (long, slender, metal tubes containing pellets of ~ssionable material, which provide fuel for nuclear reactors). Depending on the design, each reactor core may have dozens of fuel assemblies (also known as fuel bundles), each of which contains dozens of fuel rods.

Fuel Assembly Spent fuel assemblies, are typically 14 feet [4.3 meters] long and contain nearly 200 fuel rods for PWRs and 80-100 fuel rods for BWRs.

Uranium Fuel Pellet Fuel Rod 166The series of steps involved in supplying fuel for nuclear power reactors. The uranium fuel cycle includes the following:* uranium recovery to extract and concentrate the uranium to produce yellowcake

• conversion of yellowcake into uranium hexa uo ride (UF 6)* enrichment to increase the concentration of uran ium in UF 6* fuel fabrication to convert enriched UF 6 into fuel for nuclear reactors* use of the fuel in reactors (nuclear power research or naval propulsion)

• interim storage of spent nu clear fuel

• reprocessing of spent fuel to recover the ~ssionable material remaining in the spent fuel (currently not done in the Unit ed States)

• ~nal disposition of high-level radioac tive waste

• transportation of the uranium in all forms, including spent fuelThe NRC regulates these processes, as well as the fabrication of mixed-oxide (MOX) nuclear fuel, which is a combination of uranium and plutoni um oxides.The processing of reactor fuel to separate the unused ~ssionable material from waste material. Reprocessing extracts uranium and plutonium from spent nuclear fuel so they can be used again as reactor fuel. Commercial reprocessing is not practiced in the United States, although it has been in the past. However, the U.S. Department of Energy operates reprocessing facilities at Hanford, WA, and Savannah River, SC, for national defense purposes.A long, slender, zirconium metal tube containing pellets of ~ssionable material, which provide fuel for nuclear reactors. Fuel rods are assembled into bundles called fuel assemblies, which are loaded individually into the reactor core.A human resources measurement equal to one person working full time for 1 year.Uranium enrichment technology that uses many rotating cylinders that are connected in long lines to increase the concentration of uraniu m-235. Gas is placed in the cylinder, which spins at a high speed, creating a strong centrifugal force. Heavier gas molecules move to the cylinder wall, while lighter molecules collect near the center. The stream, slightly enriched, is fed into the next cylinder. The depleted stream is recycled back into the previous cylinder.An analytical technique for separating chemical substances from a mixed sample by passing the sample, carried by a moving stream of gas, through a tube packed with a ~nely divided solid that may be coated with a liquid ~lm. Gas chromatography devices are used to analyze air pollutants, blood alcohol content, essential oils, and food products.

167A uranium enrichment process used to increase the concentration of uraniu m-235 in uranium for use in fuel for nuclear reactors by separating its isotopes (as gases) based on their slight difference in mass. (Lighter isotopes diffuse faster through a porous membrane or vessel than do heavier isotopes.) This process involves ~ltering UF 6 gas to separate uraniu m-2 34 and uraniu m-235 from uraniu m-238, increasing the percentage of ura niu m-235. In May 2013, the last remaining gaseous diffusion plant in operation in the United States in Paducah, KY, shut down. A similar plant near Piketon, OH, was closed in March 2001. Another plant in Oak Ridge, TN, closed years ago and was not regulated b y the NRC.Devices used to measure, monitor, and control the thickness of sheet metal, textiles, paper napkins, newspaper, plastics, photographic ~lm, and other products as they are manufactured. Gauges mounted in ~xed locations are designed for measuring or controlling material density, ow, level, thickness, or weight. The gauges contain sealed sources that radiate through the substance being measured to a readout or controlling device. Portable gauging devices, such as moisture density gauges, are used at ~eld locations. These gauges contain a gamma-emitting sealed source, usually cesiu m-137, or a sealed neutron source, usually americiu m-2 41 and beryllium.

The total amount of electric energy produced by a power generating station, as measured at the generator terminals.Source Surface Gauge Detectors Radiation Depth Bioshield Figure 31. Moisture Density GuageGaseous Diffusion Process Enriched Stream Depleted Stream Low Pressure Low Pressure High-Pressure Feed Source: U.S. Nuclear Regulatory Commission Detector Shutter Control Material Flow Shielding Source Shutter Pipe Figure 35.

Cross-Section of Fixed Fluid Gauge 168The gross amount of electric energy produced by a generating station, minus the amount used to operate the station. Net generation is usually measured in w att-hours.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.An excavated, underground facility that is designed, constructed, and operated for safe and secure permanent disposal of high-level radioactive waste (HLW). A geological repository uses an engineered barrier system and a portion of the site's natural geology, hydrology, and geochemical systems to isolate the radioactivity of the waste.A unit of power equivalent to one billion (1,000,000,0

00) watts.One billion (1,000,000,000) w att-hours. See Electric p ower grid.The time required for half the atoms of a particular radioactive material to decay. A speci~c 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, biological half-life and effective half-life.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.A method for extracting uranium from ore. The ore is placed in piles or heaps on top of liners. The liners prevent uranium and other chemicals from moving into the ground. Sulfuric acid is dripped onto the heap and dissolves uranium as it moves through the ore. Uranium solution drains into collection basins, where it is piped to a processing plant. At the plant, uranium is extracted, concentrated, and dried to form y ellowcake.

