3 LONG-RANGE TRANSPORT MODELS COMPARED TO THE ETEX EXPERIMENT - A PERFORMANCE STUDY

For operational or research purposes (dispersion computations of radio active effluents during nuclear emergency situations, simulations of c hemical pollution in the vicinity of thermal power plants), different models of passive dispersion in the atmosphere have been developed at the Environment Department of EDF's R and D Division. This report pres ents the comparison of the performances of three such models: DIFTRA ( lagrangian puff model, with operational goal), DIFEUL (three dimension al eulerian) and DIFPAR (Monte Carlo particle model) for the simulatio n of the first ETEX release, an international tracer campaign during w hich a passive tracer cloud has been followed over Europe. The results obtained in this study give model vs, experience differences of the s ame order as the model vs. experience differences observed during an i nternational model comparison experiment using data of the Chernobyl r elease, the ATMES exercise. In addition to the standard statistical sc ores used in the evaluation of the performances of the transport model s two asymmetric scores (in contradistinction with the Figure of Merit in Space) are proposed: ''efficiency'' and ''power''. Their aim is to separate the two manners in which a model may be wrong: by predicting presence of pollutant while none is measured or conversely predicting absence when pollutant is actually detected. (C) 1998 Elsevier Scienc e Ltd. All rights reserved.