What is the severity level?
The International Atomic Energy Agency’s (IAEA) international nuclear and radiological event scale ranks nuclear and radiological accidents and incidents by severity from one to seven. Until now, the 1986 Chernobyl accident was the only nuclear accident to have been rated a level seven event, which the IAEA describes as “a major release of radioactive material with widespread health and environmental effects requiring implementation of planned and extended countermeasures.” Officials from Japan’s Nuclear and Industrial Safety Agency (NISA) estimate that the amount of radioactive material released to the atmosphere from Fukushima Dai-ichi is much less than Chernobyl. A spokesman for NISA said the new ranking did not mean the Japanese plant posed the same threat to public health or involved similarly big releases of radiation as the Chernobyl disaster.
What is the main difference between the two accidents?
At Chernobyl, explosions destroyed a reactor, releasing a cloud of radiation that contaminated large areas of Europe. At Fukushima, which was damaged by an earthquake, the reactors still have mostly intact containment vessels surrounding their nuclear cores. Japanese officials say that at Chernobyl, the reactor itself exploded while still active. At Fukushima, the magnitude 9.0 earthquake and tsunami crippled the plant’s cooling system, leading to a partial meltdown of the reactor. Earlier attempts to cool the reactor by hosing water from fire engines and helicopters left pools of contaminated water and flooded basements, hampering the containment operation and efforts to restart the cooling pumps. To make room for more highly radioactive liquid, the plant’s operator, Tokyo Electric, pumped tonnes of contaminated water into the Pacific, but stopped after the move was criticized by South Korea. Tokyo Electric appears to be no closer to restoring cooling systems at the reactors, critical to lowering the temperature of overheated nuclear fuel rods.
How much radioactive material has been released at Fukushima?
Japan’s nuclear safety commission has estimated that the Fukushima plant’s reactors had released up to 10,000 terabecquerels of radioactive iodine-131 per hour into the air for several hours after they were damaged in the March 11 earthquake and tsunami. It said emissions since then had dropped to below 1 terabecquerel per hour, adding that it was examining the total amount of radioactive materials released. A terabecquerel equals 1 trillion becquerels, a measure for radiation emissions. The government says the Chernobyl incident released 5.2 million terabecquerels into the air — about 10 times that of the Fukushima plant.
What were the effects of Chernobyl?
Fifty emergency rescue workers died from acute radiation syndrome and related illnesses, 4,000 children and adolescents contracted thyroid cancer, nine of whom died. More than 100,000 people were immediately evacuated, and the total number of evacuees from contaminated areas eventually reached 350,000. The explosions that destroyed the unit 4 reactor core released a cloud of radionuclides, which contaminated large areas of Europe and, in particular, Belarus, the Russian Federation and Ukraine, and affected livestock as far away as Scandinavia and Britain. Hundreds of thousands of people were exposed to substantial radiation doses, including workers who took part in efforts to mitigate the consequences of the accident. The IAEA said the situation had been made worse by conflicting information, exaggeration in press coverage and pseudoscientific accounts of the accident reporting, for example, fatalities in the tens or hundreds of thousands.
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