Experts are not agreed, however, as to the extent of the radiation leaks and whether it can yet be said to be as bad as the 1986 disaster in Ukraine. The International Nuclear and Radiological Event Scale defines a level 7 accident as a "major release of radioactive material with widespread health and environmental effects." The category is based on an exponential scale (similar to earthquake categories) where being within about ten times put something in the same category.
NISA (Nuclear Industrial Safety Agency of Japan) reported that the amount of radiation that has leaked from Fukushima is 1/10th of what occurred at Chernobyl.
“I don't know where they got that [estimation] from," says Yoshiaki Oka, a professor of nuclear engineering at Tokyo’s Waseda University, who believes even NISA's figure is an overestimation.
Professor Oka says he believes the idea that Fukushima is as bad as the world’s worst nuclear disaster is “completely wrong” and that according to his estimates the leak of radiation, so far, from the Japanese plant is about “1/100th of that of Chernobyl."
There is a key difference, he says, in the type of explosions at Fukushima and Chernobyl. At the Ukrainian plant 25 years ago, he explains, a series of operating errors and misjudgments resulted in an explosion and fire releasing toxic smoke that contained parts of the fuel rods and graphite particles into the atmosphere. At Fukushima, however, there have only been steam explosions.
Also, there have been no reported deaths so far due specifically to radiation at Fukushima, where at least five workers have died from other operational mistakes. The initial explosion at Chernobyl killed two workers, and then 28 of the firemen and emergency clean-up workers died in the first three months after the explosion because of radiation exposure.
Still, Oka concedes that it is very difficult to tell exactly what percent of the fuel rods have melted at Fukushima, and therefore how much radiation has actually leaked.
"Fukushima has its own unique risks, but comparing it to Chernobyl is going too far. Fukushima is unlikely to have the kind of impact on the health of people in neighboring countries, the way Chernobyl did," nuclear specialist Kenji Sumita at Osaka University told Reuters.
Geography exacerbated the Chernobyl incident. While that radiation spread to the Ukrainian countryside and blew over Europe, much of the Fukushima radiation has dispersed over the Pacific Ocean
Globe and Mail - Fukushima is reported to have thus far released between 370,000 and 630,000 terabecquerels of iodine-131. While that’s a dangerously high number (the permissible level for vegetables and fish is 2,000 becquerels per kilogram), it nonetheless remains far below 5.2 million terabecquerels released from Chernobyl. Japan’s nuclear safety commission said Tuesday that most of the radiation escaped in the first hours and days after the tsunami. It estimates the release of iodine-137 has now come down to under 1 terabecquerel per hour. As noted, there is a dispute about the level of radiation and some indicate that Fukushima has released about 50,000 terabecquerels.
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