Tuesday, August 26, 2014

In California, Earthquake Damages Wineries but not Nuclear Plant

The Associated Press yesterday ran a sensationalized account of an internal Nuclear Regulatory Commission dispute over the seismic safety of the Diablo Canyon Nuclear Power Plant. It actually wasn't much of a dispute insomuch as one NRC voice advocated to have Diablo Canyon shut down until additional seismic testing of the site could be conducted, while the larger regulatory body over many years has exhaustively analyzed seismic threats at Diablo Canyon, always concluding that the site is safe.   

Diablo Canyon Power Plant
Federal regulations require that nuclear plants be able to withstand extreme natural events that may occur in the region where they are located, and the NRC most recently required that nuclear utilities have seismic experts re-evaluate the potential earthquake impact at their sites using the latest available data and methodologies. But earlier this year the NRC reminded the public that nuclear plants’ substantial safety margins above their designs ensure they are safe for continued operation while the additional seismic assessments are being conducted. This public information would have significantly benefited the AP's reporting yesterday.    

We can credit the AP for its newsjacking instincts -- dropping the story smack in the middle of the larger 6.0 Napa earthquake coverage. That generated a great deal of interest in the file, but so much significant context was missing from it, little in the way of public service came from it.

The United States has averaged more than 3,000 earthquakes per year over the past 20 years, mostly in the mild to moderate range of severity (magnitude 2.0 to 5.9). The quake that struck Napa at the end of last weekend ranks as one of the more severe we experience. Still, there have been few large earthquakes (magnitude 5.5 or greater) near nuclear power plants. The safety performance of these plants through the years confirms the seismic ruggedness of these facilities. And as new seismic information comes to light, this is an industry that acts on it

Most of the news coverage of the quake thus far has focused principally on havoc wrought upon many northern California wineries; the state's lone nuclear plant was unaffected by the quake. That sort of contextualization also didn't make it into Monday's AP file.         

"Environmentalists," the AP wrote, "have long depicted Diablo Canyon . . . as a nuclear catastrophe in waiting." Importantly, however, seismologists have not. It's striking that the AP apparently didn't think to contact a seismologist -- particularly one in California, with expertise of earthquakes and the faults there -- to offer some context for this story. The dissenting voice at NRC cited in the piece is not identified as a seismologist but rather a former site inspector.    
Seismic infographic
Given its location, Diablo Canyon's construction history is distinctive and fascinating. The region surrounding Diablo Canyon is one of the most seismically studied and understood areas in the U.S. -- yet another fact omitted in yesterday's AP reporting. When Diablo Canyon was under construction in the early 1970s, the nearby Hosgri fault was discovered. Subsequently, Diablo Canyon was retrofitted to withstand ground motions from the Hosgri fault. The site is unique among all in the American commercial reactor fleet in that it is licensed for three earthquake designs: the Design Earthquake, Double Design Earthquake (equivalent to the Safe Shutdown Earthquake), and the Hosgri Earthquake.

As a result, the plant is able to withstand the largest ground motions, or shaking, that could be expected to be generated from any of the nearby faults. In instances of significant natural disasters in our country it's understandable that the public wonder about the robustness of America's nuclear energy facilities. That's a story we're proud to tell.

Today, Diablo Canyon's geosciences team is conducting yet another seismic hazard assessment, and Pacific Gas & Electric will report its findings to the NRC in March 2015. Existing and new seismic information is being peer-reviewed and publically evaluated by independent experts as part of the NRC required Senior Seismic Hazard Analysis Committee (SSHAC) process. Here's hoping the AP will see fit to tell that story, too.           

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