SEISMIC HAZARD ANALYSIS AS PART OF AN EARLY SITE PERMIT FOR NEW NUCLEAR POWER UNITS AT THE NORTH ANNA POWER STATION

Dominion Resources submitted an application for an Early Site Permit (ESP) to the U.S. NRC for the licensing of up to two new nuclear electrical generation units. The ESP site is located at the North Anna Power Station (NAPS) in Louisa County, Virginia, which has two existing operating nuclear reactors. The ESP process allows site suitability resolution of safety and environmental issues related to reactor siting before a large commitment of resources is made. The Dominion ESP application, currently in review by the NRC, is one of three utility applicant submittals to the NRC for this new regulatory process. As of this writing, several more nuclear utilities have expressed an interest submitting applications for new nuclear units, located primarily in the southeast US.

The NAPS ESP site is located in the northern boundary of the Central Virginia Seismic Zone (CVSZ), which has been identified as the zone that dominates the seismic analysis for the site. The CVSZ represents the densest cluster of low level, persistent seismicity in the region. There is no clear link between seismicity and known tectonic structures in the Central and Eastern United States (CEUS) region, which is not an active plate-margin.

A probabilistic seismic hazard analysis (PSHA) was conducted to determine the Safe Shutdown Earthquake (SSE) and Operating Basis Earthquake (OBE) design ground motions. Sensitivity studies show considerable conservatism in the calculated spectral accelerations associated with the referenced probability level and in the selected SSE spectrum for the ESP site.

Nuclear facilities are designed to withstand a maximum credible seismic event, having high intensity even though it has low probability, i.e., once in 10,000 years. The largest Mmax for the differing characterizations of the CVSZ range from mb 6.6 to 7.2 (M 6.5 to 7.5). A potential exists for distant, large earthquakes in the CEUS contributing to the long period ground motion hazard at the North Anna ESP site from the Eastern Tennessee, New Madrid, and Charleston seismic sources. No evidence of Quaternary fault activity exists within 5 miles of the ESP site. The potential for vibratory ground motion effects and surface faulting at the site are negligible.