NEA Sorption Project Phase II: Interpretation and Prediction of Radionuclide Sorption onto Substrates Relevant for Radioactive Waste Disposal Using Thermodynamic Sorption Models

The modelling of the key process of radionuclide sorption is of great importance in assessing the performance or safety of deep and near-surface repositories for radioactive waste. The first phase of the NEA Sorption Project ran from 1997 to 1998, and highlighted the diversity in the details of the thermodynamic descriptions of sorption processes. Phase II of the NEA Sorption Project was initiated as a major international contribution towards demonstrating the consistency and applicability of different thermodynamic sorption models to support the selection of a sorption parameter, namely Kd values for safety assessments. It was implemented in the form of a comparative modelling exercise based on selected datasets for radionuclide sorption by both simple and complex materials. This report presents the results of Phase II of the Sorption Project, conducted as a co-operative project under the auspices of the Integration Group for the Safety Case (IGSC) of the OECD/NEA Radioactive Waste Management Committee (RWMC).