State of a Bentonite Barrier after 8 Years of Heating and Hydration in the Laboratory
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0985-NN11-19
State of a Bentonite Barrier after 8 Years of Heating and Hydration in the Laboratory María Victoria Villar1, Ana María Fernández1, Roberto Gómez1, José F. Barrenechea2, F. Javier Luque2, Pedro Luis Martín1, and José Miguel Barcala1 1 CIEMAT, Madrid, 28040, Spain 2 UCM, Madrid, 28040, Spain
ABSTRACT The conditions of the bentonite in an engineered barrier for HLW disposal have been simulated in a laboratory test. Six cylindrical blocks of bentonite compacted at a dry density of 1.64 g/cm3 were piled up in a hermetic Teflon cell. The total length of the clay column inside the cell was 60 cm. The bottom surface of the bentonite was heated at 100°C while the top surface was injected with granitic water. The duration of the test was 7.6 years. The water intake was measured during the test and, at the end, the cell was dismounted and the dry density, water content, mineralogy, geochemistry, and swelling capacity of the clay were measured in different sections along the column. At the end of the test no full water saturation was reached and water content and dry density gradients were found along the column. No mineralogical changes have been detected, although the pore water chemistry and the exchangeable complex of the smectite have changed along the bentonite. None of these changes affect drastically its swelling capacity, which remains high. The material used in this test is the FEBEX bentonite. INTRODUCTION The work presented here started in the framework of FEBEX, which was a project for the study of the near field for a HLW repository in crystalline rock according to the Spanish concept [1]. Among the laboratory tests started in the framework of the FEBEX Project and continued in the NF-PRO Project are those performed in cells in which the compacted bentonite is subjected simultaneously to heating and hydration, in opposite directions, in order to simulate the conditions of the clay barrier in the repository. This allows a better understanding of the hydration process. The results of an infiltration test performed under thermal gradient dismantled after 7.6 years of operation are summarised in this paper and detailed in [2]. Dry density, water content, mineralogy, geochemistry, and swelling capacity, among others, have been studied in the samples of bentonite taken during dismantling. The values obtained are compared with those of the untreated FEBEX bentonite. EXPERIMENT The test was performed with the FEBEX bentonite, extracted from the Cortijo de Archidona deposit (Almería, Spain). It consists of more than 90 percent montmorillonite, with Ca and Mg as the main exchangeable cations, with lesser Na.
An infiltration test in a large-scale cell –whose internal diameter is 7 cm and inner length 60 cm–was run for 7.6 years. The cell was made of Teflon to prevent as much as possible lateral heat conduction, and externally covered with semi-cylindrical steel pieces to avoid the deformation of the cell by bentonite swelling (Figure 1). Six 10-cm height and 7-cm diameter blocks of FEBEX clay compacted with
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