New Seismic Model Available for US Plant Hazard Analyses

The following story originally appeared in NEI’s Nuclear Energy Overview.

A new study will help operating U.S. nuclear facilities in the central and eastern United States reassess their seismic risks as part of efforts to implement lessons learned from the events at Fukushima Daiichi. A revised seismic model resulting from the study will also be used by the U.S. Nuclear Regulatory Commission to license new nuclear facilities.

The seismic source model emerged from a four-year study conducted by the Electric Power Research Institute, the Energy Department and the NRC. It replaces models in use since the late 1980s and will help operators of nuclear energy facilities determine how they can better prepare for extreme events that might occur about once in 10,000 years.

It applies to 96 nuclear reactors at 62 sites in the central and eastern United States. Plants in the West are not included in the new model because they are in a different seismic region that is beyond the scope of the study. Operators of those facilities will need to develop site-specific seismic source characterization models, EPRI said.

The study incorporates additional peer-reviewed data on historical earthquakes in the region from 1568 through 2008 and revised geological information. A range of national and international experts used new analytical methods to develop the new seismic model.

In a statement, the NRC said, “Calculations with the new model are expected to result in a higher likelihood of a given ground motion compared to calculations done using previous models.”

However, the NRC added that other factors would determine each plant’s overall risk profile. “Plant operators must combine the information from the new model with a plant’s design and safety features to determine site-specific risks.”

As part of its ongoing response to the Fukushima accident, the NRC is requesting that nuclear facility operators re-evaluate seismic and flooding hazards at operating reactor sites. A draft information request letter says licensees will be able to base their evaluations on the new seismic model.

The draft letter sets in motion a two-phase process to address the task force recommendation on seismic re-evaluations. In the first phase, information will be gathered from licensees and potential vulnerabilities at nuclear energy facilities identified. The second phase will determine whether additional regulatory actions, such as updating the seismic design basis of a facility, are necessary.

Begun in 2008, the study was not undertaken as a result of the nuclear accident at Fukushima Daiichi or the August 2011 earthquake in Virginia. EPRI noted that the March 2011 Japan earthquake was not in the study region and occurred within a very different tectonic environment, so it does not have implications for the new seismic model. EPRI added that if the model is updated again, the Virginia earthquake will be included.

The new seismic report and model are available at http://www.ceus-ssc.com/project_report.html. A set of frequently asked questions on the study can be found at http://mydocs.epri.com/docs/Nuclear/SeismicSourceFAQs.pdf.