Both deterministic and probabilistic methods are used to assess the integrity of a reactor pressure vessel (RPV) subjected to pressurized thermal shocks (PTSs). The FAVOR code is applied to calculate the probabilities for crack initiation and failure of the RPV subjected to two transients, by considering crack distributions based on cracks observed in the Shoreham and pressure vessel research user facility (PVRUF) RPVs. The crack parameters, i.e., crack density, depth, aspect ratio, orientation, and location are assumed as random variables following different distributions. KI of the cracks with the same depth increases with its aspect ratio. Both KI and KIc at the crack tip increase with crack depth, which is the reason why a deeper crack does not necessarily lead to a higher failure probability. The underclad crack is the most critical crack and the deeper crack is the least critical one in this study. Considering uncertainties of the transients results in higher failure probabilities.