Effects of Various Factors on Durability Prediction of Nuclear Waste Containment Structures - 11546

A numerical methodology is presented in this paper to simulate the degradation of concrete vaults exposed to aggressive sulfate-containing pore solution of the low activity nuclear wastes. The methodology incorporates (i) transport of ions, (ii) chemical reactions, and (iii) damage accumulation due to cracking. The required parameters and boundary conditions for simulating structural damage are generally obtained from literature and experiments. Parameters that cannot be directly measured in experiments are often estimated using measurable quantities and empirical relations. Uncertainty in inputs, model parameters and boundary conditions due to inherent randomness, lack of data and incomplete knowledge of the physics introduces uncertainty in the model prediction, which is evaluated using sensitivity analysis and Monte Carlo simulation. This paper investigates the effects of three primary factors on the model prediction. These are – (1) chemical equilibrium models comprised of different combinations of mineral phases and initial concentrations of ionic species, (2) prescribed boundary conditions, and (3) a mechanical parameter required for initiation and propagation of cracking. The numerical model is then used to assess durability of a concrete containment structure considering uncertainty in the selected physical and chemical parameters. Various approaches for statistical representation of the uncertainties are incorporated in the durability assessment framework. Finally, the probability distribution of time to structural damage is evaluated using a single loop Monte Carlo simulation technique.