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Appendix D Glossary Advanced Joule-Heated Melter. A Joule-Heated Melter that incorporates design improvements to increase throughputs and waste loadings. Bitumen. A viscous hydrocarbon and a major component of asphalt. Cement. An inorganic material that sets and hardens as a result of hydra- tion reactions. Ceramicretes. Phosphate-bonded ceramics, also known as chemically bonded phosphate ceramics. Chemical incorporation. The process by which radioactive and hazardous constituents are bound into a material at atomic scale. Cold Crucible Induction Melter. Water-cooled tubes that are arranged to form a crucible that can be heated by induction. Cold Pressing and Sintering. A process for forming crystalline ceramics at room temperature involving the application of compressive stress. Colloid. A sub-micron particle suspended in a liquid. Congruent dissolution. Release of species in stoichiometric proportion to their presence in a waste form material. Crystalline ceramics. Inorganic, non-metallic solids that contain one or more crystalline phases. Diffusion-controlled release. Release of constituents by diffusion through the waste form material, including through an encapsulant and/or sur- face layers containing reaction products, if present. Disposal environment. The time-dependent physical and chemical condi- tions in a facility designed for the disposal of radioactive waste. 285

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286 APPENDIX D Disposal facility. Physical infrastructure of the facility, including tunnels or surface excavations, the surrounding host rock, and engineered barriers, including the waste form if present. Disposal system performance. The ability of a disposal system to sequester radioactive and hazardous constituents in the near field. Disposal system. Refers to both physical infrastructure and how the natu- ral and engineered barriers in that infrastructure function to sequester radioactive and hazardous constituents. Dissolution. A process (or processes) by which mass transport from a solid waste form to a liquid takes place as the result of mechanistic reactions in which chemical bonds are broken and constituents are released from a material and become solvated in a test solution. Dissolution rate. The rate of mass removal per unit time normalized to surface area of the material. Durability. The resistance of a waste form material to chemical and physi- cal alteration and the associated release of contained radioactive and hazardous constituents. Encapsulation. The process by which radioactive and hazardous constitu- ents are physically surrounded and isolated by the material. Experiment. The application of tests to a waste form material to gain a better understanding of its degradation behavior and the release of radioactive constituents. Far-field environment. The region beyond the near field, including the biosphere. Fluidized bed. A bed of granular material that exhibits fluid-like properties by passing a liquid or gas through it. Fluidized Bed Steam Reforming. A process for thermally treating and im- mobilizing waste through the use of fluidized bed technologies. Geologic repositories. Facilities constructed in geologic formations located hundreds of meters below Earth’s surface that are designed for the disposal of higher-hazard wastes such as spent nuclear fuel, high-level radioactive waste, and transuranic waste. Geopolymers. Ceramic-like, inorganic polymers made from aluminosilicates cross-linked with alkali metal ions. Glass. An amorphous solid material produced by cooling a material from a molten to a solid state without crystallization. Glass-ceramic materials. Materials that contain both crystalline and glass phases.

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287 APPENDIX D Hazardous waste. Waste that is toxic or otherwise hazardous because of its chemical properties. Waste can be designated as hazardous in any of three ways: (1) It contains one or more of more than 700 materials listed as hazardous; (2) it exhibits one or more hazardous characteris- tics, which include ignitability, corrosivity, chemical reactivity, or toxic- ity; or (3) it arises from treating waste already designated as hazardous. High-level radioactive waste. Waste material resulting from the reprocess- ing of spent nuclear fuel, including liquid waste produced directly in reprocessing and any solid material derived from such liquid waste that contains fission products in sufficient concentrations; and other highly radioactive material that the Nuclear Regulatory Commission, consistent with existing law, determines by rule to require permanent isolation. Hot Isostatic Pressing. A process for producing waste forms through the simultaneous application of heat and isostatic pressure. Hot Uniaxial Pressing. A process for forming crystalline ceramics at ele- vated temperature that involves the application of uniaxial compressive stress. Hydroceramics. Concrete-type materials that are made by curing a mixture of inorganic waste, calcined clay, vermiculite, sodium sulfide (Na2S), and sodium hydroxide (NaOH) with water under hydrothermal conditions. Immobilization. The solidification, embedding, or encapsulation of radioac- tive and chemically hazardous waste to create a waste form. Incongruent dissolution. Preferential release of some species from a waste form material relative to other species. In-Container Vitrification. A batch process by which contaminated soil, liquid waste mixed with soil, and glass formers are vitrified in situ in a refractory-lined steel vessel. Joule-Heated Melter. A refractory-lined container with nickel-chromium alloy electrodes that is used for vitrifying waste. Joule heating. Heating obtained by passing an electrical current through a resistively conducting material. Leaching. The loss of radioactive or chemical constituents from a waste form by diffusion or dissolution. Low-level radioactive waste. Radioactive material that is not high-level radioactive waste, spent nuclear fuel, transuranic waste, or 11(e)(2) byproduct material (mill tailings) that the Nuclear Regulatory Com- mission, consistent with existing law, classifies as low-level radioactive waste. Mesoporous materials. Materials that have regularly arranged pores rang- ing from 2-50 nanometers in diameter.

