Investigation of colloid-facilitated effects on the transport of N-member radionuclide chains in the fractured medium

A previous analytical model for N-member radionuclide decay chains has been extended to include the effect of radionuclide sorption with groundwater colloids. Site-specific distribution coefficients were employed in the nuclide decay chain to illustration the present model. The colloid concentration was assumed constant in time and space owing to equilibrium between colloid generation and sedimentation by chemical and/or physical perturbations. Furthermore, the diffusion of colloids into the rock matrix was ignored because the diameter of colloid is relatively large and colloids and fracture surfaces are like-charged. The results indicated that colloids could facilitate the transport of radionuclides and the large adsorbability of nuclides with colloids enlarged the effect of acceleration by colloids. The influence of colloids on the radionuclide transport was expected to be crucial to the actinides with large adsorbability; however, the present results revealed that the low-adsorbing nuclides whose parent nuclides have large capability of sorption could be also facilitated significantly by colloids indirectly. Therefore, the role of colloids played in the transport of the radionuclides decay chain should be assessed carefully in the radioactive waste disposal. The analytical method presented herein is helpful to verify/validate further complex far-field models. (authors)