Figure 36. The Heap Leach Uranium Recovery Process Heap Dried Yellow-cake Acid Recirculation Liner System Collection Basin Processing Plant PROCESSING PLANTExtractedConcentrated StrippedDrying Acid Drip Slope 169The highly radioactive materials produced as byproducts of fuel reprocessing or of the reactions that occur inside nuclear reactors. HLW includes the following:* irradiated spent nuclear fuel discharged from commercial nuclear power reactors

• highly radioactive liquid and solid materials resulting from the reprocessing of spent nuclear fuel, which contains ~ssion products in concentration, including some reprocessed HLW from defense activities and a small quantity of reprocessed commercial HLW

• other highly radioactive materials that the Commission may determine require permanent isolationUranium enriched to at least 20 percent uraniu m-235 (a higher concentration than exists in natural uranium ore).A common method currently used to extract uranium from ore bodies without physical excavation of the ore. ISR is also known as "solution mining" or in situ leaching.Activities that address the short-term, direct effects of a natural or human-caused event and require an emergency response to protect life or property.A complex designed and constructed for the interim storage of spent nuclear fuel; solid, reactor-related, greater-than-Class-C waste; and other associated radioactive materials. A spent fuel storage facility may be considered independent, even if it is located on the site of another NRC-licensed facility.A United Nations agency established in 1957 to serve as a world center of cooperation in the nuclear ~eld. The agency works with nearly 170 member States and multiple partners worldwide to promote safe, secure, and peaceful nuclear technology.An association established in January 1997 to give national nuclear regulators with mature civilian nuclear reactor and materials programs a forum to discuss nuclear safety and security issues of mutual interest. Canada, France, Germany, Japan, South Korea, Spain, Sweden, the United Kingdom, and the United States of America ar e members.Exposure to ionizing radiation. Irradiation may be intentional, such as in cancer treatments or in sterilizing medical instruments. Irradiation may also be accidental, such as from exposure to an unshielded source. Irradiation does not usually result in radioactive contamination, but damage can occur, depending on the dose received.

170Two or more forms (or atomic con~gurations) of a given element that have identical atomic numbers (the same number of protons in their nuclei) and the same or very similar chemical properties but different atomic masses (different numbers of neutrons in their nuclei) and distinct physical properties. Thus, carbo n-12, carbo n-1 3, and carbo n-14 are isotopes of the element carbon, and the numbers denote the approximate atomic masses. Among their distinct physical properties, some isotopes (known as radioisotopes) are radioactive, because their nuclei are unstable and emit radiation as they decay spontaneously toward a more stable nuclear con~guration. For example, carbo n-1 2 and carbo n-13 are stable, but carbo n-1 4 is unstable and ra dioactive.A unit of power equivalent to 1, 000 watts.Source material, byproduct material, or special nuclear material that is received, possessed, used, transferred, or disposed of under a general or speci~c license issued by the NRC or Agreement States and is not otherwise exempt from r egulation.A company, organization, institution, or other entity to which the NRC or an Agreement State has granted a general or speci~c license to construct or operate a nuclear facility, or to receive, possess, use, transfer, or dispose of source, byproduct, or special nuclear material.The collection of documents or technical criteria that provides the basis upon which the NRC issues a license to construct or operate a nuclear facility; to conduct operations involving the emission of radiation; or to receive, possess, use, transfer, or dispose of source, byproduct, or special nuclear material.A library providing access to publicly available documents related to the hearings regarding the Department of Energy's application for authorization to construct a high-level nuclear waste geologic repository at Yucca Mountain, NV. The LSN Library is af~liated with Agencywide Documents Access and Management System (ADAMS), the agency's of~cial recordkeeping system. A term used to describe reactors using ordinary water as a moderated coolant, including boiling-water reactors (BWRs) and pressurized-water reactors (PWRs), the most common types used in the Unit ed States.A general term for a wide range of waste that is contaminated with radioactive material or has become radioactive through exposure to neutron radiation. A variety of industries, hospitals and medical institutions, educational and research institutions, private or government laboratories, and nuclear fuel cycle facilities 171generate LLW. Some examples include radioactively contaminated protective shoe covers and clothing; cleaning rags, mops, ~lters, and reactor water treatment residues; equipment and tools; medical tubes, swabs, and hypodermic syringes; and carcasses and tissues from laborator y animals.A potential accident in which a breach in a reactor's pressure boundary causes the coolant water to rush out of the reactor faster than makeup water can be added back in. Without suf~cient coolant, the reactor core could heat up and potentially melt the zirconium fuel cladding, causing a major release of radioactivity.A unit of power equivalent to 1,000, 000 watts.A unit of energy equivalent to 1,000 kilowatts of electricity used continuously for 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />.About 2,2 00 pounds.Primarily, the solid residue from a conventional uranium recovery facility in which uranium or thorium ore is crushed and processed mechanically or chemically to recover the uranium, thorium, or other valuable materials. This naturally radioactive ore residue contains the radioactive decay products from the uranium chains (mainly the uraniu m-238 chain). Although the milling process recovers about 93 percent of the uranium, the "tailings" contain several naturally occurring radioactive elements, including uranium, thorium, radium, polonium, and radon, as well as heavy metals and other con stituents.A type of nuclear reactor fuel that contains plutonium oxide mixed with either natural or depleted uranium oxide, in ceramic pellet form. This differs from conventional nuclear fuel, which is made of uranium oxide before it is irradiated in a reactor. Using plutonium reduces the amount of enriched uranium needed to produce a controlled reaction in commercial light-water reactors. However, plutonium exists only in trace amounts in nature and, therefore, must be produced by neutron irradiation of uraniu m-238 or obtained from other manufactured sources. As directed by Congress, the NRC regulates the fabrication of MOX fuel by DOE, a program that is intended to dispose of plutonium from excess nuclea r weapons.Periodic or continuous determination of the amount of ionizing radiation or radioactive contamination in a region. Radiation monitoring is a safety measure to protect the health and safety of the public and the environment through the use of bioassay, alpha scans, and other radiological survey methods to monitor air, surface water and ground water, soil and sediment, equipment surfaces, and personnel.

