Analysis of pore structure effects on diffusive reactive transport in Bentonite via pore network models

AP Jivkov, Qingrong Xiong, S Kwang

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    Abstract

    Bentonite is widely considered as one of the most suitable backfill materials for deep geological disposal of radioactive nuclear waste. In order to assess the long-term containment performance of radioactive waste repositories, good knowledge of transport behaviour of radionuclides in bentonite is required. While it is possible to study the complex diffusion phenomena using pore network models, accurate description of the morphology of real porous media is required to support model parameterisation (i.e. pore size distribution, throat size distribution and connectivity parameters). However, for bentonites with tight pore spaces that are of interest to potential geological repository applications, current experimental techniques do not allow resolution of sufficient number of throat sizes (if at all). Consequently, often only pore size distribution is available, while connectivity data, e.g. pore coordination statistics/spectra are lacking.In order to circumvent this problem, a meso-scale model for diffusion of foreign species through porous media is proposed. The model considers diffusion as a continuum process operating on a discrete geometrical structure dictated by the pore size distribution. The effect of connectivity can be derived indirectly from macroscopically measured mass transport. Local diffusivities and hence connectivity are seen to be dependent on the size of the diffusing species and the sorption of those species onto the pore walls. As such, the bulk diffusivity of the medium can be analysed by considering the effects of pore structure alone, and in combination with sorption. This paper presents initial results for the effects of solute sizes on the topological and physical properties of the porous network. Besides emulating the effect of sorption, the approach could in principle be extended to other pore space changing mechanisms (e.g. precipitation, dissolution, micro-cracking, etc.) for deriving mechanism-based evolution laws for the transport parameters of porous media.
    Original languageEnglish
    Title of host publicationProceedings of WM2014 Conference
    Place of PublicationPhoenix, Arizona, USA
    PublisherWM Symposia
    Pages14068
    Publication statusPublished - 6 Mar 2014
    EventWaste Management 2014 Conference - Phoenix, Arizona, USA
    Duration: 2 Mar 20146 Mar 2014

    Conference

    ConferenceWaste Management 2014 Conference
    CityPhoenix, Arizona, USA
    Period2/03/146/03/14

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