APPENDIX N
GLOSSARY OF TERMS

A

absorption

Incorporation of the physical or molecular structure (see sorption).

accessible environment

Those portions of the environment directly in contact with or readily available for use by human beings. Includes the Earth's atmosphere, the land surface, aquifers, surface waters, and part of the oceans.

actinide

An element with an atomic number from 89 to 103, inclusive. All are radioactive.

activation product

An element made radioactive by bombardment with neutrons.

activity

For an amount of radioactive nuclide in a particular energy state at a given time, the quotient of dN by dt is the expectation value of the number of spontaneous nuclear transitions from that energy state in the time interval dt. The SI unit of activity is the becquerel (Bq); the curie (Ci) is being phased out.

Alara

An acronym for ''as low as reasonably achievable" a concept meaning that the design and use of sources, and the practices associated therewith, including their disposal, should be such as to ensure that exposures are kept as low as is reasonably practicable, economic and social factors being taken into account.

alpha-bearing waste

Waste containing one or more alpha emitting radionuclides, usually actinides, in quantities above acceptable limits for uncontrolled release. The limits are established by the national regulatory body.

aluminosilicate glass

A durable type of glass in which some of the silicon atoms that normally form the amorphous, polymeric structures that are characteristic of glasses (networks) are replaced by aluminium atoms. Aluminosilicate glasses are candidate matrices for solidifying some kinds of radioactive waste.



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Nuclear Wastes: Technologies for Separations and Transmutation APPENDIX N GLOSSARY OF TERMS A absorption Incorporation of the physical or molecular structure (see sorption). accessible environment Those portions of the environment directly in contact with or readily available for use by human beings. Includes the Earth's atmosphere, the land surface, aquifers, surface waters, and part of the oceans. actinide An element with an atomic number from 89 to 103, inclusive. All are radioactive. activation product An element made radioactive by bombardment with neutrons. activity For an amount of radioactive nuclide in a particular energy state at a given time, the quotient of dN by dt is the expectation value of the number of spontaneous nuclear transitions from that energy state in the time interval dt. The SI unit of activity is the becquerel (Bq); the curie (Ci) is being phased out. Alara An acronym for ''as low as reasonably achievable" a concept meaning that the design and use of sources, and the practices associated therewith, including their disposal, should be such as to ensure that exposures are kept as low as is reasonably practicable, economic and social factors being taken into account. alpha-bearing waste Waste containing one or more alpha emitting radionuclides, usually actinides, in quantities above acceptable limits for uncontrolled release. The limits are established by the national regulatory body. aluminosilicate glass A durable type of glass in which some of the silicon atoms that normally form the amorphous, polymeric structures that are characteristic of glasses (networks) are replaced by aluminium atoms. Aluminosilicate glasses are candidate matrices for solidifying some kinds of radioactive waste.

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Nuclear Wastes: Technologies for Separations and Transmutation annual dose equivalent limit The value of the annual dose equivalent that must not be exceeded, according to the International Commission on Radiological Protection (ICRP) system of dose limitation. anoxic condition A chemical condition, often existing in underground waste repositories, in which the partial pressure of oxygen in the groundwater is very low. This affects the oxidation state of chemical species in the groundwater as well as bacteriological processes that can occur. aquifer A water-bearing formation below the surface of the earth. An aquifer can furnish an appreciable supply of water for a well or spring. area survey The first stage of siting a waste repository, during which a broad area is examined to eliminate obviously unsuitable regions and to identify other regions that may contain suitable sites. argillaceous A term applied to all rocks and substances composed of clay or having a notable proportion of clay in their composition. arid sites A term often applied to a shallow, land waste-disposal site located in an area that receives very little annual precipitation, typically less than 250 mm per year. B back end of the fuel cycle The part of the fuel cycle that includes spent-fuel storage, fuel reprocessing, mixed-oxide fuel fabrication, and waste management including spent-fuel disposal. backfill The material used to refill the excavated portions of a repository or of a borehole after waste has been emplaced. barrier (natural or engineered) A feature that delays or prevents material migration to or from disposal components. Facilities may include multiple barriers. becquerel (Bq) The SI unit of radioactivity, equivalent to 1 disintegration per second (approximately 2.7 × 10-11 Ci).

