Uncertainty Assessments in Severe Nuclear Accident Scenarios

Managing uncertainties in industrial systems is a daily challenge to ensure improved design, robust operation, accountable performance and responsive risk control. This paper aims to illustrate the different depth analyses that the uncertainty software LEONAR, devoted to a specific application, can propose. The physical model of LEONAR describes some of the phenomena, related to the molten core behavior, which may arise in severe accidents in pressurized water reactors, starting from the core degradation and ending either with stabilization or with the complete ablation of the concrete of the pit. LEONAR computes several statistical quantities (failure probabilities of the reactor vessel and pit, probability distributions of output variables) and performs sensitivity analyses. This paper presents several examples of LEONAR use: precise and punctual needs for not specialist engineers, detailed analyses for confirmed users and helps to physical model developers.