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 Plants in many countries have survived quakes more powerful than the one that hit Japan on Monday, suggesting that the poor performance of the Kashiwazaki Kariwa reactor is more illustrative of recent safety problems in the country's nuclear industry than any inherent vulnerability of the technology.
"It did what it was supposed to," said William Miller, a University of Missouri at Columbia nuclear engineering professor. "It shut down. It did not release radioactive material into the atmosphere."
Miller said he considers the relatively small amounts of radioactivity that were released when the earthquake knocked over several waste-containing barrels to be "negligible."
But environmentalists and nuclear watchdogs expressed concern that fire and power failure, both of which resulted at Kashiwazaki on Monday, can trigger nuclear meltdown.
Historically, Japanese nuclear power plants have performed quite well in previous earthquakes, even the one that sustained minor damage in Monday's magnitude 6.6 quake. The Kashiwazaki Kariwa plant experienced a 6.8 magnitude quake in October 2004 without incident, though an aftershock two weeks later caused the automatic shutdown of one of its reactors. In August 2005 three reactors at the Onagawa plant in northeastern Japan shut down automatically during a 7.2 earthquake.
"Barring an extraordinary seismic event, it is expected that the nuclear plants based energy supply in Japan can be maintained with manageable disruptions," Rice University engineers concluded in a 2000 analysis.
Generally, plants adhering to government guidelines drawn up after 1995 Kobe earthquake are considered safe in quakes up to 7.75 magnitude. Facilities in especially active regions are designed to withstand even greater intensity.
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 Even in the absence of earthquakes, however, Japanese nuclear plants have had safety problems. In 2004, five workers were killed and six were injured after a corroded pipe ruptured and sprayed plant workers with boiling water and steam at the Mihama nuclear plant in western Japan. In 2002, four out of the five companies operating nuclear plants in Japan confessed to hiding the presence of cracks in their reactors from the government.
U.S. nuclear plants have stood up well to earthquakes. In 2003, a strong quake that rocked California's Central Coast was felt in the control room of the Diablo Canyon nuclear power plant, a pair of 1,100-megawatt reactors near a series of faults running parallel to the San Andreas.
Onsite inspectors did a walkthrough of the plant following the magnitude-6.5 temblor and did not find any broken or leaking pipes, damaged support braces or displaced equipment.
Pipes, pumps and other components of the liquid cooling system are the most vulnerable elements of a reactor in an earthquake. If they fail, the reactor's core could heat up to the point that a meltdown occurs.
"It's not just a case of remaining standing after the earthquake," said Scott Burnell, a spokesman for the U.S. Nuclear Regulatory Commission.
The U.S. Nuclear Regulatory Commission requires utilities to design nuclear plants so they can safely shut down in the event of a powerful earthquake, typically the strongest that geologists consider possible in the region. Plants are also required to be able to operate without disruption through a weaker earthquake, usually one about half as strong as the maximum.
 Even some of the deadliest earthquakes in recent history have produced little or no damage to nuclear reactors in the affected area. Though a December 1988 earthquake in northwestern Armenia killed 25,000 people, two Soviet-designed reactors about 50 miles from the epicenter continued to operate normally.
[Associated Press;
by Matt Crenson] |
