The 2011 nuclear accident at Fukushima Daiichi and the 1986 incident at Chernobyl may both be rated 7 on the International Nuclear and Radiological Event Scale, but the events are starkly different.
No deaths from radiation exposure have been attributed to the accident in Japan. At Chernobyl, 28 highly exposed reactor staff and emergency workers died from radiation and thermal burns within four months of the accident, and 19 more by the end of 2004. Officials believe the accident also was responsible for some 4,000 cases of thyroid cancer. A United Nations study published in September 2005 estimated that 56 deaths could be attributed to radiation exposure from the Chernobyl accident.
The radiation released into the atmosphere from Fukushima was about 10 percent of that from Chernobyl.
At Chernobyl, the reactor exploded, leading to a fire that lasted several days. The less-intense explosions at Fukushima Daiichi were from hydrogen that had built up inside the reactor buildings and did not involve the reactors themselves.
Comparing Chernobyl and FukushimaUnconventional reactor operations at Chernobyl resulted in a runaway power surge followed by steam and hydrogen explosions and a sustained fire in the reactor. Without a containment structure, the explosions propelled radioactive material from the reactor core high into the atmosphere and across eastern and western Europe for at least 10 days.
The earthquake and tsunami that struck the Fukushima Daiichi reactors resulted in the loss of electric power to the site and temporarily halted cooling the fuel in the reactor cores. There were explosions at three of the reactor buildings as a result of hydrogen buildup. Although the uranium fuel overheated and partially melted, there were no releases of radiation into the atmosphere at the levels seen during the Chernobyl accident. In December 2011, the Japanese government said the three damaged reactors had reached a “cold shutdown condition,” indicating the coolant temperature had stabilized below the boiling point and further release of radioactive material from the site had been stopped.
The uncontrolled release of the Chernobyl reactor’s fission products was exacerbated by the failure of Soviet authorities to take immediate action to protect surrounding populations. The most discernible health effect from Chernobyl—thyroid cancer in children—could have been mitigated by the early and widespread use of radiation protection procedures, including distribution of potassium iodide and control of the food supply in affected areas.
By contrast, Japanese authorities took early steps to evacuate people from a 12.5-mile zone around the Fukushima plant. Authorities also distributed potassium iodide to residents near the plant and restricted the transport and sale of milk, leafy vegetables and other food from the region.
Besides child thyroid cancer, no other discernible health effects have been detected in the populations around Chernobyl, according to a 2008 report of the United Nations Scientific Committee on the Effects of Atomic Radiation.
Based on all information to date, no discernible health effects are expected among the Japanese people as a result of the events at Fukushima.