Colloid-Radionuclide Transport Within Fractured Rock: Potential Impact of Nonlinear Sorption Kinetics

A numerical model was developed to analyze radioniclide transport within saturated fractured rock that accounts for the effect of nonlinear kinetic sorption of radionuclides on groundwater colloids. The interactions between radionuclides and colloids are assumed to be nonlinear and kinetic, while sorption of radionuclides on fracture surfaces and in rock matrix is described by a sorption distribution coefficient. Colloids may move with a velocity that is higher than the mean groundwater velocity. However, as there are insufficient data with which to assign a priori colloid velocity, we use a theoretical model based on hydrodynamic chromatography to evaluate the colloid velocity within a single fracture.

Calculation results show that external surface forces acting on colloids could alter both the mobility of colloids and the host population of radionuclides in groundwater. The results also indicate that colloid-facilitated transport occurs depending on colloid concentration. Moreover, a simple two-member radionuclide decay chain is assumed and incorporated into the kinetic model.