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A six-member team dispatched by the International Atomic Energy Agency concluded a four-day investigation Thursday at the Kashiwazaki-Kariwa Nuclear Power Station, which was hit and damaged by a strong jolt last month.
Philippe Jamet, director of the IAEA's Nuclear Installation Safety division, predicted that reopening the station could take months, after briefing Japanese officials Friday. He also said his team would prepare a full report for the agency. The earthquake, which killed 11 people and injured nearly 2,000 in Niigata Prefecture, about 150 miles northwest of Tokyo, caused serious damage to a reactor crane in one of the seven units at the power station owned by Tokyo Electric Power Company.
Although TEPCO officials tried to take a positive view, stressing that no serious radiation occurred as the reactors were automatically shut down, critics were confirmed in their long-standing apprehensions about nuclear reactors in the land of daily jolts.
For instance, the seismograph near the damaged reactor crane recorded more than 1,500 Gal, beyond the acceleration of gravity of 980 Gal. If pushed up from below by an impact above the acceleration of gravity, any physical object, however heavy, would be rendered into a zero-gravity state and float in space temporarily. This is what happened in reactor unit No.7.
"If a quake occurred while the reactor crane was in operation, the reactor's lid might fall with the crane down into a pool of the spent nuclear fuel near the reactor. This could melt the core of the reactor, or cause meltdown, the worst accident that could happen in a nuclear power plant," said Hisataka Yamazaki of No Nukes Plaza, a private initiative to stop nuclear facilities.
Shockingly, TEPCO executives had failed to notice that the nuclear plant was built right on top of an active fault, which was affected by the Magnitude 6.8 earthquake. TEPCO had openly claimed that its researchers had confirmed there was no fault under the building site.
However, the National Research Institute for Earth Science and Disaster Prevention had pointed out the possibility that the fault reached to the area of the station. Similar opinions had been expressed by the Geographical Survey Institute, an agency affiliated to the Ministry of Land, Infrastructure and Transportation.
Research of active faults is critically important in assessing Design Basis Earthquake Ground Motion, which in turn determines earthquake-resistant designs and structural strength.
Some environmentalists suspect that certain pressures exist to underestimate the risk factors in order to allow the construction of nuclear facilities. "Our nation's safety review agency and electric power companies tend to underestimate risks," says Hiroaki Koide of the Kyoto University Research Reactor Institute. "The safety review agencies have assumed Magnitude 6.5 as the strongest jolt that ever occurs. With the quake of Magnitude 6.8, they were proved wrong."
According to Yamazaki, the latest incident was the fourth case since 2003 in which a nuclear station was directly afflicted by a jolt stronger than the plant was designed to tolerate. "This fact indicates that the conventional method of measuring DBEGM is no longer scientifically relevant," he insisted.
In one of the four cases, when Shiga Nuclear Power Station was hit in March this year, an 11-mile long active fault was discovered. Later, its owner and operator, Hokuriku Electric Power Company, was found to have excluded part of the site from the necessary quake-related assessment in its construction application.
Japan has come a long way toward overcoming its "nuclear allergy;" it is now the third highest user of nuclear power in the world, after the United States and France. Its nuclear sector generates roughly one-third of the power in a country where almost all oil has to be imported.
To maintain this nuclear option, policymakers and power companies must not only raise the plants' resistance to earthquakes but also raise public confidence in their transparency. To this end, all 55 nuclear power units across the country will be re-examined with renewed alertness, in hopes of preventing a more serious accident in the future.