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Nuclear Wastes: Technologies for Separations and Transmutation bedded salt A salt formation in which the salt is roughly horizontal, laterally extensive, and relatively thin in the vertical direction. bentonite A soft, plastic light-colored clay formed by chemical alteration of volcanic ash. It is composed essentially of montmorillonite and related minerals of the smectite group. The properties of bentonite depend largely on its ion exchange characteristics. Bentonite may be used as a buffer material for surrounding waste packages in a deep repository. biosphere That portion of the Earth's environment inhabited by any living organisms. It comprises parts of the atmosphere, the hydrosphere (oceans, seas, inland waters and subterranean waters), and the lithosphere. The biosphere includes the human habitat or environment in the widest sense of these terms. bitumen A general name for various solid and semisolid hydrocarbons that are fusible and are soluble in carbon bisulphide. Petroleums, asphalts, natural mineral waxes, and asphaltites are all considered bitumens. Bitumen is known to be very stable in the terrestrial environment and is sometimes used as a matrix for immobilizing low-and intermediate-level waste. borehole A cylindrical excavation, made by a rotary drilling device. For disposal at relatively shallow depth, boreholes can be drilled from the surface; for deep disposals, they can be drilled from an access shaft in a mine or from the surface. borosilicate glass (1) A supercooled liquid based on a random lattice of silica tetrahedra, modified with boron and other cations. (2) A glass composition used as an immobilization matrix for a radioactive waste. brine An aqueous solution containing a high concentration of dissolved salts. Any water in a repository in a salt formation, for example, would certainly be brine, and its ability to corrode waste forms would be expected to differ considerably from ordinary groundwater. buffer material Any substance, frequently a natural clay, placed around a waste container in a repository. Often, a primary purpose of such material is to serve as an additional barrier to prevent water from contacting the waste container and, by adsorption, to reduce the rate of radionuclide migration from the waste into the repository.

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Nuclear Wastes: Technologies for Separations and Transmutation burial ground An area of land that has been dedicated for the shallow disposal of short-lived low-and medium-level waste. Access by the public, as well as future use of the land, will probably be restricted. C canister (can) A closed or sealed container for nuclear fuel or other radioactive material, which isolates and contains the contents; it may rely on other containers (e.g., a cask) for shielding. cask A massive container to transport or store irradiated nuclear fuel and other radioactive materials. It provides chemical, nuclear, and radiological protection and dissipates heat generated by radioactive decay. cement A standard material used by the construction industry that has many uses in waste management because of its low cost and ease of handling. Properties of cement mixtures and of the final solid product can be modified considerably by the use of additives. The mixture of final product is referred to as "concrete" if it contains aggregate (usually small stones) or without aggregate, "a grout." cementation The process of incorporating wastes into a concrete matrix as a means of immobilization. ceramic materials Solid materials, usually containing SiO2 and metal oxides, that generally require fabrication at an elevated temperature (typically greater than 800° C) and often elevated pressure. Their microscopic structure is crystalline, which distinguishes them from amorphous glasses. They are very stable and have been considered as good candidates for solidifying high-level waste. cladding (material) An external layer of material (usually of Zircaloy, stainless steel, magnesium) directly surrounding nuclear fuel or other substance that seals and protects it from the environment and protects the environment from radioactive material produced during irradiation. For high temperature reactor (HTR) fuel particles, the multilayer protective claddings are known as coatings.

