Some uses for natural analogues in assessing the function of a HLW repository

Abstract

Radionuclides migrating with water in a fractured rock may diffuse into the porous matrix of the rock and have access to a very large surface for sorption. This will retard their movement very much, in excess of what only sorption on the fissure surfaces would do. There are some potential natural systems which might be used to show that this process has been active over very long times. The transport of U in the bulk rock, the salt-water content of the micropores of the rock and the interaction of oxygenated water with ferrous minerals in the rock are potential systems to study further. A simplified analysis shows that the observed leaching of U in surficial rocks and the observed oxidizing waters in surficial rock is consistent with the assumed diffusion of oxygen into the rock matrix. The analysis also shows that the values of observed reducing waters in deeper rock are consistent with the matrix diffusion data. Oxygenated waters cannot penetrate more than a few meters or tens of meters into rock with the hydraulic properties prevailing at depths below a few hundred meters during several million years of exposure.