Seismic issues related to nuclear reactor safety in the United States

The threat of earthquakes to nuclear power plants is described, as are the special safety requirements not imposed in conventional practice. The difficulties associated with characterizing design earthquakes are discussed, and US licensing problems that have resulted from uncertainties in seismic input definition are outlined. The two-earthquake design approach in the US is treated, and the role of seismology and geology is delineated. Engineering methods for estimating soil-structure interaction, structural response and subsystem behavior are described. The issue of excessive seismic conservatism and its impact on balanced design is considered. The importance of seismic qualification of electrical and mechanical equipment is indicated, and the need for experimental validation of analysis procedures is shown. Finally, the potential use of probabilistic risk assessment in leading the way to more realistic seismic design requirements is addressed