Analysis of radionuclide release through EBS of conceptual repository for Lithuanian RBMK spent nuclear fuel disposal : case of canister with initial defect

This paper presents research on radionuclide transport from generic geological repository for the RBMK-1500 SNF of 2.8 235U initial enrichment (with Er absorber) and average burn-up of ~ 29 MWd/kgU. Radionuclide transport analysis was focused on the engineered barrier system (EBS) and performed taking into account possible differences in the data on the initial size of a canister defect, defect enlargement time and radionuclide release start time. For the numerical simulations, computer code AMBER (UK) was used. The analysis of radionuclide transport regularities demonstrates that the release from the EBS is the most intensive after the defect enlargement. Most relevant radionuclides were identified based on the mass transfer analysis complemented by the analysis of radiotoxicity flux. The results showed that, depending on the differences of the initial defect size, defect enlargement time and release start time, the peak flux from the EBS may vary by a factor of 2 (for 129I) and 1.5 (for 226Ra) for RBMK-1500 SNF.