Inelastic analysis of cylindrical steel containment vessels under internal accident conditions

The present paper is concerned with the structural safety assessment of a proposed nuclear steel containment shell during a postulated loss-of-coolant accident scenario. The structural evaluation is performed using a computational second-order refined plastic-hinge method, which is capable of accurately predicting all possible modes of failure in an efficient and computationally less expensive way than the general FEM formulation. A tangent modulus model and a gradual reduction of the inelastic resistance surface are used to take into account directly the structural strength and stability performances in the element formulation. The implemented numerical method provides more reliable safety margins and maintainability, exhibiting a more uniform structural safety level than the linear elastic analysis. A simplified non-linear heat transfer model, developed for symmetrical cross-sections, is used to determine the steel temperature gradient and to establish a link between the thermo and the mechanical analysis. The load resulting from pressure and temperature thermodynamic calculations, obtained for the accident scenario, are considered in the structural quasi–static analysis, so that the structural response can be tracked for the entire duration of the simulated accident.