Double-packer-based Hydrochemical Investigations in Deep Fractured Rock Boreholes: Case Studies and Application Constraints

This study presents a comprehensive analysis of the principles, application procedures, domestic and international case studies, and application constraints of double-packer-based groundwater sampling in deep fractured rock boreholes, with the aim of precisely identifying the hydrochemical characteristics of the candidate sites for the disposal of high-level radioactive waste.The hydrochemical characteristics of deep groundwater are crucial factors that must be identified to ensure the long-term safety of the disposal system.To obtain reliable data on these factors, both precise groundwater sampling techniques and clearly defined quantitative criteria for the application procedures must be established and implemented.The results of this study highlight the technical requirements that must be considered at each stage of the groundwater sampling process, which include drilling methods, preliminary planning before the sampling, removal of drilling-disturbed fluid, stabilization of water quality, and maintenance of closed-system sampling conditions.In addition, application cases from leading countries in geological disposal, such as Sweden, Switzerland, and Japan, were reviewed and compared with domestic cases to analyze differences in technological maturity and the level of procedural refinement.Furthermore, key technical limitations were identified, including short-circuiting caused by fracture networks, pumping constraints in ultra-low permeability zones, reduced mechanical stability in highly fractured zones, and equipment performance limitations under highpressure deep subsurface conditions.Based on these findings, potential countermeasures and supplementary tasks were proposed to address these challenges and enhance domestic technological capabilities.