172The guiding principles, roles, and structures that enable all domestic incident response partners to prepare for and provide a uni~ed national response to disasters and emergencies. It describes how the Federal Government, States, Tribes, communities, and the private sector work together to coordinate a national response. The framework, which became effective March 22, 2008, builds upon the National Incident Management System, which provides a template for managing incidents.A secure, Web-based data system that helps the NRC and its Agreement States track and regulate the medical, industrial, and academic uses of certain nuclear materials, from the time they are manufactured or imported to the time of their disposal or exportation. This information enhances the ability of the NRC and Agreement States to conduct inspections and investigations, communicate information to other government agencies, and verify the ownership and use of nationally tracked sources.Uranium containing the relative concentrations of isotopes found in nature: 0.7 percent uraniu m-235, 99.3 percent uraniu m-238, and a trace amount of uraniu m-234 by mass. In terms of radioactivity, however, natural uranium contains about 2.2 percent uraniu m-235, 48.6 percent uraniu m-238, and 49.2 percent uraniu m-234. Natural uranium can be used as fuel in nuclear reactors or as feedstock for uranium enrichment f acilities.The gross amount of electric energy produced by a generating station, minus the amount used to operate the station. Note: Electricity required for pumping at pumped-storage plants is regarded as electricity for station operation and is deducted from gross generation. Net electric generation is measured in watt-hours, except as otherw ise noted.A nuclear reactor that is used for research, training, or development purposes (which may include producing radioisotopes for medical and industrial uses) but has no role in producing electrical power. These reactors, which are also known as research and test reactors, contribute to almost every ~eld of science, including physics, chemistry, biology, medicine, geology, archeology, and ecology.The primary center of communication and coordination among the NRC, its licensees, State and Tribal agencies, and other Federal agencies regarding operating events involving nuclear reactors or materials. Located in Rockville, MD, the Headquarters Operations Center is staffed 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> a day by employees trained to receive and evaluate event reports and coordinate incident response a ctivities.See Atomic energy.

173A specialized agency within the Organisation for Economic Co-operation and Development (OECD), which was created to assist its member countries in maintaining and further developing the scienti~c, technological, and legal bases for safe, environmentally friendly, and economical use of nuclear energy for peaceful purposes. The NEA's current membership consists of 31 countries in Europe, North America, and the Asia-Paci~c region, which account for about 86 percent of the world's installed nuclear capacity.Fissionable material that has been enriched to a composition that will support a self-sustaining ~ssion chain reaction when used to fuel a nuclear reactor, thereby releasing energy (usually in the form of heat or useful radiation) for use in other processes.See Special nuclear material, Source material, and Byproduct material.A centralized U.S. Government database used to track and account for source and special nuclear material. The system contains current and historical data on the possession, use, and shipment of source and special nuclear material within the United States, as well as all exports and imports of such material. The database is jointly funded by the NRC and DOE and is operated under a DOE contract.In reactor physics, a substance (other than ~ssionable material) that has a large capacity for absorbing neutrons in the vicinity of the reactor core. This effect may be undesirable in some reactor applications, because it may prevent or disrupt the ~ssion chain reaction, thereby affecting normal operation. However, neutron-absorbing materials (commonly known as "poisons") are intentionally inserted into some types of reactors to decrease the reactivity of their initial fresh fuel load for fuel intended to achieve higher burnup levels during the fuel cycle. Adding poisons, such as control rods or boron, is described as adding "negative reactivity" to the reactor.A thermal power plant, in which the energy (heat) released by the fissioning of nuclear fuel is used to boil water to produce steam. The steam spins the propeller-like blades of a turbine that turns the shaft of a generator to produce electricity. Of the various nuclear power plant designs, pressurized-water reactors and boiling-water reactors are in commercial operation in the United States. These facilities generate about 20 percent of U.S. e lectrical power.

174An annex to the National Response Framework that provides for a timely, coordinated response by Federal agencies to nuclear or radiological accidents or incidents within the United States. This annex covers radiological dispersal devices and improvised nuclear devices, as well as accidents involving commercial reactors or weapons production facilities, lost radioactive sources, transportation accidents involving radioactive material, and foreign accidents involving nuclear or radioactive material.The heart of a nuclear power plant or nonpower reactor, in which nuclear ~ssion may be initiated and controlled in a self-sustaining chain reaction to generate energy or produce useful radiation. Although there are many types of nuclear reactors, they all incorporate certain essential features, including the use of ~ssionable material as fuel, a moderator (such as water) to increase the likelihood of ~ssion (unless reactor operation relies on fast neutrons), a reector to conserve escaping neutrons, coolant provisions for heat removal, instruments for monitoring and controlling reactor operation, and protective devices (such as control rods and s hielding).A subset of radioactive waste that includes unusable byproducts produced during the various stages of the nuclear fuel cycle, including extraction, conversion, and enrichment of uranium; fuel fabrication; and use of the fuel in nuclear reactors. Speci~cally, these stages produce a variety of nuclear waste materials, including uranium mill tailings, depleted uranium, and spent (depleted) fuel, all of which are regulated by the NRC. (By contrast, "radioactive waste" is a broader term, which includes all wastes that contain radioactivity, regardless of how they are produced. It is not considered "nuclear waste" because it is not produced through the nuclear fuel cycle and is generally not regulated by the NRC.)The internal and external dose of ionizing radiation received by workers in the course of employment in such areas as fuel cycle facilities, industrial radiography, nuclear medicine, and nuclear power plants. These workers are exposed to varying amounts of radiation, depending on their jobs and the sources with which they work. The NRC requires its licensees to limit occupational exposure to 5,000 millirem (50 millisievert) per year. Occupational dose does not include the dose received from natural background sources, doses received as a medical patient or participant in medical research programs, or "second-hand doses" to members of the public received through exposure to patients treated with radioactive materials.An intergovernmental organization (based in Paris, France) that provides a forum for discussion and cooperation among the governments of industrialized countries committed to democracy and the market economy. The primary goal of OECD and its member countries is to support sustainable economic growth, boost employment, raise living standards, maintain ~nancial stability, assist other countries' economic development, and contribute to growth in world trade. In addition, 175OECD is a reliable source of comparable statistics and economic and social data. OECD also monitors trends, analyzes and forecasts economic developments, and researches social changes and evolving patterns in trade, environment, agriculture, technology, taxation, and other areas.Sealed sources of radioactive material contained in a small volume (but not radioactively contaminated soils and bulk metals) in any one or more of the following c onditions:

