Ruling on Oi Nuclear Plant Lacks Understanding of Safety Screenings

It can be said that a court’s ruling, which found the government’s judgment on the safety of a nuclear power plant to be legally invalid, was based not on the actual safety of the nuclear power plant itself, but solely on the court’s view of whether the screening procedure was appropriate.

The Osaka District Court has handed down a ruling that nullified the government’s approval of the restart of the Nos. 3 and 4 reactors at Kansai Electric Power Co.’s Oi nuclear power plant in Fukui Prefecture. It was the first judicial decision to order the cancellation of an approval based on Japan’s new safety standards, which were worked out after the accident at Tokyo Electric Power Company Holdings Inc.’s Fukushima No. 1 nuclear power plant.

The main point of contention is the validity of the “design basis earthquake ground motion” calculated by KEPCO based on an estimation of the biggest possible earthquake that could hit the plant. The term “design basis earthquake ground motion” refers to a figure used as the premise for designing the quake resistance of a nuclear power plant. The government’s Nuclear Regulation Authority (NRA) has confirmed that the nuclear reactors met the new safety standards in the screening.

The ruling concluded that the NRA’s judgment is unreasonable as it has errors and insufficiencies that cannot be overlooked. It contained criticism that the NRA did not conduct the screening in line with the internal regulatory guide for the screening procedure.

The design basis earthquake ground motion is decided based on the average scale of past earthquakes and other factors. The guide said that variations in the scales of earthquakes also need to be considered. The ruling said that the possibility of above-average earthquakes must also be taken into consideration.

The NRA uses the same screening method to check the safety levels of other nuclear power plants. If the ruling is finalized, it is expected to have an enormous impact.

In formulating the design basis earthquake ground motion, it is common to set numerical values that can ensure sufficient safety, taking into account not only the scale of past earthquakes but also various factors such as the length and area of faults.

For the Nos. 3 and 4 reactors at the Oi plant, the NRA required KEPCO to drastically raise the figure initially set by the electric power company. It was a step based on lessons from past major earthquakes, including the Great East Japan Earthquake. It can be said that the NRA effectively conducts the screenings on the assumption of earthquakes on an above-average scale.

If risks are overestimated, nothing will be able to function. The ruling appears to have been a foregone conclusion, and it is impossible to dispel the impression that the actual practice of the screening was disregarded.

The Fukuoka High Court in July last year rejected an appeal by residents who sought an injunction to halt the operations of two reactors at Kyushu Electric Power Co.’s Genkai nuclear power plant in Saga Prefecture. The residents claimed that variations in the scale of earthquakes need to be considered. However, the high court dismissed their claim as simply their own view, saying that giving consideration to the variations is only a “matter to keep in mind.”

If the guide’s description is open to differing interpretations, then the NRA should revise the description.

Since the accident at the Fukushima No. 1 nuclear power plant, there have been six judicial rulings that barred the operations of nuclear power plants. With the exception of one case currently at trial, those rulings have been overturned mainly in higher courts. In the case of the two reactors at the Oi plant, a higher court decision, which nullified a lower court ruling that had ordered the suspension of their operations, has been finalized.

If the government appeals the ruling at the Osaka District Court to a higher court, every means must be employed to prove the actual situation and the validity of the NRA’s screening based on science.

(From The Yomiuri Shimbun, Dec. 8, 2020)