Opalinus and Callovo Oxfordian clays are being considered as potential host rocks for a deep geological repository of radioactive waste. The diffusion and retention of radionuclides through these argillaceous formations are relevant to assess the performance of the repository. Most of the experimental work in this field has focused on laboratory experiments performed on small samples.
In situ diffusion experiments are performed at underground research laboratories to overcome the limitations of laboratory diffusion experiments and to investigate possible scale effects.
Numerical models of different complexity have been used in this dissertation to interpret the data of the DIB, DIR and DR in situ diffusion experiments. Dimensionless sensitivities of tracer concentrations have been computed numerically in a systematic and comprehensive manner for different tracers. Computed sensitivities are tracer dependent and vary with time. They have been used to identify which parameters can be estimated with the least uncertainty from tracer dilution and overcoring data. Synthetic experiments generated with prescribed known parameters have been interpreted automatically with INVERSE CORE2D and used to determine parameter identifiability in the presence of random errors. They have been used also to evaluate the relevance of experimental uncertainties in the volume of water of the injection system, the presence of the filter and an excavation disturbed zone and those arising from the sampling methods.
In addition, conceptual and numerical models of radionuclide diffusion and sorption around the high level radioactive waste repository have been evaluated.