Nuclear Energy Facilities Designed and Built to Withstand Earthquakes
June 2014
Key Facts

Nuclear energy facilities are unyielding
structures with multiple layers of safety
designed and built into them. Federal
regulations require that these plants be able
to withstand extreme natural events that may
occur in the region where they are located,
including earthquakes, hurricanes, tornadoes
and floods.

The independent U.S. Nuclear Regulatory
Commission re-examines seismic safety at
nuclear energy facilities as new information
becomes available. The NRC has required the
companies that operate U.S. nuclear plants to
have seismic experts re-evaluate the potential
earthquake impact at their sites using the
latest data and methodologies.
This cut-away graphic shows the layers of safety built
into a nuclear plant. For added safety, huge shock
absorbers are used to support piping and equipment
in the event of seismic motion or other vibration.

The first part of the analysis was submitted to
the NRC on March 31 for sites east of the
Rocky Mountains; the analysis for western
sites is due by March 12, 2015.

Although these studies are still under way, the NRC staff’s independent review found that seismic risk
estimates are consistent with the agency’s conclusions from a 2010 study and that the plants are safe
to continue operating.

Based on the results, some companies will perform more detailed evaluations of their plants’ ability
to withstand stronger ground motion than they originally expected. In the meantime, the NRC has
approved expedited evaluations that will reveal whether and where seismic safety should be enhanced
in the near term. The results of the expedited evaluations are due by the end of this year.
Maintaining a High Standard for Seismic Safety
The industry’s highest priority is the safety of our workers, their families and others who live near our
nuclear power plants. Since the future of nuclear energy depends on continued safe operation, nothing is
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more important. The nuclear energy industry has a simple approach to ensuring safety during extreme
events: Expect the unexpected and prepare for it.
Federal regulations require that nuclear power plants be able to withstand extreme natural events that
may occur in the region where they are located, including earthquakes, hurricanes, tornadoes and floods.
The original seismic hazard estimates provided a baseline for nuclear plant design and construction. In
licensing each facility, the NRC required that additional safety measures be built into the facility so that it
can withstand even stronger ground motion than indicated by the data, and the industry’s standard
practice is to add layer upon layer of safety so that a nuclear plant not only meets regulatory standards—
it exceeds them.
Thus, our nuclear plants have a wide
margin of safety between the ground
motions originally estimated for each
site and what the facility is capability of
withstanding. With new information
about seismic hazards now in hand, the
industry will conduct risk evaluations over
the next few years to refine our
knowledge about the seismic capabilities
of our plants and identify ways to make
them even safer.
Independent Federal Agency
Three types of information are required to estimate the
Reviews Earthquake Safety
seismic hazard for a site: earthquake source, how regional
The independent U.S. Nuclear Regulatory
geology transmits earthquake energy (attenuation) and how
the individual site’s geology affects that energy before it
Commission re-examines seismic safety
reaches the reactor (site amplification). Source: U.S. Nuclear
at nuclear energy facilities as new
Regulatory Commission
information becomes available. The NRC
initiated its most recent review in light of
new information indicating that the
potential earthquake impact might be different from previous estimates for some locations in the central
and eastern United States. The agency concluded in 2010 that all nuclear energy facilities are safe, but it is
examining earthquake safety in more detail.
Earthquake safety standards are more stringent for nuclear energy facilities than for any other type of
infrastructure. Models and methodologies developed expressly for these facilities are used to assess the
types of ground motion they may experience. Between 2008 and 2012, the nuclear energy industry worked
with the NRC and the Department of Energy to develop a new model to identify the potential sources of
earthquakes for the central and eastern United States.
Earthquake safety drew increased attention in 2011 after a tsunami triggered by a powerful earthquake
disabled safety systems at the Fukushima Daiichi nuclear power plant in Japan and led to an accident.
Although it was flooding from the tsunami rather than shaking from the earthquake that led to the
accident, the NRC folded its ongoing review of seismic safety into its post-Fukushima recommendations for
U.S. reactors.
Industry Evaluations Use State-of-the-Art Methodologies
Seismic experts are re-evaluating earthquake protection at nuclear power plants using the latest available
data and methodologies. The first part of the analysis was submitted to the NRC on March 31 for sites east
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of the Rocky Mountains; analysis for western sites is due by March 12, 2015. Different models must be
developed for the western sites because of significant differences in geology between that region and the
area east of the Rocky Mountains.
Although these studies are still under way, the NRC staff’s independent review found that seismic risk
estimates for nuclear plants in this region are consistent with the agency’s 2010 conclusions and that the
plants are safe to continue operating.
Based on the results of the studies, some
companies will perform more detailed evaluations
of their plants’ ability to withstand stronger ground
motion than they originally expected. In the
meantime, the NRC has approved expedited
evaluations that will reveal whether and where
seismic safety should be enhanced in the near
term. The results of the expedited evaluations are
due by the end of this year.
All US Nuclear Power Plants Built to
Stringent Earthquake Safety Standards
All nuclear power plants in the United States are
designed and built to stringent seismic standards
appropriate for the region in which they are
located.
This map shows the geographical distribution of
earthquakes of magnitude 5.5 and higher. Source:
U.S. Geological Survey
The United States has averaged more than 3,000
earthquakes per year over the past 20 years,
mostly in the mild to moderate range (magnitude 2.0 to 5.9), according to the U.S. Geological Survey.
Magnitude is a measure of the energy released in an earthquake. Earthquakes exceeding magnitude 5.5
are relatively rare in the central and eastern United States. However, large earthquakes can and have
occurred. These include earthquakes that exceeded magnitude 7 in the New Madrid, Mo., zone in 1811
and 1812 and at Charleston, S.C., in 1886. These earthquakes were taken into account when existing
nuclear power plants were built.
One of the differences in seismic hazard between the West Coast and the region east of the Rocky
Mountains is that ground motion is transmitted over greater distances in the East. The U.S. Geological
Survey estimates that a magnitude 4.0 earthquake will be felt 60 miles away; a 5.5 earthquake can be felt
as much as 300 miles away.
Experience Confirms Seismic Safety of Nuclear Energy Facilities
There have been few large earthquakes (magnitude 5.5 or greater) near nuclear power plants. The safety
performance of these plants confirms the seismic ruggedness of these facilities.

The North Anna nuclear energy facility in central Virginia (2011). North Anna experienced a
magnitude 5.8 earthquake—the second-largest earthquake recorded in the state—that originated 11
miles from the site. The closeness of the 2011 quake was significant because ground motion dissipates
over time and distance from the source. Although the plant experienced stronger ground motion than
had been predicted for the area, all systems were protected and performed as designed to maintain
safety.
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
Chūetsu Offshore Earthquake (Japan, 2007). The Kashiwazaki-Kariwa plant experienced stronger
ground motions than it was designed to withstand from a large earthquake, just offshore of Japan. All
seven reactors were safely shut down as they were designed to do during an earthquake.

Great Japan Earthquake (2011). Several nuclear power plants on the east coast of Japan were
affected by one of the largest earthquakes in recorded history. The Onagawa nuclear plant, closest to
the source of the earthquake, safely shut down, and it even provided temporary shelter for displaced
neighbors. All safety-related systems of the three reactors performed as designed. The Fukushima
Daiichi and Daini plants also were structurally sound and were safe after the earthquake. However, the
tsunami generated by the earthquake caused significant damage at both sites.
Experience demonstrates that the extensive safety features built into nuclear power plants to prepare for
the unexpected ensures safety for workers and the public in the event of large earthquakes.
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