Predictive and Inverse Modeling of a Radionuclide Diffusion Experiment in Crystalline Rock at ONKALO (Finland)

The REPRO-TDE test was performed at a depth of about 400 m in the ONKALO underground research facility Finland. Synthetic groundwater containing radionuclide tracers [tritiated water tracer (HTO), 36Cl, 22Na, 133Ba, and 134Cs] circulated for 4 years packed-off interval injection borehole. Tracer activities were additionally monitored two observation boreholes. subject modeling exercise by SKB GroundWater Flow Transport Solutes Task Force. Eleven teams participated exercise, using different model concepts approaches. Predictive calculations based on laboratory-based information concerning porosities, diffusion coefficients, sorption partition coefficients. After experimental results made available, able to revise their models reproduce observations.General conclusions from these back-analysis include need reduced effective coefficients 36Cl compared those applicable HTO (anion exclusion), implement weaker 22Na laboratory batch experiments, large differences between theoretical initial concentrations strongly sorbing 133Ba 134Cs, first measured values few hours after injection.Different applied concepts, mainly implementation isotropic versus anisotropic diffusion, or possible existence borehole disturbed zones around role microstructure also addressed models.