Dispersion modelling of radionuclide releases to marine environments : A marine dispersion and dose assessment study of a floating SMR in the Baltic Sea

Sammanfattning

Deployment of Floating Nuclear Power Plants (FNPPs) utilizing Small Modular Reactor (SMR) technology offers a flexible, low-carbon energy source, but necessitates rigorous safety assessments to understand radionuclide dispersion patterns. This study evaluates the dispersion and bioaccumulation of radionuclides (137Cs, 90Sr, and 131I) released into the marine environment from a hypothetical floating SMR located in the semi-enclosed coastal waters of Öregrundsgrepen, Sweden. A three-dimensional compartment transport model was developed using the POSEIDON-R framework within the software AFRY Intelligent Scenario Modelling (AISM) and validated against historical empirical monitoring data from the IAEA Marine Radioactivity Information System (MARIS). Two operational scenarios were analysed: continuous routine releases over a 50-year period and a severe 30-day accidental release. A dynamic food web model (BURN) and a dose assessment module were integrated to estimate radionuclide transfer across multiple trophic levels and the resulting ingestion doses to humans. The results indicate that routine operational releases result in radiation doses to the public that remain well below regulatory limits. Under the accidental release scenario, the model demonstrates that radionuclides clear rapidly from the water column but persist long-term in seabed sediments, leading to a delayed biological uptake (trophic lag) in top predators, while the cumulative human ingestion dose remains within manageable emergency reference levels. Global sensitivity analysis using Morris and eFAST methodologies identifies sedimentation rate and resuspension as the dominant drivers of model uncertainty, highlighting the importance of utilizing site-specific parameters in radioecological safety assessments when modelling radionuclide dispersion from FNPPs to the marine environment.