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Nuclear Wastes: Technologies for Separations and Transmutation clay Minerals that are essentially hydrous aluminium silicates, and occasionally hydrous magnesium silicates, with sodium, calcium, potassium and magnesium cations. Also denotes a natural material with plastic properties, which is essentially a composition of fine to very fine clay particles. Clays differ greatly mineralogically and chemically and consequently in their physical properties; especially because of their large surface areas, most of them have good sorption characteristics. cold testing Testing of method, process, apparatus, or instrumentation with the highly radioactive materials replaced by nonradioactive materials or materials that may contain radioactive tracers. competent authority An authority designated or otherwise recognized by a government for specific purposes in connection with radiation protection or nuclear safety. complexation A chemical term that refers to complex formation, in which a central metal ion is chemically bonded to atoms surrounding it. Depending on the circumstances, complexation can be used to remove radionuclides from solution, or by the formation of a neutral molecule, it may greatly enhance the mobility of a radionuclide in the environment. computer code See computer model. computer model A mathematical description of a facility or sequence of events that is evaluated via a computer. Computer models are usually indispensable for performing a safety analysis of a waste facility. In particular, models are used extensively to evaluate long-term events associated with a waste repository that cannot be tested directly and to predict the resulting radiation dose to man. conditioning of waste Those operations that transform waste into a form suitable for transport or storage or disposal. The operations may include converting the waste to another form, enclosing the waste in containers, and providing additional packaging. confinement (or isolation) of waste The segregation of radionuclides from the human environment and the prevention of their release into that environment in unacceptable quantities or concentrations.

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Nuclear Wastes: Technologies for Separations and Transmutation containment A term signifying either: (1) the confinement of radioactive material in such a way that it is prevented from being dispersed into the environment or is only released at a specified rate or (2) the device used to effect such confinement. contamination, radioactive The presence of a radioactive substance or substances in or on a material or in a place where they are undesirable or could be harmful. controlled area An area where workers might receive doses in excess of three-tenths of the occupational dose equivalent limits during the anticipated working period and where appropriate controls (such as restricted access, individual assessment of dose, and special health supervision) are accordingly applied. critical group For a given radiation source, the members of the public whose exposure is reasonably homogeneous and is typical of individuals receiving the highest effective dose equivalent or dose equivalent (whichever is relevant) from the source. crystalline rock (1) A rock consisting of minerals in an obviously crystalline state. (2) An inexact general term for igneous and metamorphic rocks as opposed to sedimentary ones (see granite). curie (Ci) The former unit of activity, equal to 3.7 × 1010 becquerels. D decommissioning The work required for the planned permanent retirement of a nuclear facility from active service. Different regulations will apply thereafter. decontamination The removal of radioactive contaminants with the objective of reducing the residual radioactivity level in or on materials, persons, or the environment. deep geological repository A repository constructed, usually in consolidated rock, at a depth of several hundred meters or more in a continental formation.

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Nuclear Wastes: Technologies for Separations and Transmutation de minimis Part of the maxim de minimis non jurat lex (the law does not concern itself with trifles), sometimes used with reference to sources of radiation that a competent authority may decide to exempt from defined regulatory requirements, because individual and collective effective dose equivalents received from them are both so low that they may be ignored. dispersion The summed effect of the processes of transport, diffusion, and mixing, which tend to distribute materials from wastes or effluents through an increasing volume of water or air. The ultimate effect appears as a dilution of the materials. disposal The emplacement of waste in a repository, or at a given location, without the intention of retrieval. Disposal also covers the approved direct discharge of wastes into the environment, with subsequent dispersion. disruptive event An event (e.g., faulting, meteorite impact) that disrupts a waste repository. distribution coefficient A quantitative measure of how a given chemical species partitions itself between two phases at equilibrium. In waste processing, this parameter is used to predict the effectiveness of separation methods such as solvent extraction, ion exchange, or gas scrubbing. In environmental studies, the quantity is sometimes used to predict how soils or backfill materials can retard radionuclide movement. documentation Written, recorded, or pictorial information describing, defining, specifying, reporting, or certifying activities, requirements, procedures, or results. domal (or dome) salt A local geologic formation of salt in which the salt thickness is greater vertically than laterally. The top of the formation may bear resemblance to a dome or to a mushroom. dose assessment An estimate of the radiation exposure of an individual or population group, usually by means of predictive modeling techniques, sometimes supplemented by the results of measurements. E emanation Radioactive gas formed by decay of a radioactive solid. The emanation may or may not be retained within the pore space of the solid phase.

