Radiotoxicity flux and concentration as complementary safety indicators for the safety assessment of a rock-cavern type LILW repository

Abstract

This study presents a practical application of complementary safety indicators, which can be applied in a safety assessment of a radioactive waste repository by excluding a biosphere simulation and comparing the artificial radiation originating from the repository with the background natural radiation. Complementary safety indicators (radiotoxicity flux from geosphere and radiotoxicity concentration in seawater) were applied in the safety assessment of a rock-cavern type low and intermediate level radioactive waste (LILW) repository in the Republic of Korea. The natural radionuclide (40K, 226,228Ra, 232Th, and 234,235,238U) concentrations in the groundwater and seawater at the Gyeongju LILW repository site were measured. Based on the analyzed concentrations of natural radionuclides, the levels of natural radiation were determined to be 8.6 × 10−5 – 8.0 × 10−4 Sv/m2/yr and 6.95 × 10−5 Sv/m3 for radiotoxicity flux from the geosphere and radiotoxicity concentration in seawater, respectively. From simulation results obtained using a Goldsim-based safety assessment model, it was determined that the radiotoxicity of radionuclides released from the repository is lower than that of the natural radionuclides inherently present in the natural waters. The applicability of the complementary safety indicators to the safety case was discussed with regard to reduction of the uncertainty associated with biosphere simulations, and communication with the public. Keywords: Complementary safety indicator, Flux and concentration indicators, Natural radiation, Safety assessment, Rock-cavern type LILW repository in Korea