Design of system and method on field-scale solute migration experiment for evaluating radionuclide’s migration properties at a deep borehole

Disposal methods for storing high-level radioactive waste deep underground are being researched and implemented worldwide. In constructing a high-level radioactive waste disposal facility, groundwater reaction front moves and geochemical buffering capacity may be changed, affecting the long-term storage stability. Although various studies have been conducted in this regard in Korea, field-scale studies are still in shortage, in cases compared to overseas cases. This study aims to establish a long-term solute migration experiment system and experimental method for deep depths, to identify the migration and retardation characteristics of released nuclides in the deep underground environment.

For field-scale tests, KURT(KAERI Underground Research Tunnel) was constructed in 2006 and in-situ solute migration tests were conducted. However, that was conducted in shallow depth, which has limitations in realizing an actual disposal environments. Therefore, the long-term solute migration experiment to be designed in this study targets underground depths, where reduced-state groundwater exists and disposal site construction is considered, to get empirical data in deep depth. The in-situ solute migration experiment system designed in this study is composed of an injection part and an extraction part. The injection unit was designed to be in charge of injecting simulated nuclides into the injection borehole. The extraction unit was designed to extract groundwater, including the injected tracer, to obtain a sample for analysis and to measure the properties of groundwater flowing through fractured rock in real-time. Both sorbing and non-sorbing tracers are used in long-term solute migration experiments. The non-sorbing tracers are suitable such as Eosin B, fluorescein sodium, and potassium bromide. The sorbent tracers which can simulate the behavior characteristics of radionuclides are suitable such as rubidium, nickel, zirconium, and samarium. Using the solute migration experiment system and experimental method designed in this study, a long-term solute migration experiment will be carred out in the deep depths around KURT, to obtain the results of the radionuclides’ migration and retardation characteristics for the deep depths.

Acknowledgements

This research was supported by the National Research Foundation of Korea(NRF) under the project 'Development of Core Technologies for the Safety of Used Nuclear Fuel Storage and Disposal; NRF-2022M2E1A1052570'.