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Nuclear Wastes: Technologies for Separations and Transmutation embedding A process of putting solid or liquid waste into a matrix to form a heterogeneous waste form. emplacement Placing the waste in its location for storage or disposal. emplacement density Amount of waste emplaced per unit area or volume of a storage or disposal site (e.g., canisters per hectare). engineered storage The storage of radioactive wastes, usually in suitably sealed containers, in any of a variety of structures especially designed to protect them and to help keep them from leaking to the biosphere by accident or sabotage. They may also provide for extracting heat of radioactive decay from the waste. entombment decommissioning Placement of radioactive wastes and structural materials within an entombment structure (often comprising a portion of the existing production structure) for permanent disposal. Only those materials with hazardous lifetimes, as determined by radiological assessments, less than or equal to the expected lifetime of the entombment structure are intended to be so placed. Other radioactive materials are removed from the site for disposal. environmental restoration project A group of activities initiated to access a Department of Energy facility or radioactive waste site that may require restoration to acceptable radiation levels. exclusion area A term used in some countries to designate a zone that may be established around a nuclear facility or other radiation source, to which access is permitted under controlled conditions and in which residence is normally prohibited. exposure Irradiation of persons or materials. Exposure of persons to ionizing radiation may be either: 1. external exposure (irradiation by sources outside the body) or 2. internal exposure (irradiation by sources inside the body). The term occupational exposure refers to exposure of a worker received or committed during a period of work.

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Nuclear Wastes: Technologies for Separations and Transmutation F far-field Rock formations outside of the repository, including the surrounding strata, at a distance from the waste disposal site such that, for modeling purposes, the site may be considered as a single entity, and the effects of individual waste packages are indistinguishable in the effects of the whole. fission product A nuclide produced either by fission or by the radioactive decay of nuclides formed by fission. fissure An extensive crack, break, or fracture in the rock. fixation (of radionuclides) The practice of immobilizing radionuclides so that they are not easily dispersed. The term often refers to the application of paint or a similar material to a contaminated surface in order to prevent the radionuclides from becoming airborne or transferred by casual contact. food chain (or web) A figure of speech for the dependence of organisms on others for food in a series, beginning with plants or scavenging organisms and ending with the largest carnivores. A web is a network or series of food-chains. formerly utilized site A site contaminated with radioactive wastes that was previously used for supporting nuclear activities of the Department of Energy's predecessor agencies, the Manhattan Engineering District (Manhattan Project) and the Atomic Energy Commission. fracture A crack, joint, fault, or other break in rock. In underground repositories, fractures are of concern as possible paths for water flow and radionuclide migration. front end of the fuel cycle Mining, milling, enrichment, and fabrication of nuclear fuel; sometimes irradiation in reactors is included. fuel reprocessing plant Plant where spent-fuel elements are dissolved, waste materials are removed, and reusable materials are segregated.

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Nuclear Wastes: Technologies for Separations and Transmutation G geological repository A final disposal facility located deep underground in a stable formation such as salt, granite, etc. Usually such a repository would be provided for long-lived radioactive waste such as alpha bearing or high-level waste or spent fuel. glass ceramic The product resulting after a glass has been transformed into a crystalline material by a controlled process such as heating. The product may retain the desirable properties of both a glass and a ceramic (see ceramic materials). granite Broadly applied, any holocrystalline quartz-bearing plutonic rock. Granite formations are being considered as possible hosts for repositories deep underground for high-level waste. gray (Gy) The SI unit of absorbed dose equal, for ionizing radiation, to 1 joule of radiant energy absorbed in 1 kg of the material of interest (1 Gy = 1 J•kg-1). H 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). By analogy, in biology this term is used in connection with the clearance of a substance from a tissue, an organ, or the whole body (when the kinetics of such a phenomenon roughly follow an exponential dependence) to mean the time for one-half of this substance to be eliminated (biological half-life). The time necessary for a radioactive material in a living organism to be reduced to one-half of its initial value by a combination of biological elimination and radioactive decay is termed effective half-life. high-level waste (HLW) (1) The highly radioactive liquid, containing mainly fission products, as well as some actinides, which is separated during chemical reprocessing of irradiated fuel (aqueous) waste from the first solvent extraction cycle and those waste streams combined with it. (2) Spent reactor fuel, if it is declared a waste. (3) Any other waste with a radioactivity level comparable to (1) or (2). host rock (or host medium) A geological formation in which a repository is located. hulls and spacers Radioactive waste, comprising cladding hulls and assembly grid spacers, generated during reprocessing when spent-fuel assemblies are disassembled and the fuel is dissolved.

