Modeling cesium migration through Opalinus clay: a benchmark for single- and multi-species sorption-diffusion models

Abstract Sophisticated modeling of the migration sorbing radionuclides in compacted claystones is needed for supporting safety analysis deep geological repositories radioactive waste, which requires robust tools/codes. Here, a benchmark related to long term laboratory scale diffusion experiment cesium, moderately radionuclide, through Opalinus clay presented. The was performed with following codes: CORE 2D V5, Flotran, COMSOL Multiphysics, OpenGeoSys-GEM, MCOTAC and PHREEQC v.3. setup solved two different conceptual models, i) single-species model by using look-up table cesium sorption isotherm ii) multi-species including complex mechanistic model. calculations were three boundary concentrations (10 ?3 , 10 ?5 ?7 mol / L) investigate models/codes capabilities taking into account nonlinear behavior cesium. Generally, good agreement both single- concepts could be achieved, however, some discrepancies have been identified, especially near boundaries, where code specific spatial (and time) discretization had improved achieve better at expense longer computation times. In addition, exercise yielded useful information on performance, options, input output data management, post processing options. Finally, comparison showed that approach generally earlier breakthrough, because this accounts neither cation exchange Cs + K Na nor pore water.