HIROSHIMA -- Recognizing the risk of a volcanic eruption, the Hiroshima High Court on Dec. 13 ordered the suspension of a reactor at Shikoku Electric Power Co.'s Ikata Nuclear Power Plant -- a decision that could deal a blow to power companies' finances and the government's energy policy, as there are many nuclear plants located near volcanoes.
In its decision, which overturned a lower court ruling, the high court judged that new regulatory standards for nuclear power plants implemented in the wake of the Fukushima nuclear disaster were reasonable, but that the Nuclear Regulation Authority (NRA)'s judgment on the risks of damage from a volcanic eruption were "irrational." The court mentioned the danger of pyroclastic flows from a catastrophic eruption at the Aso Caldera, located about 130 kilometers away from the Ikata plant in Ehime Prefecture, together with the threat of volcanic ash and other falling material.
The court decision to order suspension of the plant's No. 3 reactor was based on an "evaluation guide on the effects from volcanoes" that the NRA had produced to screen nuclear plants' volcanic eruption countermeasures.
Based on the guide, the court in its ruling stated that there was a need to demonstrate that there was a low possibility of a pyroclastic flow reaching the plant even in the event of a massive eruption at the Aso Caldera on the scale of one that is said to have occurred some 90,000 years ago. The court criticized a geological survey by Shikoku Electric Power Co., and judged that the location was not fit for the building of a nuclear power plant. It also judged that the utility had underestimated the effects of a volcanic eruption.
The high court acknowledged that it is the social norm to ignore the risks of events whose frequency of occurrence was extremely low. However, it ruled that it was impermissible for the district court to alter the framework for the judgment criteria by saying that there would be no safety deficiencies even if a catastrophic eruption were not envisaged as a natural disaster -- and overturned the lower court's decision.
A representative of the secretariat of the NRA expressed dissatisfaction with the latest ruling.
"It's been 90,000 years since the last catastrophic eruption at the Aso Caldera, and there's no large magma chamber underground. We've already judged that there will be no catastrophic eruption during the operation period," the representative said.
There are cases in which claims of local residents calling for the halt of nuclear reactor operations have been accepted in the past on the grounds that officials' assumptions on the possible level of shaking from earthquakes under new safety standards are too lenient. Such was the case with an injunction issued by the Otsu District Court in March 2016 to halt the No. 3 and 4 reactors at the Takahama Nuclear Power Plant in Fukui Prefecture -- although the injunction was overturned by the Osaka High Court in March 2017.
The latest ruling in the Hiroshima High Court stated that the "new standards (for safety implemented after the Fukushima nuclear disaster), and the decisions by the NRA are reasonable." It also judged that estimates on other points of contention including earthquake ground motion, the maximum tsunami envisaged and countermeasures against serious accidents and terrorist attacks were "reasonable."
In response to the court's acknowledgement of the risks of a volcanic eruption, Hiroyuki Kawai, a lawyer representing the plaintiffs, commented, "The risks from volcanic eruptions extend to other nuclear power plants, and the framework of the Hiroshima High Court's decision can be applied laterally (to other nuclear power plant lawsuits)." Kawai predicted that the effects of the ruling would spread to Kyushu Electric Power Co.'s Sendai and Genkai nuclear plants, which are close to the Aso Caldera and Sakurajima in Kagoshima Prefecture, and Chugoku Electric Power Co.'s Shimane Nuclear Power Plant in the city of Matsue, which is near the volcano Mount Daisen.