Probabilistic site dependent design spectra for a NPP

A methodology is proposed to compute the design spectra for a NPP site. Near field earthquakes are included by using an appropriately scaled sample of response spectra. Site effects are considered through a probabilistic site response analysis in the frequency domain which considers nonlinear behaviour of soils. The uncertainties of the soil shear modulus, G, are introduced by using Rosenblueth's point estimates. Strong motion duration is treated by using sensitivity analysis. The procedure is applied to a NPP site and the results are: a) the USNCR R.G.1.60 underestimate the spectral amplitudes for frequencies of interest; b) the omission of the uncertainties on the G leads to under or over-estimate the spectral amplitudes at certain frequency bands; c) the effect of considering the actual strong motion duration instead of an average value is to reduce the peak spectral amplitudes by a ten per cent. (orig.)