Tomographic analysis of advective flow and diffusive flux toward improved migration predictability in host rocks for radioactive waste

The predictive power of numerical approaches for the analysis of flow fields, e.g. for radionuclide
migration, depends on the quality of the underlying pore network geometry. Validation of the
obtained simulation results can only be performed with a limited number of methods. Positron
emission tomography (PET) is a suitable technique that has been established in geomaterial
sciences in recent years. The use of suitable radiotracers allows the analysis of advective transport
and diffusive flux in a variety of complex porous materials. In addition to the visualization of timeresolved
transport patterns, the statistical analysis of transport controlling parameters is currently
in the focus of investigations using PET techniques.
Using potential host rock types with low permeability for underground radioactive waste
repositories as examples, we have analyzed the heterogeneity of the flow field at laboratory scale.1
Diagenetic and sedimentary components and their pore size distributions and pore network
geometries are responsible for the flow field properties. The resulting generalized pore network
geometries are used in digital rock models to calculate effective diffusivities, using a combined
upscaling workflow for transport simulations from the nanometer to the micrometer scale.2 For
advective transport in fractured crystalline rocks, PET provides evidence for the influence of
fracture wall geometries over a wide range of the length scale. Surface building blocks from nm to
mm size are responsible for the observed changes in breakthrough curve behavior. Finally,
another hot topic is the testing of reactive PET tracers for materials analysis. In addition to the use
of conservative tracers described above, reactive tracers provide insight into the density of
reactive surface sites in complex porous materials.
1Bollermann, T.; Yuan, T.; Kulenkampff, J.; Stumpf, T.; Fischer, C., Pore network and solute flux
pattern analysis towards improved predictability of diffusive transport in argillaceous host rocks.
Chemical Geology 2022, 606, 120997.
2Yuan, T.; Fischer, C., The influence of sedimentary and diagenetic heterogeneity on the
radionuclide diffusion in the sandy facies of the Opalinus Clay at the core scale. Applied
Geochemistry 2022, 146, 105478.
Powered by