Uncertainty Characterization of Reactor Vessel Fracture Toughness Available to Purchase

To perform fracture mechanics analysis of reactor vessel, fracture toughness (K_Ic) at various temperatures would be necessary. In a best estimate approach, K_Ic uncertainties resulting from both lack of sufficient knowledge and randomness in some of the variables of K_Ic must be characterized. Although it may be argued that there is only one type of uncertainty, which is lack of perfect knowledge about the subject under study, as a matter of practice K_Ic uncertainties can be divided into two types: aleatory and epistemic. Aleatory uncertainty is related to uncertainty that is very difficult to reduce, if not impossible; epistemic uncertainty, on the other hand, can be practically reduced. Distinction between aleatory and epistemic uncertainties facilitates decision-making under uncertainty and allows for proper propagation of uncertainties in the computation process. Typically, epistemic uncertainties representing, for example, parameters of a model are sampled (to generate a “snapshot,” single-value of the parameters), but the totality of aleatory uncertainties is carried through the calculation as available. In this paper a description of an approach to account for these two types of uncertainties associated with K_Ic has been provided.