Effect of γ-radiation on radionuclide retention in compacted bentonite

Compacted bentonite is proposed as an engineered barrier in many concepts for disposal of high level nuclear waste. After the initial deposition however, the bentonite barrier will inevitably be exposed to ionizing radiation (mainly γ) under anoxic conditions. Because of this, the effects of γ-radiation on the apparent diffusivity values and sorption coefficients in bentonite for Cs+ and Co2+ were tested under different experimental conditions. Radiation induced effects on sorption were in general more noticeable for Co2+ than for Cs+, which generally showed no significant differences between irradiated and unirradiated clay samples. For Co2+ however, the sorption to irradiated MX80 was significantly lower than to the unirradiated clay samples regardless of the experimental conditions. This implies that γ-radiation may alter the surface characteristics contributing to surface complexation of Co2+. With the experimental conditions used, however, the effect of decreasing sorption was not large enough to be reflected on the obtained Da values.

► Irradiated Bentonite clay significantly decreases sorption of Co2+, but not Cs+.
► The decrease of Co2+ sorption is explained by direct effects in the clay particles.
► Irradiation under oxic conditions or H2O2 pre-treatment decreases the sorption of Co2+ and Cs+.