Uncertainty analysis of containment resistance subjected to seismic loading

Because of the possibility of leakage of any radioactivity which may accidentally be present within a nuclear power plant containment vessel, a best estimate of the containment resistance is required. This paper represents a portion of a project sponsored by the USNRC, the objective of which is to assess the uncertainty of the containment resistance to seismic and other types of loading. The present work is to characterize the statistical properties of the vessel resistance to seismic excitation. The results yield the cumulative probability distribution of the structural system resistance, i.e., fragility curve. For seismic analysis, the earthquake input is often specified in terms of a design response spectrum. In this paper, a random vibration analysis technique is presented which is calibrated to a standard design response spectrum. The ground excitation is considered to be a non-stationary random process. The standard deviation of the response is related to the ground excitation by a random vibration analysis. A reduced mean zero crossing rate is empirically obtained to best fit thirty-nine historical strong motion records. The statistical parameters of the maximum response, i.e., mean and standard deviation of an Extreme Value Type I distribution, are developed. The multi-degree-of-freedom solution is given in the form of cross-modal contributions that explicitly account for the correlation between modal responses which can be highly significant when the modal frequencies are closely spaced. Also given are the statistical parameters of the induced forces which cause instability of the containment structure. (orig./RW)