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GLOSSARY Accessible Those portions of the environment clirectly in environment contact with or readily available for use by human beings. Includes the earth's atmosphere, the land surface, aquifers, surface waters, and the oceans. In 40 CFR 191, the environment outside a surface cleaned as enclosing a controlled area. ALARA An acronym for "as low as reasonably achievable", a concept meaning that the design ant! use of sources, and the practices associated therewith, should be such as to ensure the exposures are kept as low as is reasonably practicable, economic ant} social factors being taken into account. Backfill Becquerel Biosphere The material used to refill the excavated potions of a repository or of a borehole after waste has been emplaced. International unit of radioactivity. Symbol Bq = 1 (lisintegration per second. The region of the earth in which environmental pathways for transfer of radionuclicles to living organisms are locater} ant! by which radionuclicles in air, ground water, and soil can reach humans to be inhaled, ingested, or absorbed through skin. Humans can also be exposed to direct irradiation from radionuclides in the environment. Borehole A cylindrical excavation in the earth, made by a rotary drilling device. 189

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I90 YUCCA MOUNTAIN STANDARDS Canister A closed or sealer! container for nuclear fuel or other radioactive material, which isolates ant! contains the contents; it might rely on other containers (e.g. a cask) for shielcling. Collective dose The sum of the indiviclual closes received in a given period of time by a specified population from exposure to a specifier] source of radiation. Critical group Originally clefined for close by the ICRP (ICRP, 1977, p.17; ICRP, 19SSb, pp.3-4) as a relatively homogeneous aroun of neonie whose location and -- of r -- r- -r habits are such that they are representative of those individuals expected to receive the highest doses as a result of the discharges of radionuclides. The definition is extencled to risk in Chapter 2 of this report. Critical pathway Disposal Disposal package Dose The dominant environmental pathway through which a given radionuclide reaches the critical group. Permanent isolation of spent nuclear fuel or radioactive waste from the accessible environment with no intent of recovery, whether or not such isolation permits the recovery of such fuel or waste. The primary container that hoicis, ant! is in contact with, solidifies! high-level radioactive waste, spent nuclear fuel, or other radioactive materials, and any overpacks that are emplaced at a repository. A measure of the radiation received or absorbent by a target.

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GLOSSARY 191 Absorbed close per unit time. Engineered The waste form, cladding, backfill, anti canister, all barrier system of which are intended to retarc! disperson of raclionuclides. Irradiation of persons or materials. Exposure of persons to ionizing radiation can be either: I. external exposure, irradiation by sources outside the body; or 2. internal exposure, irradiation by sources inside the body. Fault A surface or zone of rock fracture along which there has been clisplacement. Geologic A system that is intended to be used for, or might repository be used for, the disposal of radioactive wastes in excavated geologic media. A geologic repository includes: (~) the geologic repository operations area and (2) the portion of the geologic setting that provides isolation of the radioactive waste. Ground water Water that permeates the rock strata of the Earth, filling their pores, fissures and cavities. (It excludes water of hydration.) Ground water The principal means by which radionuclides can be transport mobilized from an underground repository ant} moved into the biosphere. Avoiding or minimizing such transport is the basis for selecting and designing repository systems.

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192 YUCCA MOUNTAIN STANDARDS Half-life In physics, the time required for the transformation of one-half of the atoms in a given radioactive decay process, following the exponential law (physical half-life). High-level The highly radioactive material resulting from the radioactive reprocessing of spent nuclear fuel, including liquic] waste waste procluced directly in reprocessing and any solid material clerivec! from such liquid waste that contains fission products in sufficient concentrations. Other highly radioactive material that the U.S. Nuclear Regulatory Commission, consistent with existing law, determines by rule requires permanent isolation. Also referred to as high-level waste (HEW). IAEA International Atomic Energy Agency is an autonomous intergovernmental organization establisher! by the Uniter! Nations. It is authorized to foster research and development in the peaceful uses of nuclear energy, to establish or administer health and safety standards, and to apply safeguards in accordance with the Treaty of the Non Proliferation of Nuclear Weapons.

