Interactive Map: The Real Seismic Threat to Our Nation's Nuclear Power Plants
After we heard that local utilities in Virginia were shutting down the local nuclear power plant in the wake of the earthquake that shook the East Coast today, we pulled this map from our archives to see which other plants might be in harm's way. —The Editors, August 23, 2011
Last week, we posted a link to a map mashup of nuclear reactor sites and the USGS-described "seismic hazard zones" in the United States. Climate Central dug a little deeper into the data, and created a really interesting interactive map that further explores the earthquake risk to America's nuclear power plants.
The map shows all 104 active nuclear power plants within the Lower 48 states, the sites of all earthquakes within the past four months, and the sites of the 15 largest earthquakes in the region. Here's a screenshot, but if you go to the original you can click around and learn more about the acute risks to each plant.
When you click on a reactor site, you can see what type of reactor it is, who operates the plant, and, most importantly, the maximum ground acceleration risk. The what what?
During an earthquake, the ground shakes back and forth, and the damage is roughly proportional to the ground’s maximum acceleration (PGA). The map shows the two percent likelihood that the PGA will exceed the shown values in the next 50 years.
In other words, if the map shows that the PGA is 1.0g for a given spot (say, southeast Missouri), that means there is a two percent chance that the peak ground acceleration will be greater than 1.0g at some point in the next 50 years. PGA is measured in “g,” with one g being how quickly an object accelerates in free fall (you can also think about “pulling Gs,” as in a fighter plane).
The PGA risk is what is typically used to set building codes. Most nuclear power plants are designed to operate under 0.2g PGA, and automatically shut off if the PGA exceeds 0.2g. However, they can withstand a PGA many times larger than that.
Nobody will be all that surprised that California's three nuclear reactors have a relatively high (emphasis on relatively) risk of seismic shaking. But there are
I, for one, was pretty shocked to learn that the power plant in Seabrook, New Hampshire—which I grew up just about nine miles from—actually has a 2 percent likelihood of a maximum ground acceleration exceeding 0.15 in the next 50 years.
Here's the full list of nuke plants in the Lower 48 that have that same level of risk:
- Diablo Canyon, Calif.
- San Onofre, Calif.
- Sequoyah, Tenn.
- H.B. Robinson, SC.
- Watts Bar, Tenn.
- Virgil C. Summer, SC.
- Vogtle, GA.
- Indian Point, NY.
- Oconee, SC.
- Seabrook, NH.
Before you get too alarmed, article author and map-creator David Kroodsma emphasizes:
The bottom line is that a major earthquake would probably not result in a nuclear meltdown at the reactors on the above map, but it could present significant engineering challenges. Quantifying the risks, and minimizing them as much as possible, is a key task for everyone involved in the nuclear energy industry.
You can't help but wonder how seriously the engineers were taking these seismic risks 30-40 years ago when many of these were first built.
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