America's Nuclear Industry - How Earthquake Proof Is It?

Updated April 2016

With the advent of global climate change, nuclear has looked like a clear winner when it comes to cutting greenhouse gas emissions.  With that in mind, let’s take a brief look at the nuclear power situation in the United States and the relationship between nuclear power plants and seismic activity.

The website of the United States Nuclear Regulatory Commission (NRC) contains a wealth of information about the American nuclear industry.  The NRC was founded in January 1975 primarily to focus attention on issues relating to the protection of public health and safety.  They have put into practice standards that are in place to protect the general public from hazardous levels of radiation.  The 1979 Three Mile Island accident and near meltdown was a wake up call for the nuclear industry; this incident caused the NRC to place greater emphasis on operator training and emergency planning.

Let’s start with a map and a list showing the locations of operating nuclear power reactors:

I actually found it rather surprising how many reactors there are and how many of them are located on the east coast of the United States.  In total, there are 104 reactors that are licensed to operate, all of them located in the continental United States and the vast majority of them in the eastern half of the country.

In addition, there are 32 operating nuclear research and test reactors and an additional 9 regulated nuclear research and test reactors located throughout the continental United States, most of which are located at colleges and universities.  These reactors are primarily used for research, training and development and contribute to many fields of science including geology, chemistry, medicine, physics, biology and archeology.  The 9 non-operating reactors are currently undergoing decommissioning and have had their licenses amended to allow possession of radioactive material only.   Here is a map showing the location of research and test reactors:

Now, let’s look at information from the United States Geological Survey (USGS).  The USGS has a National Seismic Hazard Mapping Project, a group of scientists that study earthquakes with the goal of reducing earthquake hazards in the United States.  This is particularly critical because earthquakes pose a significant risk for 75 million Americans.

From their research, the USGS has created a series of maps showing the probability of earthquakes of varying magnitudes.  From the list of maps they have created, I have selected the maps showing peak ground acceleration, a measure of the acceleration (or motion) of the ground during an earthquake.  This is an important parameter that must be considered during the engineering design phase of various structures such as roads, bridges, buildings and, for the purposes of this posting, nuclear power plants.  These maps also were created using various probabilities, for example, the 2 percent in 50 year probability of exceedance, the 5 percent in 50 year probability of exceedance and the 10 percent in 50 year probability of exceedance.  The higher the percentage level of probability, the more likely that the peak ground acceleration will be exceeded during an earthquake over a 50 year period.  When looking at the 2 percent in 50 year map, the map emphasizes less likely events (i.e. there is only a 2 percent chance of the peak ground acceleration being exceeded over a 50 year period) meaning that large magnitude earthquakes with large ground motions are more likely to show up.  When looking at the 10 percent in 50 year map, the map emphasizes small magnitude earthquakes with small ground motions.

Here is a map showing the peak ground acceleration 10 percent in 50 year map (shows smaller and more likely earthquakes):

Here is a map showing the peak ground acceleration 2 percent in 50 year map (shows larger  and less likely earthquakes):

Notice how the areas along the eastern seaboard show up as potentially seismically active, particularly through Georgia and the northeast, especially on the 2 percent in 50 year map?  While the risk is far lower than for the western United States, the risk of seismically significant activity still exists.  If you look back at the NRC map, there are a large number of nuclear reactors throughout this area.  As well, the junction of the states of Arkansas, Tennessee and Missouri appears to have potential for seismic activity; these states are also the home to several nuclear reactors.  I certainly realize that prior to the construction of nuclear power plants that engineers extensively study the risk of ground movement, however, all risks can’t be quantified and the risk of significant seismic activity is never zero in historically seismically active areas.

While the likelihood of a significant and highly damaging earthquake is unlikely for many of the areas where reactors are operating, my posting of yesterday shows that the risk of a rather major tsunami along the eastern seaboard of the United States does exist.  From the NRC database, reactors in Florida, North Carolina and Massachusetts, among others, are very close to sea level and very close to open water.  From the recent events in Japan, we can see that even though backup power generation was in place to prevent reactors from overheating if power from the grid was not otherwise available, that tsunamis can have a very detrimental impact on the operation of critically needed backup diesel generators.  While we cannot plan for every contingency, let's hope that the operators of nuclear reactors in the United States that are located very close to sea level have learned an important lesson from the Japanese experience.