The Yomiuri Shimbun
The Nuclear and Industrial Safety Agency on Tuesday raised the provisional severity level of the nuclear accident at the Fukushima No. 1 nuclear power plant to the worst rating of seven on the International Nuclear Event Scale (INES), up from the previous level of 5.
The only other nuclear crisis to have been rated level 7 was the 1986 Chernobyl accident in the former Soviet Union. The latest rating reflects the seriousness of the Fukushima plant accident that was caused by the March 11 Great East Japan Earthquake and subsequent tsunami.
The government and Tokyo Electric Power Co., the operator of the nuclear plant, must work harder to bring the situation under control.
The INES assessment is based on the amount of radioactive material emitted, the estimated damage to nuclear reactors and other factors.
The agency, which is under the Economy, Trade and Industry Ministry, calculated the amount of radioactive substances emitted after explosions at buildings of the Fukushima plant's Nos. 1 to 3 reactors and the other events based on radiation levels monitored around the plant. The agency estimated the amount of radiation released so far to be second only to that emitted during the Chernobyl accident.
The crippled Fukushima plant has released far more radiation than the 1979 accident at the Three Mile Island nuclear power plant in the United States.
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Not the same as Chernobyl
However, the amount of radioactive material released so far is equal to only about 10 percent of that released in the Chernobyl accident.
Explosive nuclear reactions in Chernobyl destroyed the reactor and set off a fire. A huge amount of radioactive material spread over vast swathes of Europe and far beyond for about 10 days.
In the Fukushima accident, nuclear reactions were stopped immediately after the powerful earthquake. Most functions of the reactors have been maintained and nuclear fuel is being cooled by emergency injections of water into the reactors. The amount of radioactive substances being emitted into the atmosphere has fallen compared with just after the explosions.
The government should carefully explain the vital differences between the Chernobyl and Fukushima Prefecture accidents to prevent public anxiety from spreading and to control damage that could be whipped up by groundless rumors.
Work to restore cooling functions at the Fukushima plant's reactors, however, is proceeding with difficulty. This leaves the possibility that the reactors could sustain further serious damage and a massive amount of radioactive material could be released into the air.
However, temperatures at the reactors are now under control. It seems the worst is apparently over in this regard. The agency did not raise the provisional severity level of the accident because the situation is deteriorating.
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Keep guard up against quakes
Meanwhile, aftershocks centered around the nuclear plant have been occurring with unnerving frequency. Tremors with a seismic intensity of 5 or more on the Japanese scale of 7 have often disrupted restoration work at the plant. It was frightening to hear that cooling systems of the reactors lost power for about 50 minutes following a strong aftershock Monday.
Aftershocks are expected to continue for a while yet. We urge the government and TEPCO to do everything they can to protect the reactors' cooling functions from being affected by these temblors.
A huge amount of radioactive substances has been released into the environment. It will become increasingly important to determine which areas have been contaminated with radiation and to minimize any negative health impacts on people living there. The government must take necessary countermeasures as soon as possible.
(From The Yomiuri Shimbun, April 13, 2011)
(Apr. 14, 2011)
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