Radionuclide Migration: Laboratory Experiments with Isolated Fractures
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Science Publishing Company, NUCLEAR WASTE MANAGEMENT
RADIONUCLIDE MIGRATION:
Inc.
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LABORATORY EXPERIMENTS WITH ISOLATED FRACTURES*
R. S. RUNDBERG, J. L. THOMPSON, AND S. MAESTAS Los Alamos National Laboratory, MS-514, Los Alamos,
New Mexico, USA
ABSTRACT Laboratory experiments examining flow and element migration in rocks containing isolated fractures have been initiated at the Los Alamos National Laboratory. Techniques are being developed to establish simple fracture flow systems which are appropriate to models using analytical solutions to the matrix diffusion - flow equations, such as those of I. Neretnieks [I]. These experiments are intended to be intermediate steps toward larger scale field experiments where it may become more difficult to establish and control the parameters important to nuclide migration in fractured media. Laboratory experiments have been run on fractures ranging in size from 1 to 20 cm in length. The hydraulic flow in these fractures was studied to provide the effective apertures. The flows established in these fracture systems are similar to those in the granite fracture flow experiments of Witherspoon et al. [2]. Traced solutions 13 7 containing 85Sr and Cs were flowed through fractures in Climax Stock granite and welded tuff (Bullfrog and Tram members, Yucca Mountain, Nevada Test Site). The results of the elutions through granite agree with the matrix diffusion calculations based on independent measurements of Kd. The results of the elutions through tuff, however, agree only if the Kd values used in the calculations are lower than the Kd values measured using a batch technique. This trend has been previously observed in chromatographic column experiments with tuff.
INTRODUCTION The study of fracture flow and element transport through flow in fractures is essential to provide a complete understanding of the geologic barriers surrounding a nuclear waste repository. The ability to correctly model radionuclide transport in fractured systems is necessary to the performance assessment of a repository. Fracture flow is an important transport mechanism because fluid velocities in fractures can be many orders of magnitude greater than the fluid velocity in the porous matrix. This is especially true of crystalline rock such as granite. There are many chemical and physical processes which can affect the transport of radionuclides by flow in fractures. The principal processes studied in the experiments to be discussed are sorption and diffusion into the rock matrix. These experiments are part of a program to examine the mechanisms contributing to the retardation of radionuclides in flow through fractures. The objectives of the program are to test existing theoretical models and to *This work was supported by the U.S.
Department of Energy.
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perform laboratory experiments with rock samples of varying size to see if the results of small scale laboratory experiments can be extrapolated to the field. 85 3T The elution of Sr and 1 Cs was observed in flow through fractured Climax Stock (
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