What Does Fukushima's Level 7 Mean?

It sounds really, really bad. Is it?

By Kate Seamons,  Newser Staff

Posted Apr 12, 2011 7:47 AM CDT

(Newser) – Japan has made the decision to raise the Fukushima Dai-ichi nuclear disaster severity level from 5 to 7. That obviously means "worse." But what else does it mean?

  • Japan finally has an estimate on how much radiation has been released: The level is an indication of the total radioactive materials emitted. Data has revealed that the cumulative amount of radioactive particles released into the atmosphere had reached levels that apply to a Level 7 incident, reports the AP.

  • So what is that estimate? According to two estimates, the equivalent of about 500,000 terabecquerels of radiation from iodine-131 has been released. The Level 7 threshold is "several tens of thousands of terabecquerels."
  • But all 7s are not created alike: The Wall Street Journal notes that officials were careful to say this this is still not a Chernobyl-size disaster. "The amount of released radiation is about a tenth of Chernobyl"—about 5.2 million terabecquerels—said a rep for Japan's Nuclear and Industrial Safety Agency.
  • But it could still top Chernobyl in one regard: TEPCO today warned that the plant continues to release radioactive materials, and that the total levels emitted could eventually top those released by Chernobyl.
  • Level 7 also indicates widespread effects on the environment and health: The Telegraph noted that Japan's safety commission now says radiation in excess of the amount considered safe for humans during an entire year has been found as far as 37 miles from the plant; the evacuation zone is only 18 miles.
  • Is there another big one we haven't been talking about? Sort of. Besides Chernobyl, Time notes that a 1957 accident in Kyshtym, Russia, was the only one that's come close to being a 7; it was a 6. Most nuclear accidents tend to be a 3 or less.

In this photo released by TEPCO, a small fire breaks out from facilities sampling seawater located a few dozen meters from Unit 4 inside the tsunami-crippled Fukushima Dai-ichi nuclear power plant.
In this photo released by TEPCO, a small fire breaks out from facilities sampling seawater located a few dozen meters from Unit 4 inside the tsunami-crippled Fukushima Dai-ichi nuclear power plant.   (AP Photo/Tokyo Electric Power Co.)
A man uses a radiation detector to measure level of a pack of strawberry produced in Iwaki City, Fukushima Prefecture, during an event to promote safety of their agricultural products in Tokyo.
A man uses a radiation detector to measure level of a pack of strawberry produced in Iwaki City, Fukushima Prefecture, during an event to promote safety of their agricultural products in Tokyo.   (AP Photo/Koji Sasahara)
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