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As part of the site characterization efforts at Yucca Mountain, Nevada, a series of unsaturated zone tracer tests has been performed at nearby Busted Butte. The phase 2 tracer test was conducted within an instrumented 10 m by 10 m by 7 m in situ block of vitric tuff. A complex tracer solution containing both reactive and nonreactive tracers was pumped into the block during a period of 27 months. Throughout the test, thousands of unsaturated zone pore water samples were collected on sorptive pads attached to inverting membranes and then analyzed for tracer concentration. Partway through the experiment, three new boreholes were drilled into the block, and two intercepted the tracer plume. The rock core was removed for pore water extraction and analysis, and the boreholes were then instrumented with inverting membranes and sorptive pads. The initial set of pore water-soaked pads was removed from the boreholes a week after they were emplaced, and the pore water was extracted and analyzed. This paper compares the tracer concentration data from the rock cores and the pads to evaluate the effectiveness of the inverting membrane collection technique for a variety of tracers. While the sorptive pads sample only dissolved tracers, rock cores contain both dissolved and sorbed tracer. For nonreactive tracers, such as halides (bromide and iodide) and fluorinated benzoic acids (FBAs), this distinction is immaterial, and the rock and pad data agree quantitatively for the halide tracers, and qualitatively for the FBAs. For reactive tracers, such as lithium, the dissolved tracer concentrations can be estimated from rock analyses by dividing by the tracer's retardation factor; when this correction is applied, the rock and pad lithium data are also in reasonable agreement. [ABSTRACT FROM AUTHOR]

This paper examines several dimensions of public opposition to the proposed siting of the high-level nuclear waste repository at Yucca Mountain. In order to provide a context for the public's view of the repository in metropolitan Clark County, both governmental studies of the repository siting process are analyzed, as well as elements of the Nuclear Waste Policy Act. This analysis suggests that one potentially key component of the public's opposition to the siting, as well as their perceptions of risk of the facility, may be the result of a lack of trust in the Department of Energy. Empirical analysis of survey data collected in Nevada in 1988 confirms the strong relationship between political trust and repository risk perceptions. [ABSTRACT FROM AUTHOR]

No public policy issue has been as difficult as high-level nuclear waste. Debates continue regarding Yucca Mountain as a disposal site, and -- more generally -- the appropriateness of geologic disposal and the need to act quickly. Previous research has focused on possible social, political, and economic consequences of a facility in Nevada. Impacts have been predicted to be potentially large and to emanate mainly from stigmatization of the region due to increased perceptions of risk. Analogous impacts from leaving waste at power plants have been either ignored or assumed to be negligible. This paper presents survey results on attitudes of residents in three counties where nuclear waste is currently stored. Topics include perceived risk, knowledge of nuclear waste and radiation, and impacts on jobs, tourism, and housing values from leaving waste on site. Results are similar to what has been reported for Nevada; the public is concerned about possible adverse effects from on-site storage of waste. [ABSTRACT FROM AUTHOR]

This paper describes a particle-tracking technique for dual-permeability media suitable for simulation of radionuclide transport through unsaturated, fractured rock. The model is used to conduct sensitivity analyses of radionuclide transport travel times for the Yucca Mountain unsaturated zone, from the repository horizon to the water table. This paper describes the numerical methods developed to simulate the transport of radionuclides through the unsaturated, fractured rock below the proposed repository at the Yucca Mountain. Regardless of the disposition of the Yucca Mountain License Application, this method has general applicability for modeling contaminant transport through deep vadose zones. Using a dual-permeability solution for fluid flow as a basis, the transport model represents contaminant transport with a cell-based particle-tracking technique in which particles move from cell to cell in the three-dimensional large-scale grid of two overlapping continua. Particle movement between cells, and the residence time within a cell, is computed probabilistically based on transfer functions using numerical solutions of the transport equations for an idealized fracture-matrix system. Using this approach, the following transport phenomena are simulated: advection through fracture and matrix continua, including between these continua, dispersion, sorption of dissolved radionuclides to the matrix continuum, and within the fault zones, and molecular diffusion between the fractures and matrix. In addition to providing a realistic representation of the relevant processes, this method has the virtue of computational efficiency. After describing the numerical method, this paper presents sensitivity analyses for radionuclide transport travel time distributions from the proposed repository to the water table through the unsaturated zone for the Yucca Mountain system. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive treatment of radionuclide transport behavior for the unsaturated zone at Yucca Mountain, Nevada. A transport model is developed, informed by in situ tests and field observations. Flow processes, heterogeneities, fast pathways, and radionuclide interactions with the host rock and colloids are included in the model. This paper presents a comprehensive treatment of large-scale unsaturated zone (UZ) transport below the repository at the Yucca Mountain, Nevada, reporting on studies investigating the UZ as a component of the Lower Natural Barrier to radionuclide transport from the site. Regardless of the disposition of Yucca Mountain as the site for a nuclear waste repository, these studies and models of radionuclide transport through the UZ have relevance to the study of contaminant transport through deep vadose zones in general. For many radionuclides, including most strongly sorbing species, the Yucca Mountain UZ was found to prevent or substantially reduce the rate of movement of radionuclides to the accessible environment. The UZ radionuclide transport models developed for Yucca Mountain simulate the features and processes that influence the capability of the UZ below the repository to reduce the movement of radionuclides. Transport of radionuclides away from the repository depends on the rate and pathways of flow within the UZ, the retardation of radionuclides, and the rate of transport by colloids. Several basic processes affect radionuclide transport in the UZ, including the quantity of recharge and deep percolation of water, flow partitioning between fractures and rock matrix, diffusion of radionuclides from water flowing in fractures into the pores of the rock matrix, sorption of radionuclides onto rock or mineral surfaces, and colloid filtration. This paper summarizes the treatment of these and other processes, describing the experimental and observational basis for the models, conceptualizations, and predictions, and then presents some representative results. [ABSTRACT FROM AUTHOR]

