Adding a Piece to the Seismic Puzzle

Clifford Munson
Sr. Technical Advisor for Nuclear Plant Siting
Office of New Reactors

One of the important lessons from 2011’s Fukushima Dai-ichi accident was the need for U.S. reactors to better understand their earthquake hazard. Reaching that understanding is a bit like assembling a jigsaw puzzle, and reactor owners in the central and eastern parts of the country are sending the NRC one of their pieces this month.

seismicThe graphic shows the three pieces of information U.S. reactor owners need in order to analyze their specific hazard:

• Where quakes are generated

• How the country’s overall geology transmits quake energy, and

• How an individual site’s geology can affect quake energy before it hits the reactor.

The first two pieces are taken care of. The NRC partnered with the Department of Energy and the Electric Power Research Institute to publish updated earthquake source information last year. We also recently approved the most recent model of quake energy transmission.

U.S. plants east of the Rocky Mountains have been enhancing their ability to describe their sites’ soil and rock properties, in some cases obtaining more information on what lies beneath the reactors. Sites made up primarily of hard rock (at left in the graphic) tend to amplify high-frequency quake energy, while sites with more of a soil-like makeup (at right) tend to amplify low-frequency energy.

Central and eastern U.S. reactor owners are starting the process of putting all three pieces together to update their site’s hazard. They’ll report the results to the NRC by March of next year. They’ve provided updates on their sites’ soil/rock makeup now so the NRC can examine the information and ensure it meets the basic standards needed for the overall hazard review. Plants west of the Rockies have a more complicated version of the puzzle to consider, so they’ll submit information to the NRC later.

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: