For purposes of this part:

Applicable radiation protection standard means (1) For the preclosure period, the preclosure numerical radiation dose limits in 10 CFR 63.111(a) and (b) and 63.204; and

(2) For the postclosure period, the postclosure numerical radiation dose limits in 10 CFR 63.311 and 63.321 and radionuclide concentration limits in 10 CFR 63.331.

Barrier means any material, structure or feature that prevents or substantially reduces the rate of movement of water or radionuclides from the Yucca Mountain repository to the accessible environment, or prevents the release or substantially reduces the release rate of radionuclides from the waste. For example, a barrier may be a geologic feature, an engineered structure, a canister, a waste form with physical and chemical characteristics that significantly decrease the mobility of radionuclides, or a material placed over and around the waste, provided that the material substantially delays movement of water or radionuclides.

Cladding is the metallic outer sheath of a fuel rod element; it is generally made of a corrosion resistant zirconium alloy or stainless steel, and is intended to isolate the fuel from the external environment.

Closure means the final closing of the remaining open operational areas of the underground facility and boreholes after termination of waste emplacement, culminating in the sealing of shafts and ramps, except those openings that may be designed for ventilation or monitoring.

Colloid means any fine-grained material in suspension, or any such material that can be easily suspended.

Criteria means the characterizing traits relevant to assessing the performance of a geologic repository, as defined by this section, at the Yucca Mountain site.

Design means a description of the engineered structures, systems, components and equipment of a geologic repository at Yucca Mountain that includes the engineered barrier system.

Design bases means that information that identifies the specific functions to be performed by a structure, system, or component of a facility and the specific values or ranges of values chosen for controlling parameters as reference bounds for design. These values may be constraints derived from generally accepted “state-of-the-art” practices for achieving functional goals or requirements derived from analysis (based on calculation or experiments) of the effects of a postulated event under which a structure, system, or component must meet its functional goals. The values for controlling parameters for external events include:

(1) Estimates of severe natural events to be used for deriving design bases that will be based on consideration of historical data on the associated parameters, physical data, or analysis of upper limits of the physical processes involved; and

(2) Estimates of severe external human-induced events to be used for deriving design bases, that will be based on analysis of human activity in the region, taking into account the site characteristics and the risks associated with the event.

DOE means the U.S. Department of Energy, or its duly authorized representatives.

Engineered barrier system means the waste packages, including engineered components and systems other than the waste package (e.g., drip shields), and the underground facility.

Event sequence means a series of actions and/or occurrences within the natural and engineered components of a geologic repository operations area that could potentially lead to exposure of individuals to radiation. An event sequence includes one or more initiating events and associated combinations of repository system component failures, including those produced by the action or inaction of operating personnel. Those event sequences that are expected to occur one or more times before permanent closure of the geologic repository operations area are referred to as Category 1 event sequences. Other event sequences that have at least one chance in 10,000 of occurring before permanent closure are referred to as Category 2 event sequences.

Geologic repository means a system that is intended to be used for, or may be used for, the disposal of radioactive wastes in excavated geologic media. A geologic repository includes the engineered barrier system and the portion of the geologic setting that provides isolation of the radioactive waste.

Geologic repository operations area means a high-level radioactive waste facility that is part of a geologic repository, including both surface and subsurface areas, where waste handling activities are conducted.

Geologic setting means geologic, hydrologic, and geochemical system of the region in which a geologic repository is or may be located.

High-level radioactive waste means

(1) The highly radioactive material resulting from the reprocessing 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 concentration; and

(2) Other highly radioactive material that the Commission, consistent with existing law, determines by rule requires permanent isolation.

Human intrusion means breaching of any portion of the Yucca Mountain disposal system within the repository footprint by any human activity.

Infiltration means the flow of a fluid into a solid substance through pores or small openings; specifically, the movement of water into soil and fractured or porous rock.

Initiating event means a natural or human induced event that causes an event sequence.

Near-field means the region where the adjacent natural geohydrologic system has been significantly impacted by the excavation of the repository and the emplacement of the waste.

NRC means the U.S. Nuclear Regulatory Commission or its duly authorized representatives.

Perched water means ground water of limited lateral extent separated from an underlying body of ground water by an unsaturated zone.

Preclosure means the period of time before and during closure of the geologic repository.

Preclosure safety evaluation means a preliminary assessment of the adequacy of repository support facilities to prevent or mitigate the effects of postulated initiating events and event sequences and their consequences (including fire, radiation, criticality, and chemical hazards), and the site, structures, systems, components, equipment, and operator actions that would be relied on for safety.

Postclosure means the period of time after the closure of the geologic repository.

Radioactive waste or waste means high-level radioactive waste and other radioactive materials, including spent nuclear fuel, that are received for emplacement in the geologic repository.

Reasonably maximally exposed individual means the hypothetical person meeting the criteria specified at 10 CFR 63.312.

Reference biosphere means the description of the environment, inhabited by the reasonably maximally exposed individual. The reference biosphere comprises the set of specific biotic and abiotic characteristics of the environment, including, but not limited to, climate, topography, soils, flora, fauna, and human activities.

Seepage means the inflow of ground water moving in fractures or pore spaces of permeable rock to an open space in the rock such as an excavated drift.

Sensitivity study means an analytic or numerical technique for examining the effects on model outcomes, such as radionuclide releases, of varying specified parameters, such as the infiltration rate due to precipitation.

Site characterization means activities, whether in the laboratory or in the field, undertaken to establish the geologic conditions and the ranges of the parameters of a candidate site relevant to the location of a repository, including borings, surface excavations, excavations of exploratory shafts, limited subsurface lateral excavations and borings, and in situ testing needed to evaluate the suitability of a candidate site for the location of a repository, but not including preliminary borings and geophysical testing needed to assess whether site characterization should be undertaken.

Surface facilities means all permanent facilities within the restricted area constructed in support of site characterization activities and repository construction, operation, and closure activities, including surface structures, utility lines, roads, railroads, and similar facilities, but excluding the underground facility.

System performance means the complete behavior of a geologic repository system at Yucca Mountain in response to the features, events, and processes that may affect it.

Total system performance assessment means a probabilistic analysis that is used to:

(1) Identify the features, events and processes (except human intrusion) that might affect the Yucca Mountain disposal system and their probabilities of occurring during 10,000 years after disposal;

(2) Examine the effects of those features, events, processes, and sequences of events and processes (except human intrusion) on the performance of the Yucca Mountain disposal system; and

(3) Estimate the dose incurred by the reasonably maximally exposed individual, including associated uncertainties, as a result of releases caused by all significant features, events, processes, and sequences of events and processes, weighted by their probability of occurrence.

Underground facility means the underground structure, backfill materials, if any, and openings that penetrate the underground structure (e.g., ramps, shafts and boreholes, including their seals).

Waste form means the radioactive waste materials and any encapsulating or stabilizing matrix.

Waste package means the waste form and any containers, shielding, packing, and other absorbent materials immediately surrounding an individual waste container.

Yucca Mountain disposal system means the combination of underground engineered and natural barriers within the controlled area that prevents or substantially reduces releases from the waste.

Yucca Mountain site means the candidate site in the State of Nevada recommended by the Secretary to the President under section 112(b)(1)(B) of the Nuclear Waste Policy Act of 1982 (NWPA) (42 U.S.C. 1032(b)(1)(B)) on May 27, 1986.