The Effect of Montmorillonite Partial Density on the Role of Colloid Filtration by a Bentonite Buffer

Abstract

Japan's concept for high-level radioactive waste disposal includes a barrier of compacted bentonite (montmorillonite) that, based on its microstructure, buffers the waster package and prevents migration of colloids with sizes between 1 and 1,000 nm. However, results of experimental studies indicate that colloid migration through the barrier (breakthrough) depends upon the partial density of the montmorillonite buffer. To assess the possibility of colloid breakthrough, interstitial pore size as a function of montmorillonite partial density is estimated through a homogenization analysis. Homogenization analysis indicates that interstitial pores sizes of <1 nm may be achieved for montmorillonite partial densities in excess of 1.2Mg/m3. It should be noted that this estimation depends upon the specific structural/geometric parameters of the compacted bentonite under consideration.