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Diffusive Transport of Carbon Dioxide through USW-G4 Topopah Spring Tuffs

Published online by Cambridge University Press:  25 February 2011

M. Sarwar Ali ,
Franklin G. King  and
Shamsuddin Ilias
M. Sarwar Ali
Affiliation:
North Carolina A&T State University, Department of Chemical Engineering, Greensboro, NC 27411
Franklin G. King
Affiliation:
North Carolina A&T State University, Department of Chemical Engineering, Greensboro, NC 27411
Shamsuddin Ilias
Affiliation:
North Carolina A&T State University, Department of Chemical Engineering, Greensboro, NC 27411
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Abstract

The estimation of diffusive transport of gases through tuffs is important in order to assess whether Yucca Mountain is an environmentally safe and acceptable repository for high-level radioactive waste. The purpose of this study is to provide effective diffusivity data which may be used to calculate the amount of diffusion of carbon dioxide through Yucca Mountain tuff layers to the environment. The effective diffusivity of carbon dioxide was measured for tuff samples from five different layers of the USW-G4 drillhole, which is located in the central part of the proposed repository horizon. The tuff samples studied are from the following layers and depths: Vapor Phase (83.6 m), Upper Lithophysal (130.1 m), Middle Nonlithophysal (224.5 m), Lower Lithophysal (243.9 m, 266.9 m, 297.3 m and 335.2 m), and Lower Nonlithophysal (356.3 m and 371.0 m). A steady-state, counter-diffusion method, using gas chromatographic analysis, was used to determine the effective diffusivity of carbon dioxide through tuff samples. Effective diffusivity increased with temperature between 25°C and 125°C for all layers. The effect of temperature on diffusivity correlated well using second-order polynomials. The porosity, specific surface area and mean pore radius were also determined. In general, diffusivity increased with porosity, specific surface area and mean pore radius, but did not correlate well. From the measured data , it appears that the diffusion takes place primarily in the combined Knudsen and bulk diffusion regimes.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 333: Symposium V – Scientific Basis for Nuclear Waste Management XVII , 1993 , 827
Copyright
Copyright © Materials Research Society 1994

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References

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