Comparison of biospheric models of radionuclides transfer

The international BIOMOVS A4 exercise has made possible that a set of biospheric transfer models could predict the daily radionuclide concentration in soils, forage and some animal products (cow milk and beef) after the Chernobyl accident. The aim was to compare these predictions with experimental results in 13 locations around the world. The data provided were essentially the daily air contamination and precipitation and some site-dependent parameters. It was a blind test, the locations and experimental measures were not revealed in advance. Twenty-three models (quasi-steady state and time-dependent models) were involved in the study. In this paper an explicit criterion has been used in order to select the models that better fitted the experimental results. In nine selected locations a comparative analysis between these models has been carried out for obtaining the structural and parametric coincidences that could explain their relatively good performance. The first evidence obtained has been that a wide set of models were able to predict the order of magnitude of the nuclides time-integrated concentrations in several important biospheric comportments. But only a few models, all of them with a 'dynamical' structure, fitted the daily behavior with the reasonable agreement. The dynamical structure of the five most successful models at predicting for Caesium 137 (CIRCLE, ECOSYS, PATHWAY, PRYMA and RAGTIME) shows some common patterns that may be relevant for a better modelling of nuclear accident scenarios. (author)