ABSTRACTIn the safety assessment of nuclear waste repositories, sorption of radionuclides on the surfaces of colloids may significantly modify transport behaviour where colloid concentration is sufficiently high. In the case of fractured geological media, colloids may be excluded from matrix pores, in which case radionuclides bound to them are not subject to the retarding effects of matrix diffusion and sorption onto matrix pore surfaces.A model is presented describing colloid facilitated transport through fractured media with non-linear sorption. A simple criterion is developed to predict when the presence of colloids will have a significant influence on transport and effects resulting from non-linearity of sorption are described. However, lack of comprehensive sorption data, as well as computational efficiency, mean that the use of a simplified transport model, with linear sorption both on pore surfaces and colloids, is desirable if it can be demonstrated to be conservative. A further criterion is developed to predict where such a model, with linear sorption calculated for the highest concentration encountered along the flow path, would be expected to yield conservative results.
Regional channelized transport in fractured media with matrix diffusion and linear sorption