Photo/IllutrationLawyer Hiroyuki Kawai, center, explains the Hiroshima High Court’s decision on Sept. 25 to lift a temporary injunction barring operations of the Ikata nuclear plant. (Koichi Ueda)

  • Photo/Illustraion

HIROSHIMA--The Hiroshima High Court has significantly raised the bar for plaintiffs seeking suspensions of nuclear plant operations on grounds of a possible volcanic eruption.

In a ruling handed down on Sept. 25, the court overturned a temporary injunction order that had halted operations at the Ikata nuclear plant, saying the plaintiffs must present highly credible evidence of the risk of a catastrophic volcanic eruption.

The plaintiffs argued that Shikoku Electric Power Co. must suspend operations of its Ikata plant in Ehime Prefecture because of the dangers posed by Mount Aso in central Kyushu, Japan’s southern main island.

They said a pyroclastic flow from the volcano would reach the plant about 130 kilometers away in the event of an eruption on a scale similar to one that occurred about 90,000 years ago.

But the high court dismissed their argument by referring to “socially accepted ideas.”

“The frequency of such an eruption is extremely low,” Presiding Judge Masayuki Miki said. “The government has not taken any measures to deal with it, and a large majority of the public don’t see the risks of a major eruption as a problem, either.”

He added, “Unless the court is given reasonable grounds for the possibility of a major eruption, it is a socially accepted idea that the safety of a facility will not be undermined even if measures are not in place to prepare for such a scenario.”

The ruling was based on an assessment issued in March by the Secretariat of the Nuclear Regulation Authority that risks to nuclear facilities from a catastrophic volcanic eruption are within a socially acceptable range.

Kenta Tsunasaki, one of the plaintiffs, said he was appalled by the ruling.

“We are again witnessing the exact same attitude toward a massive eruption of a volcano,” he said, referring to the magnitude-9.0 Great East Japan Earthquake and tsunami that caused the 2011 triple meltdown at the Fukushima No. 1 nuclear plant. “The judiciary must have forgotten about the Fukushima disaster.”

Tokyo Electric Power Co., the plant operator, has argued that the scale of the tsunami that struck the nuclear complex could not be foreseen.

Many volcanologists agree that catastrophic eruptions rarely occur.

But Yoshiyuki Tatsumi, professor of volcanology at Kobe University, questioned the court’s dismissal of the possibility of a huge eruption.

“The low occurrence does not assure safety,” he said. “A catastrophic eruption is one of the worst disasters in terms of the degree of danger, which is calculated by multiplying the expected number of victims and the rate of occurrence.”

Tatsumi also said it is difficult to predict when Mount Aso will have a major eruption because its eruption cycle is irregular.

(This article was compiled from reports by Sotaro Hata, Toshio Kawada and Shigeko Segawa.)