Modeling radionuclide migration from activated metallic waste disposal in a generic geological repository in Lithuania

There are two RBMK-1500 type reactors in Lithuania, which are under decommissioning now. Long-lived low and intermediate level radioactive metallic waste generated during operation and decommissioning of the nuclear power plant is foreseen for deep geological disposal (DGR). A preliminary assessment of the radionuclide release from metallic waste and migration through the engineered barriers of the generic DGR in crystalline rocks is presented in this study. The radionuclide flux to backfill and geosphere is investigated for three different container alternatives: (1) disposal of metallic waste in stainless steel containers, (2) disposal in carbon steel containers and (3) disposal in which the container is not a barrier for radionuclide migration. In addition, the impact of surface contamination of the activated waste on the radionuclide flux is investigated. Comparison of maximum fractional flux to backfill between Alternatives 1 and 2 revealed that the container material plays a noticeable role in the migration of long-lived low mobility radionuclides. The maximum fractional flux to the geosphere for all radionuclides increases from Alternative 1 to Alternative 3. Surface contamination is an important parameter when the maximum radionuclide flux to backfill is observed during the early post-closure period. This work was supported by the European Union’s Horizon 2020 Project Theramin (H2020-755480, 2017-2020) and by the Lithuanian state budget under a long-term program (2017-2021).