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288 APPENDIX D Metal-organic frameworks. A relatively new class of porous materials that consist of metal atoms (ions) linked together by multifunctional organic ligands. Mixed low-level waste. Waste that contains both low-level waste and haz- ardous waste components. Mixed transuranic. Waste that meets the definitions of both transuranic and hazardous wastes. Near-field environment. The engineered barriers in a disposal system (e.g., waste canisters) as well as the host geologic media in contact with or near these barriers whose properties have been affected by the presence of the repository. Orphan waste stream. A waste stream that has no clear-cut disposition pathway. Performance. The ability of a waste form (waste form performance) or a disposal system containing the waste form (disposal system perfor- mance) to sequester radioactive and chemical constituents. Performance assessment. Methodology for estimating the future behavior of a disposal system involving the modeling of processes and events that might lead to releases and exposures. Plasma heating. An electrical heating process in which plasma is created by passing a gas through an electrical arc. Portland cement. A common cement type that consists of calcium silicates, other aluminum and iron containing phases, and additives such as gypsum to control set time. Qualification. See Waste Form Qualification. Reaction affinity-controlled release. Release of constituents from a material that is controlled by the difference in Gibbs free energy between the thermodynamically stable state and the metastable reactants. Release mechanisms. The process that controls the rate of mass transport out of a waste form material during dissolution. Shallow-land disposal facilities. Facilities excavated into sediments located within 10 meters or so of Earth’s surface that are designed for the disposal of lower-hazard wastes such as low-level radioactive waste. Solubility. The thermodynamically limited saturation state or equilibrium concentration limit of species in solution. Solubility-controlled release. Release of constituents from a material that is bounded by the use of the maximum saturation of a constituent spe- cies from the waste form in the given leachant (solution) environment. Spent nuclear fuel. Fuel that has been withdrawn from a nuclear reactor following irradiation, the constituent elements of which have not been separated by reprocessing. Standard test protocols. A standardized procedure for testing a specific type of material to generate a clearly defined test response.

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289 APPENDIX D Transuranic (TRU) waste. Waste containing more than 100 nanocuries of alpha-emitting transuranic isotopes, with half-lives greater than 20 years, per gram of waste, except for: (1) high-level radioactive wastes; (2) wastes that the Department [of Energy] has determined, with the concurrence of the [EPA] Administrator, do not need the degree of isolation required by this part; or (3) wastes that the [Nuclear Regula- tory] Commission has approved for disposal on a case-by-case basis in accordance with Title 10, Part 61 of the Code of Federal Regulations. Waste acceptance criteria. Specific requirements that waste must meet to be acceptable for disposal in a given facility. Waste form. Radioactive waste material and any encapsulating or stabiliz- ing matrix in which it is incorporated. Waste form performance. The ability of a waste form to sequester and re- tain its radioactive and chemically hazardous constituents. Waste form qualification. Demonstration that a waste form material will have acceptable performance in a specific disposal facility and can be fabricated with acceptable performance control. Waste form test protocols. Standard tests developed by organizations such as the American Nuclear Society, American Society of Testing and Materials, International Atomic Energy Agency, and the International Organization for Standardization. Waste incidental to reprocessing. Waste resulting from reprocessing spent nuclear fuel that is determined to be incidental to reprocessing and is not high-level waste. Waste loading. The quantity of waste, usually expressed as a weight per- cent, that can be incorporated into a waste form.

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