Optimization of a portable hollow-fiber-based device for extracting radiokrypton dissolved in deep groundwater and selection of Rn-222 as an indicator of Kr extraction efficiency

摘要

Groundwater dating information is important for safety assessment for geological disposal of high-level radioactive waste. Radiokrypton (Kr-81) is an excellent tracer for dating old groundwater with a residence time up to 1 Ma. We have optimized a hollow-fiber-based device for extracting Kr-81 from deep groundwater with low hydraulic conductivity for the purpose of estimating its residence time. Such a device must show a high Kr extraction efficiency and an ultra-low level of contamination from modern air and must allow for in situ evaluation of Kr extraction efficiency. The optimal devices reported herein showed minimal contamination by Kr-81 from modern air, and the efficiency of Kr extraction from high-salinity groundwater exceeded 90%. Furthermore, we confirmed that the Rn-222 was a suitable indicator of Kr extraction efficiency.