Uncertainty analysis in an accidental situation. Radionuclide transfer in environment and assessment of human exposure by food

Major nuclear accidents of Chernobyl (April, 1986) and Fukushima (March, 2011) have led to a huge environmental contamination with important amounts of radionuclides released in the atmosphere. Risk assessment, in case of nuclear emergency, is confronted to uncertainties on the transfer of radioactive substances in terrestrial ecosystems and to human population through the food chain, which could affect the reliability of decisions. The extent of the repercussions of Chernobyl and Fukushima accidents highlighted the difficulty of managing the consequences of such disasters and specifically to accommodate the different sources of uncertainty within decision-making processes. The objective of this research project is to develop a methodology to take into account uncertainties within environmental and food risk assessment models in order to improve decision support tools used for accidental situations. In this regard, different hierarchical Bayesian models aiming at capturing, within a unique modelling framework, uncertainty and variability about radioecological parameters of great important for accidental situation (dry and wet interception fractions and weathering loss parameter) were developed. Models parameters were estimated by Bayesian inference applied on databases obtained by an extended literature review. The impact on the risk assessment models of uncertainty and variability about these radioecological parameters was then assessed by stochastic simulations and sensitivity analyses applied on two case-studies: a hypothetical accident simulating a standardized deposition of radionuclides and the accident of Fukushima nuclear power plant. The works developed in this project contribute to enhance knowledge on key processes governing environmental transfer of radionuclides and to improve the parameterization of the radioecological risk assessment models with respect to the research lines outlined by the scientific community in radioecology. (author)