Thousands of protesters in front of his office last week weren’t enough to dissuade prime minister Yoshihiko Noda from his plan to restart Japan’s nuclear reactors, starting with a pair in Oi, Fukui Prefecture.
On June 26, two seismological experts took their turns, speaking at the Foreign Correspondents’ Club of Japan in Tokyo.
Mitsuhisa Watanabe, tectonic geomorphologist at Toyo University, and Katsuhiko Ishibashi, seismologist and professor emeritus at Kobe University, argued that the Oi nuclear power plant reactors sit far more precariously than their operator, Kansai Electric Power Co. (KEPCO), has claimed in order to rush their restart.
If the utility and the government have their way, the Oi No. 3 and 4 reactors will be the first to power up since May 5, when all of Japan’s 50 remaining reactors went offline for maintenance or safety checks. The No. 3 reactor is scheduled to be restarted on July 1.
Using KEPCO’s own data, some of which was first published more than 20 years ago, the pair point to a set of seismic faults under the facilities the importance of which, they claim, the utility has skated over.
“I find it difficult to understand how the utility can offer such varying data from the same area,” said Watanabe. “Yet it has consistently presented the least serious interpretation to the government.”
The seaside Oi facilities sit in a gap between three known faults, FO-A, FO-B -connected to each other and running beneath Wakasa Bay-and the inland Kumagawa fault, which with the first two form a 63-kilometer line.
KEPCO foresees the possibility of the first two faults moving at once, but not all three together. Moreover there is a smaller fault, possibly a branch, directly beneath the reactors. The utility claims it is inactive, based on a sketch of the vertical displacement of its southeastern wall. A sketch of its northwestern wall, revealing slippage and a “shattered zone” in the clay, however, seems to indicate otherwise.
“The Japanese government should have done a rigorous back-check” based on the Revised Seismic Design Guide of 2006, said Ishibashi. “But it has skipped this fundamental process. The back-check should also be reformulated carefully to properly take active faults into account.”
To do so yields starkly different figures: Japan’s Nuclear and Industrial Safety Agency, for example, estimates that the two submarine faults in Wakasa Bay could produce as much as 700 Gal-a measure of peak earthquake ground motion. KEPCO believes a three-fault quake would reach 760 Gal.
For comparison the greatest ground motion ever measured at a Japanese nuclear power plant is 1,699 Gal, recorded at the TEPCooperated Kashiwazaki-Kariwa facility in Niigata Prefecture during the 2007 Niigata Chuetsu-oki Earthquake. The plant survived, but was shut down for 21 months.
“The actual motion was more,” explained Ishibashi, who says that the utility’s questionable building practices helped avert a possible disaster. “The reactor was constructed on poor land, with a thick sedimentary layer, which attenuated the motion.”
A shock would hit the Oi plant more directly, he adds, because the sedimentary layer there is more shallow.
Ishibashi has gained public attention, having predicted an earthquake-caused nuclear accident as early as 2005-six years before the accident at the Fukushima No. 1 nuclear power plant-but so far no government ears.
“I don’t claim to be able to predict earthquakes, I can only point out tendencies,” said Ishibashi, calling on the government to base its decisions on data gathered from shaking recorded at Kasahiwazaki-Kariwa, instead of the averaged figures presented by utilities.
“There’s a reason why they prefer averages. To reinforce facilities to withstand such stresses would make them unfeasible,” he said.