Despite widespread public opposition to a restart of nuclear reactors across the country, Japan recently approved the restart of two reactors at the Oi nuclear plant which could go back online as early as July 1st. Today, however, two prominent Japanese seismologists, have argued that that plant reactors sit far more precariously than their operator, Kansai Electric Power Co. (KEPCO), has claimed in order to rush their restart, that officials are moving too fast and that grave dangers still exist.
Mitsuhisa Watanabe, tectonic geomorphologist at Toyo University, and Katsuhiko Ishibashi, seismologist and professor emeritus at Kobe University, according to the Asahi Shibum, argued that a set of seismic faults run beneath the facilities and claim the utility has skated over their significance to regulators and the public.
“I find it difficult to understand how the utility can offer such varying data from the same area,” said Watanabe in a press conference, referring to internal KEPCO data they obtained for review. “Yet it has consistently presented the least serious interpretation to the government.”
“The Japanese government should have done a rigorous back-check,” said Ishibashi. “But it has skipped this fundamental process. The back-check should also be reformulated carefully to properly take active faults into account.”
Ishaibashi gained notoriety in Japan after a series of warnings he issued regarding the threat of nuclear disasters from specific seismic activity were proved prescient by the devastating Fukushima disaster in 2011.
“I don’t claim to be able to predict earthquakes, I can only point out tendencies,” he said, but called for the government to take more cautious positions and remain skeptical of industry assurances.
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Japan has approved the restart of the two reactors at the Kansai Electric Power Ohi nuclear plant, northwest of Tokyo, despite mass public opposition.
They will be the first to come back on line after all reactors were shut following a massive earthquake and tsunami last March that caused the worst nuclear crisis since Chernobyl at Tokyo Electric Power's Daiichi Fukushima plant.
Seismic modeling by Japan's nuclear regulator did not properly take into account active fault lines near the Ohi plant, Katsuhiko Ishibashi, a seismologist at Kobe University, told reporters.
"The stress tests and new safety guidelines for restarting nuclear power plants both allow for accidents at plants to occur," Ishibashi told reporters. "Instead of making standards more strict, they both represent a severe setback in safety standards."
Experts advising Japan's nuclear industry had underestimated the seismic threat, Mitsuhisa Watanabe, a tectonic geomorphology professor at Tokyo University, said at the same news conference.
"The expertise and neutrality of experts advising Japan's Nuclear Industrial Safety Agency are highly questionable," Watanabe said.
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Asahi Shimbun: Scientists warn of 3 faults under soon-to-restart reactors
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. [...]
“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 TEPCO-operated 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.
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