Intercomparison of Model Calculation of the Turnover of Ra-226 within an Aquatic Ecosystem

Within the international BIOMOVS project a broad comparison and testing of assessment models is undertaken for different release and dispersion scenarios.One of these scenarios dealt with the turnover of Ra-226 and Th-266 in a lake ecosystem. This ecosystem is continuously contaminated by inflow from a river over a period of 100 years with a concentration of 1 Bq/1 of each nuclide.This paper discusses the results from seven models which have been used to calculate results for Ra-226. Best estimates and associated uncertainties of the concentration in fish, sediment and drinking water are compared as well as major contributions to the uncertainties. The reasons for discrepancies between the results from the different models are summarized. Some recommendations on how to improve the confidence in results and reduce the uncertainty are given.