• an uncontrolled condition that requires removal to protect public health and safety from a radiological threat

• a controlled or uncontrolled condition for which a responsible party cannot be readily identified

• a controlled condition compromised by an inability to ensure the continued safety of the material (e.g., the licensee may have few or no options to provide for safe disposition of the material)

• an uncontrolled condition in which the material is in the possession of a person who did not seek, and is not licensed, to possess it

• an uncontrolled condition in which the material is in the possession of a State radiological protection program solely to mitigate a radiological threat resulting from one of the above conditions and for which the State does not have the necessary means to provide for the appropriate disposition of th e materialThe period during which a generating unit, transmission line, or other facility is out of service. Outages may be forced or scheduled and full o r partial.The shutdown of a generating unit, transmission line, or other facility for emergency reasons, or a condition in which the equipment is unavailable as a result of an unanticipated breakdown. An outage (whether full, partial, or attributable to a failed start) is considered "forced" if it could not reasonably be delayed beyond 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> from identi~cation of the problem, if there had been a strong commercial desire to do so. In particular, the following problems may result in force d outages:

• any failure of mechanical, fuel handling, or electrical equipment or controls within the generator's ownership or direct responsibility (i.e., from the point the generator is responsible for the fuel through to the electrical connect ion point)

• a failure of a mine or fuel transport system dedicated to that power station with a resulting fuel shortage that cannot be economical ly managed

• inadvertent or operator error

• limitations caused by fu el qualityForced outages do not include scheduled outages for inspection, maintenance, or refueling.

176A forced outage that causes a generating unit to be removed from the committed state (when the unit is electrically connected and generating or pumping) or the available state (when the unit is available for dispatch as a generator or pump but is not electrically connected and not generating or pumping). Full-forced outages do not include fail ed starts.The shutdown of a generating unit, transmission line, or other facility for inspection, maintenance, or refueling, which is scheduled well in advance (even if the schedule changes). Scheduled outages do not include forced outages and could be deferred if there were a strong commercial reason to do so.A thimble-sized ceramic cylinder (about 3/8-inch in diameter and 5/8-inch in length), consisting of uranium (typically uranium oxide), which has been enriched to increase the concentration of uraniu m-235 to fuel a nuclear reactor. Modern reactor cores in PWRs and BWRs may contain up to 10 million pellets stacked in the fuel rods that form fuel a ssemblies.A regulatory approach that focuses on desired, measurable outcomes, rather than prescriptive processes, techniques, or procedures. Performance-based regulation leads to de~ned results without speci~c direction on how those results are to be obtained. At the NRC, performance-based regulatory actions focus on identifying performance measures that ensure an adequate safety margin and offer incentives for licensees to improve safety without formal regulatory intervention by the agency.A quantitative measure of a particular attribute of licensee performance that shows how well a plant is performing when measured against established thresholds. Licensees submit their data quarterly; the NRC regularly conducts inspections to verify the submittals and then uses its own inspection data plus the licensees' submittals to assess each plant's pe rformance.A license, issued by the NRC, that authorizes the licensee to possess speci~c nuclear material but does not authorize its use or the operation of a nuclear facility.The process of increasing the maximum power level at which a commercial nuclear power plant may operate. This power level, regulated by the NRC, is included in the plant's operating license and technical speci~cations. A licensee may only change its maximum power output after the NRC approves an uprate application. The NRC analyses must demonstrate that the plant could continue to operate safely with its proposed new con~guration. When all requisite conditions are ful~lled, the NRC may grant the power uprate by amending the plant's operating license and technical speci fications.

177A common nuclear power reactor design in which very pure water is heated to a very high temperature by ~ssion, kept under high pressure (to prevent it from boiling), and converted to steam by a steam generator (rather than by boiling, as in a BWR). The resulting steam is used to drive turbines, which activate generators to produce electrical power. A PWR essentially operates like a pressure cooker, where a lid is tightly placed over a pot of heated water, causing the pressure inside to increase as the temperature increases (because the steam cannot escape) but keeping the water from boiling at the usual 212 degrees Fahrenheit (100 degrees Celsius). About two-thirds of the operating nuclear reactor power plants in the United States are PWRs.

Typical Pressurized-Water ReactorWalls made of concrete and steel 3-5 feet thick (1-1.5 meters)

SteamlineCore Containment Cooling SystemTurbineGenerator Condenser Heater Condensate PumpsDemineralizer Reactor Coolant PumpsPressurizerEmergency Water Supply Systems SteamGenerator ReactorVessel Control Rods Coolant Loop Feed Pumps 4 ContainmentStructure Source: U.S. Nuclear Regulatory Commission 3 2 1How Nuclear Reactors WorkIn a typical design concept of a commercial PWR, the following process occurs:

1. The core inside the reactor vessel creates heat.

2. Pressurized water in the primary coolant loop carries the heat to the steam generators.

3. Inside the steam generators, heat from the primary coolant loop vaporizes the water in a secondary loop, producing steam.

4. The steamline directs the steam to the main turbine, causing it to turn the turbine generators, which produces electricity.The steam is exhausted to the condenser, where it is condensed intowater. The resulting water is pumped out of the condenser with a series ofpumps, reheated, and pumped back to the steam generators. The reactor's corecontains fuel assemblies that are cooled by water circulated using electricallypowered pumps. These pumps and other systems in the plant receivetheir power from the electrical grid. If offsite power is lost, coolingwater is supplied by other pumps, which can be powered by onsite diesel generators. Other safety systems, such as the containment cooling system, alsoneed electric power. PWRs contain between 120-200 fuel assemblies.

