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| Fig. 1: Schematic for seismic invisibility cloak after the Institute Fresnel. [1] |
Since the March 2011 Great Tohoku Earthquake that devastated parts of Japan and caused a tsunami which caused three nuclear reactors to fail, much debate has been in the news regarding the feasibility of nuclear power generation. Additionally, this debate is heightened when regarding nuclear power generators that are located in areas that are prone to seismic activity.
A research group in France has expanded upon currently existing work on the steering of acoustic waves around specific regions. This was done by drilling holes in the ground, which changes the way in which sound waves (the same as seismic waves) propagate through the ground medium. According to the research group conducting the experiments (S. Brûlé et al., Institut Fresnel, paper submitted for publication), the seismic waves were reflected from the region of interest. This method has enormous potential for creating areas of land in earthquake-prone regions where the buildings built on top of this land are mostly impervious to earthquakes. However, the shortcomings to this method are that there is no feasible option for retrofitting existing buildings. In terms of nuclear power generators, this would mean decommissioning and dismantling all reactors and power plants that are in earthquake-prone regions and rebuilding them on top of the specially-prepared ground.
Reactors in Japan and the United States have both been cited as lying on or near active faults. In particular, the Tsuruga reactor in Fukui prefecture, Japan, and the San Onofre and Diablo Canyon Power Plants in California are at high seismic risk. [1-3] After March 2011, the 50 nuclear reactors that Japan had been using for power generation were sitting idle out of fear that another earthquake/tsunami pairing could cause another situation such as the Fukushima Daiichi one. As of February 2013, several reactors have been re-started but others are shut down indefinitely as the fault activity in that region is explored. [1,2]
The uncertainty of nuclear power generation in areas at high risk of earthquake activity is a topic of concern. Currently, the industry and government practice is to shut down the reactors while the seismic risk is evaluated.
Interestingly, however, the U.S. Nuclear Regulatory Commission has determined that the reactors in the United States that are at the highest risk are those that are located in areas of relatively low seismic risk - the Eastern Sea Board and areas of New York State. This is due to the fact that power plants built in areas of low earthquake risk are not built with the same factors of safety and design intent as power plants built in areas which anticipate a high-magnitude earthquake. Nine out of the top ten nuclear power plants at risk for sustaining significant damage to the reactor core from a major earthquake are located in Eastern states (as evaluated by the U.S. Nuclear Regulatory Comission). [3]
Aside from seismic retrofitting, there are currently no other standard practices for improving a power plant's ability to withstand a major earthquake. In fact, in the United States, there is still insufficient data to know what risk exists to certain plants. In Japan, the industry practice now is to keep reactors shut down until it is decided that the risk is low enough to restart. Even with the possibility of using acoustic steering as a method of protecting buildings from earthquakes, it seems as though there is very little that is possible to be done to prevent this type of disaster.
© Sayuri Yapa. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] D. Cyranoski, "Quake Fears Rise at Japan's Reactors," Nature 494, 14 (2013).
[2] M. Winter, "Japan Nuclear Plant Atop Likely Active Quake Fault," USA Today, 28 Jan 13.
[3] B. Dedman, "What Are the Odds? US Nuke Plants Ranked By Quake Risk," MSNBC, 17 Mar 11.