ABSTRACT

In the deep geological disposal facility for radioactive waste to be built in France, it is planned to encapsulate high level waste in carbon-steel overpacks before inserting them into horizontal micro-tunnels. The main function of the overpack is to isolate the waste from the environment long enough for its radio-toxicity and heat to significantly decrease. Several phenomena affect the overpack during its lifetime. The prediction and modelling of these phenomena are subjected to many uncertainties due to their complexity and their extrapolation over long time periods (several centuries). This paper presents an overall framework for the estimation of the failure probability of the overpacks over time. The failure scenario considered is the fracture of the overpack. The analysis is based on a parameterized finite element model taking into account the evolution of the geometry due to the non-uniform corrosion process, the evolution of the mechanical loading and their variability. In addition the manufacturing process may induce defects which are modeled as cracks and included in the model of uncertainty. The whole process is run for several time steps until the complete failure of the overpack. The reliability estimation is based on a two-level Monte Carlo analysis and according to a fracture mechanics criterion based on a probabilistic critical stress intensity factor.