U.S. Nuclear Plants Most Likely to Suffer Damage from an Earthquake
Assessing the Earthquake Risk at U.S. Nuclear Plants
CNBC - As Japan's nuclear crisis continues to unfold, many are wondering whether the U.S.'s nuclear plants face a similar threat.
After all, there are an average of six magnitude 6 or greater earthquakes, and 57 magnitude 5 or greater earthquakes each year in the U.S., according to the U.S. Geological Survey.
Alaska is the most earthquake-prone state, and is one of the most seismically active regions in the world, experiencing at least one magnitude 7 earthquake almost every year and a magnitude 8 or greater earthquake every 14 years.
Still, the events that seem to stand out in most people's minds are the ones that strike in heavily populated areas such as the magnitude 6.7 earthquake that struck in Northridge, Calif., in 1994. That quake killed 33, injured 9,000 and displaced more than 20,000.
But even that quake wasn't as strong as the New Madrid quakes of 1811-12, which hit Missouri and Arkansas. That tremor was so strong it made the Mississippi River run backward for a time.
The following is a map from the USGS that shows where the greatest earthquake hazards are located. During a 50-year time period, the probability of strong shaking increases from very low—the areas shown in white—to moderate—the areas in blue, green and yellow. The highest risk areas are show in orange, pink and red.
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Source: USGS This map shows relative shaking hazards in the United States and Puerto Rico. During 50-year time period, the probability of strong shaking increases from very low (white), to moderate (blue, green and yellow), to high (orange, pink, and red). Map not to scale. |
However, the threat of a Japan-style nuclear accident may depend more on the nuclear reactor's design rather than its location.
Looking at an assessment the Nuclear Regulatory Commission has done of the seismic risks at the nation's nuclear power sites as well as some separate data supplied to the organization, MSNBC.com compiled a list of the nuclear reactors most at risk. The list was completely its own, as the NRC does not rank nuclear plants nor does it compare the facilites to each other.
The NRC study was published last year, and considered both the likelihood of a seismic event as well as the strength of the design of the power plant.
All the plants met the agency's requirement for being able to withstand the ground motions from the strongest earthquake that would be expected in the area around the plant.
MSNBC took the research and ranked the nuclear power sites by the chance of an event occurring. In all cases, the chances were pretty low.
US Nuclear Plants Most Likely to Suffer Damage from an Earthquake |
| Plant | Location | Chance of Occurance |
| Indian Point 3 | Buchanan, NY | 1 in 10,000 chance each year |
| Pilgrim 1 | Plymouth, Mass. | 1 in 14,493 |
| Limerick 1 and 2 | Limerick, Pa. | 1 in 18,868 |
| Sequoyah 1 and 2 | Soddy-Daisy, Tenn. | 1 in 19,608 |
| Beaver Valley 1 | Shippingport, Pa. | 1 in 20,833 |
| Saint Lucie 1 and 2 | Jensen Beach, Fla. | 1 in 21,739 |
| North Ana 1 and 2 | Louisa, Va. | 1 in 22,727 |
| Oconee 1, 2 and 3 | Seneca, S.C. | 1 in 23,256 |
| Diablo Canyon 1 and 2 | Avila Beach, Calif. | 1, in 23,810 |
| Three Mile Island | Middletown, Pa | 1 in 25,000 |
While there will be numerous lessons that come out of Japan's nuclear disaster, one is already clear: the fundamental problem at the Fukushima Daiichi plant was that the facility lost electric power, its pumps went down and backup pumping systems failed.
And indeed, one proposed solution to the current crisis is to restore power, and therefore the ability to restart the cooling pumps at the damaged nuclear plant.
Therefore, one of the key takeaways is that there could be other events that could cause a plant to lose power and see its cooling pumps fail, including violent storms or a terrorist attack.
In the U.S., nuclear power plants have several layers of redundant systems to assure that power is not lost at the facility.
According to NRC spokesman Scott Burnell, all U.S. nuclear plants must have a source of power that is off its own grid. There also have to be back-up generators that contain fuel for at least seven days, and these generators have to work even while being refueled.
All in all, the NRC requires that there be emergency power supplies that are available for about a month, which is about the time it takes to cool down a reactor. (Although the time required does vary based on a number of variables, including the reactor's design.)
