The
International Atomic Energy Agency (IAEA) explains level 7 disasters as a major release of radioactive material with widespread health and environmental effects requiring implementation of planned and extended countermeasures. And Fukushima is still leaking radioactivity.
Japanese authorities, meanwhile, stated that the situation at the stricken plant was stabilizing. Japanese prime minister
Naoto Kan said that total radioactivity released from Fukushima was just 10% of what was blown out from Chernobyl.
However, in a separate news conference, an official of
Tokyo Electric Power Company, which operated the Fukushima plant, gave a different assessment of the disaster. He said, "The radiation leak has not stopped completely and our concern is that it could eventually exceed Chernobyl."
According to the
IAEA, so far "there are no health risks to people living in other countries from radioactive material released into the atmosphere from the Japanese nuclear power plants. Radiation levels measured to date in other countries are far below the level of background radiation that most people are exposed to in every day circumstances." Globally radiation levels are being monitored at 63 stations.
With the threat level upgraded, authorities have also rolled out plans to evacuate several towns and villages, based on wind directions and radiation measurements. This is beyond the 20km radius evacuation zone around the plant already in place.
The Japanese nuclear safety authorities have been giving out different figures for the amount of radiation blown into the atmosphere, ranging between 370,000 terabecquerels (TBq) to 630,000 TBq. Radiation is measured in units called becquerels and tera means a million million. This clearly puts the disaster in the level 7 range which is usually defined as tens of thousands of TBq. Chernobyl was estimated to have released 5.2 million TBq.
International experts have divergent calculations on how much radioactivity has been released from Fukushima. Gerhard Wotawa of Vienna based Central Institute for Meteorology and Geodynamics has calculated that Fukushima released 20-50% of the amounts of radioactivity released from Chernobyl. But France's radiation protection and safety institute has suggested that it was just 10% of Chernobyl.
While both Chernobyl and Fukushima have been graded as level 7, the nature of accidents in them was different. In Chernobyl, the reactor had exploded sending a plume of deadly radioactive particles, including hot particles from the nuclear fuel 30,000 feet high into the sky. These were carried by strong winds into five different directions ultimately spreading as far as Germany and
Sweden in the east.
The Chernobyl reactors were using graphite rods as moderators which burst into flames and burnt for four days, sending radioactivity streaming up. In all 150,000 sq km area in
Belarus,
Russia and
Ukraine was declared contaminated and evacuated. Another 45,000 sq km was declared affected.
In Fukushima, the tsunami destroyed backup generators, causing the reactors and storage pools to overheat and nuclear fuel rods to partially melt. Hydrogen explosions occurred carrying radioactive particles of iodine and cesium up to Tokyo, over 240 km away.
The situation in Fukushima is still not under control, as power has not been restored fully, leaving external water spraying as the only way of keeping the nuclear cores from warming up. Meanwhile the overflowing water itself is carrying radioactive particles in it and poses a threat.
Aftershocks, one of them of 7.1 magnitude have caused repeated disruption of work at the plant. Experts have repeatedly pointed out that the steel and concrete containers in which nuclear reactions take place must have cracked as the nature of radioactive particles found outside, including the lethal plutonium, couldn't otherwise have leaked.
Workers have been unable to physically verify these matters because of dangerous levels of radioactivity near the reactors. There is about 250 tonnes of nuclear material in the six reactors and their storage pools at Fukushima. Experts believe that this continues to be a threat till the situation is normalized.
