Migration of Radionuclides in Fracture Columns

Abstract

ABSTRACTRadionuclides transported by ground water flowing through fractures may be delayed by interactions with the fracture surfaces. The migration of radionuclides in fractures was studied under well defined laboratory conditions using tonal-ite drill core columns with a fracture running parallel to the core axis. The hydrodynamic characterization of the columns was performed using tritiated water, pertechnetate and chloride ions as non-sorbing tracers. Strontium and neptunium were used to study the retardation of radionuclides on the fracture surfaces.The experimental set-up is described, and break-through curves of non-sorbing tracers, strontium and neptunium are presented. The results were interpreted using models for dispersion and diffusion into the rock matrix. From the shape of the break-through curves it was concluded that for non-sorbing tracers there was very little or no diffusion at all into the rock matrix. Retardation of strontium in a column with intact tonalite surfaces indicated a Ka factor identical with that earlier determined by batch experiments. The break-through curve of neptunium indicated a non-sorbing fraction.