The Study of Structural Fragility for Containment Performance under Pressurization

The reactor containment is the last confinement barrier offission products, and, therefore, its integrity is greatlyconcerned in nuclear industry. As a result, it must beinsured if a structural failure occurs, it will fail in amanner that will present the least possible danger to thepublic.In order to perform a severe accident simulation, arepresentation of the containment performance underinternal pressurization must be developed. Whenstudying the pressure capacity of reactor containment, itis important to have an understanding of how thesestructures behave under loading. The critical task is tochoose a criterion and then measure the performance ofthe containment structure using structural analysis. Thecontainment performance goal is intended to ensure thatthe containment structure has a high probability ofwithstanding the loads associated with severe accidentphenomena, and that the potential for significantradioactive releases from containment is small.In this paper, the methodology of containmentperformance analysis is thoroughly reviewed, and aframework for practical analysis of overpressureprobability is proposed. Application of the method on atypical Pressurized Water Reactor (PWR) containment isstudied. The reactor containments is analyzed withANSYS, and the ultimate pressure is computed.Containment performance is analyzed using the structuralfragility method. The structural fragility serves as theinterface between the structural analysis model and therisk model of the systems. Therefore, a probabilisticscheme is used to represent the structural fragility. Finaloutcome of this study is the overpressure fragility curvewhich depicts the probability of failure of thecontainment at a given value of pressure. This curve is asignificant tool for conducting probabilistic safetyassessment (Level 2 PSA) of nuclear power plants.