Thermodynamic models and data for assessing radionuclide migration in the near field. Uses and limitations

The focus of the present contribution is on the use of thermodynamic data and models to explain and predict the effects of solubility limits and sorption/uptake reactions on dissolved concentrations and migration of radionuclides in clay- and cement-water systems. This topic is approached by addressing the current state, limitations, and possible pitfalls of relatively common applications of speciation and sorption models: calculation of near field water chemistry as influenced by compacted clay or cement, prediction of radionuclide solubility limits in homogeneous solutions. Subsequently, promising developments, as well as critical shortcomings and future challenges in this field are discussed, in particular with regard to: model-supported selection of Kd values for clays and cement, extrapolation to 'intact' materials, such as compacted bentonite or whole concrete, linking to diffusive and advective transport. (author)