Uncertainties : new ways to take them into account

Titre du congrès :IRPA 2006 2nd European IRPA Congress on Radiation Protection Ville du congrès :Paris Date du congrès :15/05/2006

The uncertainties analysis has become a stage impossible to circumvent in the evaluation and risk management process. However, the realization of an analysis of uncertainties raises many technical difficulties because it often runs up against the limits of scientific knowledge and the formalization of some sources of uncertainties rests on an incomplete or subjective knowledge. Moreover, the propagation of vague knowledge, i.e. the characterization of its effect on the computation result, requires the use of theories still badly known in the field of radioprotection, the theories of the uncertain. The present communication proposes to present the work completed for several years by the Institut de Radioprotection et de Sûreté Nucléaire (IRSN) in collaboration with the Bureau de Recherches Géologiques et Minières (BRGM), the Institut National de l'Environnement Industriel et des Risques (INERIS) and the Institut de Recherche en Informatique de Toulouse (IRIT - Université Paul Sabatier) on the representation and the propagation of incomplete or vague information and its application in the case of the contamination of the food chain by radioactivity. The main objective of this work is to promote coherence between the way the information is mathematically represented and information really available. To achieve this objective, alternative methods are proposed to represent and propagate uncertainties. In particular, this work highlighted that the systematic use of probability distributions to represent environmental knowledge is often subjective and arbitrary and can result in underestimating the risk. To exceed this problem, the possibilities of use of various theories of uncertain were studied (probabilities, possibilities, functions of belief, p-boxes and fuzzy numbers). This utilisation required mathematical and numerical developments to elaborate tools usable for the representation and the propagation of knowledge available in environmental sciences. These tools will be described through their application to the case of the contamination of milk following a chronic strontium 90 deposit. This concrete example makes it possible to compare the impact of the different mathematical methods and to discuss the difficulties of the use of the various kinds of results produced within the framework of the decision-making.