PREDICTING THE LONG-TERM BEHAVIOR OF SR-90 IN LACUSTRINE SYSTEMS BY ACOLLECTIVE MODEL

This paper describes a model for predicting the behaviour of Sr-90 in lakes. The model, which accounts for the mass balances of the contamin ant in water, includes the processes of radionuclide migration through the lacustrine abiotic components and from the drainage area. It is a pplied to seven Italian lakes contaminated by Sr-90 due to nuclear wea pon tests in the atmosphere over past decades. The results of the sens itivity and uncertainty analyses are described. The uncertainty of the model is less than a factor of 1.5 around the predicted values (68% c onfidence levels) over a period of more than 40 years. The model makes use of 'collective parameters' which summarise, in single quantities, complex sets of competing processes occurring in the lacustrine envir onment. Such parameters are scantily variable and uncertain despite th e large range of lake characteristics. Therefore, the model may be suc cessfully applied to a variety of different environmental situations a s a generic tool for evaluating the concentration of the radionuclide in water. The values of the most important migration parameters are th e following: migration velocity from water to sediment is 1.2 x 10(-7) m s(-1) (deep lakes) and 3.5 x 10(-7) m s(-1) (shallow lakes); migrat ion rate from sediment to lake water is 3.0 x 10(-8) s(-1); transfer c oefficient from drainage area to lake is 0.2 m(-1). (C) 1998 Elsevier Science B.V. All rights reserved.