A prominent volcanologist disputed regulators’ conclusion that two nuclear reactors are safe from a volcanic eruption in the next few decades, saying Friday that such a prediction is impossible.
A cauldron eruption at one of several volcanoes surrounding the Sendai nuclear plant in Kagoshima Prefecture could not only hit the reactors, but also cause a nationwide disaster, said Toshitsugu Fujii, a professor emeritus at the University of Tokyo who heads a state-commissioned panel on eruption prediction.
The Nuclear Regulation Authority last month said two Sendai reactors fulfilled tougher safety requirements set after the 2011 Fukushima crisis began.
The NRA ruled out a major eruption over the next 30 years until the reactors reach the end of their usable life span.
The surprise eruption of Mount Ontake on the border of Gifu and Nagano prefectures on Sept. 27 has renewed concerns about the volcanoes in the region.
“It is simply impossible to predict an eruption over the next 30 to 40 years,” Fujii said. “The level of predictability is extremely limited.”
He said eruptions can only be predicted in hours or days, at best.
Studies have shown that pyroclastic flow from an eruption 90,000 years ago at one of the volcanoes near the Sendai plant reached as far as 145 km (90 miles) away, Fujii said.
He said that a pyroclastic flow from Mount Sakurajima, an active volcano that is part of the larger Aira cauldron, could easily hit the nuclear plant, which is only 40 km (25 miles) away.
Heavy ash falling from an eruption would make it impossible to reach the plant, and could also affect many parts of the country, including Tokyo, he said. Many nuclear power plants could also be affected in western Japan.
The Sendai reactors are the first to pass the safety checks, which added resistance to volcanic eruption as part of the new evaluation.
Prime Minister Shinzo Abe is pushing to restart any viable reactors deemed safe, saying nuclear power is stable and relatively cheap compared to other energy sources and key to Japan’s recovery. Ironically, the utilities, many of which operate atomic plants, are revolting against the feed-in tariff system — for producing a solar energy glut.
Kyushu Electric Power Co., which runs the Sendai plant, promised steps to ensure worker access in up to 15 cm (6 inches) of ash and a monitoring system to detect changes in volcanic activity.
It also promised to transfer fuel rods to safer areas ahead of time if eruption signs are detected — a time-consuming process experts say is unrealistic.
Fujii said 10 cm (4 inches) of ash will render any vehicle except tanks virtually inoperable. Power lines would be cut by the weight of the ash, causing blackouts that could shut reactor cooling systems.
Only after approving the reactors’ safety did the NRA establish a volcano panel to discuss eruptions and countermeasures.
Fujii, a member of that panel, said experts are opposed to the NRA’s views.
Even though a catastrophic eruption might occur only once in 10,000 years, the likelihood of one cannot be ruled out either, he said.
“Scientifically, they’re not safe,” he said of the Sendai reactors. “If they still need to be restarted despite the uncertainties and risks that remain, it’s for political reasons, not because they’re safe, and you should be honest about that.”