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Only Chernobyl was Rated Level 7 BeforeThe International Nuclear and Radiological Event Scale (INES) was created about 20 years ago to enable prompt and relatively un-ambiguous communication about the safety significance of nuclear accidents. "The scale is intended to be logarithmic, similar to the moment magnitude scale that is used to describe the comparative magnitude of earthquakes. Each increasing level represents an accident approximately ten times more severe than the previous level." Until today, the Fukushima 1 nuclear crisis was categorized as a level 5 incident (like Three Mile Island in 1979), but it has now been upgraded to a level 7 event, like Chernobyl in 1986.
While the level was upgraded because of the likely amount of radioactive materials released, which is now estimated to be between 370,000 and 630,000 terabecquerels emitted in the air from the Nos. 1 to 3 reactors of the plant, Japanese officials are quick to draw a distinction with the soviet reactor catastrophe:
"It is quite different from Chernobyl," said Mr. Nishiyama. "First, the amount of released radiation is about a tenth of Chernobyl," he said, adding that while there were 29 deaths resulting from short-term exposure to high doses of radiation at Chernobyl, there were no such deaths at Fukushima.
"At Chernobyl, the nuclear reactor itself exploded," he said, adding that at the Fukushima plant, the pressure vessel and the containment vessel were largely intact. (source)
While that is true, the severity of the situation in Fukushima shouldn't be downplayed. Workers have been making heroic efforts for now more than a month and things aren't yet under control. Radioactive materials are still being emitted, so over time it is possible that Fukushima 1 could end up releasing more radiation, cumulatively, than Chernobyl. Hopefully the workers and local citizens will have been better protected, though.
This decision to upgrade the INES level is coming only a day after the Japanese authorities broadened the 12-mile nuclear evacuation zone around the plant. It now includes all or part of 5 towns.
More on Japan's Nuclear Crisis
-March 14: Mini-FAQ About Japan's Nuclear Power Plant Crisis
-March 15: 6 Important Questions About the Crisis at Japanese Nuclear Power Plants
-March 16: Update on Japan's Nuclear Crisis at Fukushima I
-March 17: Ongoing Crisis at Japan's Fukushima I Nuclear Power Plant
-March 18: Japan's Nuclear Crisis, One Week Later
-March 21: Limited Progress Cooling Fukushima's Nuclear Reactors
-March 22: Light at the End of the Tunnel for Japan's Nuclear Crisis?
-March 23: Japan Nuclear Crisis: External Power Reconnected at Fukushima 1
-March 24: Japan Nuclear Crisis: Slow Progress with Emergency Cooling Systems
-March 25: Japan's Nuclear Crisis: 2 Weeks After the Mega-Quake & Tsunami
-March 30: Japan's Nuclear Crisis: 19 Days Later and Not Much Better
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