By Megumi Yamanaka
Dec. 7 (Bloomberg) -- Tokyo Electric Power Co., Japan's biggest power utility, said it knew in 2003 an undersea fault near its Kashiwazaki Kariwa nuclear facility could cause a magnitude 7 earthquake.
A survey by the utility in 2003 found the fault near the nuclear plant was active, conflicting with results from a survey conducted between 1979 and 1980, according to documents Tokyo Electric filed to a trade ministry committee on Dec. 5.
Tokyo Electric didn't reveal the 2003 findings because the company didn't expect that to affect plant safety, Masaaki Kobayashi, a company spokesman, said by phone today. The company informed the ministry's nuclear safety agency of the result at that time.
"The nuclear safety agency also concluded at that time there was no danger,'' Yoshinori Moriyama, director of the agency's nuclear power licensing division, said by phone. The nuclear watchdog made the decision based on data provided by the utility.
The safety agency in 2002 asked Tokyo Electric and Japan's other nuclear plant operators to conduct surveys using the latest seismological knowledge as a safety precaution.
The power company used the results of the 1979 and 1980 survey when it applied to add two reactors to the facility in 1988. The Kashiwazaki Kariwa nuclear plant has seven reactors with a total generation capacity of 8,212 megawatts. The first reactor started operation in 1985.
According to the 2003 assessment, the fault was 20 kilometers (12 miles) long, nearly triple the 7 kilometers discovered during the 1979 and 1980 survey.
The company expects to complete a new seismic survey of the Kashiwazaki Kariwa area by the end of March.
To contact the reporter on this story: Megumi Yamanaka in Tokyo at.