Analysis of the pore water chemical composition of a Spanish bentonite used in an engineering barrier

Abstract:

Compacted bentonites are being considered in many countries as a backfill material in highlevel radioactive waste disposal (HLW) concepts because of its low permeability, high swelling capacity and high plasticity. A knowledge of the pore water chemistry in the clay barrier is essential for perforinance assessment since the pore water composition is an important parameter influencing the release and transport of the radionuclides: canister corrosion, dissolution of the waste matrix, sorption on mineral surfaces, solubility of radionuclides etc. However, obtaining reliable data on the pore water chemistry of compacted bentonite (dry density of 165 g/cm3) under initial and saturated conditions where the water contents Wc-) are so low, 14 wt% and 23.8 wt% of the dry mass respectively; is very difficult. Many of the different laboratory techniques employed so far to obtain pore water compositions tend to perturb the system and introduce sampling artefacts into the resulting data. For example, squeezing at high pressures may produce the oxidation and dissolution of the accessory minerals present in the bentonite, the outgassing Of C02, and some type of chemical fractionation. Furthermore, squeezing techniques can not extract pore water from bentonites with water contents below 20%.

Año de publicación:

2002

Keywords:

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