Simulating 241Pu, 241Am and 237Np transport released from a nuclear fuel reprocessing plant in the European Shelf Seas and their fluxes into the Arctic

A three-dimensional Lagrangian particle-tracking model has been applied to simulate the dispersion, sediment interactions and radioactive decay of 241 Pu, 241 Am and 237 Np released from the Sellafield nuclear fuel reprocessing plant into the European Shelf Seas over the period 1952-2014. The model incorporates advection by currents, turbulent diffusion, reversible sediment-water exchanges and the explicit representation of the 241 Pu → 241 Am → 237 Np decay chain. Simulated concentrations in surface waters and bottom sediments are compared with available measurements in the Irish Sea, North Sea and adjacent regions, reproducing the contrasting environmental behaviours of the three radionuclides. Results highlight the strong sediment retention of 241 Am and 241 Pu, whereas 237 Np exhibits a more conservative behaviour and wider dispersal. Fluxes into the Arctic Ocean through the Norwegian Coastal Current are quantified, yielding cumulative exports of 2 . 07 × 1 0 14 Bq for 241 Pu and 1 . 43 × 1 0 14 Bq for 237 Np, and suggesting an average transit time of approximately 10 years for 241 Pu from Sellafield to the Arctic boundary. Basin-scale inventories in water and sediments are also estimated, revealing the dominant role of sediments as long-term sinks for particle-reactive radionuclides. The results demonstrate the capability of the modelling framework to provide internally consistent multi-decadal inventories and fluxes for complex radioactive decay chains in shelf-sea environments.