Dynamic modeling of radionuclide transfers in the marine Environment in the English Channel from discharges to biota

Abstract

International audienceRadionuclide transfer parameters between water and biota recommended in the literature are generally limited to the concentration factor values (CF). So a steady state must be assumed when using them for modeling. But in the event of an accident or in the close vicinity of a regular input source where concentrations are maximal, sharp changes in seawater concentration are likely to occur and the assumption of a steady state is usually not met. Dynamic modeling requires taking into account the kinetics of the transfer, usually characterized by the radionuclide biological half-life (tb1/2), but recommendations for tb1/2 values are still scarce. The nuclear reprocessing plant of ORANO La Hague (France, Normandy) is the major source of liquid radioactive discharges to the marine environment in the English Channel. A hydrodynamic model has been extensively validated by matching several thousands of calculated and locally observed concentrations in seawater. It is now available to reliably predict the dispersion of radioactive discharges in this area. It is also possible to calculate the corresponding seawater radionuclide concentrations in locations where long time-series measurement in biota are available. Using the calculated signal in seawater and the observed signal in biota, it is possible to derive dynamic transfer parameters (CF, tb1/2) to model radionuclide transfers between seawater and the biota. This data processing was performed with radionuclides data including Cs-137, Co-60, I-129, monitored in algae, mollusks, crustacean and fish, around La Hague Cape. In addition, a distribution analysis of the residual between the calculated and observed values was carried out. On the basis of this data processing, recommendations for dynamic transfer parameters (CF, tb1/2) values are proposed for these radionuclides and these recommendations are supported by documenting the reliability of the modeling from the discharges down to the biota