A ruling Friday by the Osaka District Court canceling central government approval for the operation of two reactors at the Oi nuclear plant run by Kansai Electric Power Co. (Kepco), saying its calculations for standards involving earthquake safety were flawed, has stunned the nuclear power industry.

The decision, which is the first of its kind, is likely to be appealed and could still be overturned. But the result has resurrected fundamental questions about nuclear power safety and the future role of the energy source.

What was at issue in the court case?

The Nos. 3 and 4 reactors at the Oi power plant were restarted in July 2012 and were the first in Japan to be switched back on after the March 11, 2011, Tohoku quake and triple meltdown at the Fukushima plant forced the country’s entire nuclear power fleet offline.

In the case, which was filed in June 2012, some 130 plaintiffs argued that despite the presence of earthquake fault lines near the plant's location, in Fukui Prefecture next to the Sea of Japan, Kepco had underestimated the size and power of a potential earthquake when it designed the Nos. 3 and 4 reactors, which went into operation in 1991 and 1993, respectively.

The government’s Nuclear Regulation Authority was established in September 2012, vowing to place the highest priority on public safety and a genuine safety culture. Prior to that, the plaintiffs had argued that tsunami and volcano risks warranted an injunction against a restart under then-tentative safety rules that had been adopted after March 11, 2011. After the NRA’s establishment, the Oi reactors went on to win restart approval in 2017 under newer, stricter safety standards. At that point, the plaintiffs charged that the government had then failed to follow the regulations under those new safety standards.

The NRA consists of nuclear power and earthquake experts who drew up more stringent earthquake safety standards that utilities would have to meet first if they wanted permission to restart their reactors.

One of the new standards involves calculations of what is known as the basic earthquake ground motion figure, a statistic used to determine structural vulnerability to earthquakes and one used by utilities when they engineer quake resistance in nuclear plants. The lower the ground motion number, the lower the requirements that must be met for quake-proof structures.

Kepco, under the NRA’s direction, used a figure for its design that was based on an average calculation of potential ground motion strength from a quake. But the Osaka court ruled that approach was not appropriate, and that the NRA had not considered the possibility of a quake that would produce ground motion much stronger than the average.

The government countered that the NRA`s calculation was appropriate and that the plaintiff's claim lacked a scientific rationale.

What makes this case different from past court decisions on nuclear power plants?

The Oi case is unique because it’s the first time a court has specifically ruled against the central government, in the form of the NRA, over the way it operates its screening process and the nature of its earthquake safety standards, adapted after Fukushima, which it uses to determine whether to approve reactor restarts.

There have been a number of court cases filed to stop the opening or reopening of nuclear power plants, including requests for temporary injunctions. In 2016, the Otsu District Court issued an injunction on two other Kepco reactors in Fukui — the Takahama Nos. 3 and 4 reactors — that the power company successfully got lifted. But those cases, and the subsequent overturning, were often based on highly technical arguments. The Oi case charged that the government had violated its own standards, and its own declaration that its safety standards would be the world’s most stringent.

What has the reaction been in other localities with nuclear power plants?

Miyagi Gov. Yoshihiro Murai, who just approved the restart of Tohoku Electric Power Co.’s Onagawa No. 2 reactor last month, would not comment on the Oi reactor verdict but said his decision had not been a mistake, saying that while he is not a nuclear expert, it is natural to prioritize the judgment of the NRA.

In Shizuoka Prefecture, where Chubu Electric’s Hamaoka nuclear power plant is located, there has been a mixed reaction in towns near the plant, with some saying the Osaka court case would not affect the plant and others expressing uncertainty.

Other local leaders have not commented directly on the case but laid out their own criteria for approving nuclear reactor restarts in their own neighborhood. Earlier this week, Kashiwazaki Mayor Masahiro Sakurai, re-elected last month, indicated he’d approve the restart of Tokyo Electric Power Company Holdings Inc.’s Kashiwazaki-Kariwa No. 7 reactor under certain conditions.

These included national funding for improving evacuation plans in case of an emergency at the plant, such as a better system for snow removal on local access roads and better port facilities.

But in Fukui, the ruling has stunned other towns where nuclear power plants are located and created questions about what happens next. In Mihama, the No. 3 reactor was scheduled to go back online sometime after January. Kepco’s Takahama Nos. 1 and 2 reactors had also received approval, and the utility had plans to switch them back on after March and May 2021.

What is the decision likely to mean for the future of Japan’s nuclear industry?

An appeal to the Osaka High Court by the government means that the Oi reactors could still be restarted, despite the lower court ruling. But the Oi case could form the basis of similar lawsuits in other nuclear towns against the government.

Regardless of eventual individual rulings in those cases, a rash of lawsuits would create new political headaches for the central government. It would have to work harder, and provide more local financial assistance, to convince towns hosting nuclear plants that NRA quake standards are safe in order to win restart approval from local leaders. All of this could create further delays on the part of utilities seeking quick restarts.

More potential delays, in turn, raise questions and concerns about the role of nuclear power in Japan’s 2030 energy mix. Nuclear power is supposed to provide between 20% and 22% of the nation’s electricity by then. It is also expected to play a role in helping Japan become carbon neutral by 2050.

Utilities were already grappling with tough questions regarding the costs of decommissioning old plants and finding medium- and long-term storage facilities for nuclear waste. They now also face the task of convincing the public and local leaders that nuclear power, despite the Osaka ruling, still remains a safe and price competitive energy source — even as renewable energy investment increases and costs for some renewable sources continue to decline.

The Oi decision means those questions and doubts, including those over the extent to which the government should still rely on nuclear to meet its energy and carbon neutral goals, are likely to get louder.

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