Probabilistic evaluation of the leak-tightness function of the nuclear containment structure subjected to internal pressure

This study evaluates the leak-tightness of the nuclear containment structure subjected to internal pressure from a probabilistic perspective. A global FE model of the containment and four refined sub-models in the critical region of the containment are established by the ABAQUS platform, and the leak-tightness of each critical region under overpressure conditions is investigated by the sub-model analysis technique. Based on reliability theory, an analytical method considering the spatial variability of the fracture strain of the steel liner is proposed to evaluate the functional failure probability of the containment. Combining the developed script and the proposed method, the fragility and the total failure probability of the containment corresponding to the functional failure mode are discussed in detail. Results indicate that the tearing sequence of the steel liner in the four critical regions of the containment is the equipment hatch, personnel airlock, emergency airlock, and truncated cone. Moreover, the concrete is severely cracked prior to the tearing of the steel liner, and thus the leak-tightness of the containment under severe accident loads is guaranteed by the steel liner. When the fracture strain of the steel liner in each critical region is completely correlated, the functional failure of the whole containment is controlled by the equipment hatch. As the correlation coefficient decreases, the mean value of the pressure capacity of the containment decreases, and the risk of containment leakage increases at the same internal pressure. When the spatial variability of the fracture strain of the steel liner is neglected, the total failure probability of the containment will be underestimated. In general, the containment investigated in this study can meet the probabilistic performance goal.