A general approach to assess hydro-mechanical changes of natural clay barriers due to physico-chemical interactions with radwaste in deep disposal sites

Radwaste must be isolated from the biosphere for a long periods. To isolate waste, engineered clay barriers can be constructed. The functional life of such engineered barriers must be much longer (factor 100–1000) than that of more common engineered structures. Can the responsible engineer guarantee a functional life of several thousand years? Probably not, therefore waste like radwaste is stored at great depths, in a combination of geological and engineered barriers. During the storage period the waste itself (radiation) or derived products (oxidation of containers) can interact with the engineered and geological clay barriers. In this contribution it is discussed how such interactions affect the hydro-mechanical properties of clay barriers. First some examples are given that show how properties of clays change at surface conditions if clays are exposed to typical waste products like different cations. Thereafter a method is proposed to classify the potential of hydro-mechanical modifications at three different scales: the particle level, the interlayer level and the tetrahedral–octahedral level. Next it is explained why the reactivity of clays at depth during long-term waste isolation is different (smaller) from the better known reactivity of clays at the surface. Instead of directing too much attention to such well known interactions, the focus for a safe deep disposal of radwaste should be directed to reactions that play a role at depth if, e.g. damage due to radiation occurs. Only if such reactions can be excluded, a safe storage of waste is possible.