Radioactive waste is a serious environmental concern, as it can have detrimental effects on biological systems. The major sources of anthropogenic radioactive contamination to the marine environment are related to nuclear weapon and fuel cycles, in particular global fallout from atmospheric test detonations, accidental and authorized discharges from nuclear installations and leakages from nuclear waste dumped in or near the oceans. Offshore industry also contributes considerably through releases of naturally occurring radionuclides as by-products from petroleum production.
Once released, where does this waste travel?
Where does it go?
In the marine environment, radionuclides can be present in a number of different forms, called species, affecting their transport properties.
"For safety reasons as well as for scientific purpose, there is a need for model systems predicting accurately the spatio-temporal dispersion of radionuclide species in the marine environment,” PhD candidate Magne Simonsen says.
In his doctorate, Simonsen has looked at topics in the crossing point between physical oceanography and radioecology. He has investigated the impact of numerical model representation of biogeochemical and geophysical processes, a numerical model system for marine radionuclide transport was developed and utilized. Simonsen has performed a set of case studies, including historical and hypothetical radionuclide discharges as well as estuarine transport of a trace metal.
The effects of eddies and tides
Focusing on hydrodynamic processes, the impact of including mesoscale eddies and tides was investigated in a long-term (12 years) simulation of historical discharges of technetium (99Tc) radionuclides from Sellafield, UK. The results pointed to systematic Lagrangian tidal drift in the Irish Sea and the North Sea that eventually impacted the 99Tc activity concentration levels also far downstream.
“To avoid systematic errors due to sub-grid scale processes, mesoscale eddies and tides should be included also in long-range transport simulations,” Simonsen says.
Interactions with solid matter
Simonsen has also investigated the impact of key processes on the transport estimates in the hypothetical case involving coastal dispersion of river-discharged 137Cs. His results showed that the effects of including interactions with solid matter were found to be considerable, locally affecting the results with orders of magnitude.
To address the effects of changing environmental conditions on the elemental speciation, a more complex speciation scheme was implemented, where the transfer rates
were dependent on the local salinity to fit the observed behavior of aluminium (Al) in River Storelva and Sandnesfjorden estuary. The general patterns of observational total Al concentrations and speciation data were well reproduced by the model.