Seismic safety margins research program

A probabilistic methodology that realistically estimates the behavior of nuclear power plants during an earthquake was developed. Models for seismic input, soil structure interaction, dynamic response of structures and subsystems, and fragility are developed and combined using a probabilistic computational procedure. Sensitivity studies to gain engineering insight into seismic requirements were started. Degree of conservatism of the SRP seismic safety requirements are estimated and improved methods for safety assessment developed. The probability of failure of systems, components, and structures, and the probability of radioactive releases from a range of earthquake levels were used to define needed improvements in the methodology. Necessary validation improvements were carried out and the validated methodology was used to refine estimates of conservatism and define the seismic contribution to reactor risk.