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Nuclear Wastes: Technologies for Separations and Transmutation humid sites A near-surface repository located in an area at which annual precipitation exceeds water loss by evaporation, hence there is a significant downward flux of moisture through the soil that could transport radionuclides. Uptake of radionuclides by plant roots may also be significant in a humid site. hydrogeology The study of the geological factors related to the Earth's water. hydrology The study of all waters in and on the Earth. It includes underground water, surface water, and rainfall and embraces the concept of the hydrological cycle. I ingest Take into the body by way of the digestive tract. institutional control Control by an authority or institution designated under the laws of a country or state. This control may be active (monitoring, surveillance, remedial work) or passive (land-use control). interim storage (storage) Storage of radioactive materials such that: (1) isolation, monitoring, environmental protection, and human control are provided, and (2) subsequent action involving treatment, transport, and disposal or reprocessing is expected. intermediate-level waste; medium-level waste Waste of a lower activity level and heat output than high-level waste, but which still requires shielding during handling and transportation. The term is used generally to refer to all wastes not defined as either high-level or low-level (see alpha-bearing waste and long-lived waste for other possible limitations). International Commission on Radiological Protection (ICRP) limit A primary dose equivalent limit recommended by the ICRP. Dosimetric models may be used to derive the annual limit on intake and derived air concentration. intrusive rock A body of igneous rock that has forced itself into an existing rock formation. ion exchange A usually reversible exchange of one ion with another, either in a liquid, on a solid surface, or within a crystalline lattice.

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Nuclear Wastes: Technologies for Separations and Transmutation multibarrier A system using two or more independent barriers to isolate the waste from the human environment. These can include the waste form, the container (canister), other engineered barriers, and the emplacement medium and its environment (see barrier). N natural analogues Radioactive minerals or mineral deposits, or even man-made objects, whose migration history or corrosions over very long times can be determined and used to forecast the possible behavior of chemically similar waste radionuclides. O off-gas The gas streams that arise from a process. Typical processes in radioactive waste management facilities, such as dissolution, evaporation, incineration, vitrification, bituminization, and cementation, will generate process off-gases that contain water vapor, acid vapors, aerosols, radioactive constituents, and gaseous chemical constituents. off-gas treatment The removal of radioactive components or chemical pollutants from gases prior to their release under controlled conditions into the atmosphere. operating records A set of documents, such as instrument charts, certificates, log books, computer printouts, and magnetic tapes, kept at each nuclear facility and organized in such a way that they provide a complete and objective history of the operation of the facility. operational period The period during which a nuclear facility is being used for its intended purpose after which it is shut down and decommissioned. operations, waste management Broad classification of waste management activities in terms of their basic function (e.g., waste storage, treatment, transportation, or disposal). operator Any person, government, or other entity that conducts or carries on operations at a nuclear facility. overpack Secondary (or additional) external containment for packaged radioactive waste.

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Nuclear Wastes: Technologies for Separations and Transmutation P pathways model A mathematical description, usually in the form of a computer algorithm, that determines the relative significance of possible radionuclide transport vectors, (e.g., air, groundwater, surface water, intrusive roots, animals, etc.). percolating groundwater Groundwater that seeps via saturated flow conditions through soil or rock strata (see saturated zone). performance assessment Analysis to predict the performance of the system or its subsystem, followed by comparison of the results of such analysis with appropriate standards or criteria. When the system under consideration is the overall waste disposal system and the performance measure is radiological impact or some other global measure of impact safety, performance assessment becomes the same as safety assessment. permeability (of rock) The capacity of a porous or previous rock to transmit a fluid (see darcy). plasticity The property of a material (e.g., rock salt) that enables it to undergo permanent deformation without appreciable volume change or elastic rebound and without rupture. porosity The ratio of the aggregate volume of interstices in a rock or soil to its total volume. porous media Material that contains pores or cracks through which water or gas can flow. Often the term is applied to the geological formations around a waste repository and could denote an undesirable situation. postsealing period The period after a waste repository has been shut down and sealed. preliminary site selection The second stage of siting a waste repository, during which a manageable number of potentially suitable sites is examined, using existing information or information from limited explorations, to determine whether one or more regions contain sites suitable for additional site confirmation studies.