178A systematic method for assessing three questions that the NRC uses to de~ne "risk." These questions consider (1) what can go wrong, (2) how likely it is to happen, and (3) what the consequences might be. These questions allow the NRC to understand likely outcomes, sensitivities, areas of importance, system interactions, and areas of uncertainty, which the staff can use to identify risk-signi~cant scenarios. The NRC uses PRA to determine a numeric estimate of risk to provide insights into the strengths and weaknesses of the design and operation of a nuclear po wer plant.Production expense is one component of the cost of generating electric power, which includes costs associated with fuel, as well as plant operation and ma intenance.One of the two units used to measure the amount of radiation absorbed by an object or person, known as the "absorbed dose," which reects the amount of energy that radioactive sources deposit in materials through which they pass. The radiation-absorbed dose (rad) is the amount of energy (from any type of ionizing radiation) deposited in any medium (e.g., water, tissue, air). An absorbed dose of 1 rad means that 1 gram of material absorbed 100 ergs of energy (a small but measurable amount) as a result of exposure to radiation. The related international system unit is the gray (Gy), where 1 Gy is equivalent t o 100 rad.A form of radiation, which includes alpha particles, beta particles, gamma rays, x-rays, neutrons, high-speed electrons, and high-speed protons. Compared to nonionizing radiation, such as found in ultraviolet light or microwaves, ionizing radiation is considerably more energetic. When ionizing radiation passes through material such as air, water, or living tissue, it deposits enough energy to break molecular bonds and displace (or remove) electrons. This electron displacement may lead to changes in living cells. Given this ability, ionizing radiation has a number of bene~cial uses, including treating cancer or sterilizing medical equipment. However, ionizing radiation is potentially harmful if not used correctly, and high doses may result in severe skin or tissue damage. It is for this reason that the NRC strictly regulates commercial and institutional uses of the various types of ionizing radiation.Energy given off by matter in the form of tiny, fast-moving particles (alpha particles, beta particles, and neutrons) or pulsating electromagnetic rays or waves (gamma rays) emitted from the nuclei of unstable radioactive atoms. All matter is composed of atoms, which are made up of various parts; the nucleus contains minute particles called protons and neutrons, and the atom's outer shell contains other particles called electrons. The nucleus carries a positive electrical charge, while the electrons carry a negative electrical charge. These forces work toward a strong, stable balance by getting rid of excess atomic energy (radioactivity). In that process, unstable radioactive nuclei may emit energy, and this spontaneous emission is called nuclear radiation.

179All types of nuclear radiation are also ionizing radiation, but the reverse is not necessarily true; for example, x-rays are a type of ionizing radiation, but they are not nuclear radiation because they do not originate from atomic nuclei. In addition, some elements are naturally radioactive, as their nuclei emit nuclear radiation as a result of radioactive decay, but others become radioactive by being irradiated in a reactor. Naturally occurring nuclear radiation is indistinguishable from induced radiation.A radioactive material or byproduct that is speci~cally manufactured or obtained for the purpose of using the emitted radiation. Such sources are commonly used in teletherapy or industrial radiography; in various types of industrial gauges, irradiators, and gamma knives; and as power sources for batteries (such as those used in spacecraft). These sources usually consist of a known quantity of radioactive material, which is encased in a manmade capsule, sealed between layers of nonradioactive material, or ~rmly bonded to a nonradioactive substrate to prevent radiation leakage. Other radiation sources include devices such as accelerators and x-ray g enerators.Exposure limits; permissible concentrations; rules for safe handling; and regulations on the receipt, possession, use, transportation, storage, disposal, and industrial control of radioactive material.The therapeutic use of ionizing radiation to treat disease in patients. Although most radiotherapy procedures are intended to kill cancerous tissue or reduce the size of a tumor, therapeutic doses may also be used to reduce pain or treat benign conditions. For example, intervascular brachytherapy uses radiation to treat clogged blood vessels. Other common radiotherapy procedures include gamma stereotactic radiosurgery (gamma knife), teletherapy, and iodine treatment to correct an overactive thyroid gland. These procedures use radiation sources, regulated by the NRC and its Agreement States, that may be applied either inside or outside the body. In either case, the goal of radiotherapy is to deliver the required therapeutic or pain-relieving dose of radiation with high precision and for the required length of time, while preserving the surrounding healt hy tissue.An of~cially prescribed magenta or black trefoil on a yellow background, which must be displayed where certain quantities of radioactive materials are present or where certain doses of radiation could be received.Undesirable radioactive 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 (people, animals, or plants) in a concentration that may harm people, equipment, or the environment.

180The spontaneous transformation of one radionuclide into one or more decay products (also known as "daughters"). This transformation is commonly characterized by the emission of an alpha particle, a beta particle, or gamma ray photon(s) from the nucleus of the radionuclide. The rate at which these transformations take place, when a suf~cient quantity of the same radionuclide is present, depends on the half-life of the radionuclide. Some radionuclides (e.g., hydroge n-3, also known as "tritium") decay to stable daughters that are not radioactive. However, other radionuclides (e.g., uraniu m-238) decay to radioactive daughters (e.g., thoriu m-234) and may be part of a radioactive decay chain consisting of two or more radionuclides linked in a cascading series of radioactive decay.The property possessed by some elements (such as uranium) of spontaneously emitting energy in the form of radiation as a result of the decay (or disintegration) of an unstable atom. Radioactivity is also the term used to describe the rate at which radioactive material emits radiation. Radioactivity is measured in units of becquerels or disintegrations p er second.The use of sealed sources of ionizing radiation for nondestructive examination of the structure of materials. When the radiation penetrates the material, it produces a shadow image by blackening a sheet of photographic ~lm that has been placed behind the material, and the differences in blackening suggest aws and unevenness in the material.An unstable isotope of an element that decays or disintegrates spontaneously, thereby emitting radiation. About 5,000 natural and arti~cial radioisotopes have been i dentified.A pharmaceutical drug that emits radiation and is used in diagnostic or therapeutic medical procedures. Radioisotopes that have short half-lives are generally preferred to minimize the radiation dose to the patient and the risk of prolonged exposure. In most cases, these short-lived radioisotopes decay to stable elements within minutes, hours, or days, allowing patients to be released from the hospital in a relatively s hort time.The central portion of a nuclear reactor, which contains the fuel assemblies, water, and control mechanisms, as well as the supporting structure. The reactor core is where ~ssion ta kes place.The process by which the NRC monitors and evaluates the performance of commercial nuclear power plants. Designed to focus on those plant activities that are most important to safety, the ROP uses inspection ~ndings and performance indicators to assess each plant's safety pe rformance.

