Diffusion Measurements in Concrete and Compacted Bentonite

Abstract

A laboratory method for measurement of diffusion of radionuclides inconcretes and compacted bentonite has been developed. In this method a tracer is introduced through one end into the cylindrical sample closed in a tube and preequilibrated with water. After the introduction period of the tracer the tube is sealed hermetically and the concentration profiles of the radionuclides are measured periodically from the outside of the sample using a collimated detector. Diffusivities are calculated from the activity profiles by fitting the theoretical curve with the measured profile. The paper will give diffusion data for Co, Sr and Cs in some concrete products and for Co and Cs in compacted sodium bentonite.

Diffusion of Iodide in Compacted Clays

“…It was indicated that significant constriction and tortuosity were resulted. However, the iodide ion diffusion in the interstitial water at a steady-state flux NA can be described by ( 7) where D; and D, are the respective pore diffusivities in interstitial and surface water, s; and s, are the respective porosities available for diffusion in interstitial and surface water, and 'IC; and 'IC, are the respective ionic concentration gradients in interstitial and surface water. Assuming ( 8) where kd is the distribution coefficient, ()the fraction of surface water available for diffusion, and Pc the clay dry density, Eq.…”