IRSN, Centre d'études de Cadarache, 13105Saint-Paul-lez-Durance, France.
Taking uncertainties into account has become an essential stage in the risk assessment process. The lack of scientific knowledge can, however, make it difficult to perform an uncertaintyanaly sis. It is then necessaryto relyon subjective knowledge, that is, expert judgment, to determine the distributions to be used in the uncertaintyanaly sis. Moreover, the characterization of the results of these calculations must be based on theories not yet clearly understood in the field of radioecology. Finally, the communication of the results to the public and to decision-makers is a crucial but sensitive step. These difficulties are illustrated with examples of radioactive and chemical risk assessments bythe Nord-Cotentin Radioecology Working Group for emissions, effluents and discharges from the Nord-Cotentin nuclear facilities.