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Appendix D
Glossary
Actinide: Element with atomic number 90 (thorium) or greater.
Anhydrite: Anhydrous calcium sulfate.
Backfill: Earth or other material used to replace material removed during construction or mining. Back-fill in excavations may or may not be the material originally removed. In the WIPP, magnesium oxide is the engineered backfill that replaces the mined salt and is placed in the free spaces surrounding the waste containers. Magnesium oxide is intended to chemically stabilize the radionuclides and minimize their solubility.
Borehole: Deep, circular hole of small diameter, such as an oil well or a water well.
Borehole Plugs: Engineered plugs to block the flow of liquid in either direction and to curtail the potential for movement of contaminants to the human environment. Several unplugged boreholes, presently being used to collect information for the WIPP, exist within the WIPP Land Withdrawal Area.
Brine: Water with dissolved salts at levels higher than seawater. Generally, brines are considered to have a total dissolved solids content of more than 100,000 milligrams per liter.
Brine Reservoir: Groundwater containing high levels of dissolved solids (brine) that may occur beneath the WIPP site either as discrete pockets (brine pockets) or as a saturated continuum. The committee uses the term “brine reservoir” to refer to both of these occurrences. At present, there is a great deal of uncertainty as to the location and form (i.e., discrete pocket or saturated continuum) of brine reservoirs beneath the WIPP repository.
Brucite: Magnesium dihydroxide, Mg(OH)2.
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Casing: Heavy metal pipe lowered into a borehole during or after drilling and cemented into place. It prevents the sides of the hole from caving and, prevents loss of drilling mud or other fluids into the hole.
Castile Formation: Oldest of the late Permian stratigraphic sequence of rocks, consisting of alternating layers of anhydrite and thin layers of limestone, with several thick layers of halite. See Figure 1.3.
Culebra Dolomite: Second-oldest member of the Rustler Formation ranging from approximately 7-8 meters thick at the WIPP site. The Culebra consists of dolomite with some clay minerals. Because it is a relatively transmissive unit, the Culebra is important to the groundwater flow model for the WIPP site.
Curie: Measure of the quantity of radioactive material in a sample, equal to 3.7 × 1010 disintegrations per second.
Cuttings: Rock chips cut by a bit in the process of well drilling and removed from the hole in the drilling mud in rotary drilling or by the bailer in cable-tool drilling. Well cuttings collected at closely spaced intervals provide a record of the strata penetrated.
Delaware Basin: Sedimentary basin in which the WIPP site is located. The Delaware Basin formed in the Permian sea and was gradually filled with thick, extensive layers of sediments and evaporite deposits.
Disturbed Rock Zone (DRZ): Zone around an excavation, in the host rock salt, where the stress field has been modified sufficiently to cause the formation of microfractures in the rock salt. Compared to the intact rock salt, the DRZ will have increased porosity because of the microfracturing, increased permeability as a result of interconnection of the microfractures, and decreased load-bearing capacity or strength.
Dolomite: Sedimentary rock consisting mostly of the mineral dolomite, calcium magnesium carbonate.
Dose: Energy imparted to matter in a volume element by ionizing radiation, divided by the mass of irradiated material in that volume element. The International System (IS) derived unit of absorbed dose is the gray (Gy); 1 Gy = 100 rad = 1 (Joule) per kilogram.
Drillbit or drill: A tool that cuts with its end by revolving or by a succession of blows.
Engineered Barriers: Man-made waste-isolating features that complement and strengthen natural wasteisolating barriers. These barriers are shaft seals, panel closures, borehole plugs, and backfill.
G-Value: Radiolytic yield unit. It corresponds to the number of molecules produced per 100 electronvolts of energy absorbed in the medium interacting with the ionizing radiation.
Half-Life: Time required for half of the atoms of a radioactive substance present at the beginning to disintegrate.
Hydraulic Fracture: Fracture of a rock in an oil or gas reservoir by pumping in water (or other fluid) and sand under high pressure. The purpose is to produce artificial openings in the rock to increase
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permeability. The pressure opens cracks and bedding planes, and sand introduced into these serves to keep them open when the pressure is reduced.
Hydrogen Getter: Material capable of capturing hydrogen gas.
Hydromagnesite: Mixed compound of magnesium carbonate and hydroxide, 4MgCO3•Mg(OH)2•4H2O.
Injection Well: Well in an oil or gas field through which water, gas, steam, or chemicals are pumped into a reservoir or formation for pressure maintenance or secondary recovery, or for storage or disposal of the injected fluid.
Karst: Type of topography that is formed of limestone, gypsum, and other rocks by dissolution and is characterized by sinkholes, caves, and underground drainage.
Lithostatic Pressure: Pressure exerted by a column of overlying rock at a point in the earth's crust.
