Nuclide Migration Field Experiments in Tuff, G Tunnel, Nevada Test Site
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NUCLIDE MIGRATION FIELD EXPERIMENTS IN TUFF,
Inc.
207
G TUNNEL,
NEVADA TEST SITE*
B. R. ERDAL, R. S. RUNDBERG, W. R. DANIELS, AND K. WOLFSBERG Los Alamos National Laboratory, Los Alamos, New Mexico, USA
A. M. FRIEDMAN, S. FRIED, AND J. J. HINES Argonne National Laboratory, Argonne, Illinois, USA
ABSTRACT A project to begin to address the phenomena of flow and element migration in fractured porous rock has recently been started by the Los Alamos National Laboratory, Sandia National The work has Laboratories, and Argonne National Laboratory. three objectives: 1) to develop the experimental, instrumental, and safety techniques necessary to conduct controlled, small-scale, radionuclide migration, field experiments; 2) to use these techniques to define radionuclide migration through rock by performing generic, at-depth experiments under closely controlled conditions in a single fracture in porous rock; and 3) to determine whether available lithologic, geochemical, and hydraulic properties together with existing or developed transport models are sufficient and appropriate to describe real field conditions (i.e., to scale from small-scale laboratory studies to bench-size studies to field studies). The detailed scope of this project and its current status are described.
INTRODUCTION The intrinsic appeal of deep burial as a means for safe disposal of nuclear reactor waste is the concept that the rock surrounding the repository will provide a significant barrier between the radioactive waste and natural barrier man's environment. Because the host rock provides the first of radionuclide migration and strongly influences the detailed design of the engineered repository within it, an understanding of the properties of Such an understanding will the host rock is of considerable importance. also be the basis for predicting the performance of a repository and for identifying potential deficiencies in the models used for the predictions. Clearly, such information will also be essential in the process of selecting and licensing a repository and indeed in convincing the general public of the ultimate safety of such disposal. In order to estimate the concentrations and travel times for radionuclides that may leave a repository, one must develop predictive models based on the understanding of the dynamic processes that occur at each location in the total repository-rock system. These models must include appropriate equilibrium and rate expressions that adequately describe the various domidiffusion, dissolution, complexation, nant chemical phenomena involved, i.e., precipitation, ion exchange, surface adsorption, hydrolysis, coprecipitation, *Work supported by the U.S.
Department of Energy.
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formation of solid solutions, colloid and polymer formation, etc., for each of the waste elements involved. The knowledge of the regional hydrologic regime must then be superimposed on the chemistry. This includes effects such as hydrodynamic dispersion, distance, pore-fluid velocity, and saturated or unsaturated flow. For many rocks,
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