A fault found just off the shore of the Diablo Canyon Nuclear Power Plant has shown that the plant is more earthquake prone than previously thought. And there could be even more faults.
There is a lot still unknown about the unnamed fault. It could be as close as 1,600 feet from the plant based on early estimates. It could also be anywhere from less than a mile long to about a mile and a half.
Geologists have long been aware of the much larger Hosgri fault zone, which is about three miles from the plant. The United States Geological Survey discovered the new fault after they pinpointed the origins of historical earthquakes. Together those points formed a line that forks off the Hosgri fault zone toward the shore. More studies are needed, but the consensus is there is a fault capable of producing a magnitude 6.5 earthquake.
“The first thing we need to do is understand the geology because if we don’t we’re just guessing and this is too important of an issue to guess,” Republican Assemblyman Sam Blakeslee said.
Blakeslee holds a doctorate in geophysics and has made seismic studies at Diablo Canyon one of his key legislative issues. Blakeslee’s Assembly Bill 1632 prompted a statewide study of California’s two nuclear power plants: Diablo Canyon and Southern California Edison’s San Onofre Nuclear Generating Station.
According to Blakeslee, the latest study is a step in the right direction, but he believes PG&E should take a closer look at the entire region using advanced three-dimensional mapping technology.
“There’s a good chance that there is a major geographic feature that has yet to be explained,” he said.
For now, officials are optimistic that Diablo Canyon is still relatively safe. The plant can sustain a magnitude 7.5 earthquake, PG&E spokesperson Pete Ressler told New Times.
“The key thing right now is the plant continues to operate safely and based on this new information we’re still totally confident that the plant is designed to withstand what we would expect from any activity on that fault,” he said.
That tempered response roused worries from at least one local watchdog, the Alliance for Nuclear Responsibility. David Weisman of the Alliance said PG&E typically downplays risk to the plant.
“PG&E has a history, when it comes to earthquake faults, of first not finding them, and then denying them, and then having to spend ratepayers’ money [to retrofit them],” he said.
It will be more than a year before PG&E has enough information to take the next step, which could involve mean retrofits. Another round of USGS studies will begin in the summer and the results should be ready by spring 2010.
Diablo Canyon’s future will ultimately rest on how shaky the ground is underneath. The plant is up for a license renewal from the Nuclear Regulatory Commission in 2025. Ressler said it is too early to tell whether PG&E’s license renewal could be in jeopardy.
“This is all very preliminary and somewhat incomplete information,” he said. “There’s some gaps in the data that we need to fill in before we can make any final determination.”
Blakeslee said he will push for more seismic studies using three-dimensional maps, adding that he plans to draft legislation that will accelerate the process. Future studies could expose even more faults in the area. The California Energy Commission recently reported that a “San Simeon-type earthquake directly beneath the plant” is a possibility.
If there were an earthquake, Diablo Canyon’s safety system would trigger an automatic shutdown and minimize public risk, according to Ressler and Blakeslee. However, if the same earthquake damages other areas of the plant it could take Diablo Canyon out of commission.
An earthquake in July 2007 forced the shutdown of a Japanese nuclear plant, along with its 8,200 megawatts of power. The plant has yet to reopen.
“It could take years to get a plant restarted if some components are damaged as a result of a shutdown,” Blakeslee said.