レベル7 「最悪」の更新を防げ

(Mainichi Japan) April 13, 2011
Japan must prevent another Level 7 nuclear plant crisis by all means
社説:レベル7 「最悪」の更新を防げ

The Chernobyl disaster in 1986, which was rated Level 7 on the International Nuclear and Radiological Event Scale (INES), is still regarded as the world's worst nuclear power plant accident in history. Level 7 crises are accidents that lead to "major releases of radioactive materials."

Just recently, the government has raised the level of the crisis at the Fukushima No. 1 Nuclear Power Plant that was hit hard by a massive tsunami generated by the March 11 Great East Japan Earthquake to Level 7 on the INES.

The decision will not cause any change in the work underway to place the crippled nuclear plant under control. Now, there is no choice but to take all possible measures to cool down the cores of the affected reactors.

Still, questions remain as to why the crisis level was raised at this time. It would be a problem if it reflects the government's underestimation of the seriousness of the crisis and reluctance to fully release information on the accident.

The government raised the crisis level of the Fukushima nuclear accident from 4 to 5 on March 18. By that time, explosions and fires had occurred near the affected reactors one after another. It was obvious that a considerable amount of radioactive substances had been leaking from the reactors, judging from the levels of radiation around the plant.

Nevertheless, an estimation of the total amount of radiation leaked from the plant, based on which the crisis level was rated 7, had not been released until recently. The government explained that it took a long time to increase the accuracy of the data. However, it will lose the public's confidence if it had been aware that the accident should be rated Level 7 but delayed the announcement by saying it was still analyzing figures.

The government was also slow in releasing the cumulative radiation levels, based on which evacuation plans are worked out. The data, which is indispensable in ensuring the safety of residents near the plant, must be transparent and released promptly.

The government has also emphasized the differences between the Fukushima plant accident and the Chernobyl crisis. It is true that the Fukushima accident is different from Chernobyl in which massive levels of radiation were released in a short period of time and that some people died of acute radiation exposure. The amount of radiation that has leaked from the Fukushima plant is estimated at one-tenth of that which leaked from the Chernobyl plant.

At the same time, the Fukushima crisis is unprecedented in that four of its reactors simultaneously became out of control. Slow but constant radiation leaks from the plant have confused local residents. No one can tell how long the crisis will continue or whether it will develop into a more serious catastrophe.

Therefore, Japan is required by the international community to reconfirm the seriousness of the Fukushima nuclear plant crisis and respond to it rather than compare the degree of the accident with that of the Chernobyl crisis. Tokyo Electric Power Co. (TEPCO) that operates the crippled Fukushima No. 1 Nuclear Power Plant as well as the government should reflect on their overly optimistic thinking that an accident like the Chernobyl crisis would never happen in Japan, which led to the serious situation at the Fukushima plant.

Powerful aftershocks following the March 11 earthquake have been occurring in not only Fukushima Prefecture but also many other areas. The crisis has illustrated the vulnerability of nuclear power plants -- they tend to lose external electric power sources necessary to cool down the reactor cores if hit by powerful temblors. It is also obvious that some of the nuclear power plants across the country face risks of being paralyzed by powerful quakes and ensuing tsunami.

While working to place the plant under control, the government and power suppliers must inspect nuclear power plants across the country and take measures to prevent major earthquakes and tsunami from causing major crises at these facilities. Another Level 7 nuclear power plant catastrophe must be prevented by all means.

毎日新聞 2011年4月13日 東京朝刊

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