Natural Tracer Profiles Across Argillaceous Formations

The CLAYTRAC Project

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This technical report describes the results of the Nuclear Energy Agency's CLAYTRAC project, in which natural tracer data from nine sites was evaluated to assess potential impacts of disposal of radiological waste in geological repositories. It shows scientific information from numerous sites and applies robust analytical methods to improve the understanding of radionuclide migration and evolution of sites for deep geological disposal. These results improve the understanding of sites, and thus the confidence in safety, for geological disposal of radioactive waste.



Discussion and Conclusions

Nuclear Energy Agency

Natural tracers are powerful evidence of non-sorbing solute transport and water movement in clay-rich rocks. Moreover, the interpretation of natural tracers is in general scientifically robust and consistent with physical concepts. For the sites and clay-rich formations that have been studied, there is strong evidence that movement is controlled by diffusion. In the model cases where advective movement was also considered, the goodness of the model fits to the data could not be improved. Therefore, the advective transport rate is at best comparably slow with diffusion, if not slower or absent. 


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