Heat continues to be generated even after the nuclear reaction is halted. During the time that heat is being generated, it must be carried away or it will begin building up again.
Could U.S. Nuclear Plants Withstand a Tsunami?
In the wake of the crisis gripping Japan, should we take a second look at nuclear plants closer to home?- Experts are calling for new risk assessments of the vulnerability of nuclear plants in the path of natural disasters.
- Each of the 104 reactors in the United States has to undergo individual testing for local risks.
- More than 80 reactors worldwide are located in seismically active areas.
Discover News - Operators of California's two nuclear plants say they are well prepared for a possible tsunami strike. Some experts, however, are calling for new risk assessments that take into account the deadly earthquake, tsunami and nuclear crisis in Japan.
The San Onofre plant near San Clemente is built to withstand a 7.0-magnitude earthquake, while the Diablo Canyon plant is engineered up to magnitude 7.5, according to plant officials. Both are expected to survive tsunamis of up to 25 feet.
They are among the 88 reactors worldwide that are located in seismically active areas, according to the UN's International Atomic Energy Agency. The California plants are the only nuclear facilities along the U.S. Pacific Coast.
However, some critics say federal regulators need to take a second look at the California plants, given the scope of destruction that occurred in Japan. Ed Lyman of the watchdog group Union of Concerned Scientists says current risk estimates for seismic and tsunami hazards may be outdated.
"Across the board, the NRC (Nuclear Regulatory Commission) has not set standards at a high enough level to protect the public from accidents that are more credible and plausible than previously considered," Lyman told reporters at a Wednesday press conference in Washington.Twenty-three of the 104 reactors in the United States are the same design as the nuclear plant in Japan that's now in crisis. Each of these U.S. plants has to undergo individual testing for local risks such as earthquakes, hurricanes, high waves, extreme heat or flooding as part of their federal licensing requirements.
In 2008, the California Energy Commission released a report stating that San Onofre lacked safeguards for an earthquake greater than magnitude 7.0, which was the level expected when the plant was designed in the 1960s.
The state Public Utilities Commission agreed and ordered the company that owns the facility to perform a new earthquake and tsunami risk analysis of the reactors using the latest technology before seeking a renewal of the plant's federal operating license, which expires in 2022, the San Diego Union-Tribune reported. The same request was made of PG&E, which operates Diablo Canyon.
Edison turned in its initial report on earthquake and tsunami risks to the utilities commission last month, but the document lacked the three-dimensional seismic analysis that the agencies requested.
Both nuclear facilities are located above the water on coastal bluffs.
The California coast has experienced tsunamis in the past, the worst from the 1964 "Good Friday" earthquake in Alaska that measured 9.2 on the Richter scale. That quake and resulting wave swept away 11 people in Crescent City and killed a total of 17 people along the coast.
Southern California -- where the nuclear plants are located -- is in a high seismic area. But it doesn't face the large waves generated by big temblors in Japan or Alaska because its coastline is not as exposed, said Peggy Hellweg, a seismologist at the University of California at Berkeley.
Hellweg also doubts that the local earthquake faults near the nuclear plants can generate the kind of power felt in Japan. The Newport-Inglewood and Rose Canyon fault system near the San Onofre plant and the Hosgri fault and the Shoreline fault, which was discovered in 2008, run near the Diablo Canyon plant.
"The size of the earthquake depends on the size of the uninterrupted fault you have," Hellweg told Discovery News. "The length of those faults isn't enough to get a magnitude eight or nine."Researchers across California have been assembling a comprehensive study of the risk to the state from tsunamis over the past two years. The first phase of the study found that the region probably faces a bigger tsunami threat from earthquakes generated off the coast of Oregon and Washington, called the Cascadia subduction zone, or from the Aleutian Islands off Alaska.
The other danger is from underwater landslides just off the coast, said Stephen Mahin, director of the Pacific Earthquake Engineering Research Center at UC Berkeley.
"You have these big cliffs and those can cause local tsunamis which are far bigger than the distant ones," Mahin said. "But those are extremely hard to predict."In the 35 years since Indian Point 3 got its license to operate in 1976, the same era when most of today's U.S. nuclear reactors were built, geologists have learned a lot about the dangers of earthquakes in the eastern and central U.S.
Based on 2008 data, a map of earthquake damage risk in the United States. The highest risk areas are purple, red and orange. [Source]
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