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Modeling of the Thermohydrodynamic and Reactive Behavior of Compacted Clay for High-Level Radionuclide Waste-Management Systems

Published online by Cambridge University Press:  01 January 2024

Ricardo Juncosa ,
Vicente Navarro ,
Jordi Delgado  and
Ana Vázquez
Ricardo Juncosa*
Affiliation:
Civil Engineering School, University of La Coruña, Campus de Elviña s/n, 15192, A Coruña, Spain
Vicente Navarro
Affiliation:
Civil Engineering School, University of Castilla-La Mancha, Avda. Camilo José Cela s/n, 13071, Ciudad Real, Spain
Jordi Delgado
Affiliation:
Civil Engineering School, University of La Coruña, Campus de Elviña s/n, 15192, A Coruña, Spain
Ana Vázquez
Affiliation:
Civil Engineering School, University of La Coruña, Campus de Elviña s/n, 15192, A Coruña, Spain
*
* E-mail address of corresponding author: rjuncosa@udc.es
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Abstract

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Bentonite is often proposed as an engineered-buffer material in high-level radionuclide waste-management systems. For effective design of the barrier that will provide protection over the long time periods required, the physical/thermal/chemical processes taking place in the barrier material must be understood thoroughly. These processes, which interact, include the flow of water and gas, the flow of heat, and the transport and reaction of chemical constituents. The purpose of this study was to better understand the processes that occurred in a small-scale experiment within a confined bentonite space. A conceptual and mathematical model (FADES-CHEM) was built in order to simulate the results of an experiment conducted in 2000, and thereby to gain a better understanding of the controlling processes. In that experiment, a block of compacted bentonite was placed in an air-tight cell and subjected, for 6 months, to simultaneous heating and hydration from opposite sides. The bentonite block was then sliced into five sections each of which was then analyzed in order to obtain a series of physicochemical parameters illustrating the changes that had occurred. Before modeling, the chemical composition of the bentonite pore waters was restored in order to account for different processes such as gas outgassing and cell cooling. Modeling indicated that gas-pressure build up was a relevant process when computing the saturation of bentonite, and the computations in the present study suggested that evaporation/condensation processes played a crucial role in the final distribution of the water content. Gas pressure and evaporation/ condensation also affected the geochemical system, and the numerical model developed gives results that were consistent with the experimental values and trends observed. The model reproduced the results obtained and enable use at the repository scale and over longer time frames, provided that adequate data are available.

Keywords

BentoniteContaminant TransportMultiphase FlowNumerical ModelingReactive Transport
Type
Article
Information
Clays and Clay Minerals , Volume 58 , Issue 4 , August 2010 , pp. 486 - 500
Copyright
Copyright © The Clay Minerals Society 2010

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