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Nuclear Wastes: Technologies for Separations and Transmutation pretreatment of waste Any step carried out prior to operations that have been defined as treatment, conditioning, offsite transport, or disposal. Pretreatment techniques and practices include: —collection and segregation, —size reduction, and —chemical adjustment. primary waste As-generated form and quantity of a waste. Q quality assurance Planned and systematic actions aimed at providing adequate confidence that an item of a facility will perform satisfactorily in service. quality control Actions that provide a means to control and measure the characteristics of an item, process, facility, or person in accordance with quality assurance requirements. R rad A unit of absorbed dose of ionizing radiation equal to one-hundredth of a gray (1 cGy). radiation damage Deleterious changes in the physical or chemical properties of a material resulting from exposure to ionizing radiation. This term does not apply to biological systems. radiation protection or radiological protection (1) All measures associated with the limitation of the harmful effects of ionizing radiation on people, such as limitation of external exposure to such radiation, limitation of bodily incorporation of radionuclides, and the prophylactic limitation of bodily injury resulting from either of these. (2) All measures designed to limit radiation-induced chemical and physical damage in materials. radioactive material A material of which one or more constituents exhibit radioactivity. radioactive source term An expression used to denote information about the actual or potential release of radioactive material from a given source, which may include a specification of the composition, the amount, the rate, and the mode of the release.

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Nuclear Wastes: Technologies for Separations and Transmutation radioactive waste management All activities, administrative and operational, that are involved in the handling, treatment, conditioning, transportation, storage, and disposal of waste. radiolysis Chemical decomposition caused by ionizing radiation. radiolytic effect An effect caused by radiation-induced degradation of chemical compounds. radionuclide migration The movement of radionuclides through various media due to fluid flow or by diffusion. radionuclide transport The action of a particular vector that results in movement of radionuclides in the environment (e.g., radionuclide transport by ground water). This specific term does not refer to the intentional transportation of radioactive materials by man (e.g., transportation of nuclear wastes in transport casks, etc.). reactor waste Waste arising from the routine operation of a nuclear reactor. reinserted fuel Irradiated reactor fuel that is discharged in one cycle and inserted in the same reactor during a subsequent refueling. In a few cases, fuel discharged from one reactor has been used to fuel a different reactor. rem A unit of dose equivalent to one-hundredth of a sievert (Sv). remedial action Corrective measures imposed at a near-surface repository to prevent a previously unforeseen circumstance from causing unacceptable releases or radionuclides. retardation A reduction in the velocity of radionuclide movement through the environment due to reversible adsorption on an immobile matrix. Soils often retard movement of waterborne nuclides, and the degree of retardation can be quantified. retrievability The capability to remove waste from where it has been stored.

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Nuclear Wastes: Technologies for Separations and Transmutation risk With respect to radiation protection, the probability that a given individual will incur any given deleterious stochastic effect as a result of radiation exposure. rock To the geologist, any mass of mineral matter, whether consolidated or not, which forms part of the Earth's crust. Rocks may consist of only one mineral species, in which case they are called monomineralic, but they more often consist of an aggregate of mineral species. routine discharges Planned and controlled release of radionuclides to the environment. Such releases will meet all restrictions imposed by appropriate regulatory authorities. S safety Protection of all persons from undue radiological hazard. safety analysis The analysis and calculation of the hazards (risks) associated with the implementation of a proposed activity. safety assessment A comparison of the results of safety analyses with acceptability criteria, its evaluation, and the resultant judgments made on the acceptability of the system assessed. salt A geological formation containing mainly halite (NaCl) with smaller inclusions of other minerals, usually the chloride or sulfate derivatives of the alkaki or alkaline earth elements. Salt formations occur as bedded or domal deposits. These dry, stable formations are considered to be good hosts for deep underground waste repositories. salt dome A dome-like salt structure resulting from the upward movement of a salt mine. sea-bed disposal Placement of waste packages in deep ocean sediments. sea dumping (disposal) The practice of periodically dumping shiploads of drummed, solidified waste at specified locations in the ocean.

