Term - Definition

Accessible Environment - "(1) The atmosphere, (2) land surfaces, (3) surface waters, (4) oceans, and (5) all of the lithosphere that is beyond the controlled area" (40 CFR Part 191.12).

Actinide - An element in the actinide series beginning with element 89 and continuing through 103. All the transuranic nuclides considered in this document are actinides.

Activity - A measure of the rate at which a material emits nuclear radiation, usually given in terms of the number of nuclear disintegrations occurring in a given length of time. The unit of activity used in this document is the curie (Ci).

Alpha Radiation - A positively charged particle emitted in the radioactive decay of certain nuclides. Made up of two protons and two neutrons bound together, it is identical to the nucleus of a helium atom. It is the least penetrating of the three common types of radiation alpha, beta, and gamma radiation.

Anhydrite - A mineral consisting of anhydrous calcium sulfate. It is gypsum without water but is denser, harder, and less soluble.

Anoxic Corrosion - Corrosion of metals by chemical decomposition in the absence oxygen.

Beta Radiation - A negatively charged particle emitted in the radioactive decay of certain nuclides; a free electron.

Brine - Saline water containing calcium (Ca), sodium (Na), potassium (K), chlorides (Cl), and minor amounts of other elements located in deep sedimentary basins.

Canister - As used in this document, a container, usually cylindrical, for remotely handled TRU waste. The waste will remain in this canister during and after burial. A canister affords physical containment but not shielding; during shipment, shielding is provided by a cask.

Cask - A massive shipping container providing shielding for highly radioactive materials and holding one or more canisters.

Certification - Any action taken by the Administrator of the U.S. Environmental Protection Agency under Section 8(d) of the WIPP Land Withdrawal Act.

Complementary Cumulative Distribution Function (CCDF) - A graphical display of the probability of an occurrence (the ordinate) and a quantitative measure associated with that occurrence (the abscissa). For the WIPP, a CCDF shows the probability of occurrence of specific scenarios and the cumulative radionuclide releases estimated to result from those scenarios. Radionuclide releases are normalized as stipulated in 40 CFR Part 191, Appendix A, and the CCDF is compared to the quantitative release limits specified in 40 CFR Part 191.13(a).

Consultation and Cooperation Agreement - An agreement that affirms the intent of the Secretary of Energy to consult and cooperate with the State of New Mexico with respect to state public health and safety concerns. The term "Agreement" means the July 1, 1981, Agreement for Consultation and Cooperation, as amended by the November 30, 1984, "First Modification," the August 4, 1987, "Second Modification," and the March 22, 1988, modification to the Working Agreement.

Contact-Handled (CH) Waste - Transuranic waste that has a measured radiation dose rate at the container surface of 200 millirems per hour or less and can be safely handled without special equipment when placed in containers.

Containment - The retention of radioactivity within prescribed boundaries, such as within a waste package. In this document, containment usually refers to retention within a system to exclude its release to the biosphere in unacceptable quantities or concentrations.

Culebra Dolomite - The lower of two layers of dolomite within the Rustler Formation that are locally water bearing.

Curie (Ci) - A quantitative measure of radioactivity equal to 3.7 X 10(to the 10th power) disintegrations per second.

Cuttings - During exploratory drilling, waste contained in the cylindrical volume created by the cutting action of the drill bit through the waste. This volume is approximated by the cross-sectional area of the drill bit multiplied by the repository thickness.

Daughter Product - A nuclide that results from radioactive decay. Thus radium-226 decays to radon-222, which in turn decays to polonium-218. The radon is the daughter of the radium, and polonium is its daughter.

Decay, Radioactive - The decrease in the number of radioactive nuclei present in a radioactive material due to their spontaneous transmutation. Also, the transmutation of a radionuclide into another nuclide by the emission of a charged particle.

Disposal - The term "disposal" means permanent isolation of transuranic waste from the accessible environment with no intent of recovery, whether or not such isolation permits the recovery of such waste. Disposal of waste in a mined geologic repository occurs when the waste has been emplaced and all the shafts to the repository are sealed.

Disposal System - The disposal system is any combination of engineered and natural barriers that isolate transuranic waste after disposal. For the purposes of the Waste Isolation Pilot Plant, this will include the combination of the repository/shaft system and the controlled area.

Disturbed Performance - This means the predicted behavior of the disposal system, including consideration of the uncertainties in predicted behavior, if the disposal system is disrupted by human intrusion (i.e., scenarios in which the waste-disposal region is intruded by an exploratory borehole).

Dose - A general term indicating the amount of energy adsorbed per unit mass from incident radiation.

Dose Rate - The rate at which dose is delivered.