Magnesite: Magnesium carbonate, MgCO3.
Marker Bed: Horizontally extensive formation that can be identified readily at different locations. For instance, the nonhalite interbed in the Salado, is numbered from the top of the Salado to the bottom and used to keep the repository at the same level within the Salado.
Panel Closures: Panel closures will limit the interaction of brine and gases among waste disposal panels. These closures will consist of a rigid concrete barrier and an isolation wall made of concrete construction block with an isolation zone between them.
Parameter: Algebraic symbol representative of a well-defined physical quantity with a numerical value. An adjustable parameter is envisioned to assume any value within its range (between the maximum and minimum numerical bounds). Any particular choice of a value renders a parameter a numerical constant.
Performance Assessment: Risk-based assessment of the safety performance of a nuclear waste facility.
Permeability: Capacity of a material to transmit fluids. A measure of the relative ease with which a porous medium can transmit a liquid under a potential gradient. Permeability depends on the size, shape, and degree of interconnectedness of pores and is generally measured in square meters. It is a property of the medium alone and is independent of the nature of the liquid.
pH: Measure of the acidity of a solution phase; negative logarithm of the hydrogen ion concentration.
Post-closure Period: Period beginning when the shafts of the disposal system are backfilled and sealed and ending 100 years later.
Pre-closure Period: Period between the beginning of operation and the time at which the shafts of the disposal system are backfilled and sealed. The operation period has been set as 35 years.
Radiogenic: Said of a product of a radioactive process.
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Radiolysis: Decomposition brought about by ionizing radiation.
Radionuclide: Radioactive atom characterized by its mass and atomic number.
Retardation: Parameter that describes the ratio of the net apparent velocity of the concentration of a particular chemical species to the velocity of a non-reactive species. It is proportional to the slope of a sorption isotherm; thus, if the isotherm is nonlinear, the retardation factor is not constant and depends on solute concentration.
Rustler Formation: Second-youngest Permian Ochoan Formation, overlying the Salado, and consisting of five sequences (members) of thin-bedded strata. The lowermost beds consist of mudstone and sandstone interbedded with evaporites. The upper part of the formation consists of alternating evaporite and dolomite beds. The Culebra Dolomite member is the second member from the bottom of the formation. The total thickness of the Rustler Formation near the WIPP site is approximately 100 meters.
Salado Formation: Second-oldest Ochoan geologic formation consisting of a 230 million-year-old deposit of rock salt (halite) in near-horizontal beds; its total thickness lies between 200 and 400 meters. Very thin layers of clay, anhydrite, and potash minerals are interbedded with the halite beds. Lying at a depth of approximately 660 meters (2,160 feet) at the WIPP site, the Salado hosts the WIPP repository.
Salt Creep: Slow movement of salt over time as shear stresses cause movement within or between individual crystals. Mined salt “heals” as the creep restores its integrity.
Shaft: Vertical or inclined excavation through which a mine is worked.
Shaft Seals: Engineered barrier designed to limit fluid flow through the repository shafts. Once the repository has been filled, the entire column of each shaft will be backfilled with materials that prevent vertical flow of fluid. Materials include concrete, clay, asphalt, compacted salt, grout, and earthen fill.
Spallings: Chipping, fracturing, or fragmentation, and the upward and outward heaving, of rock caused by the interaction of a shock (compressional) wave at a free surface. Spallings in the WIPP can be caused by oil extraction and other human intrusion activities.
Transuranic (TRU) Waste: Radioactive waste consisting of radionuclides with atomic numbers greater than 92 in excess of agreed limits. A more precise definition, in DOE Order 5820.2A, EPA regulation 40 CFR 191, and the Land Withdrawal Act, is waste that is not high-level waste but is “contaminated with alpha-emitting radionuclides of atomic number greater than 92 and half-lives greater than 20 years in concentrations greater than 100 nanocuries per gram.” The regulatory definition excludes actinide elements with atomic numbers between 90 and 92 (most significantly, thorium and uranium isotopes), which is in agreement with the literal meaning of “transuranic.” However, common usage of the term “transuranic waste” is often understood to include all actinides.
TRUPACT-II: Transuranic Package Transporter, Model II. Container for road transport of contact-handled transuranic waste (see Figure 3.2). The TRUPACT-II container has been certified by the U.S. Nuclear Regulatory Commission.
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Waste Characterization: Process of identifying and classifying the chemical, physical, and radiological constituents of each drum of waste.
Water Flooding: Technique used in the secondary recovery of petroleum and gas whereby water is injected into a petroleum or gas reservoir so that the pressure of the water expels the petroleum or gas.
Wattage Limit: In this report, the allowed maximum amount of heat generated by radioactive decay during transportation of TRU waste. The wattage limit for TRUPACT-II containers is 40 watts (40 joules per second).