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Nuclear Wastes: Technologies for Separations and Transmutation separations (partitioning) Separations in this report implies separation of a process stream into two or more components for waste management purposes; rather complete separations are usually envisaged. shallow ground disposal  Disposal of radioactive waste, with or without engineered barriers, above or below the ground surface, where the final protective covering is a few meters thick. Some member nations of the International Atomic Energy Agency consider shallow ground disposal to be a mode of storage rather than a mode of disposal. shipping cask (transport cask) A heavy protective container that shields and contains radioactive materials, dissipates heat, and prevents criticality during transport and handling. short-lived nuclide For waste management purposes, a radioactive isotope with a half-life shorter than about 30 years (e.g., 137Cs, 90Sr, 85Kr, 3H). short-lived waste Waste that will decay to a level that is considered to be insignificant from a radiological viewpoint, in a time period during which administrative controls can be expected to last. Such waste can be determined by radiological assessment of the storage or disposal system chosen (see long-lived waste). shutdown Actions taken at a repository after disposal operations have ceased, in order to prepare the facility for abandonment. This includes decommissioning of ancillary facilities and sealing the repository. Shutdown may occur immediately or after a period of surveillance following the final emplacement of waste. sievert (Sv) The unit of dose equivalent (1 Sv = 100 rem). site The area containing a nuclear installation (e.g., waste repository) that is defined by a boundary and that is under effective control of the implementing organization.

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Nuclear Wastes: Technologies for Separations and Transmutation site confirmation Actions involved in establishing the suitability of an intended repository site. Extensive onsite investigations will be made to assure its capability for achieving all performance criteria, especially radiation protection requirements. The type of waste to be emplaced and the proposed repository design are of importance in this assessment. siting The process of selecting a suitable site for an installation, including appropriate assessment and definition of the related design bases. solidified waste, radioactive Liquid waste or otherwise mobile waste materials (ion exchange resins, etc.) that have been immobilized by incorporation (either physical or chemical) into a solid matrix by some specific treatment. solid waste, radioactive Untreated waste that possesses physical properties commonly associated with the solid state. Animal carcasses are usually considered to be in this category. sorption A broad term referring to reactions taking place within pores or on the surfaces of a solid. Its use avoids the problem of technical distinction between absorption and adsorption reactions. Absorption is generally used to refer to reactions taking place largely within the pores of solids, in which case the capacity of the solid to absorb is proportional to its volume. Adsorption refers to reactions taking place on solid surfaces, so that the capacity of a solid is proportional to its effective surface area. An example of the latter process is ion exchange, whereby ions occupying charged sites on the surface of the solid are displaced by ions from solution. speciation A term that refers to the chemical form(s) and properties of a radionuclide under a particular set of environmental conditions (pH, eH, ligands present, etc.). Speciation study is valuable because the environmental behavior of a nuclide is largely determined by its chemical form. spent fuel Irradiated fuel units not intended for further reactor service. subsequent control Any long-term safety measures, such as land-use restrictions, imposed to assist in achieving repository safety after shut-down and sealing has been completed and after the operating license for the repository has been cancelled.

