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Editorial: Quake-prone Japan must remain on guard against nuclear accidents

In earthquake-prone Japan, a major temblor could strike anywhere, at any time. Moreover, such a quake is impossible to predict -- a fact that was thrust upon us by the recent Kumamoto Earthquake.

Following two deadly earthquakes measuring a maximum 7 on the Japanese intensity scale with a widening focal region, many people no doubt felt concerned about the safety of the Sendai Nuclear Power Plant in Kagoshima Prefecture operated by Kyushu Electric Power Co. Concern has been also raised over Shikoku Electric Power Co.'s Ikata Nuclear Power Plant, across the ocean from Oita Prefecture. Of course, these are not the only places at risk of quakes. Yet the government is moving ahead with plans to restore nuclear power in Japan. Can Japan coexist with nuclear power plants? The recent earthquakes provide a chance for us to consider this matter.

The magnitude-6.5 quake that hit Kumamoto Prefecture on the evening of April 14, which was focused in the Hinagu fault zone, registered a maximum 7 on the Japanese intensity scale. Another magnitude-7.3 quake focused in the Futagawa fault zone to the north, which occurred in the predawn hours of April 16, also registered a 7 on the intensity scale. After these quakes, seismic activity spread to the Aso district and to the northeast, and strong shaking has been felt over a wide area, from Kumamoto Prefecture to Oita Prefecture.

When will this seismic activity subside? Could it get worse? Will it affect the Mount Aso volcano? The limitations of seismology and volcanology prevent us from answering these questions with certainty.

The Nuclear Regulation Authority (NRA) decided at a special meeting on April 18 not to halt operation of the Sendai Nuclear Power Plant. The effects of shaking on nuclear power plants are measured in gal, a unit of acceleration defined as one centimeter per second squared. The maximum acceleration measured at the plant during the recent quakes was 8.6 gal. In a safety assessment, the plant was deemed able to withstand up to 620 gal. At the time of screening, officials judged that even if a magnitude 8.1 quake were to occur in the Futagawa and Hinagu fault zones, ground acceleration would not exceed 150 gal.

Considering these figures alone, there seems to be no problem with safety. But the projected scenario is only applicable for earthquakes whose scales fall within what has been envisioned.

Responding to the latest quakes, the Japan Meteorological Agency and experts repeatedly expressed their views that that was no precedent of a magnitude-6.5 level inland quake being followed by an even bigger quake, and that they could think of no other cases wherein seismic activity had occurred in three separate locations at the same time. The government's Earthquake Research Committee also expressed the view that the Futagawa fault was longer than originally thought.

There are 2,000 known active faults in Japan. The latest quakes occurred along active faults that were previously known to scientists, but there have been past cases wherein quakes exceeding magnitude 7 have occurred along unknown active faults, including the 2000 Tottori earthquake and the 2008 Iwate-Miyagi inland earthquake.

Hokuriku Electric Power Co.'s Shika nuclear plant is said to have active faults lying beneath it, and decisions regarding this plant -- as well as others in similar situations -- must be made from the viewpoint of safety. This does not apply only to inland quakes, moreover. The massive earthquake that occurred five years ago on a plate boundary in the Pacific Ocean off Japan's Tohoku region greatly exceeded experts' predictions. We cannot imagine, therefore, that all earthquakes will remain within the scales envisioned by nuclear power companies and the NRA.

Furthermore, just because a nuclear power plant has passed the regulatory authority's screening does not necessarily mean it is safe -- and other threats exist in addition to earthquakes. The NRA itself acknowledges this, and such dangers must be considered as realistic possibilities. In this sense, preparation for an accident is indispensable -- but we cannot say that presently existing measures are adequate.

The latest earthquakes caused a bridge to collapse, triggered mudslides, and sank roads -- thereby cutting off transportation routes in various areas. A bullet train also derailed. If a nuclear accident occurs at the same time as such a natural disaster, will plans to evacuate residents proceed as planned? Concerns remain. Such damage would likely also hamper efforts to bring a nuclear accident under control, while continuing aftershocks would additionally hinder the accident response.

Kyushu Electric has withdrawn plans to build a seismically-isolated emergency response center at the Sendai nuclear plant. We would like power company officials to consider whether they have let their guard down over the threat of earthquakes.

April 26 marked 30 years since the Chernobyl nuclear disaster in the former Soviet Union. At the time, Japan judged that the accident had occurred due to unique circumstances there, and that a similar accident would not occur in Japan. Consequently, countermeasures were neglected to be implemented here. When the Fukushima nuclear disaster occurred 25 years later, insufficiencies in Japan's safety countermeasures were blatant.

Five years have now passed since the outbreak of the disaster at the Fukushima No. 1 Nuclear Power Plant, and the government has indicated that it will proceed to reactivate nuclear reactors. It has also in effect accepted the reactivation of aging reactors -- originally envisaged as an extremely rare exception to a new rule setting the life of nuclear reactors at 40 years, after which they were to be decommissioned.

We fear that there is a re-emergence of a safety myth stating that an accident like the one in Fukushima will never happen again. We cannot approve of a gradual slip back to nuclear power.

Thirty years after the Chernobyl nuclear catastrophe, the disaster is still a long way from being brought under control. The concrete sarcophagus that was built at the time of the accident to contain radioactive materials has deteriorated significantly, and construction of a new shelter is proceeding. In Fukushima, meanwhile, nearly 100,000 people remain evacuated from their hometowns. There is no clear outlook for decommissioning of the reactors, which is expected to take 40 to 50 years. And people suffer from anxiety about the effects of radiation.

Though the chance of a disaster may be small, nuclear accidents are different from other types of calamities in that they can rob people of a future. Meanwhile, risks such as terrorist acts targeting nuclear power plants have come into the global spotlight.

As a country prone to earthquakes and one that has suffered a severe nuclear disaster, Japan must not forget to remain on guard.

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