NEHRP Clearinghouse

Title
Some Probabilistic Aspects of the Seismic Risk of Nuclear Reactors.
File
PB265020.pdf
Author(s)
Hsieh, T.; Okrent, D.
Source
National Science Foundation, Washington, D.C. Research Applied to National Needs., December 1976, 85 p.
Identifying Number(s)
UCLA-ENG-76113
Abstract
The potential for existing cracks in piping systems to grow to critical size and cause system failure during a severe earthquake was examined, and the critical crack size based on linear elastic mechanics was reviewed. A simple and crude method of relating the initial crack size, the range of strain produced in a component, and the number of cycles to failure, was proposed and discussed. The significance of piping failure due to ordinary crack growth other than the intergranular stress corrosion under seismic loading was found to be comparable with the potential for failure due to crack growth under severe seismic loads. A simplified piping system with only a few snubbers and hangers as seismic restraints was devised. The inverse of the maximum Von Mises ratios at a few nodal points of the piping system was used as the basis for indicating the change in safety factor due to piping restraint failures. The potential importance of seismic events leading to a core melt accident was examined by factoring the effect of design errors and system degradation into an estimate of the probability of a core-melt accident due to seismic events.
Keywords
Failure; Risk; Risk benefit analysis; Earthquakes; Uncertainty; Numerical analysis; Nuclear reactor safety; Piping systems; Mathematical models