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

• Published in: The Science of the total environment 2019-06, Vol.669, p.856-871
• Main Authors: Simonsen, Magne, Lind, Ole Christian, Saetra, Øyvind, Isachsen, Pål Erik, Teien, Hans-Christian, Albretsen, Jon, Salbu, Brit
• Format: Article
• Language: English
• Subjects: Cesium-137 speciation; Dynamic phase interactions; Hypothetic nuclear accident scenario; Lagrangian coastal dispersion model; River discharges
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2019.01.434

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 × 160 m in horizontal direction) and temporal resolution (1 hour), considering a hypothetical accident scenario including river discharges of 137Cs 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 137Cs particle affinity greatly affected the specie distribution (> factor 103 increase in concentration of particle-associated 137Cs) as well as the settling of radionuclides towards the seabed (up to factor 102 increase in 137Cs sediment concentrations). These factors were therefore identified as important contributors to the overall uncertainty. [Display omitted] •Coastal 137Cs transport simulated with high spatial and temporal resolution model•The model includes speciation and dynamic transformation processes•Key factors influencing the overall uncertainty of model output were identified•Implementing transformation processes enables identifying far field hot spots•Transformation kinetics simulations recommended also for conservative radionuclides