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
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.
In an earthquake, seismographs record the amplitude of quake waves from their epicenters. Each whole number increase in magnitude equals an amplitude increase of 10 and a release of 31 times more energy than the last unit. Tohoku was a magnitude 9.0 on the Richter scale, so its waves were 10 times greater in amplitude and released 31 times more energy than a magnitude 8.0.
But the Richter scale isn’t the best barometer to measure plant resilience, according to the NRC. Plants are designed to withstand levels of ground shaking, and the way the ground shakes depends on variables including magnitude and the plant’s distance from the quake’s epicenter.
“They’re designed with components and structures that are tested to withstand the ground motion and acceleration at the time that would result from the maximum postulated earthquakes on nearby faults,” Raftery said.
Peak ground acceleration is expressed in g, a symbol for the average acceleration produced by gravity. Southern California’s Edison said San Onofre was built to withstand 0.67g, while Raftery said Diablo Canyon can handle ground motion that’s even stronger than the ground motion that came from Japan’s quake.
“That 9.0, which was a subduction zone fault, produced 0.5g in ground motion acceleration,” Raftery said. “At Diablo Canyon, we are designed and tested to 0.75g. It’s over and above what scientists postulate could occur from the faults nearby.”
Hellweg said she wasn’t worried about a major earthquake harming California’s nuclear territory — and she and colleagues may be ready if one comes years from now.
Scientists at UC Berkeley’s Seismological Laboratory have developed an earthquake early warning system prototype as part of a larger project involving other research partners, including the U.S. Geological Survey and California Institute of Technology. The equipment detects tremors and calculates the magnitude almost instantly after a quake hits, Hellweg said. “These algorithms recognize that an earthquake is happening and evaluate the magnitude very quickly in the first four seconds.”
Although the system is in early development, it could eventually alert people to an earthquake before the aftershocks reach them.
Conflict of Interest?
Weeks after Tohoku, the NRC instructed inspectors to assess American plants’ ability to deal with similar events and found some weaknesses. The investigation entailed various criteria, including: verifying if equipment was available and functional; verifying the training and qualifications of operators and support staff; assessing plants’ abilities to mitigate station blackout conditions; and assessing their ability to mitigate internal and external flooding.
Twelve out of 65 reactor sites had discrepancies with requirements, most of them involving staff training. Three sites had issues dealing with station blackouts, and two had issues with extreme flooding. However, the NRC wrote on May 20 that neither the blackout nor extreme flooding issues undermined the plants’ ability to respond to extreme events.
But not everyone has faith in the conclusions. “They have a huge conflict of interest,” Hirsch said. “It’s just not in the cards that the NRC is going to inspect these reactors and determine that the NRC has failed to adequately keep them safe.”
The organization issued a June 6 news release about a follow-up inspection, divulging more faults in staff emergency training. The NRC instructed resident inspectors at every plant to examine the local severe accident management guidelines, which were voluntarily established in the 1990s to contain or reduce the impact of crises that damage reactor cores.
These voluntary guidelines are supposed to buttress mandatory ones. “Of course we have requirements that the plants must meet,” said Scott Burnell, an NRC public affairs officer, “but there are circumstances that go beyond our regulations, beyond the point where we have the ability to require the plants to do something, and that is the point where these voluntary initiatives come into play.”
Inspectors found the guidelines in 89 percent of plant control rooms and 71 percent of plant emergency operations facilities, but only 42 percent of the plants include the guidelines in periodic reviews. Staff at 92 percent of plants received initial training on the guidelines, but only 61 percent of plants include the guidelines in emergency drills.
The NRC formed a Japan task force, in addition to the others, to determine what, if any, improvements U.S. nuclear plants should take in light of a possible disaster of Fukushima-like proportions. Findings from inspections and the task forces were included in an NRC report that made 12 recommendations to improve plan regulations, including: requiring plants to re-evaluate and upgrade design-basis seismic and flooding protection of plant components every 10 years; strengthening station blackout mitigation capability for design-basis and beyond-design-basis events; and requiring that emergency plans address prolonged blackouts and extreme events involving multiple reactors.
