OA Publication of the Month (September 2024): Dr. Naila Ait-Mouheb
In the open access article Retention of 226Ra in the sandy Opalinus Clay facies from the Mont Terri rock laboratory, Switzerland, Dr. Naila Ait-Mouheb at al. write about the retention behaviour of 226Ra, a critical radionuclide to be considered in safety cases for the deep geological disposal of spent nuclear fuel, in the heterogeneous sandy facies of the Opalinus Clay (OPA-SF).
Germany is currently searching for a site for the disposal of heat-generating, high-level radioactive waste (HLW). The repository will be located in a geological formation of crystalline rock, salt rock, or clay rock. The OPA formation in southern Germany is currently under consideration as a potential site for a repository for HLW. In this context, the effects of natural heterogeneities of 226Ra migration in clay rocks in the repository far field were investigated, using the lower OPA-SF from the Mont Terri underground research laboratory, as an example.
The article enables a better comprehension of the retention of 226Ra in heterogeneous clay host rocks and demonstrates that a simplified bottom-up approach addressing cation exchange/surface complexation reactions significantly underestimated the experimental findings. Modelling solid-solution formation of Ra with (Ba,Sr)-sulphates revealed that considerably higher amounts of sulphate minerals in the OPA-SF would be required to make this retention mechanism effective and to explain the experimental findings. Furthermore, it emphasizes the necessity of further assessing the formation of Ra-bearing carbonate solid solutions as a potential retardation mechanism for 226Ra in carbonate-bearing clay rocks.