TOKYO -- After a deadly earthquake struck northwestern Japan last week, the nation was stunned when a nuclear power plant near the earthquake's center sustained widespread damage, including minor radiation leaks, pipe ruptures, flooding, and a fire that belched black smoke for more than an hour on live television.
But perhaps the most startling discovery came in the days that followed, when scientists used data from the magnitude-6.8 earthquake to conclude that the builders of the Kashiwazaki-Kariwa plant, the world's largest by electrical output, may have unknowingly constructed it directly on top of an active seismic fault.
"Not finding the fault was a miss on our part," said Toshiaki Sakai, who heads the engineering group in charge of Tokyo Electric's nuclear plants. "But it was not a fatal miss, by any means."
The earthquake, which killed 11 people and destroyed hundreds of homes in the nearby city of Kashiwazaki, has raised questions about the safety of Japan's nuclear plants.
The plants in this earthquake-prone nation are supposed to be nearly quake-proof, built to withstand powerful temblors. Tokyo Electric Power, the plant's operator, said the tremors last week were more than twice as strong as the plant's design limits. So the plant's vulnerability to damage has distressed many Japanese.
Nuclear specialists applaud the fact that all four of the Kashiwazaki plant's seven reactors that were operating when the earthquake struck were safely shut down, despite the unexpected strength of the tremors. But Tokyo Electric's failure to predict the possible size of the tremors that could strike the area and to detect the fault line have left many wondering whether regulators and plant operators could also have underestimated the potential for devastating earthquakes at Japan's 48 other nuclear reactors.
Yesterday, the Ministry of Economy, Trade and Industry, which oversees energy-related policy, said it would create an independent panel to investigate the damage at the Kashiwazaki plant, in Niigata prefecture.
The discovery of the fault line below the Kashiwazaki plant has attracted intense media attention in Japan, partly because it echoes problems that have plagued nuclear plants in the country. There have been lawsuits seeking the closure of at least four other plants because of nearby fault lines, including a plant in the western town of Shika, where a large fault was discovered in 2005, just before the plant's completion.