181The process of removing older fuel and loading new fuel. These actions are all performed underwater to supply continuous cooling for the fuel and provide shielding from the radioactive s pent fuel.Reactor Building (Containment)Fuel BuildingRefueling BayFuel Transfer CanalRefueling BridgeRefueling BridgeReactor Building CraneRefueling BridgeFuel Storage PoolFuel Inspection StandSpent Fuel Storage RacksSpent Fuel Storage RacksRefueling CavitySteam Dryer and Separator Storage PoolNew Fuel Storage RacksFuel Transfer TubeReactor CoreReactor VesselReactor VesselContainment VesselTorusPWR Refueling SummaryBWR Refueling SummaryPWR Refueling Summary:As new fuel shipping canisters arrive in the fuel building, the reactor building crane (not shown) lifts them to the fuel inspection stand, where the fuel is removed from the canister and inspected for defects. Fuel in the new fuel storage area is moved into the fuel pool prior to refueling activities. The fuel can then be stored in either the new fuel storage racks (which are dry), or in the refueling pool, depending upon the needs of the site. Fuel in the new fuel storage area is moved into the fuel pool prior to refueling activities. To refuel the reactor, the vessel head is removed, the fuel transfer canals and transfer tube areas are ~ooded, and removable gates are opened in order to connect the refueling canal to the fuel pool. The reactor building refueling bridge is used to remove a fuel assembly from the reactor vessel and transfer it to the "up-ender" basket, which is then tilted until it is horizontal, sent through the transfer tube into the fuel building, and returned upright. The refueling bridge then moves the fuel assembly into the spent fuel storage racks. This process is reversed when fuel is loaded into the reactor.BWR Refueling Summary:As new fuel shipping canisters arrive in the reactor building, the reactor building crane lifts them to the refueling ~oor, where the fuel is removed from the canister and inspected for defects. The fuel can then be stored in either the new fuel storage area (which is dry), or in the refueling pool, depending upon the needs of the site. Fuel in the new fuel storage area is moved into the fuel pool prior to refueling activities. To refuel the reactor, the containment vessel lid and the reactor vessel head are removed, the refueling cavity above the reactor vessel is ~ooded, and the gates between the reactor cavity and fuel pool are removed. The refueling bridge removes one fuel bundle at a time from the reactor and transfers it to the spent fuel storage racks until about a third of the fuel is removed. The process is reversed when fuel is removed from the fuel pool and placed in the reactor. In BWRs the fuel remains in a vertical position throughout the process.

Spent Fuel Storage PoolPWR refuelingAs new fuel shipping canisters arrive in the fuel building, the reactor building crane (not shown) lifts them to the fuel inspection stand, where the fuel is removed from the canister and inspected for defects. Fuel in the new fuel storage area is moved into the fuel pool before refueling begins. The fuel can then be stored in either the new fuel storage racks (which are dry) or in the refueling pool, depending upon the needs of the site. Fuel in the new fuel storage area is moved into the fuel pool before refueling begins. To refuel the reactor, the vessel head is removed, the fuel transfer canals and transfer tube areas are ooded, and removable gates are opened in order to connect the refueling canal to the fuel pool. The reactor building refueling bridge is used to remove a fuel assembly from the reactor vessel and transfer it to the "up-ender" basket, which is then tilted until it is horizontal, sent through the transfer tube into the fuel building, and returned upright. The refueling bridge then moves the fuel assembly into the spent fuel storage racks. This process is reversed when fuel is loaded into the reactor.BWR refuelingAs new fuel shipping canisters arrive in the reactor building, the reactor building crane lifts them to the refueling oor, where the fuel is removed from the canister and inspected for defects. The fuel can then be stored in either the new fuel storage area (which is dry) or in the refueling pool, depending upon the needs of the site. Fuel in the new fuel storage area is moved into the fuel pool before refueling begins. To refuel the reactor, the containment vessel lid and the reactor vessel head are removed, the refueling cavity above the reactor vessel is ooded, and the gates between the reactor cavity and fuel pool are removed. The refueling bridge removes one fuel bundle at a time from the reactor and transfers it to the spent fuel storage racks until about a third of the fuel is removed. The process is reversed when fuel is removed from the fuel pool and placed in the reactor. In BWRs, the fuel remains in a vertical position throughout the process.Reactor Building (Containment)Fuel BuildingRefueling BayFuel Transfer CanalRefueling BridgeRefueling BridgeReactor Building CraneRefueling BridgeFuel Storage PoolFuel Inspection StandSpent Fuel Storage RacksSpent Fuel Storage RacksRefueling CavitySteam Dryer and Separator Storage PoolNew Fuel Storage RacksFuel Transfer TubeReactor CoreReactor VesselReactor VesselContainment VesselTorusPWR Refueling SummaryBWR Refueling SummaryPWR Refueling Summary:As new fuel shipping canisters arrive in the fuel building, the reactor building crane (not shown) lifts them to the fuel inspection stand, where the fuel is removed from the canister and inspected for defects. Fuel in the new fuel storage area is moved into the fuel pool prior to refueling activities. The fuel can then be stored in either the new fuel storage racks (which are dry), or in the refueling pool, depending upon the needs of the site. Fuel in the new fuel storage area is moved into the fuel pool prior to refueling activities. To refuel the reactor, the vessel head is removed, the fuel transfer canals and transfer tube areas are ~ooded, and removable gates are opened in order to connect the refueling canal to the fuel pool. The reactor building refueling bridge is used to remove a fuel assembly from the reactor vessel and transfer it to the "up-ender" basket, which is then tilted until it is horizontal, sent through the transfer tube into the fuel building, and returned upright. The refueling bridge then moves the fuel assembly into the spent fuel storage racks. This process is reversed when fuel is loaded into the reactor.BWR Refueling Summary:As new fuel shipping canisters arrive in the reactor building, the reactor building crane lifts them to the refueling ~oor, where the fuel is removed from the canister and inspected for defects. The fuel can then be stored in either the new fuel storage area (which is dry), or in the refueling pool, depending upon the needs of the site. Fuel in the new fuel storage area is moved into the fuel pool prior to refueling activities. To refuel the reactor, the containment vessel lid and the reactor vessel head are removed, the refueling cavity above the reactor vessel is ~ooded, and the gates between the reactor cavity and fuel pool are removed. The refueling bridge removes one fuel bundle at a time from the reactor and transfers it to the spent fuel storage racks until about a third of the fuel is removed. The process is reversed when fuel is removed from the fuel pool and placed in the reactor. In BWRs the fuel remains in a vertical position throughout the process.

