Diffusion of dissolved gases in chemically perturbed clay

Chloé Roonacker, Christophe Bruggeman

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The thesis research is in the framework of safe geological disposal of high and intermediate-level radioactive waste, for which the Boom Clay is studied at the moment as the reference host formation in Belgium. Boom Clay would be a suitable host rock thanks to many beneficial properties, including its transport properties which are mainly dominated by diffusion as Boom Clay has a sufficiently low hydraulic conductivity. In previous work, the diffusion coefficient of gases in Boom Clay was studied because gas generation in a geological repository is unavoidable (corrosion of metals, radiolysis of water,...). Within this research, our focus lies on the geochemical perturbation of Boom Clay as a consequence of NaNO3 leaching from Eurobitumen bituminised waste. More concretely, we analyse the diffusion of 4 gases (He, CH4, Xe, and C2H6) and we evaluate how much their diffusion coefficients are changed after perturbation. It appears that the smallest diffusing molecule He, was very sensitive to the chemical perturbation. After the diffusion experiments, we characterized the samples to study the petrographical and petrophysical changes. With N2-adsorption measurements, we noticed that the specific surface area of the clay minerals had decreased to half of the expected value in the disturbed samples. Therefore we assume that the interlayer of the clay platelets are blocked due to NaNO3 perturbation and that this reduces the access of the interlayers. Our hypothesis is that He uses the interlayer as a pathway through the clay and when this interlayer is blocked due to NaNO3, the pathway of He is barred, which lowers the diffusion coefficient.
Original languageEnglish
QualificationMaster of Science
Awarding Institution
  • BNEN - Belgian Nuclear Higher Education Network
  • Bruggeman, Christophe, Supervisor
  • Jacops, Elke, SCK CEN Mentor
Date of Award8 Jun 2022
StatePublished - 8 Jun 2022

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