A risk-based evaluation of the impact of key uncertainties on the prediction of severe accident source terms - STU

The purpose of this project is to address the key uncertainties associated with a number of fission product release and transport phenomena in a wider context and to assess their relevance to key severe accident sequences. Th is project is a wide-based analysis involving eight reactor designs that ar e representative of the reactors currently operating in the European Union (EU). In total, 20 accident sequences covering a wide range of conditions h ave been chosen to provide the basis for sensitivity studies. The appraisal is achieved through a systematic risk-based framework developed within thi s project. Specifically, this is a quantitative interpretation of the sensi tivity calculations on the basis of 'significance indicators', applied abov e defined threshold values. These threshold values represent a good surroga te for 'large release', which is defined in a number of EU countries. In ad dition, the results are placed in the context of in-containment source term limits, for advanced light water reactor designs, as defined by internatio nal guidelines. Overall, despite the phenomenological uncertainties, the pr edicted source terms (both into the containment, and subsequently, into the environment) do not display a high degree of sensitivity to the individual fission product issues addressed in this project. This is due, mainly, to the substantial capacity for the attenuation of airborne fission products b y the designed safety provisions and the natural fission product retention mechanisms within the containment. (C) 2001 Elsevier Science B.V. All right s reserved.