Predicting the long term behaviour of 90Sr in lacustrine systems by a collective model

This paper describes a model for predicting the behaviour of 90Sr in lakes. The model, which accounts for the mass balances of the contaminant in water, includes the processes of radionuclide migration through the lacustrine abiotic components and from the drainage area. It is applied to seven Italian lakes contaminated by 90Sr due to nuclear weapon tests in the atmosphere over past decades. The results of the sensitivity and uncertainty analyses are described. The uncertainty of the model is less than a factor of 1.5 around the predicted values (68% confidence levels) over a period of more than 40 years. The model makes use of `collective parametersʹ which summarise, in single quantities, complex sets of competing processes occurring in the lacustrine environment. Such parameters are scantily variable and uncertain despite the large range of lake characteristics. Therefore, the model may be successfully applied to a variety of different environmental situations as a generic tool for evaluating the concentration of the radionuclide in water. The values of the most important migration parameters are the following: migration velocity from water to sediment is 1.2×10−7 m s−1 (deep lakes) and 3.5×10−7 m s−1 (shallow lakes); migration rate from sediment to lake water is 3.0×10−8 s−1; transfer coefficient from drainage area to lake is 0.2 m−1.