Retardation of contaminants on technical barriers or natural materials in a repository system strongly depends on the geochemical environment. Namely, the distribution of radionuclides or chemical pollutants between a liquid phase and a mineral surface (sorption) is dependent on parameters such as pH value, redox potential, ionic strength, and composition of the solution (most prominently the concentration of dissolved inorganic carbon [DIC], competing cations like Ca2+ and Al3+, or complexing ligands like sulfate. Other important boundary conditions are the available mineral surfaces (type and amount/area). As all these parameters are variable over time and space, prognostic tools to assess migration patterns in hydrogeological systems must be able to account for such variation.
Here, distribution coefficients for radionuclides on specific sediment compartments are calculated as function of the above parameters using mechanistic sorption models (yielding smart Kd-values). A sediment is defined here as a hydrological unit with a fixed mixture of selected minerals. The calculation produces a multidimensional matrix of smart Kd-values which serves, e.g., as a lookup table to be accessed by suitable reactive transport codes in each time step for each special node. A detailed description of the overall methodology is published in Stockmann et al. (2017).
Stockmann, M., Schikora, J., Becker, D.-A., Flügge, J., Noseck, U., Brendler, V.: Smart Kd-values, their uncertainties and sensitivities - Applying a new approach for realistic distribution coefficients in geochemical modeling of complex systems. Chemosphere, 187 (2017), 277-285 p.