Japan suffered its worst nuclear accident in spring 2011: On March 11, a magnitude 9.0 earthquake off Japan’s east coast caused tsunami waves in the Pacific Ocean that crippled power plants, rendering them incapable of pumping coolant to nuclear reactors. Fatality and injury estimates by Japanese authorities worsened by the day, with the number of deaths totaling 15,726 on Aug. 23.
And nuclear-related complications made things worse.
Tremors triggered the automatic shutdown of 11 nuclear reactors. Emergency generators started to run mechanics and water pumps to cool the reactors, but tsunami waves were higher than the seawalls built to protect the reactors. Flooding destroyed electrical power and cooling ability, causing reactors to overheat and some to melt down. The government evacuated more than 200,000 people to escape potential radiation exposure. Four days after the waves hit, radiation leakage prompted then-Prime Minister Naoto Kan to warn residents in northeastern Japan to stay indoors to avoid sickness.
Rapid containment efforts helped avert nuclear destruction, but the work is far from done. Power plant fissures have leaked radioactive water into the ground, requiring massive purification efforts that could take years — or even decades — according to some estimates.
The disaster raised an interesting question: If tremors and waves compromised Japan’s nuclear power plants, could other disasters threaten coastal nuclear power plants in the United States and elsewhere?
Pacific Threats
California is arguably more famous for temblors in coastal regions than anywhere else in the country. Countless fault lines crisscross the land, comprising major faults like the San Andreas, as well as smaller, collateral faults.
Southern California is home to two commercial nuclear plants: the Diablo Canyon Power Plant near San Luis Obispo and the San Onofre Nuclear Generating Station that’s southeast of Long Beach. They have two reactors each in the heart of earthquake country.
“What happened in Japan is called ‘station blackout,’ where you lose offsite electrical power and backup diesel generators, which are necessary to power the pumps to keep coolant going and prevent fuel from melting,” said Daniel Hirsch, a nuclear policy lecturer at University of California (UC), Santa Cruz, and president of the antinuclear nonprofit Committee to Bridge the Gap. “Nothing about California reactors would prevent a similar kind of blackout.”
Diablo Canyon, owned by the Pacific Gas and Electric Co., is located in Avila Beach, sandwiched between the San Andreas Fault on the right and the Hosgri Fault to the left — offshore in the Pacific. With this neighboring quake zone in the ocean, Diablo Canyon could be due for a local tsunami.
“The faults that we have offshore are strike-slip faults,” said plant spokesman Kory Raftery, “and those faults wouldn’t produce the same sort of a sea-level rise that you would get from a subduction zone fault, which was what they had in Japan.”
A thrust fault between the Pacific and North America tectonic plates generated Japan’s now-notorious Tohoku quake that ruptured the Fukushima Daiichi nuclear power plant. The shaking started underwater near the east coast of Honshu, close enough for tremors to simultaneously disrupt the ocean floor and land in populated areas. The region is a subduction zone fault, meaning one tectonic plate plunges beneath another, forcing the top plate to move higher. If this happens in the ocean, the land thrusting upward shakes water violently and creates tsunami waves. But in strike-slip zone faults, two plates slide against each other laterally, so the sea water jolt isn’t expected to be as severe. Both the Hosgri and San Andreas faults fall in the strike-slip category.
“You have these two plates running against each other, kind of moving horizontally past each other, and that’s different than what happened in Japan,” said Charles Ferguson, president of the Federation of American Scientists.
While it’s possible for some fault farther out in the Pacific to cause a major tsunami that could reach California shores, Ferguson said that because of the extreme distance, local plants wouldn’t be jeopardized the way the Tohoku earthquake affected the Fukushima nuclear power plant because of its closeness. “You wouldn’t have the intense ground shaking that would affect the plant at the same time,” he said.
But it’s possible for plate activity to produce tsunamis indirectly. According to Peggy Hellweg, a seismologist at UC Berkeley, Pacific tremors could cause underwater landslides that produce sudden waves. Both Diablo Canyon and San Onofre are located near the water. “What I have heard,” Hellweg said, “is that the tsunami hazard for the San Onofre plant is more likely to be from a local landslide along the coast there or underwater.”
Seismic Analyses
Regardless of how large or small tsunami threats actually are to California reactors, the earthquake danger is undeniable. Scientists anticipate a magnitude 7.0 quake from land, not sea. Quakes originating underground instead of underwater may threaten plants nationwide.
In the Tohoku aftermath, the U.S. Nuclear Regulatory Commission (NRC) released multiple frequently asked questions documents. According to one, all nuclear power plants are designed with natural hazards, including earthquakes and tsunamis, in mind. Their construction, according to the document, takes into account “the most severe natural phenomena historically reported for the site and surrounding area.”
Despite the perceived likelihood of an earthquake devastating the California coastline — and simultaneously causing severe damage to a nuclear reactor — an MSNBC.com article begged to differ. The article, What are the odds? US nuke plants ranked by quake risk, says it used 2008 NRC data to pinpoint that the Indian Point plant reactor in New York state is the reactor most at risk of having its core damaged by an earthquake — not the California plants.
According to the article, Indian Point had a 1-in-10,000 chance of being damaged, Diablo Canyon’s reactors had a 1-in-23,810 chance, and San Onofre’s had a 1-in-58,824 chance.
Though the article says it used NRC data, the commission stated in its frequently asked questions document that it doesn’t rank plants according to seismic risk or vulnerability. “This ‘ranking,’ was developed by a reporter using partial information and we believe an even more partial understanding of how we evaluate plants for seismic risk,” the NRC wrote.
Though the level of risk at one reactor versus another is ultimately unclear, one thing is certain: The vulnerability is there, and any potential disaster should be mitigated.
Understanding how scientists at the NRC measure plant safety is important — and its not using the commonly cited Richter magnitude scale measurements.
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