The Study of Structural Fragility for Containment Performance under Pressurization

The reactor containment is the last confinement barrier of fission products, and, therefore, its integrity is greatly concerned in nuclear industry. As a result, it must be insured if a structural failure occurs, it will fail in a manner that will present the least possible danger to the public. In order to perform a severe accident simulation, a representation of the containment performance under internal pressurization must be developed. When studying the pressure capacity of reactor containment, it is important to have an understanding of how these structures behave under loading. The critical task is to choose a criterion and then measure the performance of the containment structure using structural analysis. The containment performance goal is intended to ensure that the containment structure has a high probability of withstanding the loads associated with severe accident phenomena, and that the potential for significant radioactive releases from containment is small. In this paper, the methodology of containment performance analysis is thoroughly reviewed, and a framework for practical analysis of overpressure probability is proposed. Application of the method on a typical Pressurized Water Reactor (PWR) containment is studied. The reactor containments is analyzed with ANSYS, and the ultimate pressure is computed. Containment performance is 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 significant tool for conducting probabilistic safety assessment (Level 2 PSA) of nuclear power plants.