Three-Dimensional Numerical Simulation of Groundwater Flow and Salt and Radionuclide Transport at a Proposed Coastal Low and Intermediate Level Radioactive Waste Disposal Site in Korea

A series of three-dimensional numerical simulations using a multicomponent hydrodynamic dispersion numerical model COFAT3D is performed to predict and analyze groundwater flow and both salt and radionuclide transport at a proposed site for low and intermediate level radioactive waste disposal. The proposed site is located on the southeastern coast in Korea, and it is hydrogeologically composed of a series of anisotropic geologic formations (rock masses) dissected by several fracture zones. Each anisotropic rock mass then consists of a porous rock matrix and joint sets acting as a fractured porous medium. A series of steady-state numerical simulations is performed first to analyze groundwater flow and salt transport before the construction of the proposed repository, and its results are calibrated and validated reasonably well with respect to field measurements of water table. A series of transient-state numerical simulations is then performed to predict and analyze groundwater flow and both salt and radionuclide transport during the construction and operation and after the closure of the proposed repository assuming the leakage of radionuclides from it. The results of the steady-state numerical simulations show that the hydrogeological characteristics of each anisotropic geologic formation (porous rock matrix plus joint sets) are more dependent on the joint sets than the porous rock matrix. The results of the steady-state and transient-state numerical simulations also show that the hydrogeological characteristics of the whole geologic system (geologic formations plus fracture zones) are even more controlled by the fracture zones than the geologic formations. On the other hand, the results of the transient-state numerical simulations after the closure of the proposed repository show that both adsorption (retardation) and radioactive decay play important roles in maximizing the efficiency of the surrounding geologic formations as natural barriers and thus in minimizing the dispersion of the mother and daughter radionuclides from the proposed repository.