Travel time simulation for radionuclide transport at the Korean underground research facility, KURT

For the research on the deep geological disposal of radioactive waste, it is necessary to understand the underground environment, including the geology and hydrogeology. In Korea, KURT (KAERI Underground Research Tunnel) was constructed in 2006 at KAERI (Korea Atomic Energy Research Institute). Geological and hydrogeological field data have been obtained from the facility, and the groundwater flow system was simulated. Based on the data observed and analyzed on a groundwater flow system, the transport of potential radionuclides, which were assumed to be released at the supposed position, was then calculated in order to prepare the fundamental data for a safety assessment of a hypothetical underground repository. Several pathways with highly water-conductive features were selected to evaluate the elapsed times of radionuclide transport. The transport times were calculated using a TDRW (Time-Domain Random Walk) method. The matrix diffusion and sorption mechanisms in the host rock, as well as the advection-dispersion processes, were considered under the KURT field conditions. To reflect the radioactive decay, some decay chains were selected. The simulation results indicate that the main factors for the shapes of the mass discharge of the radionuclides were the half-life and distribution coefficient. This shows that the long-lived radionuclides must be treated accurately at the steps of determining radioactive waste source term as well as considering the transport process, and intensified research is required for the sorption between radionuclides and host rocks for making the safety assessment process more reliable and less uncertain.