Improved migration predictability in host rocks for radioactive waste by a combination of numerical and tomographic analysis

The predictive capability of numerical simulations of flow fields, such as those used to assess radionuclide migration, strongly depends on the accuracy of the underlying pore-network geometry. Experimental validation of such simulations is limited by the availability of suitable techniques. In recent years, positron emission tomography (PET) has become a powerful method for investigating transport processes in porous media¹. The use of tailored radiotracers enables the analysis of advective transport and diffusive fluxes in complex pore systems, providing time-resolved visualization and statistical evaluation of transport-controlling parameters, offering additional insight into surface reactivity^{2, 3}.

Using complex fractured and mineralized host rock types relevant to underground radioactive waste repositories, we investigate flow-field heterogeneity at the laboratory scale⁴. We demonstrate that specific structural and compositional features, together with their pore-size distributions and pore-network geometries, control transport behavior. We incorporate these characteristics into generalized pore-network models and transport simulations to determine effective diffusivities through a multiscale upscaling workflow. PET measurements demonstrate the strong influence of parameter variability over multiple spatial scales for complex transport in fractured and mineralized crystalline rocks, with surface structures ranging from nanometers to millimeters governing breakthrough-curve behavior.

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.

²Schöngart, J.; Lindemann, M.;  Klotzsche, M.;  Franke, K.; Fischer, C., Quantitative tomography of contaminant phytomobilization: β+ emitters 83Sr and 86Y as tracers of fission-product analog mobility. Journal of Hazardous Materials Advances 2026, 21, 100952.

³Schöngart, J.; Kulenkampff, J.; Fischer, C., Positron emission tomography quantifies crystal surface reactivity during sorption reactions. Chemical Geology 2024, 665, 122305.

⁴Zhou, W.; Kulenkampff, J.;  Zuna, M.;  Jankovský, F.;  Butscher, C.;  Kammel, R.;  Schäfer, T.; Fischer, C., Variability of effective diffusivity in fractured and mineralized metamorphic host rock from Bukov URF, Bohemian Massif (CZ). Applied Geochemistry 2025, 193, 106574.