Probabilistic analysis of containment structural performance in severe accidents

To study the capacity of reactor containment under pressurization, it is important to know the way that this structure reacts under internal pressure loading. This is usually performed through structural fragility analysis for assuring that the containment structure has high capability of withstanding the loads associated with severe accident phenomena and its consequent pressurization, therefore the potential for significant radioactive release is small. In this paper, the methodology of structural fragility analysis for pressurization is thoroughly reviewed, and its practical application is demonstrated on a real case Pressurized Water Reactor containment. The reactor containment is analyzed using finite element method, and the ultimate pressure is computed. Containment performance is further analyzed using the structural fragility method. The structural fragility serves as the interface between the structural analysis model and the risk model of the systems. Therefore, a probabilistic scheme is used to represent the structural fragility. Final outcome of this study is the overpressure fragility curve which depicts the probability of failure of the containment at a given value of pressure. This curve is a key element in conducting probabilistic safety assessment (level 2 PSA) of nuclear power plants.