Emplacement - At the Waste Isolation Pilot Plant, the placing of radioactive wastes in the repository.

Fission Products - Fissile products means any material consisting of or containing one or more fissile radionuclides. Fissile radionuclides are plutonium-238, plutonium-239, plutonium-241, uranium-233, and uranium-235.

Formation (Geologic) - The basic rock-stratigraphic unit in the local classification of rocks. It consists of a body of rock (usually sedimentary) generally characterized by some degree of internal lithologic homogeneity or distinctive features.

Gamma Radiation - Short wavelength electromagnetic radiation (high-energy photon) emitted in the radioactive decay of certain nuclides.

Gas Generation - The combined gas production from all species of gases produced as a result of transuranic waste transformations such as corrosion, microbial degradation, and/or radiolysis at any given time. The rate of gas production throughout the history of the repository is expected to vary depending on repository conditions with respect to humidity, total or partial brine inundation, competitive reactions that absorb specific gases, and the ability of the repository to retain the gases generated. The term is also applied to individual gases.

Generator and/or Storage Sites - Refers to the Department of Energy sites nationwide where transuranic wastes are generated and/or stored as a result of activities associated with nuclear weapons production.

Groundwater - Water below the land surface in a zone of saturation (40 CFR Part 191.12).

Half-life - The time required for the activity of a group of identical radioactive nuclei to decay to half its initial value.

Halite - The mineral rocksalt: NaCl.

Hot Cell - A heavily shielded compartment in which highly radioactive material can be handled, generally by remote control.

Human Intrusion - In advertent human disruptions of a mined geologic repository that could result in loss of containment of the waste. The most severe disruption would occur through inadvertent, intermittent intrusion by exploratory drilling (into the repository) for resources (40 CFR Part 191, Appendix C).

Interbeds - Stratigraphic horizons of geologic material within a larger horizon.

Irradiation - Exposure to any form of radiant energy.

Isotope - A species of atom characterized by the number of protons and the number of neutrons in its nucleus. In most instances an element can exist as any of several isotopes, differing in the number of neutrons, but not the number of protons, in their nuclei. Isotopes can be either stable isotopes or radioactive isotopes (also called radioisotopes or radionuclides).

Land Withdrawal Act (LWA) - Public Law 102-579, which withdraws the land at the Waste Isolation Pilot Plant site from "entry, appropriation, and disposal"; transfers jurisdiction of the land from the Secretary of the Interior to the Secretary of Energy; reserves the land for activities associated with the development and operation of the Waste Isolation Pilot Plant; and includes many other requirements and provisions pertaining to the protection of public health and the environment.

Lithostatic Pressure - Subsurface pressure due to the weight of overlying rock or soil.

Long-term - Refers to the 10,000 years after shaft sealing for which performance assessment calculations and models assess the behavior of the repository with respect to compliance with 40 CFR Part 191 and 40 CFR Part 268.6.

Lower Explosive Limit (LEL) - The minimum concentration of gas or vapor in air below which a substance does not burn when exposed to an ignition source.

Mean - The average value. For a given set of n values, the mean is the sum of their values divided by n.

Microbial Degradation - The process of consumption by microbial substances usually organic materials such as cellulosics.

No-Migration Determination - In the context of the Test Phase, the term "no-migration determination" means the Final Conditional No-Migration Determination for the Department of Energy Waste Isolation Pilot Plant published by the Environmental Protection Agency on November 14, 1990 (55 Fed. Reg. 47700), and any amendments thereto, pursuant to the Solid Waste Disposal Act (42 U.S.C. 6901 et seq.). The Department of Energy has decided not to pursue the testing activities in the WIPP underground for which the conditional No-Migration Determination was made.

Nuclide - Isotope.

Nuclide Inventory (Radionuclide Inventory) - A list of the kinds and amounts of radionuclides in a container or a source. Amounts are usually expressed in activity units: curies or curies per unit volume.

Oxic Corrosion - Oxidation of metals by molecular oxygen.

Performance Assessment (PA) - A term used to denote quantitative activities carried out to evaluate the long-term ability of the Waste Isolation Pilot Plant to effectively isolate the waste, to ensure long-term health and safety of the public by complying with 40 CFR Part 191 and 40 CFR Part 268.6, and to supply data/information to the compliance analysis for demonstrating regulatory compliance. The final analysis of compliance will consist or a qualitative assessment of the quantitative results of the performance assessment.

pH - A term used to describe the hydrogen-ion activity or concentration of a solution.

Post-Closure Phase - A designated period of time beginning with the end of the Decommissioning Phase and extending through the end of the regulatory time frame of 10,000 years. Performance assessment modeling of repository behavior will address this time frame with the exception of possible human intrusion events, which will not be modeled until 100 years after decommissioning.

