Modelling transport of 14C-labelled Natural Organic Matter (NOM) in Boom Clay

In Belgium, the Boom Clay formation is considered to be the reference formation for HLW disposal R&D. Assessments to date have shown that the host clay layer is a very efficient barrier for the containment of the disposed radionuclides. However, trivalent lanthanides and actinides form easily complexes with the fulvic and humic acids which occur in Boom Clay and in its interstitial water. Colloidal transport may possibly result in enhanced radionuclide mobility, therefore the mechanisms of colloidal transport must be better understood. Numerical modeling of colloidal facilitated radionuclide transport is regarded an important means for evaluating its importance for long-term safety. The paper presents results from modeling experimental data obtained in the framework of the EC TRANCOM-II project, and addresses the migration behaviour of relevant radionuclides in a reducing clay environment, with special emphasis on the role of the Natural Organic Matter (NOM). The laboratory experiments have been interpreted by means of the numerical code HYDRUS-1D and typical colloid transport submodels tested included kinetically controlled attachment/detachment and kinetically controlled straining and liberation.