The U.S. Code of Federal Regulations, 10 CFR Part 63, stipulates that the expected performance of the geological high-level nuclear waste repository must be demonstrated through a total system performance assessment (TSPA). The TSPA represents an analysis that identifies all features, events, and processes (FEPs) that might affect the disposal system and examines the effects of the identified FEPs upon the performance of the system. Secondary minerals from the thick unsaturated zone of Yucca Mountain were deposited from waters with temperatures up to 70–90°C. U-Pb dating constrained the ages of the elevated temperatures to the period between 10 and 5–6 million years ago. Relatively youthful circulation of thermal waters (hydrothermal activity) would be of concern for the safety of the disposal facility. A phenomenological model was advanced by the U.S. Department of Energy (DOE), which proposed that the minerals were deposited by infiltrating meteoric waters that were heated upon contact with the bedrock; it was hypothesized that the latter was conductively heated by a shallow silicic magma body. The model rendered processes responsible for elevated water temperatures inconsequential for the safety of the proposed nuclear waste facility. However, attempts by DOE at validating the model by means of numeric thermal simulations and analogue system observations were unsuccessful. Regulations specify two criteria for exclusion of a FEP from consideration in the TSPA: low probability and low consequence. The lack of a plausible phenomenological model makes it impossible to apply either of these two criteria to the FEP Hydrothermal Activity. Despite the lack of a valid criterion for exclusion, it was excluded from the TSPA. Both the development of DOE's thermal model and the formal FEP analysis were associated with deviations from DOE's quality assurance regulations. [ABSTRACT FROM AUTHOR]

As part of its preparation to review a potential license application from the U.S. Department of Energy (DOE), the U.S. Nuclear Regulatory Commission (NRC) is examining the performance of the proposed Yucca Mountain nuclear waste repository. In this regard, we evaluated postclosure repository performance using Monte Carlo analyses with an NRC-developed system model that has 950 input parameters, of which 330 are sampled to represent system uncertainties. The quantitative compliance criterion for dose was established by NRC to protect inhabitants who might be exposed to any releases from the repository. The NRC criterion limits the peak-of-the-mean dose, which in our analysis is estimated by averaging the potential exposure at any instant in time for all Monte Carlo realizations, and then determining the maximum value of the mean curve within 10,000 years, the compliance period. This procedure contrasts in important ways with a more common measure of risk based on the mean of the ensemble of peaks from each Monte Carlo realization. The NRC chose the former ( peak-of-the-mean) because it more correctly represents the risk to an exposed individual. Procedures for calculating risk in the expected case of slow repository degradation differ from those for low-probability cases of disruption by external forces such as volcanism. We also explored the possibility of risk dilution (i.e., lower calculated risk) that could result from arbitrarily defining wide probability distributions for certain parameters. Finally, our sensitivity analyses to identify influential parameters used two approaches: (1) the ensemble of doses from each Monte Carlo realization at the time of the peak risk (i.e., peak-of-the-mean) and (2) the ensemble of peak doses calculated from each realization within 10,000 years. The latter measure appears to have more discriminatory power than the former for many parameters (based on the greater magnitude of the sensitivity coefficient), but can yield different rankings, especially for parameters that influence the timing of releases. [ABSTRACT FROM AUTHOR]

Abstract This study examines the effects of the risk from transporting high–level radioactive waste to the proposed Yucca Mountain repository on housing location decisions in Southern Nevada. Using data from a survey of southern Nevada households, we develop a model–based subjective risk estimate for each household. We then explore different factors that may influence the household's location decisions if the proposed transportation route is ultimately chosen for nuclear waste transport. We extend the conventional expected utility model to allow for uncertainty surrounding the actual risks borne by the household. Finally, we examine the impact of federal government compensation on households’ location decisions. The findings indicate that residents currently living near the proposed transportation route express subjective risk estimates much larger than those reported by the Department of Energy. In general, households that are uncertain about the future risks are more likely to relocate than those expressing certainty. When everything is considered, the model predicts that between one and three percent of households living near the transportation route are likely to relocate. Compensation can influence some households to remain at their present location and bear the transport risk. [ABSTRACT FROM AUTHOR]

Reports on developments related to geology. Lung cancer risk of uranium miners; Edward Heron-Allen's research on foraminifera; Approval of the use of the Yucca Mountain as the national nuclear waste dump site in the U.S.

Presents ethnographic, ethnohistorical and legal arguments for inclusion of American Indian concerns regarding the Yucca Mountain, Nevada nuclear waste site proposal. Indians' legal or regulatory right to be part of further site characterization studies; Kinds of Indian peoples that should be part of the study; Number of Indian people that are potentially impacted; Evidence regarding Indian input that is generally applicable to other potential nuclear waste sites.