Photo/IllutrationLawyers hold up signs outside the Hiroshima High Court on Dec. 13 proclaiming an injunction had been ordered on operations at the Ikata nuclear power plant. (Koichi Ueda)

HIROSHIMA--A high court for the first time has banned operations at a nuclear power plant.

The Hiroshima High Court issued the injunction in a verdict Dec. 13 that applies to the No. 3 reactor at the Ikata nuclear power plant in Ikata, Ehime Prefecture, operated by Shikoku Electric Power Co.

In the ruling, the high court concluded there was a chance the Ikata plant could be affected by a pyroclastic flow from Mount Aso if an eruption occurred similar in scale to a massive one 90,000 years ago on the southern island of Kyushu.

A computer simulation by Shikoku Electric of the possible effects from an eruption like the one in ancient times showed there was a possibility of a pyroclastic flow reaching the grounds of the Ikata plant.

The high court concluded that the Ikata plant was located in an inappropriate location and that the Nuclear Regulation Authority's decision that new safety standards had been met was not rational.

The company suspended operations in October to carry out a periodic inspection. If a judicial decision overturning the Dec. 13 high court ruling is not issued, the Ikata reactor will not be able to resume operations--even if the inspection is completed without problems.

For that reason, the latest ruling could affect the government's plans to resume operations at other nuclear plants more than six years after the triple meltdown at the Fukushima No. 1 nuclear power plant.

An official with Shikoku Electric Power labeled the court injunction as "extremely regrettable" and lamented the fact that it did not accept the company's assertion that the plant is safe.

"The verdict is unacceptable," the official said.

The utility plans to initiate procedures immediately to have the injunction suspended.

The injunction request was made by four residents of Hiroshima and Matsuyama cities. Among the main points of contention before the high court were the rationality of new safety standards approved by the Nuclear Regulation Authority (NRA) in the aftermath of the 2011 Fukushima nuclear disaster; the rationality behind the expected maximum strength of an earthquake for the area; and an evaluation of the effect of volcanic ash on the reactor's operations.

While district courts have issued injunctions on operations at other plants, higher courts have overturned all those verdicts until now.

For example, the Fukui District Court in April 2015 and the Otsu District Court in March 2016 ordered operations stopped at the No. 3 and No. 4 reactors of the Takahama nuclear power plant in Fukui Prefecture operated by Kansai Electric Power Co., but those verdicts were later overturned.