This study evaluates the long-term performance of a multi-layer cover system (MLCS) for near-surface disposal facilities using numerical modeling to estimate infiltration rates under various rainfall scenarios. An effective cover system is essential to prevent radionuclide migration and protect groundwater inflow within disposal facility. The analysis incorporated different bedrock characteristics (homogeneous and discrete fracture networks) and rainfall patterns throughout a 300-year post-closure period, assuming constant initial hydraulic properties. A comprehensive modeling approach incorporating both saturated and unsaturated flow dynamics was employed to assess system performance. Results showed that the cover system effectively limited infiltration rates to 15.94%−21.25% of the design criterion (32 mm∙year−1) across all scenarios. Although infiltration patterns showed minimal sensitivity to bedrock heterogeneity, preferential flow along fractures was observed in the unsaturated zone, necessitating further investigation. These findings emphasize the importance of considering fracture-dominated flow in cover system design and highlight the need for detailed analysis of chemical degradation effects, experimental validation, and uncertainty quantification. The study provides valuable insights for optimizing disposal facility designs and improving long-term performance assessment methodologies.

A radioactive waste disposal facility needs to be developed in a way to protect present and future generations and its environment. A safety assessment is implemented for normal and abnormal scenarios and human intrusion scenarios as a part of a safety case in developing a disposal facility for the radioactive waste. The human intrusion scenarios include a well scenario which takes into account various potential exposure groups (PEGs) who use a groundwater well contaminated with radionuclides released from the disposal facility. It is observed that a pumping rate has a negative correlation with the biosphere dose conversion factor (BDCF) in the well scenario. C-14 is shown to be a key radionuclide in the well scenario, and a special model based on the carbon cycle is applied for C-14. For Tc-99, an adsorption coefficient should be adjusted to be suitable for the site. The safety assessment for the radioactive waste disposal facility is successfully carried out for the well scenario. However, it is observed that site-specific models needs to be developed and sitespecific input data need to be collected in order to avoid unnecessary conservatism.