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Under the International Atomic Energy Agency (IAEA)'s EMRAS (Environmental Modelling for Radiation Safety) programme, activity concentrations of (60)Co, (90)Sr, (137)Cs and (3)H in Perch Lake at Atomic Energy of Canada Limited's Chalk River Laboratories site were predicted, in freshwater primary producers, invertebrates, fishes, herpetofauna and mammals using eleven modelling approaches. Comparison of predicted radionuclide concentrations in the different species types with measured values highlighted a number of areas where additional work and understanding is required to improve the predictions of radionuclide transfer. For some species, the differences could be explained by ecological factors such as trophic level or the influence of stable analogues. Model predictions were relatively poor for mammalian species and herpetofauna compared with measured values, partly due to a lack of relevant data. In addition, concentration ratios are sometimes under-predicted when derived from experiments performed under controlled laboratory conditions representative of conditions in other water bodies.

Abstract.The existing POSEIDON compartment model, developed for modelling the dispersion of radionuclides in coastal areas for regular discharges was modified to be applicable in accidental conditions. One of the important modifications was the development of a generic uptake model for marine organisms to deal with short pulses of radionuclides after accidental releases in the coastal environment. A generic foodweb model to be used in die decision support system POSEIDON-R has been developed. Six key organisms represent the different trophic levels with identical physiological properties. To avoid the introduction of different compartments for the several organs in which radionuclides can accumulate, the so-called target tissue approach was followed. It is assumed that each radionuclide accumulates in a single specific tissue, (tie key tissue), and that the behaviour of this radionuclide is organ-and not radionuclide-dependent. To test tie reliability of this model, validation tests for various regions, and for several radionuclides, are required. Tests for the Baltic Sea and the Black Sea for the period after die Chernobyl accident in 1986 demonstrated a rather good agreement with tie measured data on radiocaesium. The model gave in some cases an overestimation, which is not unacceptable for the aim of decision support.