The Wall Street Journal has an an interesting and timely piece about the recent quake and what was learned about reactor safety. Since Farandaville is only a few miles from Indian point, it's of special interest to us!
This story is NOT in the opinion secton of the Journal, which is free, so you may not be able to access through the link if you don't have an online WSJ subscription. Because of that I've included enough of an excerpt for anyone to understand the full story.
But what's now clear is that the central Virginia plant tripped out of service when there was no real need for that to happen.
Experts believe sensitive electrical equipment at North Anna responded to high-frequency ground motion—which is a hallmark of Eastern quakes, but not of Western ones—as if it were an electrical disturbance. Nine relays designed to protect expensive transformers from damage misread that cue, temporarily cutting off the plant from the electric grid, according to Dominion's Mr. Heacock.
Every earthquake produces a broad range of ground motion frequencies, expressed in "hertz" or cycles per second. But Western quakes are more noted for the lower frequencies that are especially damaging to large, rigid structures, such as buildings and bridges. Higher frequencies are more debilitating to finely tuned equipment such as electrical or electronic devices.
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Shock waves in the East travel longer distances with tight waves—"like hitting a piece of steel with a hammer," says seismologist William Hinze, professor emeritus at Purdue University in Indiana. Western earthquakes are more like "hitting a piece of rubber," he says, with shock waves more quickly smothered. That helps explain why the Virginia quake was felt as far away as Canada.
One fix looks likely. Plant operators could change the orientation of relays so they aren't so easily fooled. That's harder than it sounds since engineers need to make sure they still can sense real danger. With the analysis still in its early stage, other changes may be required. The U.S. Nuclear Regulatory Commission has a team at the site.
Tuesday's earthquake, centered about 10 miles from the North Anna plant, may have come at just the right time and in just the right place. The NRC already was in the midst of a multiyear effort to deepen its understanding of earthquake risks in the Central and Eastern U.S. and apply that knowledge to improving existing plants and making new plants even better.
In fact, North Anna's two reactors already were on a list of 27 reactors that the NRC has concluded are in greatest need of additional seismic analysis. One reason is that additional faults have been identified since those reactors were built. North Anna has two reactors and a third one has been proposed.
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