Western U.S. Reactors are Completing Their Seismic Picture

Lauren Gibson
Project Manager
Japan Lessons-Learned Division

An ongoing lesson from 2011’s Fukushima Dai-ichi accident involves U.S. reactors better understanding their earthquake hazard. Reactor owners in the Western parts of the country have had to assemble a particularly complex jigsaw puzzle of seismic information. They’ve just sent the NRC their detailed re-analysis.

seismicgraphicThe graphic shows the three pieces of information U.S. reactor owners have used to analyze their specific hazard:

  • Where quakes are generated (seismic source)
  • How the country’s overall geology transmits quake energy, (ground motion/attenuation) and
  • How an individual site’s geology can affect quake energy before it hits the reactor building (site amplification).

Central and Eastern U.S. reactors benefitted from region-wide updated earthquake source information and a model of quake energy transmission for the first two pieces. Plants west of the Rockies, however, had to deal with the West’s more active and interconnected faults.

Columbia, Diablo Canyon Part I and Part II and Palo Verde used the Senior Seismic Hazard Analysis Committee (SSHAC) approach to develop site-specific source models and ground-motion models. This group of independent seismic experts develops guidance on major seismic studies such as this. The group has met several times the past few years to ensure the Western plants properly conduct and document their seismic activities.

The NRC carefully considers SSHAC comments and recommendations before the agency comes to its own conclusions on seismic issues. We’re currently evaluating the Western plants’ reports and will issue our short-term screening and prioritization review later this spring.

As for the Central and Eastern U.S. plants’ March 2014 submittals, we screened them to determine what other actions the plants might have to take. Plants that have more to do were grouped into three priority groups with staggered deadlines. Many of those plants submitted additional analyses in December 2014, and the NRC continues reviewing both that information and the March 2014 submittals.

Dealing with the Possibility: Nuclear Power Plants and Earthquakes

Roger Hannah
Senior Public Affairs Officer
Region II, Atlanta
 

Tquakehe NRC requires all nuclear power plants to consider the effects of possible earthquakes in their area – designing, operating and maintaining safety-related structures and equipment to ensure that they can endure a seismic event and still function.

Two events in 2011 only a few months apart highlighted the importance of the NRC’s seismic regulations.

In March 2011, a strong earthquake off the coast of Japan caused a tsunami that disabled power supplies and cooling to several nuclear reactors at the Fukushima japanquakeDaiichi nuclear station. Important safety structures and equipment were largely undamaged by the earthquake’s ground motion, but flooding created major problems.

Months later, In August 2011, a much smaller earthquake occurred near Mineral, Va., close to the North Anna nuclear station.

The quake exceeded some levels for which the plant was designed and licensed, but detailed reviews and inspections by Dominion, the plant operator, and the NRC confirmed there was no damage to safety equipment. Both North Anna units remained offline until November of that year when the NRC was certain they could be restarted safely.

NRC seismologists have worked closely with NRC inspectors, license reviewers and others within the agency to apply the real-world lessons of Fukushima and North Anna to all other U.S. nuclear plants. The NRC is working to ensure potential earthquake hazard information for each nuclear plant site accurately reflects what might be expected, and the agency is requiring nuclear plants to reanalyze those risks over the next several years.

Fortunately, the seismic risk for most U.S. nuclear plants is very low, but the NRC continues to examine information from actual earthquakes, review improved predictive models and inspect plants to be certain that people living near U.S. nuclear plants are adequately protected if an earthquake does occur in that area.

We’ll be posting a new YouTube video on the subject soon, and please join our Chat, tomorrow, with NRC seismic expert Dr. Annie Kammerer. She’ll be “chatting” about how the NRC makes sure plants can withstand any earthquakes they may experience. She can also talk about the Mineral, Va., earthquake but won’t be able to address specific questions about designs or risk at other sites.

Note: The Chat is now closed. To view the archive, go here: http://chat.nrc-gateway.gov/2013/07/31/earthquakes-and-nuclear-power-plants-this-chat-is-closed/