Spent Fuel Storage Pool 182The governmental function of controlling or directing economic entities through the process of rulemaking and adj udication.An annual NRC conference that brings together NRC staff, regulated utilities, materials users, and other interested stakeholders to discuss nuclear safety topics and signi~cant and timely regulatory activities through informal dialogue to ensure an open regulatory process.One of the two standard units used to measure the dose equivalent (or effective dose), which combines the amount of energy (from any type of ionizing radiation) that is deposited in human tissue with the biological effects of the given type of radiation. For beta and gamma radiation, the dose equivalent is the same as the absorbed dose. By contrast, the dose equivalent is larger than the absorbed dose for alpha and neutron radiation because these types of radiation are more damaging to the human body. Thus, the dose equivalent (in rem) is equal to the absorbed dose (in rads) multiplied by the quality factor of the type of radiation (Title 10 of the Code of Federal Regulations (10 CFR) 20.1004, "Units of Radiation Dose"). The related international system unit is the sievert (Sv), where 100 rem is equivalent to 1 Sv.Natural, but limited, energy resources that can be replenished, including biomass, hydro, geothermal, solar, and wind. These resources are virtually inexhaustible but limited in the amount of energy that is available per unit of time. In the future, renewable resources could also include the use of ocean thermal, wave, and tidal action technologies. Utility renewable resource applications include bulk electricity generation, onsite electricity generation, distributed electricity generation, nongrid-connected generation, and demand-reduction (energy ef~ciency) tec hnologies.The combined answer to three questions that consider (1) what can go wrong, (2) how likely it is to occur, and (3) what the consequences might be. These three questions allow the NRC to understand likely outcomes, sensitivities, areas of importance, system interactions, and areas of uncertainty, which can be used to identify risk-signi~cant scenarios.An approach to regulatory decisionmaking that considers only the results of a probabilistic risk a ssessment.An approach to regulatory decisionmaking in which insights from probabilistic risk assessment are considered with other engineering insights.

183An approach to regulation taken by the NRC that incorporates an assessment of safety signi~cance or relative risk. This approach ensures that the regulatory burden imposed by an individual regulation or process is appropriate to its importance in protecting the health and safety of the public and the environment.The term referring to a facility's system, structure, component, or accident sequence that exceeds a predetermined limit for contributing to the risk associated with the facility. The term also describes a level of risk exceeding a predetermined signi~ca nce level.The use of material control and accounting programs to verify that all special nuclear material is properly controlled and accounted for, as well as the physical protection (or physical security) equipment and security forces. As used by the IAEA, this term also means verifying that the peaceful use commitments made in binding nonproliferation agreements, both bilateral and multilateral, are honored.A special category of sensitive unclassi~ed information that must be protected. Safeguards Information concerns the physical protection of operating power reactors, spent fuel shipments, strategic special nuclear material, or other radioactive material.In the regulatory arena, this term applies to systems, structures, components, procedures, and controls (of a facility or process) that are relied upon to remain functional during and following design-basis events. Their functionality ensures that key regulatory criteria, such as levels of radioactivity released, are met. Examples of safety-related functions include shutting down a nuclear reactor and maintaining it in a safe-shutdown condition.When used to qualify an object, such as a system, structure, component, or accident sequence, a term identifying that object as having an impact on safety, whether determined through risk analysis or other means, that exceeds a predetermined signi~cance criterion.A long-term storage condition for a permanently shutdown nuclear power plant. During SAFSTOR, radioactive contamination decreases substantially, making subsequent decontamination and demolition easier and reducing the amount of low-level waste requiring disposal.The sudden shutting down of a nuclear reactor, usually by rapid insertion of control rods, either automatically or manually by the reactor operator (also known as a "react or trip").

184Information that is generally not publicly available and that encompasses a wide variety of categories, such as proprietary information, personal and private information, or information subject to attorney-client privilege.A decrease in the rate of ~ssion (and heat or energy production) in a reactor (usually by the insertion of control rods into the core).Small reactors that use water to cool the reactor core in the same way as today's large light-water reactors. SMR designs also use the same enriched-uranium fuel as current U.S. reactors. However, SMR designs are considerably smaller and can bundle together several reactors in a single containment. Each SMR module generates 300 megawatts electric (MWe) or less, compared to today's large designs that can generate 1,000 MWe or more per reactor. The NRC's discussions to date with SMR designers involve modules generating less than 200 MWe.Uranium or thorium, or any combination thereof, in any physical or chemical form, or ores that contain, by weight, 1/20 of 1 percent (0.05 percent) or more of (1) uranium, (2) thorium, or (3) any combination thereof. Source material does not include special nuclear material.Plutonium, uraniu m-2 33, or uranium enriched in the isotopes uraniu m-233 or ur aniu m-2 35.An underwater storage and cooling facility for spent (depleted) fuel assemblies that have been removed from a reactor.Nuclear reactor fuel that has been used to the extent that it can no longer effectively sustain a chain reaction.The condition of a nuclear reactor system in which nuclear fuel no longer sustains a ~ssion chain reaction (i.e., the reaction fails to initiate its own repetition, as it would in a reactor's normal operating condition). A reactor becomes subcritical when its ~ssion events fail to release a suf~cient number of neutrons to sustain an ongoing series of reactions, possibly as a result of increased neutron leakage o r poisons.Treatment in which the source of the therapeutic radiation is at a distance from the body. Because teletherapy is often used to treat malignant tumors deep within the body by bombarding them with a high-energy beam of gamma rays (from a radioisotope such as cobal t-60) projected from outside the body, it is often called "external beam radiotherapy."

