Seismic margins review of nuclear power plants: Methodology and applications

A methodology for performing the assessment of existing seismic margins in nuclear power plants in the United States has been developed by a USNRC funded research program at the LLNL. In this methodology, the seismic margin for a component/system or plant is measured in terms of a High Confidence Low Probability of Failure (HCLPF) capacity. The seismic capacity is excpressed in terms of the peak ground acceleration measured at the site. The HCLPF capacity may be defined as the peak ground acceleration value for which there is 5% probability of failure at 95% confidence. The methodology has been applied on a trial basis to estimate the seismic margin for Maine Yankee Atomic Power Station. This paper describes the seismic margin review methodology and discusses the insights obtained in the trial plant review of Maine Yankee. (orig./HP)