Coastal transport of river-discharged radionuclides: Impact of speciation and transformation processes in numerical model simulations

Following a potential nuclear accident, river run-off may potentially become a significant source of radionuclide contamination to the coastal marine environment. In the present work, code for radionuclide speciation and dynamic transfer of radionuclides between the different species was implemented in a Lagrangian marine dispersion model. A case study was performed where the model system utilized ocean circulation fields at relatively high spatial (160 m x 160 m in horizontal direction) and temporal resolution (1 hour), considering a hypothetical accident scenario including river discharges of Cs-137 to the marine environment. Results from a number of simulations were compared to identify how factors associated with radionuclide speciation and transfer between the model compartments could affect the predicted radiocesium activity concentrations. The results showed that by including dynamic transfer of radionuclides between the model compartments, the total activity concentrations at far-field sites could vary with more than two orders of magnitude, demonstrating that this model configuration enables prediction of potential local hot-spots. However, the total activity concentration near the river outlets was less affected (< factor 10). The radionuclide speciation in the river discharges and the parameterization of Cs-137 particle affinity greatly affected the specie distribution (> factor 10(3) increase in concentration of particle-associated Cs-137) as well as the settling of radionuclides towards the seabed (up to factor 10(2) increase in Cs-137 sediment concentrations). These factors were therefore identified as important contributors to the overall uncertainty. (c) 2019 Elsevier B.V. All rights reserved.