185Code of Federal Regulations The Code of Federal Regulations (CFR) addresses energy-related topics.

Chapter I, Parts 1 to 199, contain the regulations (or rules) established by the NRC. These regulations govern the transportation and storage of nuclear materials; use of radioactive materials at nuclear power plants, research and test reactors, uranium recovery facilities, fuel cycle facilities, waste repositories, and other nuclear facilities; and use of nuclear materials for medical, industrial, and academic purposes.A change in the reactor coolant system temperature, pressure, or both, attributed to a change in the reactor's power output. Transients can be caused by (1) adding or removing neutron poisons, (2) increasing or decreasing electrical load on the turbine generator, or (3) accident c onditions.Material contaminated with transuranic elements-arti

~cially made radioactive elements, such as neptunium, plutonium, americium, and others-that have atomic numbers higher than uranium in the periodic table of elements. Transuranic waste is primarily produced from recycling spent fuel or using plutonium to fabricate nuclea r weapons.A radioactive isotope of hydrogen. Because it is chemically identical to natural hydrogen, tritium can easily be taken into the body by any ingestion path. It decays by emitting beta particles and has a half-life of about 1 2.5 years.See Pow er uprate.A radioactive element with the atomic number 92 and, as found in natural ores, an atomic weight of about 238.

The two principal natural isotopes are uraniu m-235 and uraniu m-2 38. Uraniu m-235 is composed of 0.7 percent natural uranium and is ~ssile.

Uraniu m-238 is composed of 99.3 percent natural uranium, is ~ssionable by fast neutrons, and is fertile. This means that it becomes ~ssile after absorbing one neutron. Natural uranium also includes a minute amount of ur aniu m-2 34.A piece of natural uranium ore 186The process of increasing the percentage of uraniu m-2 35 (U-235) from 0.7 percent in natural uranium to about 3 to 5 percent for use in fuel for nuclear reactors. Enrichment can be done through gaseous diffusion, gas centrifuges, or laser isotope s eparation.

Figure 39. Enrichment ProcessesA. Gaseous Diffusion ProcessB. Gas Centrifuge Process Enriched Stream Depleted Stream Low Pressure Low Pressure High-Pressure Feed UF 6 Feed Fraction Enriched in U-235 Fraction Depleted in U-235 Casing Rotor Electric Motor Source: U.S. Nuclear Regulatory CommissionGas centrifuge process The gas centrifuge process uses many rotating cylinders that are connected in long lines. Gas is placed in the cylinder, which spins at a high speed, creating a strong centrifugal force. Heavier gas molecules move to the cylinder wall, while lighter molecules collect near the center. The stream, now slightly enriched, is fed into the next cylinder. The depleted stream is recycled back into the previous cylinder. A facility that converts enriched UF 6 into fuel for commercial light-water power reactors, research and test reactors, and other nuclear reactors. The UF 6, in solid form in containers, is heated to a gaseous form and then chemically processed to form uranium dioxide (UO

2) powder. This powder is then processed into ceramic pellets and loaded into metal tubes, which are subsequently bundled into fuel assemblies. Fabrication can also involve MOX fuel, which contains plutonium oxide mixed with either natural or depleted uranium oxide in ceramic pe llet form.A facility that receives natural uranium in the form of ore concentrate (known as yellowcake) and converts it into UF 6, in preparation for fabricating fuel for nuclear reactors.

187The Federal agency established by Congress to advance the national, economic, and energy security of the United States, among other missions.The Federal agency responsible for leading the uni~ed national effort to secure the United States against those who seek to disrupt the American way of life. DHS is also responsible for preparing for and responding to all hazards and disasters and includes the formerly separate FEMA, the Coast Guard, and the Secre t Service.The Federal agency responsible for protecting human health and safeguarding the environment. EPA leads the Nation's environmental science, research, education, and assessment efforts to ensure that attempts to reduce environmental risk are based on the best available scienti~c information. EPA also ensures that environmental protection is an integral consideration in U.S. p olicies.Viability assessmentA decisionmaking process used by DOE to assess the prospects for safe and secure permanent disposal of high-level waste in an excavated, underground facility known as a geologic repository. This decisionmaking process is based on (1) speci~c design work on the critical elements of the repository and waste package, (2) a total system performance assessment that will describe the probable behavior of the repository, (3) a plan and cost estimate for the work required to complete the license application, and (4) an estimate of the costs to construct and operate the repository.Radioactive materials at the end of their useful life or in a product that is no longer useful and requires proper disposal. See High-level waste, Low-level waste, and Spent nuc lear fuel.Classi~cation of low-level waste (LLW) according to its radiological hazard. The classes include Class A, B, and C, with Class A being the least hazardous and accounting for 96 percent of LLW in the U.S. As the waste class and hazard increase, the regulations established by the NRC require progressively greater controls to protect the health and safety of the public and the environment.A unit of power (in the International System of Units) de~ned as the consumption or conversion of 1 joule of energy per second. In electricity, a watt is equal to current (in amperes) multiplied by voltage (in volts).