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GLOSSARY 193 ICRP The International Commission on Radiological Protection is an international organization that clevelops guidance and standards for radiological measurement ant! protection of public and occupational health. The ICRP is composer! of a Chairman and never more than 12 other members. The selection of the members is made by the ICR* from nominations submitted to it by the National Delegations to the International Congress of Radiology en c! the ICRP staff itself. Members of the ICRP are chosen on the basis of their recognized activity in the fields of medical racliology, radiation protection, physics, biology, genetics, biochemistry, ant! biophysics. The ICRP's rules require that its members be elected every four years. Linear model Also, linear dose-effect relationship; expresses the health effect, such as mutation or cancer as a direct (linear) function of close. Natural The amount of radiation to which a member of the background population is exposed from natural sources, such as radiation terrestrial radiation due to naturally occurring radionuclides in the soil, cosmic radiation originating in outer space, and naturally occurring raclionuclides deposited in the human body. NCRP National Council on Radiation Protection ant} Measurements is an organization of nationally recognized scientists who share the belief that significant advances in radiation protection and measurement can be achieved through cooperative effort. It conducts research focusing on safe occupational exposure levels and disseminates information.

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194 YUCCA MOUNTAINSTANDARDS Performance Analysis to predict the performance of the system assessment or subsystem, followed by comparison of the results of such analysis with appropriate stanciarcis or criteria. Population dose The sum of the doses to all the individuals in a specified group. In units of person-sievert or person-rem. (Also called collective dose.) Radioactive The spontaneous transformation of a nuclide into clecay one or more different nuclides accompanied by either the emission of energy or particles. Unstable atoms decay into a more stable state, eventually reaching a form that floes not decay further or is very long-liveti. Radioactive Any material that contains or is contaminated with waste radionuclides at concentrations or radioactivity levels greater than the exempt quantities establisher] by the competent authorities ant! for which no use is foreseen. Radionuclide A radioactive species of an atom characterized by the constitution of its nucleus. Rem A unit of dose equivalent to one-hunciredth of a sievert (1 cSv).

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GLOSSARY 195 Repository Any system licensed by the U.S. Nuclear Regulatory Commission that is intended to be used for, or can be used for, the permanent deep geologic disposal of high-level radioactive waste and spent nuclear fuel, whether or not such system is ciesigned to permit the recovery, for a limited period during initial operation, of any material placed in such system. Such term includes both surface and subsurface areas at which high-level radioactive waste and spent nuclear fuel handling activities are conducted. Risk In the context of this study, risk is the probability of an individual receiving an adverse health effect and includes the probability of getting a dose. Saturated zone That part of the eari;h's crust beneath the regional water table in which all voids, large ant} small, are ideally filled with water under pressure greater than atmospheric. Seismic Pertaining to, characteristic of, or producer] by earthquakes or earth vibrations. Sievert International Unit (SI) of equivalent radiation dose. The product of the absorbed close and the quality factor of the radiation. Symbol Sv. Spent fuel Fuel that has been withdrawn from a nuclear reactor following irradiation, the constituent elements of which have not been separates} by reprocessing.

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196 YUCCA MOUNTAIN STANDARDS Stochastic Random events leading to effects whose probability health effects of occurrence in an exposeci population (rather than severity in an affected individual) is a direct function of dose; these effects are commonly regarded as having no threshold; hereditary effects are regarcled as being stochastic; some somatic effects, especially carcinogenesis, are regarciec] as being stochastic. Storage Turf Retention of high-level radioactive waste, spent nuclear fuel, or transurar~ic waste with the intent to recover such waste or fuel for subsequent use, processing, or (disposal. Rock former! from consolidate~i volcanic ash. Units Unitsa Symbol Conversion Factors Becquerel Bq I disintegration/sec=2.7 x 10 (SI) ~ ~ Curies Curie Ci 3.7 x 10~ disintegrations/sec= 3.7 x 10~ Becquerels Gray (SI) Gy 1 Joule/kg= lOOrads Rad red 100 ergs/gram = 0.01 Grays Rem rem 0.01 Sievert Sievert (SI) Sv 100 rems a International Units are designated SI. Unsaturated The zone between the land surface and the regional zone water table. Generally, fluid pressure in this zone is less than atmospheric pressure, anti some of the voids might contain air or other gases at atmospheric pressure. Beneath flooded areas or in perched water bociies the fluid pressure locally may be greater than atmospheric. Also referred to as vadose zone.

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GLOSSARY 197 Vadose zone See clefinition for unsaturated zone. Volcanism The process by which magma and the associated gases rise into the crust and are extruded onto the earth's surface and into the atmosphere. Waste form The radioactive waste materials and any encapsulating or stabilizing matrix. Waste package The waste form and any containers, shielding, packing anti other absorbent materials immecliately surrounding an individual waste container. Water table The upper surface of the saturates} zone on which the water pressure in the porous medium equals atmospheric pressure.

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