Abstract
Matrix diffusion is one of the key processes to be considered by safety assessments concerned with varied waste disposal in geological host rocks, but especially disposal of radioactive waste. An appropriate method is proposed for evaluating nuclide retardation by matrix diffusion along flow-paths in crystalline rock, using in-situ geological information. The usefulness of the method is evaluated and the results are summarized as follows:
(1) Detailed in-situ characterization of flow-path structures shows that a flow-path can be classified into three types by its structural features. The structural information is important for supporting reliable qualitative analysis of matrix diffusion by laboratory experiments, e. g. to ensure that porosity measurements and diffusion experiments investigate relevant parts of the rock mass.
(2) Information from natural analogues, such as studies of the migration of natural uranium-series isotopes along flow-paths, is useful to build confidence in short-term laboratory experiments for evaluating the long-term diffusional processes.
(3) Mineralogical studies, microscopic observations and dating of the fracture-fillings would be valuable for estimating the long-term stability of fractures and are important for evaluating the usefulness of the methodology for evaluating matrix diffusion in the host rock.