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Nuclear Wastes: Technologies for Separations and Transmutation subsidence Sinking or caving in of the ground surface. This results from the inability of the upper layers of the Earth's crust to support their own mass, or that mass with additional surface load, over an area containing poorly compacted material or voids. Such voids can be man-made, as in the case of mines. surface water Water that fails to penetrate into the subsoil and flows along the surface of the ground, eventually entering a lake, a river, or the sea. surveillance All planned activities performed to ensure that conditions at a nuclear installation remain within the prescribed limits. For a waste repository, surveillance continues well past the periods of operation and closure. synroc The name given to a group of specially formulated zirconium-based ceramics that were originally developed by Australian scientists for immobilizing high-level waste. T tailored ceramic A ceramic material whose composition has been specially formulated to optimize the incorporation of a particular set of radionuclides into the crystalline matrix. The composition of the waste form is thus tailored to fit a particular waste stream (See ceramic materials; synroc). thermal gradient A quantitatively measurable change in sensible heat as a function of distance. In a deep geological repository, the thermal gradient produced by radioactive decay heat can potentially alter the host rock and water-flow paths. thermal loading The quality of heat-generating materials placed in a given area or volume; units are power per area or per volume, respectively. topography (1) The configuration of (a portion of) the Earth's surface, including its relief and relative positions of its natural and man-made features. (2) The practice of graphical representation of the same. transmissivity, hydraulic Rate at which water is transmitted through a unit width of aquifer under a unit hydraulic gradient. It is expressed as the product of the hydraulic conductivity and the thickness of the saturated portion of the aquifer.

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Nuclear Wastes: Technologies for Separations and Transmutation transmutation Transmutation in this report generally implies the conversion of long-lived radioactive species either to short-lived or to stable species by means of nuclear processes. transuranic (TRU) waste Waste containing quantities of nuclides having atomic numbers above 92 in excess of agreed limits. The limits are established by national regulatory bodies. (See alpha-bearing waste.) treatment of waste Operations intended to benefit safety or economy by changing the characteristics of the waste. Three basic treatment concepts are —volume reduction, —removal of radionuclides from the waste, and —change of composition (see conditioning of waste). tuff One of a series of pyroclastic rocks composed of consolidated ash from fragmental volcanic material blown into the atmosphere by volcanic activity. U underground disposal Disposal of waste at an appropriate depth below the ground surface. uptake Amount of radioactive material absorbed into the extra cellular fluids. It is also used to denote the process. V validation A process carried out by comparison of model predictions with independent field observations and experimental measurements. A model cannot be considered validated until sufficient testing has been performed to ensure an acceptable level of predictive accuracy. (The acceptable level of accuracy is judgmental and will vary depending on the specific problem or question to be addressed by the model.) vault An above-or below-ground reinforced concrete structure that contains an array of storage cavities, each of which could hold one or more spent fuel units or waste packages. Shielding is provided by the exterior of the structure. Heat removal is principally by forced or natural movement of gases over the exterior of the cavities. Heat rejection to the atmosphere is either direct or via a secondary cooling system.

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Nuclear Wastes: Technologies for Separations and Transmutation verification A mathematical model, or the corresponding computer code, is verified when it is shown that the code behaves as intended, that is, that it is a proper mathematical representation of the conceptual model and that the equations are correctly encoded and solved. vermiculite A group of micaceous clay minerals closely related to chlorite and montmorillonite and having the general formula (Mg,Fe,Al) 3(Al,Si)4010(OH)2·4H20. Because of its adsorptive properties, vermiculite is often used in packaging small quantities of liquid waste. vitrification Any process of converting materials into a glass or glass-like form. volume reduction A treatment that decreases the physical volume of a waste. Volume reduction is used to facilitate subsequent handling, storage, transportation, or disposal of the waste. Typical treatments are mechanical compaction, incineration, or evaporation. Volume reduction results in a corresponding increase in radionuclide concentration. volume reduction factor The ratio of the volumes of radioactive waste prior to and following treatment. In concentration processes, the factor is greater than one; in dilution systems, the factor is less than one. W waste arisings Radioactive wastes generated by any stage in the nuclear fuel cycle and by any other activity dealing with radioactive materials. waste disposal See disposal. waste form The physical and chemical form of the waste materials (e.g., liquid, in concrete, in glass) without any packaging. waste glass The vitreous product that results from incorporating waste into a glass matrix. waste package The waste form and any container(s) as prepared for handling, transport, treatment, conditioning, storage, and disposal of waste.

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