Raul Perianez

Accidental releases of radionuclides from nuclear-powered vessels or ships carrying nuclear weapons may expose marine organisms to radioactive contaminants. The consequences of such events can differ markedly between resident fish populations and migratory species that move through affected areas. While these contrasting responses have been evaluated by the authors for coastal nuclear accidents, comparable assessments for open-sea scenarios remain limited. We simulated radionuclide releases from vessels in the North Atlantic to evaluate exposure pathways and potential ecological effects on both resident and migratory fish, since several naval bases operating nuclear-powered vessels are located along the eastern North American coastline. Physical transport of radionuclides was modeled using a Lagrangian framework that incorporates advection by ocean currents, three-dimensional turbulent diffusion, radioactive decay, and dynamic sediment–water exchanges. This transport model was coupled to a four-compartment food-web bioaccumulation model representing phytoplankton, zooplankton, non-piscivorous fish, and piscivorous fish. The approach allows evaluation of contaminant uptake in resident fish populations and along the migration routes of highly mobile species. Bluefin tuna (Thunnus thynnus), a key ecological and commercially valuable species, was selected as the migratory case study. Migration paths reconstructed from electronic tagging data were integrated to estimate radionuclide exposure along individual trajectories. This combined modeling framework provides new insight into how open-sea nuclear releases may differentially affect resident fish communities and wide-ranging migratory species in the North Atlantic, with relevance for fish ecology, population risk assessment, and fisheries management.

This paper presents an illustrative integrated assessment of human effective dose and absorbed dose rates to Reference Animals and Plants (RAPs) for a hypothetical Arctic marine dumping case. The assessment follows the IAEA MEREIA common framework and uses a hypothetical source term derived from published inventories to support method demonstration rather than site-specific prediction. Activity concentrations of Co-60, Sr-90 and Cs-137 were obtained with a three-dimensional Lagrangian transport model supported by HYCOM circulation modelling. Four receptor points were selected; the dump site, an offshore point and two coastal locations indicated by the dispersion modelling results. Human doses were calculated for adults and infants using representative habit data and age-specific dose coefficients, considering ingestion of marine foods and external exposure on the shore. Dose rates to biota were calculated for three RAPs (brown seaweed, crab and flatfish) and for the reference organism ‘seabird’, taking into account external exposure from water and sediments and internal exposure through the use of appropriate concentration ratios. Across receptor points the highest dose estimates were predicted to occur near the dump site, while coastal locations showed lower estimates and a larger relative contribution from external exposure. The results provide a transparent example of how the MEREIA assessment approach can be applied in Arctic conditions and how transport outputs can be carried through to integrated human and biota assessment.

Lagrangian particle-tracking models are increasingly used to simulate radionuclide transport in marine environments, especially for assessing the consequences of accidental releases. However, existing models generally neglect radioactive decay chains, limiting their ability to reproduce the complete behavior of radionuclides and their progeny. To the authors’ knowledge, this work presents the first implementation of radioactive decay chains within a fully three-dimensional Lagrangian marine radionuclide transport model, explicitly coupling stochastic particle tracking with decay kinetics and dynamic sediment–water interactions, enabling a realistic simulation of parent–daughter transformations in the ocean. The approach is tested for the chain in the Western Mediterranean Sea, following a hypothetical nuclear accident. Results confirm that the stochastic treatment accurately reproduces analytical decay solutions and can be seamlessly incorporated into operational-scale transport simulations. The framework can be extended to other radionuclide series and marine domains, providing a versatile and computationally efficient tool for emergency response, environmental impact assessment, and safety analysis in nuclear engineering applications.