A central safety function of radioactive waste disposal repositories is the prevention or sufficient retardation of radionuclide migration to the biosphere. Performance assessment exercises in various countries, and for a range of disposal scenarios, have demonstrated that one of the most important processes providing this safety function is the sorption of radionuclides along potential migration paths beyond the engineered barriers. Thermodynamic sorption models (TSMs) are key for improving confidence in assumptions made about such radionuclide sorption when preparing a repository's safety case. This report presents guidelines for TSM development as well as their application in repository performance assessments. They will be of particular interest to the sorption modelling community and radionuclide migration modellers in developing safety cases for radioactive waste disposal.
Tables des matières:
Overview and purpose 1. Thermodynamic sorption models and radionuclide migration -1.1. Sorption and radionuclide migration -1.2. Applications of TSMs in radioactive waste disposal studies -1.3. Requirements for a scientifically defensible, calibrated TSM applicable to radioactive waste disposal -1.4. Current status of TSMs in radioactive waste management 2. Theoretical basis of TSMs and options in model development -2.1. Conceptual building blocks of TSMs and integration with aqueous chemistry -2.2. The TSM representation of sorption and relationship with Kd values -2.3. Theoretical basis of TSMs -2.4. Example of TSM for uranyl sorption -2.5. Options in TSM development -2.6. Illustration of TSM development and effects of modelling choices -2.7. Summary: TSMs for constraining Kd values – impact of modelling choices 3. Determination of parameters for TSMs -3.1. Overview of experimental determination of TSM parameters -3.2. Theoretical estimation methods of selected model parameters -3.3. Case study: sorption modelling of trivalent lanthanides/actinides on illite -3.4. Indicative values for certain TSM parameters -3.5. Parameter uncertainty -3.6. Illustration of parameter sensitivity and uncertainty analysis 4. Approaches for applying TSMs to intact and complex materials -4.1. Introduction -4.2. Real substrates (What makes them complex?) -4.3. Determination and estimation of TSM parameters in real systems -4.4. TSM application for Kd estimation on chemically complex substrates -4.5. Sorption modelling in clay rocks and compacted clay systems -4.6. TSM applications to crystalline host rocks -4.7. Application of generalised TSMs to complex and intact materials: concluding remarks and key messages 5. General guidelines and recommendations -5.1. Framework for TSM applications in the context of radioactive waste disposal -5.2. Purposes and predictive capabilities of TSMs -5.3. Strategies for building TSMs -5.4. Recommendations -5.5. Building a scientifically defensible, calibrated TSM for radioactive waste applications -5.6. Concluding comments 6. References 7. Annexes -7.1. List of authors and external experts -7.2. List of acronyms