The Tomari nuclear plant in Hokkaido and the Tsuruga plant in Fukui Prefecture are at risk of being surprised by earthquakes that exceed their quake-resistance specifications, a report by three utilities said Monday.
The finding, based on the plants' current quake-resistance standards, was included in analyses they drafted at the request of the Nuclear and Industrial Safety Agency, which is still struggling with the Fukushima disaster.
The three utilities were asked to examine the possibility of interlocked movements taking place on active faults around their plants. The Tomari plant is run by Hokkaido Electric Power Co. and Tsuruga plant by Japan Electric Power Co.
Potential quakes near Tokyo Electric Power Co.'s massive Kashiwazaki-Kariwa plant in Niigata Prefecture, Hokuriku Electric Power Co.'s Shiga plant in Ishikawa Prefecture, and Kansai Electric Power Co.'s Mihama and Oi plants in Fukui Prefecture, were estimated as below the scale of the largest jolts that were anticipated when they were designed.
It is unclear if that includes any adjustments prompted by the magnitude 6.8 quake that triggered a fire and radiation leak at Kashiwazaki-Kariwa, the world's largest nuclear power facility, in July 2007 after it was learned that none of Japan's nuclear plants had been designed to withstand the horizontal ground movement displayed by that quake.
The three utilities concluded that the quake resistance of their nuclear power plants does not need to take interlocked movements on faults into account.
The magnitude-9.0 quake in March 2011 prompted the agency to drop its past rule that quake-resistance standards do not need to take into account the possibility of linked movements on faults separated by 5 km or more, and to order utilities to look into the possibility.