Design considerations for steel containments

Abstract

Steel containments provide a low-leakage housing for nuclear reactors. In the unlikely event of a break in the reactor primary system piping, the containment vessel is to prevent the spread of radioactivity. Steel containment vessels are essentially axisymmetric shells of revolution. Because of this, analysis models must be able to characterize three-dimensional behavior. Typically, the containment shell is represented by a discretized model composed of one-dimensional axisymmetric ring elements and solutions are found by numerical methods. The model is usually assumed to behave linear-elastically except in assessments of containment buckling capacity and localized dynamic loads. The main limitation of the axisymmetric model is that all structural characteristics of the actual containment are modeled as rotationally symmetric about a vertical axis at the containment center. The ASME Boiler and Pressure Vessel Code provides a standard for the determination of what loads must be considered in the design process. In addition to normal operating loads, the containments are designed to resist the severe loads resulting from plant mishaps or severe natural phenomena such as earthquakes or both. These loads are often dynamic in nature and thus require solutions in the time or frequency domain. Working-stress design philosophy is currently used for containmentmore » design. Therefore, the stresses are based on service load conditions. These stresses must be less than or equal to some fraction of the nominal resistance, as specified by the ASME Code. An expansion of this approach, that introduces the probabilities of load events and containment resistance, is also presented.« less