Study on flow and mass transport through fractured sedimentary rocks (Contract research)

It is important for safety assessment of HLW geological disposal to evaluate groundwater flow and mass transport in deep underground appropriately. Though it is considered that the mass transport in sedimentary rock occurs in pores between grains mainly, fractures of sedimentary rock can be main paths. The objective of this study is to obtain the data of flow and mass transport properties in fractured sedimentary rocks by laboratory tests, and to estimate these properties in larger scale rocks, such as in situ test scale with considering both data obtained by this study and one from in situ experiments such as packer tests. In this study the following three tasks were carried out: (1) laboratory hydraulic and tracer experiments using the rock specimens of Koetoi formation obtained at underground research facility under construction in the Horonobe area, (2) a numerical examination on the influence of dual porosity, fracture and permeable matrix on to the representative groundwater velocity and/or mass transport properties in the fractured sedimentary rocks, (3) a numerical study on the contributing factors to groundwater flow such as effect of low permeability layers. Non-sorbing tracer experiments using artificial fractured rock specimens were carried out. Potassium iodide was used as a tracer. The obtained breakthrough curve was interpreted and fitted by using a numerical simulator called FRAC3DVS (Therrien et al., 1996), and mass transport parameters, such as longitudinal dispersivity, matrix diffusion coefficient, transport aperture, were obtained. Several cases mass transport simulations using single fracture model that the groundwater flow velocity in the fractures is different were performed to study on the influence that a difference of the groundwater flow velocity in the fractures gives a mass transport in the fractured sedimentary rocks. Groundwater flow simulations using a numerical simulator for inverse problems called iTOUGH2 and using a numerical simulator coupled Thermo - Hydro - Mechanical processes called TOUGH-FLAC performed to study the effect of the low permeability layers on groundwater pressure distribution. (author)