Process Knowledge - The detailed knowledge of the processes and materials that generated the wastes in the DOE system.

Public Law 96-164 - The U.S. Department of Energy National Security and Military Applications of Nuclear Energy act of 1980. Public Law 96-164 directed the Department of Energy to proceed with the design and development of the Waste Isolation Pilot Plant.

Public Law 102-579 - See Land Withdrawal Act.

Rad - A unit of absorbed dose. Related to but not the same as "rem."

Radiolysis - Chemical decomposition by the action of radiation.

Radionuclide - Any isotope that emits radiation from its nucleus.

Release - Movement of regulated substances into the accessible environment as defined in 40 CFR Part 191 or beyond the unit boundary as defined for 40 CFR Part 268.6.

Rem - Roentgen equivalent in man a special unit of dose equivalent that is the product of absorbed dose, a quality factor that rates the biological effectiveness of the radiation types producing the dose, and other modifying factors (usually equal to one). If the quality and modifying factors are unity, 1 rem is equal to 1 rad: 100 rem = 1 Sievert (SI units). Also expressed in terms of millirem (mrem): 1 rem = 1,000 mrem.

Remote-Handled (RH) Waste - Transuranic wastes that have a measured radiation dose rate at the container surface of between 200 mrems per hour and 1,000 rems per hour and, therefore, must be shielded for safe handling.

Repository - The portion of the Waste Isolation Pilot Plant underground system within the Salado Formation, including the access drifts, waste panels, and experimental areas, but excluding the shafts.

Saturated - A condition in which all connected pores in a given volume of material contain fluid.

Scenario - A combination of naturally occurring or human-induced events and processes that represent realistic future changes to the repository, geologic, and geohydrologic systems that could affect disposal system performance.

Solubility - The ability or tendency of one substance to blend uniformly with another (e.g., solid in liquids, liquid in liquid, gas in liquid, and gas in gas). Solids vary from 0 to 100 percent in their degree of solubility in liquids depending on the chemical nature of the substance(s); to the extent that they are soluble, they lose their crystalline form and become molecularly or ionically dispersed in the solvent to form a true solution. Liquids and gases are often said to be miscible in other liquids and gases rather than soluble.

Source Term - The kinds and amounts of radionuclides that make up the source of a potential release of radioactivity.

Specific Activity - Radioactivity per unit mass of radioactive material.

Stabilization - The mixture and encasement of radioactive materials in cement or grout.

Standard Waste Box (SWB) - A waste container measuring approximately 6 by 4.5 by 3 feet high, with rounded ends.

Transuranic (TRU) Nuclide - A nuclide with an atomic number greater than that of uranium (92). All transuranic nuclides are produced artificially and are radioactive.

Transuranic (TRU) Waste - The term "transuranic waste" means waste containing more than 100 nanocuries of alpha-emitting transuranic isotopes per gram of waste, with half-lives greater than 20 years, except for: (1) high-level radioactive waste; (2) waste that the Secretary has determined, with the concurrence of the Administrator, does not need the degree of isolation required by the disposal regulations; or (3) waste that the Nuclear Regulatory Commission has approved for disposal on a case-by-case basis in accordance with 10 CFR Part 61.

Treatment - Means any method, technique, or process, including neutralization, designed to change the physical, chemical, or biological character or composition of any hazardous waste so as to neutralize such waste, or so as to recover energy or material resources from the waste, or as to tender such waste non-hazardous, or less hazardous; safe to transport, store, or dispose of; or amenable for recovery, amenable for storage, or reduced in volume.

Undisturbed Performance - "[T]he predicted behavior of a disposal system, including consideration of the uncertainties in predicted behavior, if the disposal system is not disrupted by human intrusion or the occurrence of unlikely natural events." (40 CFR Part 191.12)

Vitrification - Vitrification is the mixture of radioactive materials with glass by the action of heat.

Volatile Organic Compounds (VOCs) - RCRA-regulated organic compounds that readily pass into the vapor state and are present in contact-handled transuranic mixed waste.

Waste Acceptance Criteria (WAC) - A set of conditions established for permitting transuranic wastes to be packaged, shipped, managed, and disposed of at the Waste Isolation Pilot Plant.

Waste Form - A term used to emphasize the physical and chemical properties of the waste.

Continue to Appendix A
Return to Table of Contents

Notice To Users:

Use of this system constitutes consent to security monitoring and testing.
All activity is logged with your host name and IP address.


Have a question about WIPP?
Contact the WIPP Information Center at
1-800-336-9477 or email us at: